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well hello everybody and welcome again

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to the university of washington's spring

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astrobiology seminar series and a

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special welcome to our videocon

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participants

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our speaker today is dr jeremy bailey of

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macquarie university in australia

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jeremy received his ba in physics from

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oxford university in 1995

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and his phd in astronomy from sussex

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university in 1978.

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he spent a large fraction of his career

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at the anglo-australian observatory in

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sydney which is where i first met jeremy

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while i was working working on my phd

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and i think jeremy was there for over

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over 20 years

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but more recently from 2001 to 2007

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jeremy served as the associate director

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for the australian center for

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astrobiology and also as an associate

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professor of astrobiology from 2005 to

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2007.

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he is also in his spare time a member of

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the anglo-australian planet search team

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which has discovered 29 of the currently

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known exoplanets using radial velocity

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technique jeremy's interest in astronomy

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have been very broad ranging from

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cataclysmic variable stars through uh

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induction i guess of uh molecular

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homochirality in star-forming regions to

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most recently terrestrial planets in our

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own solar system and extrasolar planets

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however jeremy's diverse research has

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always been linked by his strong

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interest in the development and use of

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both infrared and polarimetric

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instrumentation

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so today jeremy will enlighten us on how

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to use polarization techniques to detect

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and characterize extrasolar planets

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so the basic idea of using polarization

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with extracellular planets

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is that sunlight is essentially

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unpolarized that we know that it's

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unpolarized to a very high level

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the polarization of the sun has been

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measured to

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be less than around one part in a

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million

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but when that light scatters

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off a planet

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such as the earth

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um it's polarized by a number of

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processes

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so scattering off off molecules radius

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scattering produces very high

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polarizations

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that peak at a 90 degree scattering

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angle

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scattering off particles such as cloud

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droplets aerosols in the atmosphere also

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produces polarization somewhat lower

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levels

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20 or less

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and the variation of this polarization

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what we call phase angle which is the

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angle between the sunlight and the

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direction it comes off

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provides some information on the size

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so there's a number of ways that

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polarization can be applied in the study

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of exoplanets and

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i'm only going to talk about some of

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them here the ones that are highlighted

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here

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um

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polarization can be used as a

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differential technique

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to to help to pick out the

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planet from the

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echonois that you get around a star and

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this applies to

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techniques that are being developed for

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looking for extra solar planets with

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large ground-based telescopes where

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they're using adaptive optics systems to

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sharpen up the light from the star and

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make it easy out the planet

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but you still get

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adaptive optic systems are not perfect

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so they still leave a halo of light

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around the star and you're trying to

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pick the planet out of that halo and

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polarization is one

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differential technique that that you can

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use to do that because the light of the

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planet should be polarized whereas the

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starlight won't be and so many of these

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instruments are incorporating

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polarization systems

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um you can also use polarization to try

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to detect the the scattered light from

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from unresolved planets and

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thinking here are hot jupiter type

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systems these are the planets that are

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being

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found

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in um

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doppler and transit planets such as

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whether where you have a giant planet

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very close to its star orbiting in a

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period of a few days

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and at the moment we have no hope of

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actually being able to resolve the

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planet from the star with it with any

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reasonable technique all we can do is

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look at the combined light of the planet

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from the star but it might be possible

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to use polarization to pick out the

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fraction of light that's coming from the

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planet and

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if i have time i'll say a bit more about

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that at the the end of this talk

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the main part of the talk is going to be

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about looking using polarization to

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characterize the atmospheres

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particularly of terrestrial type planets

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and we can use polarization in a number

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of ways it can help to distinguish

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between clear and cloudy atmospheres it

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can help us to measure the atmospheric

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pressure

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it can help us to determine the

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composition and size of cloud particles

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and one of the things we're particularly

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interested in is looking for liquid

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water and there are ways of using

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polarization to look for liquid water

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both in the liquid water droplets in

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clouds and liquid water on the surface

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of a planet

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and all these things are hard to do with

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spectroscopy

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polarimetry provides so perimetry

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provides information that's very

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complementary to what you get out of

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spectroscopy

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it's also in fact possible these

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polarization itself as a biosignature

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you can in principle detect circular

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polarization effects

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due to light scattering off chiral

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molecules

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in

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cyanobacteria where you have um

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chlorophyll there there will be a

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circular polarization signature of that

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light that's a result of the uh

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preference for one-handedness the

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chirality of the molecules and for

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example bill sparks based telescope

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science attitude is looking at such

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effects but they're very small and

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they're way beyond what we can think of

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okay so the current status of extrasolar

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planets

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so we now have 287

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extrasolar planets known according to

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the extracellular planets encyclopedia

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um

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most of these have been detected by the

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doppler method it's looking at the um

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varying radial velocity of the star as

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the as as the planet moves around it and

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causes a wobble of the motion of the

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star

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um

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increased very recently is detection by

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by the transit method where we see the

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planet passing in front of the star and

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that's

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those transit plants are very useful

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because they get

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we can actually use the transit to get

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information on the atmosphere of the

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um we now have six planets detected by

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the micro lensing method and this is

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where we see the

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the planet passing in front the star in

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the planet passing in front of a more

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distant star and causing gravitational

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lensing of the

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star

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and you can get a characteristic curve

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which allows you to deduce the presence

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of a planet

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and then there's there's five detected

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by direct imaging methods these are

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mostly planets around around very young

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stars the planet is still young and

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still producing uh light through its own

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so

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most of these current detections are are

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giant planets

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the

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masses of hundreds of earth masses or

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more comparable to jupiter and saturn in

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our red solar system

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uh there's a few lower mass planets

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found the lowest so far founder down to

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about five earth masses

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and these these planets are sometimes

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called called super earth they could be

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they could be large terrestrial planets

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almost all the current detections are

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indirect detections we are not seeing

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the planet itself we're deducing the

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presence of the planet from its effect

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on the star

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there's there's a few direct detections

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and and they're all by means of the

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thermal emission and so the spitzer

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space telescope has been used to detect

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the

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transiting planets

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and there's also these near-infrared

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um

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imaging

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observations of planets around young

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stars again we're seeing the thermal

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emission but no extracellular planet has

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yet been seen by the light reflected

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and of cour and we have yet to find

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anything else like earth orbiting

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another star we don't have the

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sensitivity in most of these methods to

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detect a planet of earth mass although

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that should become possible soon with um

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space missions such as kepler which will

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be capable of detecting earth-like

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nevertheless there's a number of

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missions to directly detect terrestrial

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planets

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this is very hard because a terrestrial

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planet is an extremely faint object it's

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probably fainter than anything

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astronomers have get measured and it's

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sitting next to a planet which is 10

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billion times brighter

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so these are pretty challenging

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observations but a number of methods

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have been proposed

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so these two

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instruments this is terrestrial planet

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finder imager

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interferometer

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and this is this is darwin which is a

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similar proposal from the european space

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agency

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these involve a number of infrared

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telescopes um

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flying in formation and combining their

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light and they can use um

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interferometric methods to to get rid of

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the light of the star and reveal the

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planet that thermal infrared wavelengths

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and then an alternative approaches is

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what's called tpfc terrestrial planet

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finder corrodograph

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and this is a large

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optical telescope but working at visible

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wavelengths and using a technique called

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a coronagraph an optical system to get

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rid of the light of the star and again

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reveal the planet at visible wavelengths

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um it's actually tpsc and similar

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instruments that are most interesting

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for what i'm going to talk about here

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because it's only ttsc that is looking

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at like reflected starlight reflected

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off the star and that's where we get the

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polarization effects

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so all of these missions are aimed to

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detect and characterize

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extracellular terrestrial planets

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and the the primary tool for planetary

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00:10:38,550 --> 00:10:36,880
characterization has usually been um

290
00:10:40,389 --> 00:10:38,560
as usually being spectroscopy in most of

291
00:10:41,750 --> 00:10:40,399
these proposals

292
00:10:43,350 --> 00:10:41,760
and what i want to point out here is

293
00:10:44,710 --> 00:10:43,360
that spectroscopy doesn't tell us

294
00:10:47,350 --> 00:10:44,720
anything everything we would like to

295
00:10:49,110 --> 00:10:47,360
know about these planets

296
00:10:50,069 --> 00:10:49,120
what it basically does is allows us to

297
00:10:53,269 --> 00:10:50,079
detect

298
00:10:54,790 --> 00:10:53,279
um some but not all of the gases that

299
00:10:56,790 --> 00:10:54,800
are pleasant present in a planetary

300
00:10:58,470 --> 00:10:56,800
atmosphere

301
00:11:01,110 --> 00:10:58,480
and i want to explain here what we can

302
00:11:02,790 --> 00:11:01,120
do by including polarization in such a

303
00:11:04,150 --> 00:11:02,800
mission

304
00:11:07,350 --> 00:11:04,160
and that can give us additional

305
00:11:12,710 --> 00:11:09,910
so these are some models of what the

306
00:11:15,030 --> 00:11:12,720
spectrum of a terrestrial planet might

307
00:11:17,430 --> 00:11:15,040
look like um

308
00:11:20,710 --> 00:11:17,440
observed with one of these missions

309
00:11:22,949 --> 00:11:20,720
so this is actually the infrared region

310
00:11:24,710 --> 00:11:22,959
up here showing showing what tpfi or

311
00:11:28,550 --> 00:11:24,720
darwin would see and that shows

312
00:11:30,230 --> 00:11:28,560
absorptions due to co2 and ozone

313
00:11:32,310 --> 00:11:30,240
and water

314
00:11:34,630 --> 00:11:32,320
and in the visible region of the region

315
00:11:36,550 --> 00:11:34,640
that tpfc would look at you can see

316
00:11:39,110 --> 00:11:36,560
again see absorption is due to oxygen

317
00:11:41,269 --> 00:11:39,120
and ozone so oxygen and ozone are

318
00:11:42,710 --> 00:11:41,279
biosignatures because they're produced

319
00:11:46,069 --> 00:11:42,720
in the atmosphere of the planet by

320
00:11:49,269 --> 00:11:47,990
we can also see water vapor in this

321
00:11:49,990 --> 00:11:49,279
region

322
00:11:56,870 --> 00:11:50,000
and

323
00:12:01,670 --> 00:11:58,710
but there's a number of things we'd like

324
00:12:03,509 --> 00:12:01,680
to do that spectroscopy can't do for us

325
00:12:04,949 --> 00:12:03,519
uh one thing it can't do is detect

326
00:12:09,670 --> 00:12:04,959
liquid water

327
00:12:12,069 --> 00:12:09,680
characteristic of a habitable planet

328
00:12:14,069 --> 00:12:12,079
and and the uh

329
00:12:16,230 --> 00:12:14,079
the mantra in astrobiology in the solar

330
00:12:18,389 --> 00:12:16,240
system has been follow the water um the

331
00:12:21,190 --> 00:12:18,399
water water is the

332
00:12:22,710 --> 00:12:21,200
one fundamental characteristic required

333
00:12:25,509 --> 00:12:22,720
for life

334
00:12:26,550 --> 00:12:25,519
and so um you want to look for liquid

335
00:12:28,310 --> 00:12:26,560
water

336
00:12:30,710 --> 00:12:28,320
to protect planets that are promising

337
00:12:33,269 --> 00:12:30,720
for life

338
00:12:34,629 --> 00:12:33,279
we can't do that with spectroscopy

339
00:12:37,509 --> 00:12:34,639
another thing we can't do very well is

340
00:12:39,430 --> 00:12:37,519
detect the presence of clouds

341
00:12:42,629 --> 00:12:39,440
and all planetary atmospheres in the

342
00:12:44,550 --> 00:12:42,639
solar system have clouds of of some sort

343
00:12:45,990 --> 00:12:44,560
and that means we can't really see tell

344
00:12:47,990 --> 00:12:46,000
if the light we're looking at is coming

345
00:12:49,590 --> 00:12:48,000
off a planet's surface or coming off the

346
00:12:52,310 --> 00:12:49,600
cloud tops and so anything we measure

347
00:12:53,590 --> 00:12:52,320
about the planet um we don't really know

348
00:12:55,269 --> 00:12:53,600
if it's telling us anything useful about

349
00:12:57,190 --> 00:12:55,279
the planet surface so for example if we

350
00:12:58,870 --> 00:12:57,200
look at a planet like venus

351
00:13:00,389 --> 00:12:58,880
the conditions of the cloud tops are

352
00:13:04,230 --> 00:13:00,399
very different from those at the surface

353
00:13:08,069 --> 00:13:05,990
another thing we can't easily get at is

354
00:13:10,389 --> 00:13:08,079
the atmospheric pressure and that's

355
00:13:11,590 --> 00:13:10,399
because we only detect some of the gases

356
00:13:13,350 --> 00:13:11,600
in the atmosphere

357
00:13:15,750 --> 00:13:13,360
some important gases

358
00:13:17,509 --> 00:13:15,760
in particular nitrogen and hydrogen

359
00:13:18,870 --> 00:13:17,519
which are the main components of the

360
00:13:20,710 --> 00:13:18,880
atmospheres of

361
00:13:22,870 --> 00:13:20,720
of hydrogen hydrogen in the case of the

362
00:13:25,030 --> 00:13:22,880
giant planets nitrogen in the case of

363
00:13:27,030 --> 00:13:25,040
earth and titan for example don't have

364
00:13:28,949 --> 00:13:27,040
any spectral features at the tpf

365
00:13:30,790 --> 00:13:28,959
wavelengths so if we're not seeing all

366
00:13:31,910 --> 00:13:30,800
the gases we can't get an idea of what

367
00:13:33,990 --> 00:13:31,920
the total

368
00:13:36,150 --> 00:13:34,000
atmospheric pressure is and that means

369
00:13:38,230 --> 00:13:36,160
we can't even measure the

370
00:13:40,710 --> 00:13:38,240
concentration of the observable gases

371
00:13:42,069 --> 00:13:40,720
properly because they're affected by the

372
00:13:43,910 --> 00:13:42,079
amount of pressure broadening by these

373
00:13:46,150 --> 00:13:43,920
gases we can't see

374
00:13:47,910 --> 00:13:46,160
so for example the co2 absorption

375
00:13:49,590 --> 00:13:47,920
features in the earth and mars

376
00:13:50,550 --> 00:13:49,600
atmosphere are actually roughly the same

377
00:13:52,710 --> 00:13:50,560
strength

378
00:13:54,629 --> 00:13:52,720
even though mars actually has a much

379
00:13:55,430 --> 00:13:54,639
bigger column of co2

380
00:13:57,030 --> 00:13:55,440
but

381
00:13:58,470 --> 00:13:57,040
in the earth case there's lots more

382
00:14:00,310 --> 00:13:58,480
pressure broadening due to nitrogen

383
00:14:02,790 --> 00:14:00,320
which brings the lines up to the same

384
00:14:04,550 --> 00:14:02,800
relative strength

385
00:14:06,389 --> 00:14:04,560
and polarization can help us to do all

386
00:14:07,990 --> 00:14:06,399
of these things

387
00:14:10,310 --> 00:14:08,000
and what the measurement we want to make

388
00:14:15,269 --> 00:14:10,320
is polarization as a function of phase

389
00:14:19,350 --> 00:14:17,670
so the features we're going to use

390
00:14:21,269 --> 00:14:19,360
to get information

391
00:14:22,790 --> 00:14:21,279
out of planetary atmospheres are

392
00:14:25,350 --> 00:14:22,800
the three that are illustrated here

393
00:14:26,629 --> 00:14:25,360
they're all very familiar phenomena on

394
00:14:29,269 --> 00:14:26,639
earth

395
00:14:32,310 --> 00:14:29,279
so so rainbows which are due to

396
00:14:33,430 --> 00:14:32,320
scattering off liquid water droplets

397
00:14:35,189 --> 00:14:33,440
um

398
00:14:37,750 --> 00:14:35,199
glint off

399
00:14:39,350 --> 00:14:37,760
of light reflected off of a water

400
00:14:41,350 --> 00:14:39,360
surface which is a possible technique

401
00:14:43,189 --> 00:14:41,360
for looking for oceans

402
00:14:45,269 --> 00:14:43,199
and rayleigh scattering which is simply

403
00:14:49,350 --> 00:14:45,279
light scattering off molecules it's what

404
00:14:53,829 --> 00:14:51,590
all of these phenomena if you looked at

405
00:14:55,750 --> 00:14:53,839
them through a polaroid sunglasses or

406
00:14:59,990 --> 00:14:55,760
any polarizing filter you will see that

407
00:15:05,110 --> 00:15:02,310
and that's how we can use detect them

408
00:15:06,150 --> 00:15:05,120
polarimetrically

409
00:15:08,069 --> 00:15:06,160
so

410
00:15:09,509 --> 00:15:08,079
i'll start by talking about rainbows

411
00:15:12,470 --> 00:15:09,519
rainbows are

412
00:15:15,509 --> 00:15:12,480
caused by light scattering off

413
00:15:17,269 --> 00:15:15,519
spherical water droplets

414
00:15:19,430 --> 00:15:17,279
and what we have is is the light passing

415
00:15:21,509 --> 00:15:19,440
into the water droplet reflecting off

416
00:15:25,030 --> 00:15:21,519
the inside of the water droplet and then

417
00:15:27,590 --> 00:15:25,040
coming out at a different angle

418
00:15:30,150 --> 00:15:27,600
and the light actually scatters through

419
00:15:32,150 --> 00:15:30,160
different angles depending on

420
00:15:34,150 --> 00:15:32,160
depending on where it's coming into the

421
00:15:35,750 --> 00:15:34,160
droplet so this impact parameter which

422
00:15:37,110 --> 00:15:35,760
measures the distance from the center of

423
00:15:38,069 --> 00:15:37,120
the droplet

424
00:15:40,790 --> 00:15:38,079
um

425
00:15:42,389 --> 00:15:40,800
but if you plot those angles

426
00:15:44,470 --> 00:15:42,399
as a function of impact parameter you

427
00:15:46,470 --> 00:15:44,480
find that there's a there's a minimum

428
00:15:50,550 --> 00:15:46,480
scattering angle where the

429
00:15:55,269 --> 00:15:52,629
where these curves turn round and there

430
00:15:58,710 --> 00:15:55,279
you get a pile up of light coming out

431
00:16:01,269 --> 00:15:58,720
coming out of these particular angles

432
00:16:02,389 --> 00:16:01,279
um i better explain these terms phase

433
00:16:03,749 --> 00:16:02,399
angle and scattering angle because i'm

434
00:16:06,629 --> 00:16:03,759
going to use them a lot

435
00:16:08,790 --> 00:16:06,639
so we have light coming in from the sun

436
00:16:11,350 --> 00:16:08,800
reflecting off

437
00:16:13,030 --> 00:16:11,360
or scattering off a particle

438
00:16:14,870 --> 00:16:13,040
and the phase angle is just this this

439
00:16:16,629 --> 00:16:14,880
angle measured from the

440
00:16:17,910 --> 00:16:16,639
direction the sunlight is coming from

441
00:16:20,470 --> 00:16:17,920
and the scattering angle is the

442
00:16:21,670 --> 00:16:20,480
complement of that 180 degrees minus the

443
00:16:23,670 --> 00:16:21,680
phase angle

444
00:16:25,749 --> 00:16:23,680
and it's observers always use phase

445
00:16:27,430 --> 00:16:25,759
angle and scattering theorists always

446
00:16:29,829 --> 00:16:27,440
use scattering angles so i'm afraid i'm

447
00:16:31,350 --> 00:16:29,839
going to have a mixture of the two but

448
00:16:32,710 --> 00:16:31,360
but they mean

449
00:16:35,269 --> 00:16:32,720
they're measuring essentially the same

450
00:16:37,670 --> 00:16:35,279
thing and for rainbow scattering from

451
00:16:40,230 --> 00:16:37,680
water droplets the scattering angle is

452
00:16:46,470 --> 00:16:40,240
about 140 degrees the phase angle is

453
00:16:50,389 --> 00:16:48,550
so this is what rainbows look like and

454
00:16:53,110 --> 00:16:50,399
i've exaggerated the contrast a little

455
00:16:55,350 --> 00:16:53,120
on this picture to show up the effects

456
00:16:58,069 --> 00:16:55,360
so the you get the circular rainbow

457
00:17:02,470 --> 00:16:58,079
that's that's the 40 degree

458
00:17:07,669 --> 00:17:06,069
you get the coloured primary rainbow

459
00:17:09,350 --> 00:17:07,679
and the region inside this rainbow is

460
00:17:10,710 --> 00:17:09,360
not dark there's light scattering at all

461
00:17:13,270 --> 00:17:10,720
these angles

462
00:17:15,110 --> 00:17:13,280
as well as the actual rainbow angles but

463
00:17:16,949 --> 00:17:15,120
we only actually see the colors of this

464
00:17:19,270 --> 00:17:16,959
this turnaround point at the minimum

465
00:17:21,029 --> 00:17:19,280
scattering angle the light can reach

466
00:17:22,710 --> 00:17:21,039
whereas this region here is actually

467
00:17:25,029 --> 00:17:22,720
dark there's no light scattering off the

468
00:17:26,549 --> 00:17:25,039
water droplets into this region and then

469
00:17:27,909 --> 00:17:26,559
outside the

470
00:17:29,669 --> 00:17:27,919
primary rainbow you get a secondary

471
00:17:31,830 --> 00:17:29,679
rainbow and you get another bright

472
00:17:36,310 --> 00:17:31,840
region here and that's that's light that

473
00:17:36,320 --> 00:17:41,669
it's a cardstock then yes that's right

474
00:17:47,029 --> 00:17:43,590
so rainbows rainbows are very highly

475
00:17:49,430 --> 00:17:47,039
polarized um if you photograph through

476
00:17:50,630 --> 00:17:49,440
polarizing filters and through the

477
00:17:53,669 --> 00:17:50,640
um

478
00:17:54,870 --> 00:17:53,679
so the polarization is in this direction

479
00:17:56,630 --> 00:17:54,880
um

480
00:17:58,390 --> 00:17:56,640
and in this direction you the rainbow

481
00:17:59,750 --> 00:17:58,400
just disappears it's essentially there's

482
00:18:01,270 --> 00:17:59,760
essentially nothing come through the

483
00:18:02,950 --> 00:18:01,280
level of polarization of the rainbow is

484
00:18:07,669 --> 00:18:02,960
actually about 96

485
00:18:11,430 --> 00:18:09,830
now the the rainbows we're actually

486
00:18:13,270 --> 00:18:11,440
interested in for for looking at

487
00:18:14,950 --> 00:18:13,280
exoplanets and not the

488
00:18:17,270 --> 00:18:14,960
familiar colored rainbows that we see

489
00:18:18,950 --> 00:18:17,280
which are rainbows coming off

490
00:18:22,630 --> 00:18:18,960
off it's actually raindrops large water

491
00:18:24,870 --> 00:18:22,640
droplets a millimeter or bigger in size

492
00:18:26,830 --> 00:18:24,880
but you also get the rainbow phenomenon

493
00:18:28,549 --> 00:18:26,840
persisting for much smaller

494
00:18:29,669 --> 00:18:28,559
droplets and

495
00:18:31,350 --> 00:18:29,679
in particular what we're interested in

496
00:18:32,870 --> 00:18:31,360
is cloud droplets

497
00:18:35,110 --> 00:18:32,880
because when we look at a planet from

498
00:18:36,150 --> 00:18:35,120
from outside um we're generally not

499
00:18:37,590 --> 00:18:36,160
going to see the raindrops because

500
00:18:38,789 --> 00:18:37,600
they're underneath the clouds but we do

501
00:18:40,390 --> 00:18:38,799
see the cloud

502
00:18:41,750 --> 00:18:40,400
the clouds themselves and the clouds of

503
00:18:43,430 --> 00:18:41,760
water droplets but they're just smaller

504
00:18:46,789 --> 00:18:43,440
water droplets

505
00:18:49,510 --> 00:18:46,799
typically about 10 microns in size

506
00:18:51,590 --> 00:18:49,520
so with what happens with small droplets

507
00:18:53,590 --> 00:18:51,600
is you still get a rainbow but

508
00:18:55,990 --> 00:18:53,600
diffraction effects broaden out the

509
00:18:58,070 --> 00:18:56,000
scattering peak of the rainbow so if you

510
00:18:59,750 --> 00:18:58,080
if you could see one of these

511
00:19:01,669 --> 00:18:59,760
sometimes called a fault bow or cloud

512
00:19:03,350 --> 00:19:01,679
bow it's not actually colored because

513
00:19:06,230 --> 00:19:03,360
the smearing of the light essentially

514
00:19:09,590 --> 00:19:06,240
smears out all the colors

515
00:19:11,430 --> 00:19:09,600
but they remain highly polarized

516
00:19:12,789 --> 00:19:11,440
and so if you look at a planet

517
00:19:14,310 --> 00:19:12,799
with clouds

518
00:19:16,549 --> 00:19:14,320
from a distance

519
00:19:18,470 --> 00:19:16,559
there should be a peak in polarized

520
00:19:23,029 --> 00:19:18,480
light at this rainbow scattering angle

521
00:19:29,190 --> 00:19:25,990
um to study these small particle

522
00:19:30,150 --> 00:19:29,200
rainbows you can't really use the uh the

523
00:19:31,669 --> 00:19:30,160
ray

524
00:19:33,029 --> 00:19:31,679
optics approximation that i showed

525
00:19:35,510 --> 00:19:33,039
earlier

526
00:19:36,390 --> 00:19:35,520
we use methods

527
00:19:39,590 --> 00:19:36,400
um

528
00:19:40,470 --> 00:19:39,600
such as the lorenz me scattering theory

529
00:19:42,789 --> 00:19:40,480
and

530
00:19:45,110 --> 00:19:42,799
which models are scattering from small

531
00:19:47,350 --> 00:19:45,120
spherical particles and there's a

532
00:19:49,110 --> 00:19:47,360
associated

533
00:19:52,230 --> 00:19:49,120
t matrix theory which we can use for

534
00:19:54,630 --> 00:19:52,240
non-spherical particles

535
00:19:55,669 --> 00:19:54,640
so from these we can calculate

536
00:19:58,710 --> 00:19:55,679
the

537
00:20:00,470 --> 00:19:58,720
which contains

538
00:20:02,150 --> 00:20:00,480
one component of this is the phase

539
00:20:03,510 --> 00:20:02,160
function which is simply the the

540
00:20:06,710 --> 00:20:03,520
fraction of light that gets scattered

541
00:20:07,510 --> 00:20:06,720
into each possible phase angle

542
00:20:09,029 --> 00:20:07,520
and

543
00:20:10,710 --> 00:20:09,039
there's another component which

544
00:20:13,350 --> 00:20:10,720
describes the same thing tendency for

545
00:20:15,590 --> 00:20:13,360
linearly polarized light so how much

546
00:20:17,669 --> 00:20:15,600
the nearly polarized light is scattered

547
00:20:18,549 --> 00:20:17,679
at any one angle

548
00:20:20,150 --> 00:20:18,559
and the

549
00:20:22,230 --> 00:20:20,160
ratio of those is the degree of linear

550
00:20:23,029 --> 00:20:22,240
polarization

551
00:20:25,830 --> 00:20:23,039
so

552
00:20:29,830 --> 00:20:25,840
i for example use fortran codes from

553
00:20:31,669 --> 00:20:29,840
machenco to to calculate these

554
00:20:33,909 --> 00:20:31,679
i'll show a few plots as to what these

555
00:20:37,430 --> 00:20:33,919
look like

556
00:20:39,190 --> 00:20:37,440
so this is so this is just the

557
00:20:40,870 --> 00:20:39,200
the the phase function amount of

558
00:20:43,270 --> 00:20:40,880
scattered light as a function of

559
00:20:44,950 --> 00:20:43,280
scattering angle and you can see it's

560
00:20:47,750 --> 00:20:44,960
actually the same features that i showed

561
00:20:50,470 --> 00:20:47,760
in the photograph of the rainbow before

562
00:20:52,870 --> 00:20:50,480
so here's the primary rainbow

563
00:20:54,789 --> 00:20:52,880
there's light inside the primary rainbow

564
00:20:57,510 --> 00:20:54,799
there's this dark region and then the

565
00:20:59,190 --> 00:20:57,520
secondary rainbow

566
00:21:00,789 --> 00:20:59,200
and if you actually have particles of

567
00:21:02,549 --> 00:21:00,799
almost the same size you get these

568
00:21:05,029 --> 00:21:02,559
things called supernumerary bows which

569
00:21:07,990 --> 00:21:05,039
appear inside the primary rainbow they

570
00:21:09,990 --> 00:21:08,000
tend to smear out somewhat if you have

571
00:21:11,510 --> 00:21:10,000
particles of a broad distribution in

572
00:21:13,350 --> 00:21:11,520
particle size but you can still

573
00:21:17,510 --> 00:21:13,360
sometimes see this supernumerary rainbow

574
00:21:21,669 --> 00:21:19,350
so this plot just shows the the effects

575
00:21:23,590 --> 00:21:21,679
of particle size on the rainbow so as

576
00:21:25,750 --> 00:21:23,600
the particles get smaller i've started

577
00:21:27,510 --> 00:21:25,760
at 100 microns here

578
00:21:29,270 --> 00:21:27,520
what happens is the width of the rainbow

579
00:21:30,870 --> 00:21:29,280
peak

580
00:21:33,669 --> 00:21:30,880
broadens out

581
00:21:36,549 --> 00:21:33,679
and eventually it starts to shift to

582
00:21:38,390 --> 00:21:36,559
um larger scattering angles

583
00:21:40,149 --> 00:21:38,400
so this is the the phase function the

584
00:21:42,390 --> 00:21:40,159
total intensity of the light and this is

585
00:21:44,230 --> 00:21:42,400
the the polarized intensity

586
00:21:46,310 --> 00:21:44,240
and they're on the same scale so if the

587
00:21:47,590 --> 00:21:46,320
polarized intensity is the same height

588
00:21:49,990 --> 00:21:47,600
as the

589
00:21:52,549 --> 00:21:50,000
uh phase function plot then that's

590
00:21:53,909 --> 00:21:52,559
essentially highly polarized light

591
00:21:56,470 --> 00:21:53,919
and one of the things you can see is

592
00:21:57,350 --> 00:21:56,480
that as you get down to small particles

593
00:22:00,470 --> 00:21:57,360
um

594
00:22:02,870 --> 00:22:00,480
you you start to see this feature at

595
00:22:04,870 --> 00:22:02,880
around 180 degrees scattering angle

596
00:22:06,710 --> 00:22:04,880
which that's actually a related optical

597
00:22:10,549 --> 00:22:06,720
phenomenon called the glory

598
00:22:14,870 --> 00:22:12,789
which occurs at this angle and as you

599
00:22:16,470 --> 00:22:14,880
get to small particles the rainbow and

600
00:22:18,470 --> 00:22:16,480
the glory sort of more or less join

601
00:22:19,990 --> 00:22:18,480
together and there's light at all

602
00:22:21,990 --> 00:22:20,000
wavelengths

603
00:22:25,190 --> 00:22:22,000
at all angles between between the

604
00:22:26,950 --> 00:22:25,200
rainbow peak and 180 degrees

605
00:22:29,510 --> 00:22:26,960
but if you look at polarization you

606
00:22:31,510 --> 00:22:29,520
still get a well-defined rainbow peak

607
00:22:34,390 --> 00:22:31,520
going down to quite small

608
00:22:35,750 --> 00:22:34,400
um particle sizes it broadens and shifts

609
00:22:38,070 --> 00:22:35,760
but there's still a fairly well defined

610
00:22:40,470 --> 00:22:38,080
peak in this small particle sizes

611
00:22:43,110 --> 00:22:40,480
typical cloud particle sizes range from

612
00:22:44,789 --> 00:22:43,120
about three to 30 microns so

613
00:22:46,549 --> 00:22:44,799
the uh um

614
00:22:48,390 --> 00:22:46,559
average size that the global mean is

615
00:22:51,029 --> 00:22:48,400
actually about 11.4 microns so it's

616
00:22:52,710 --> 00:22:51,039
close to this 10 micro plot here so this

617
00:22:57,669 --> 00:22:52,720
is the sort of rainbow peak you would

618
00:23:02,390 --> 00:22:59,590
now where that

619
00:23:04,070 --> 00:23:02,400
the angle at which you see that rainbow

620
00:23:07,990 --> 00:23:04,080
depends on the refractive index of the

621
00:23:09,990 --> 00:23:08,000
liquid so um

622
00:23:12,549 --> 00:23:10,000
i've shown here the the rainbows

623
00:23:14,870 --> 00:23:12,559
calculated for three different liquids

624
00:23:16,149 --> 00:23:14,880
that we know occur in clouds within the

625
00:23:19,110 --> 00:23:16,159
solar system

626
00:23:20,470 --> 00:23:19,120
so water at the top this is sulfuric

627
00:23:21,510 --> 00:23:20,480
acid which is what we get in the venous

628
00:23:23,430 --> 00:23:21,520
clouds

629
00:23:26,149 --> 00:23:23,440
and this is methane

630
00:23:27,909 --> 00:23:26,159
which we get in clouds in titan

631
00:23:29,590 --> 00:23:27,919
and you can see that you could

632
00:23:31,830 --> 00:23:29,600
you could clearly distinguish these

633
00:23:37,830 --> 00:23:31,840
liquids from the the shifting angle at

634
00:23:42,630 --> 00:23:40,390
um this is these plots show the effects

635
00:23:44,230 --> 00:23:42,640
of particle shape on the rainbow so you

636
00:23:45,990 --> 00:23:44,240
get nice rainbows with spherical

637
00:23:47,590 --> 00:23:46,000
particles but

638
00:23:49,350 --> 00:23:47,600
as soon as you the particle shape

639
00:23:52,149 --> 00:23:49,360
deviates from the sphere so these are

640
00:23:55,750 --> 00:23:52,159
spheroids with different axis ratios

641
00:23:58,390 --> 00:23:55,760
the rainbow peak rapidly disappears

642
00:23:59,990 --> 00:23:58,400
and these are these are some

643
00:24:03,510 --> 00:24:00,000
different shapes overlapping prolates

644
00:24:04,950 --> 00:24:03,520
varieties and cylindrical particles

645
00:24:06,789 --> 00:24:04,960
so so rainbows are very a very

646
00:24:09,669 --> 00:24:06,799
distinctive indicator

647
00:24:11,430 --> 00:24:09,679
of spherical droplets and spherical in

648
00:24:12,950 --> 00:24:11,440
practice in most practical conditions

649
00:24:14,549 --> 00:24:12,960
means you must be looking at a liquid

650
00:24:15,990 --> 00:24:14,559
because a liquid naturally forms a

651
00:24:19,029 --> 00:24:16,000
spherical shape because of surface

652
00:24:21,830 --> 00:24:20,390
and then the other thing you need for to

653
00:24:23,990 --> 00:24:21,840
get a rainbow is it has to be a

654
00:24:26,789 --> 00:24:24,000
transparent liquid so this is the

655
00:24:29,110 --> 00:24:26,799
effect of putting some absorption in the

656
00:24:32,149 --> 00:24:29,120
into the particle and that that also

657
00:24:33,750 --> 00:24:32,159
causes the rainbow to disappear and that

658
00:24:35,990 --> 00:24:33,760
means that if you actually looked at the

659
00:24:38,070 --> 00:24:36,000
spectrum of this rainbow scattered light

660
00:24:40,549 --> 00:24:38,080
you could see absorption features due to

661
00:24:41,750 --> 00:24:40,559
the liquid that caused to cause the

662
00:24:42,630 --> 00:24:41,760
rainbow

663
00:24:44,149 --> 00:24:42,640
um

664
00:24:46,310 --> 00:24:44,159
the best place to look for that for a

665
00:24:47,669 --> 00:24:46,320
water rainbow would be at about 1.95

666
00:24:49,909 --> 00:24:47,679
microwaves

667
00:24:51,190 --> 00:24:49,919
outside the wavelength range of any of

668
00:24:55,430 --> 00:24:51,200
the tpf

669
00:24:58,149 --> 00:24:56,710
so to summarize the properties of

670
00:25:00,470 --> 00:24:58,159
rainbows they generate it by scattering

671
00:25:02,630 --> 00:25:00,480
from spherical particles any small

672
00:25:04,470 --> 00:25:02,640
departure from sphericity inhibits

673
00:25:06,149 --> 00:25:04,480
rainbow production

674
00:25:10,310 --> 00:25:06,159
they're present for sizes down about one

675
00:25:14,070 --> 00:25:10,320
micron which which covers all the clouds

676
00:25:15,830 --> 00:25:14,080
particles that we know about

677
00:25:17,430 --> 00:25:15,840
highly polarized and for small particles

678
00:25:20,710 --> 00:25:17,440
they're better defined in polarized

679
00:25:22,149 --> 00:25:20,720
light than in total intensity

680
00:25:23,830 --> 00:25:22,159
the the peak scattering angle is a

681
00:25:25,590 --> 00:25:23,840
measure of the refractive index and

682
00:25:28,149 --> 00:25:25,600
could help to tell us the the nature of

683
00:25:29,669 --> 00:25:28,159
the liquid responsible for the rainbow

684
00:25:32,870 --> 00:25:29,679
and any absorption in the particle

685
00:25:35,110 --> 00:25:32,880
inhibits rainbow production

686
00:25:36,710 --> 00:25:35,120
and that means that rainbows are a very

687
00:25:41,750 --> 00:25:36,720
strong indicator of the presence of

688
00:25:45,830 --> 00:25:44,149
so um in natural conditions the only way

689
00:25:48,070 --> 00:25:45,840
we're going to get a spherical particle

690
00:25:48,950 --> 00:25:48,080
is is due to

691
00:25:50,470 --> 00:25:48,960
um

692
00:25:52,070 --> 00:25:50,480
surface tension which

693
00:25:54,070 --> 00:25:52,080
causes a liquid to form spherical

694
00:25:56,470 --> 00:25:54,080
droplets

695
00:25:58,230 --> 00:25:56,480
and the solid particles are very

696
00:26:00,789 --> 00:25:58,240
unlikely to produce rainbows in in

697
00:26:02,710 --> 00:26:00,799
natural conditions or all the solid

698
00:26:04,390 --> 00:26:02,720
particle aerosols that we know about in

699
00:26:05,510 --> 00:26:04,400
in the earth and other planets

700
00:26:07,750 --> 00:26:05,520
atmospheres

701
00:26:08,549 --> 00:26:07,760
would have conditions that would prevent

702
00:26:10,149 --> 00:26:08,559
the

703
00:26:11,669 --> 00:26:10,159
formation of a rainbow due to

704
00:26:14,310 --> 00:26:11,679
non-sphericity

705
00:26:18,950 --> 00:26:14,320
small size or absorption and in most

706
00:26:22,870 --> 00:26:20,950
okay now the models i've i've shown you

707
00:26:25,029 --> 00:26:22,880
so far are single scattering models so

708
00:26:26,710 --> 00:26:25,039
they just look at what light scattered

709
00:26:28,630 --> 00:26:26,720
once offer

710
00:26:31,110 --> 00:26:28,640
water droplet would do what we're

711
00:26:32,870 --> 00:26:31,120
looking at in a realistic atmosphere is

712
00:26:35,190 --> 00:26:32,880
is a multiple scattering situation so

713
00:26:38,230 --> 00:26:35,200
light can scatter many times off various

714
00:26:41,430 --> 00:26:38,240
particles before it finds its way out

715
00:26:43,350 --> 00:26:41,440
um it turns out though that the

716
00:26:45,590 --> 00:26:43,360
effect of multiple scattering is mostly

717
00:26:47,830 --> 00:26:45,600
to remove polarization

718
00:26:49,350 --> 00:26:47,840
so the polarized light you see from an

719
00:26:51,029 --> 00:26:49,360
atmosphere is mostly going to be due to

720
00:26:53,269 --> 00:26:51,039
light that's that has actually single

721
00:26:55,510 --> 00:26:53,279
scattered that's only scattered once off

722
00:26:58,070 --> 00:26:55,520
um droplets at the top of the clouds

723
00:27:00,149 --> 00:26:58,080
and there will be diluting light coming

724
00:27:01,990 --> 00:27:00,159
from multiple scattering cases

725
00:27:03,350 --> 00:27:02,000
which is which can be

726
00:27:04,950 --> 00:27:03,360
considered

727
00:27:07,350 --> 00:27:04,960
to reverse approximation be unpolarized

728
00:27:08,950 --> 00:27:07,360
and so it just dilutes the polarization

729
00:27:11,269 --> 00:27:08,960
so it actually means that the single

730
00:27:13,590 --> 00:27:11,279
scattering curves are pretty much what

731
00:27:15,110 --> 00:27:13,600
you would actually expect to see in the

732
00:27:17,269 --> 00:27:15,120
polarized light from an atmosphere

733
00:27:18,950 --> 00:27:17,279
except that the degree of polarization

734
00:27:21,190 --> 00:27:18,960
will be reduced because

735
00:27:23,430 --> 00:27:21,200
there's this diluting

736
00:27:24,630 --> 00:27:23,440
unpolarized radiation and you can see

737
00:27:27,430 --> 00:27:24,640
this this is an actual multiple

738
00:27:28,470 --> 00:27:27,440
scattering model of rainbows off water

739
00:27:30,310 --> 00:27:28,480
clouds

740
00:27:32,870 --> 00:27:30,320
and the shape is pretty much the same as

741
00:27:34,630 --> 00:27:32,880
the single scattering

742
00:27:38,310 --> 00:27:34,640
polarization that i showed in one of the

743
00:27:42,470 --> 00:27:40,870
um you can also see that in the multiple

744
00:27:44,870 --> 00:27:42,480
scattering case

745
00:27:46,870 --> 00:27:44,880
the the rainbow shows up very clearly in

746
00:27:50,549 --> 00:27:46,880
polarized light

747
00:27:53,669 --> 00:27:50,559
but is a relatively weak feature in the

748
00:27:55,269 --> 00:27:53,679
total intensity of the light

749
00:28:00,310 --> 00:27:55,279
so polarization is really the way to

750
00:28:03,350 --> 00:28:01,830
now just to show that this actually

751
00:28:06,389 --> 00:28:03,360
works that you can look at a planet from

752
00:28:08,389 --> 00:28:06,399
space and see rainbows um these are some

753
00:28:10,230 --> 00:28:08,399
observations from an instrument called

754
00:28:11,990 --> 00:28:10,240
polder

755
00:28:13,909 --> 00:28:12,000
which is polarization and directionality

756
00:28:15,750 --> 00:28:13,919
of earth reflectances this is a

757
00:28:17,750 --> 00:28:15,760
french-build instrument that's the first

758
00:28:19,190 --> 00:28:17,760
version flew on a japanese satellite

759
00:28:20,549 --> 00:28:19,200
called adios

760
00:28:22,470 --> 00:28:20,559
and there's a second version now

761
00:28:23,750 --> 00:28:22,480
operating on a micro satellite called

762
00:28:24,950 --> 00:28:23,760
parasol

763
00:28:26,870 --> 00:28:24,960
and this is an instrument that looks

764
00:28:29,190 --> 00:28:26,880
down at clouds from earth orbit it's

765
00:28:31,830 --> 00:28:29,200
about 800 kilometers

766
00:28:34,950 --> 00:28:31,840
altitude and it looks at this phase

767
00:28:37,830 --> 00:28:34,960
curve of reflection from clouds

768
00:28:39,510 --> 00:28:37,840
and the basic aim of polder of the at

769
00:28:41,350 --> 00:28:39,520
least the polarization part of polar is

770
00:28:43,430 --> 00:28:41,360
to distinguish between liquid water

771
00:28:44,470 --> 00:28:43,440
clouds and ice clouds and it does this

772
00:28:46,310 --> 00:28:44,480
very clearly

773
00:28:48,630 --> 00:28:46,320
so red is a

774
00:28:49,750 --> 00:28:48,640
liquid water cloud and it produces a

775
00:28:51,430 --> 00:28:49,760
nice

776
00:28:53,590 --> 00:28:51,440
polarized rainbow curve just like the

777
00:28:55,430 --> 00:28:53,600
ones i've shown you and the blue is

778
00:28:56,710 --> 00:28:55,440
scattering off ice clouds and it's

779
00:28:58,389 --> 00:28:56,720
completely different

780
00:28:59,590 --> 00:28:58,399
there is still some polarization but the

781
00:29:04,549 --> 00:28:59,600
curve is completely different and

782
00:29:09,350 --> 00:29:06,389
so that shows you can really see these

783
00:29:11,430 --> 00:29:09,360
things looking at the earth from space

784
00:29:14,549 --> 00:29:11,440
and then the other good example is that

785
00:29:17,029 --> 00:29:14,559
they've been seen from the planet venus

786
00:29:19,269 --> 00:29:17,039
um polarization from of light from venus

787
00:29:21,350 --> 00:29:19,279
was first detected by by bernard leo

788
00:29:22,870 --> 00:29:21,360
back in the 1920s

789
00:29:24,470 --> 00:29:22,880
but for a long time it wasn't fully

790
00:29:27,350 --> 00:29:24,480
explained

791
00:29:29,750 --> 00:29:27,360
and the the explanation was largely due

792
00:29:32,149 --> 00:29:29,760
to the work of james hansen

793
00:29:34,389 --> 00:29:32,159
this is the james hansen who went on to

794
00:29:35,909 --> 00:29:34,399
be director of the goddard institute for

795
00:29:37,669 --> 00:29:35,919
space studies and the

796
00:29:39,830 --> 00:29:37,679
leading advocate for action on climate

797
00:29:41,830 --> 00:29:39,840
change climate modeler and so on he

798
00:29:43,510 --> 00:29:41,840
started by working on venus

799
00:29:45,430 --> 00:29:43,520
and he came up with the explanation for

800
00:29:47,590 --> 00:29:45,440
the polarization

801
00:29:49,909 --> 00:29:47,600
in the venous atmosphere

802
00:29:51,430 --> 00:29:49,919
and this is the polarization phase curve

803
00:29:54,789 --> 00:29:51,440
of venus

804
00:29:56,470 --> 00:29:54,799
observations here and hansen's model

805
00:29:58,630 --> 00:29:56,480
and what we see is a primary rainbow

806
00:30:00,470 --> 00:29:58,640
here this this peak which is actually

807
00:30:01,590 --> 00:30:00,480
for venus is about 20 degrees phase

808
00:30:03,909 --> 00:30:01,600
angle

809
00:30:06,789 --> 00:30:03,919
is is just the same rainbow scattering

810
00:30:09,590 --> 00:30:06,799
effect water droplets but it's shifted

811
00:30:12,630 --> 00:30:09,600
from 40 degrees where we see a

812
00:30:14,549 --> 00:30:12,640
water rainbow down to about 20 degrees

813
00:30:16,950 --> 00:30:14,559
and that's because the the liquid in

814
00:30:18,710 --> 00:30:16,960
this case is sulfuric acid it has a much

815
00:30:20,310 --> 00:30:18,720
higher refractive index

816
00:30:22,710 --> 00:30:20,320
but also because the particles are very

817
00:30:24,789 --> 00:30:22,720
small the small particle also causes a

818
00:30:29,190 --> 00:30:24,799
shift in the rainbow position

819
00:30:30,789 --> 00:30:29,200
so from this polarization phase curve um

820
00:30:33,350 --> 00:30:30,799
it was possible to work out how

821
00:30:36,549 --> 00:30:33,360
particles were spherical droplets

822
00:30:39,750 --> 00:30:36,559
radius of 1.05 microns

823
00:30:41,830 --> 00:30:39,760
and the refractive index was

824
00:30:44,389 --> 00:30:41,840
was measured to be 1.44

825
00:30:46,549 --> 00:30:44,399
with considerable accuracy and the only

826
00:30:49,190 --> 00:30:46,559
possible

827
00:30:50,950 --> 00:30:49,200
liquid consistent with that is uh is

828
00:30:53,590 --> 00:30:50,960
it's actually concentrated sulfuric acid

829
00:30:55,990 --> 00:30:53,600
so 75 h2so4

830
00:30:57,510 --> 00:30:56,000
25 water

831
00:30:59,110 --> 00:30:57,520
so this shows that looking at the total

832
00:31:02,230 --> 00:30:59,120
light of a planet we can see a rainbow

833
00:31:08,470 --> 00:31:02,240
signal which tells us about the

834
00:31:13,430 --> 00:31:10,789
now i've tried to work out what the

835
00:31:14,950 --> 00:31:13,440
the total rainbow signal from the earth

836
00:31:17,029 --> 00:31:14,960
should be if we were looking at the

837
00:31:20,070 --> 00:31:17,039
integrated light of the earth

838
00:31:22,870 --> 00:31:20,080
and i'm using for this i'm using

839
00:31:24,950 --> 00:31:22,880
i'm basically modeling it as a combined

840
00:31:27,190 --> 00:31:24,960
from three components

841
00:31:28,870 --> 00:31:27,200
um clear sky

842
00:31:30,549 --> 00:31:28,880
regions where we won't see any rainbow

843
00:31:32,470 --> 00:31:30,559
signal

844
00:31:34,950 --> 00:31:32,480
liquid cloud regions that will show a

845
00:31:37,029 --> 00:31:34,960
rainbow signal an ice cloud which won't

846
00:31:39,509 --> 00:31:37,039
show a rainbow signal

847
00:31:41,990 --> 00:31:39,519
and i'm i'm using a couple of different

848
00:31:45,669 --> 00:31:42,000
models of what the typical global cover

849
00:31:47,590 --> 00:31:45,679
of these three components is

850
00:31:50,470 --> 00:31:47,600
total reflectance

851
00:31:51,350 --> 00:31:50,480
from the work of tinnetti

852
00:31:52,789 --> 00:31:51,360
and

853
00:31:55,029 --> 00:31:52,799
the polarized reflectance from the

854
00:31:56,470 --> 00:31:55,039
rainbow according to the multiple

855
00:31:57,590 --> 00:31:56,480
scattering models i've shown earlier

856
00:31:59,509 --> 00:31:57,600
golovkin

857
00:32:02,230 --> 00:31:59,519
and if you combine all this together you

858
00:32:05,350 --> 00:32:02,240
get a global signal of

859
00:32:06,950 --> 00:32:05,360
something between 12.7 and 15.5 and

860
00:32:08,310 --> 00:32:06,960
percent for the two different cloud

861
00:32:10,710 --> 00:32:08,320
models

862
00:32:12,470 --> 00:32:10,720
if the earth was totally cloud-covered

863
00:32:14,549 --> 00:32:12,480
out you get a 20

864
00:32:16,710 --> 00:32:14,559
signal so these are these are reasonably

865
00:32:17,669 --> 00:32:16,720
large polarizations that should be

866
00:32:21,990 --> 00:32:17,679
possible

867
00:32:26,149 --> 00:32:24,389
okay now rainbows tell us about liquid

868
00:32:27,590 --> 00:32:26,159
water but but liquid water in the

869
00:32:29,029 --> 00:32:27,600
atmosphere what we really want to know

870
00:32:30,310 --> 00:32:29,039
about is if there's liquid water on the

871
00:32:32,470 --> 00:32:30,320
surface because that's really the

872
00:32:34,549 --> 00:32:32,480
defining characteristic

873
00:32:35,830 --> 00:32:34,559
of a habitable planet

874
00:32:38,070 --> 00:32:35,840
there is a way of doing this using

875
00:32:39,430 --> 00:32:38,080
polarization and that's using what's

876
00:32:41,430 --> 00:32:39,440
called glint so

877
00:32:42,630 --> 00:32:41,440
so simply

878
00:32:45,029 --> 00:32:42,640
sunlight

879
00:32:49,350 --> 00:32:45,039
glinting off water and

880
00:32:52,630 --> 00:32:51,669
under under most conditions but you do

881
00:32:55,669 --> 00:32:52,640
get this

882
00:32:57,669 --> 00:32:55,679
glint of water which occurs

883
00:33:00,549 --> 00:32:57,679
at for light that's actually reflected

884
00:33:01,750 --> 00:33:00,559
at the specular reflection angle so

885
00:33:03,350 --> 00:33:01,760
angle of incidence and angle of

886
00:33:04,710 --> 00:33:03,360
reflection the same

887
00:33:07,830 --> 00:33:04,720
so these are these are some actual

888
00:33:09,590 --> 00:33:07,840
photos of blind spots off water

889
00:33:10,950 --> 00:33:09,600
um through two different polarizing

890
00:33:12,870 --> 00:33:10,960
filters

891
00:33:14,389 --> 00:33:12,880
and you can see there's a there's a big

892
00:33:15,990 --> 00:33:14,399
difference this light is highly

893
00:33:17,509 --> 00:33:16,000
polarized not quite as high as the

894
00:33:21,190 --> 00:33:17,519
rainbows but um

895
00:33:25,590 --> 00:33:23,750
and you can also see the pattern of the

896
00:33:27,750 --> 00:33:25,600
glint depends on or what the wind's

897
00:33:29,990 --> 00:33:27,760
doing to the surface of the water

898
00:33:32,950 --> 00:33:30,000
this changed

899
00:33:35,430 --> 00:33:32,960
between these two cases in in

900
00:33:37,029 --> 00:33:35,440
a minute or so

901
00:33:38,870 --> 00:33:37,039
now you could this is a

902
00:33:41,830 --> 00:33:38,880
photo of the earth from space and you

903
00:33:43,750 --> 00:33:41,840
can see the blitz spot there um

904
00:33:45,750 --> 00:33:43,760
it's clearly visible

905
00:33:47,190 --> 00:33:45,760
but you could also see that it's not

906
00:33:49,190 --> 00:33:47,200
going to be easy to observe this in the

907
00:33:50,950 --> 00:33:49,200
total light of the planet because

908
00:33:52,630 --> 00:33:50,960
there's a lot of other light coming from

909
00:33:54,870 --> 00:33:52,640
clouds

910
00:34:03,590 --> 00:33:54,880
around there which is going to dilute

911
00:34:09,109 --> 00:34:07,909
these are some models of the glint

912
00:34:11,030 --> 00:34:09,119
effects

913
00:34:13,750 --> 00:34:11,040
from a recent paper by

914
00:34:15,349 --> 00:34:13,760
williams and gaydos

915
00:34:17,589 --> 00:34:15,359
and these show the

916
00:34:20,470 --> 00:34:17,599
polarization

917
00:34:21,589 --> 00:34:20,480
here and the total intensity as a

918
00:34:24,710 --> 00:34:21,599
function of

919
00:34:29,909 --> 00:34:25,750
and

920
00:34:31,990 --> 00:34:29,919
this so this top model is a model for a

921
00:34:34,869 --> 00:34:32,000
for a completely ocean covered earth

922
00:34:37,030 --> 00:34:34,879
with no clouds and that's

923
00:34:39,270 --> 00:34:37,040
um that's a favorable case for seeing

924
00:34:40,629 --> 00:34:39,280
glint because the oceans themselves are

925
00:34:43,669 --> 00:34:40,639
largely dark

926
00:34:44,550 --> 00:34:43,679
and the glitz spot bright

927
00:34:49,430 --> 00:34:44,560
so

928
00:34:53,030 --> 00:34:51,589
here it's going up to about 70

929
00:34:55,109 --> 00:34:53,040
polarization

930
00:35:01,750 --> 00:34:55,119
and

931
00:35:02,710 --> 00:35:01,760
simply because

932
00:35:04,390 --> 00:35:02,720
your

933
00:35:06,390 --> 00:35:04,400
the total light of the planet is is

934
00:35:08,550 --> 00:35:06,400
reduced relative to the glenn's blood

935
00:35:10,230 --> 00:35:08,560
spot is a larger proportion of the light

936
00:35:11,109 --> 00:35:10,240
coming from the planet

937
00:35:15,910 --> 00:35:11,119
this is

938
00:35:17,589 --> 00:35:15,920
has been added so it's got continents as

939
00:35:19,270 --> 00:35:17,599
well as the ocean and the continents are

940
00:35:20,870 --> 00:35:19,280
brighter than the ocean

941
00:35:24,870 --> 00:35:20,880
so you get a much smaller

942
00:35:28,829 --> 00:35:24,880
glint polarization now about 30

943
00:35:32,150 --> 00:35:28,839
and it's shifted over to smaller smaller

944
00:35:33,750 --> 00:35:32,160
angles um more or more extreme present

945
00:35:34,630 --> 00:35:33,760
phases

946
00:35:36,630 --> 00:35:34,640
and

947
00:35:38,390 --> 00:35:36,640
what hasn't been modeled here is what

948
00:35:39,589 --> 00:35:38,400
happens if you add clouds

949
00:35:41,190 --> 00:35:39,599
and that's the real problem because

950
00:35:43,270 --> 00:35:41,200
clouds are brighter than both oceans and

951
00:35:44,710 --> 00:35:43,280
continents so if you put clouds into the

952
00:35:47,349 --> 00:35:44,720
model this this peak is going to get

953
00:35:50,230 --> 00:35:47,359
smaller and it's going to shift further

954
00:35:50,240 --> 00:35:54,310
more to more extreme present phases

955
00:35:57,910 --> 00:35:55,990
so glint is

956
00:36:00,150 --> 00:35:57,920
certainly potentially a way of detecting

957
00:36:02,550 --> 00:36:00,160
oceans but i think it's actually quite

958
00:36:04,150 --> 00:36:02,560
hard to do in practice at least for for

959
00:36:05,990 --> 00:36:04,160
a realistic planet like the earth where

960
00:36:07,750 --> 00:36:06,000
you've got the blind spot competing with

961
00:36:08,630 --> 00:36:07,760
reflection from clouds

962
00:36:13,030 --> 00:36:08,640
and

963
00:36:16,870 --> 00:36:14,870
um the other feature that produces

964
00:36:18,390 --> 00:36:16,880
polarization in these atmospheres is

965
00:36:20,310 --> 00:36:18,400
radius scattering

966
00:36:23,349 --> 00:36:20,320
and radial scattering is just scattering

967
00:36:24,950 --> 00:36:23,359
off molecules in in the atmosphere so so

968
00:36:26,950 --> 00:36:24,960
just a clear atmosphere without any

969
00:36:28,550 --> 00:36:26,960
clouds will produce polarization due to

970
00:36:30,710 --> 00:36:28,560
rainy scattering

971
00:36:33,990 --> 00:36:30,720
and rayleigh scattering is

972
00:36:36,470 --> 00:36:34,000
is blue it's what makes the sky blue

973
00:36:38,790 --> 00:36:36,480
in the case of the earth so it's so it's

974
00:36:40,790 --> 00:36:38,800
it's the best at short wavelengths

975
00:36:43,190 --> 00:36:40,800
and it's also seen best at phase angles

976
00:36:44,630 --> 00:36:43,200
of about 90 degrees

977
00:36:46,550 --> 00:36:44,640
now you can see rayleigh scattering

978
00:36:49,030 --> 00:36:46,560
without polarization

979
00:36:51,910 --> 00:36:49,040
so if you have a spectrum of the earth

980
00:36:53,750 --> 00:36:51,920
this rise at the blue end

981
00:36:55,109 --> 00:36:53,760
is due to radius scattering

982
00:36:56,870 --> 00:36:55,119
if you have enough of it you may be able

983
00:36:58,230 --> 00:36:56,880
to pick out rayleigh scattering on that

984
00:36:59,270 --> 00:36:58,240
basis

985
00:37:00,950 --> 00:36:59,280
but

986
00:37:02,069 --> 00:37:00,960
um you can do it a lot better and more

987
00:37:04,069 --> 00:37:02,079
convincingly if you measure the

988
00:37:05,750 --> 00:37:04,079
polarization

989
00:37:08,630 --> 00:37:05,760
this stuff this really scattered light

990
00:37:09,990 --> 00:37:08,640
is highly polarized so radio scattering

991
00:37:14,470 --> 00:37:10,000
is a very

992
00:37:16,390 --> 00:37:14,480
signature of rayleigh scattering and

993
00:37:18,390 --> 00:37:16,400
this is the the venus

994
00:37:20,150 --> 00:37:18,400
phase curve that i showed earlier here's

995
00:37:23,910 --> 00:37:20,160
the rainbow but the bit we're interested

996
00:37:25,670 --> 00:37:23,920
in now is this peak at 90 degree phase

997
00:37:27,030 --> 00:37:25,680
angle which is rainy scattering

998
00:37:29,430 --> 00:37:27,040
polarization

999
00:37:30,310 --> 00:37:29,440
and you wouldn't be able to pick out

1000
00:37:32,630 --> 00:37:30,320
um

1001
00:37:34,069 --> 00:37:32,640
a spectral rise to the blue in the case

1002
00:37:35,670 --> 00:37:34,079
of venus because there is much less

1003
00:37:37,190 --> 00:37:35,680
rainy scattering going on in the case of

1004
00:37:38,950 --> 00:37:37,200
the earth and in fact there are

1005
00:37:40,950 --> 00:37:38,960
absorbers in

1006
00:37:42,230 --> 00:37:40,960
the venus atmosphere which absorb at the

1007
00:37:43,990 --> 00:37:42,240
in the ultraviolet which would actually

1008
00:37:44,950 --> 00:37:44,000
bring the spectrum down so competing

1009
00:37:47,030 --> 00:37:44,960
with that

1010
00:37:48,870 --> 00:37:47,040
but in the polarization curve you can

1011
00:37:51,349 --> 00:37:48,880
clearly see the signature of radius

1012
00:37:52,870 --> 00:37:51,359
scattering and what you can measure from

1013
00:37:53,910 --> 00:37:52,880
that is the

1014
00:37:56,150 --> 00:37:53,920
um

1015
00:37:58,069 --> 00:37:56,160
is an estimate of the total atmospheric

1016
00:37:59,670 --> 00:37:58,079
pressure and that's because because

1017
00:38:01,190 --> 00:37:59,680
unlike unlike spectroscopy we're only

1018
00:38:03,030 --> 00:38:01,200
seeing some of the gases all the gases

1019
00:38:04,710 --> 00:38:03,040
in the atmosphere contribute to radius

1020
00:38:06,710 --> 00:38:04,720
scattering so the amount of radio

1021
00:38:08,069 --> 00:38:06,720
scattering

1022
00:38:09,589 --> 00:38:08,079
allows you to tell the atmospheric

1023
00:38:11,750 --> 00:38:09,599
pressure of course in the case like

1024
00:38:13,510 --> 00:38:11,760
venus is the pressure cloud tops that

1025
00:38:22,230 --> 00:38:13,520
you're measuring you can't obviously see

1026
00:38:28,470 --> 00:38:25,589
so a combination of these um these three

1027
00:38:30,310 --> 00:38:28,480
effects the the glint the rainbows

1028
00:38:32,390 --> 00:38:30,320
and the rayleigh scattering can tell us

1029
00:38:35,670 --> 00:38:32,400
quite a lot about the atmosphere of the

1030
00:38:37,430 --> 00:38:35,680
terrestrial planet and even surface

1031
00:38:39,910 --> 00:38:37,440
so what what you would actually need to

1032
00:38:42,230 --> 00:38:39,920
do to observe this is use an instrument

1033
00:38:45,190 --> 00:38:42,240
like like tpfc

1034
00:38:46,470 --> 00:38:45,200
to observe the planet but to get any

1035
00:38:47,910 --> 00:38:46,480
useful information

1036
00:38:49,589 --> 00:38:47,920
from polarization you really need to be

1037
00:38:52,870 --> 00:38:49,599
able to follow the planet for a

1038
00:38:54,470 --> 00:38:52,880
significant part of its face cycle

1039
00:38:56,230 --> 00:38:54,480
so you can't just observe it when it's

1040
00:38:57,829 --> 00:38:56,240
at its greatest distance from the star

1041
00:38:59,510 --> 00:38:57,839
which is what you might otherwise think

1042
00:39:01,990 --> 00:38:59,520
of doing you need to be able to follow

1043
00:39:04,310 --> 00:39:02,000
it through a range of phases so if you

1044
00:39:06,390 --> 00:39:04,320
want to get the rainbow you need to be

1045
00:39:08,710 --> 00:39:06,400
able to look at this 40 degree phase

1046
00:39:09,910 --> 00:39:08,720
angle here if you want to see the glitch

1047
00:39:13,190 --> 00:39:09,920
you're going to be able to need to look

1048
00:39:16,069 --> 00:39:13,200
at phase phases over here

1049
00:39:19,589 --> 00:39:17,829
and you can't always do this because you

1050
00:39:22,550 --> 00:39:19,599
may just just not be lucky if the orbit

1051
00:39:24,550 --> 00:39:22,560
is face on you don't get any range of

1052
00:39:26,550 --> 00:39:24,560
phase angles and it just goes around the

1053
00:39:28,390 --> 00:39:26,560
star and it's always at 90 degrees phase

1054
00:39:29,349 --> 00:39:28,400
angle

1055
00:39:30,790 --> 00:39:29,359
but

1056
00:39:32,069 --> 00:39:30,800
um

1057
00:39:33,670 --> 00:39:32,079
but

1058
00:39:35,510 --> 00:39:33,680
for

1059
00:39:36,310 --> 00:39:35,520
most cases you should be able to reach

1060
00:39:39,270 --> 00:39:36,320
the

1061
00:39:41,109 --> 00:39:39,280
40 degree phase angle

1062
00:39:43,349 --> 00:39:41,119
that requires that the inclination of

1063
00:39:46,230 --> 00:39:43,359
the planet must be less than 50 degrees

1064
00:39:47,910 --> 00:39:46,240
and if they're randomly oriented

1065
00:39:50,470 --> 00:39:47,920
then about 64

1066
00:39:53,109 --> 00:39:50,480
of systems should be within that range

1067
00:39:59,349 --> 00:39:53,119
so it should be feasible for a large

1068
00:40:02,230 --> 00:40:01,190
but the as the planet is going around

1069
00:40:04,630 --> 00:40:02,240
the star it's also changing in

1070
00:40:05,349 --> 00:40:04,640
brightness quite a lot and

1071
00:40:09,430 --> 00:40:05,359
this

1072
00:40:12,870 --> 00:40:09,440
light curve of venus as a function of

1073
00:40:18,710 --> 00:40:14,230
so

1074
00:40:21,109 --> 00:40:18,720
phase it's fully eliminated

1075
00:40:23,109 --> 00:40:21,119
down here is present phases

1076
00:40:24,790 --> 00:40:23,119
and you can this helps to see why why

1077
00:40:26,950 --> 00:40:24,800
glimp observations are so difficult

1078
00:40:28,390 --> 00:40:26,960
because not that you would see in the

1079
00:40:30,230 --> 00:40:28,400
case of venus but other planets are

1080
00:40:31,990 --> 00:40:30,240
going to do similar things

1081
00:40:34,470 --> 00:40:32,000
observing the glint means observing down

1082
00:40:36,710 --> 00:40:34,480
here where the planet is only about 10

1083
00:40:38,310 --> 00:40:36,720
of its maximum brightness

1084
00:40:40,470 --> 00:40:38,320
the rayleigh scattering is a bit better

1085
00:40:42,230 --> 00:40:40,480
that's up here about 30

1086
00:40:43,750 --> 00:40:42,240
maximum brightness and also where the

1087
00:40:46,230 --> 00:40:43,760
planet is furthest from its star so

1088
00:40:47,990 --> 00:40:46,240
that's an optimum time to observe

1089
00:40:49,750 --> 00:40:48,000
and the primary rainbow is up where the

1090
00:40:50,870 --> 00:40:49,760
planet is really bright although it is

1091
00:41:00,790 --> 00:40:50,880
starting to get

1092
00:41:06,069 --> 00:41:02,870
so this is just a picture of the the

1093
00:41:07,829 --> 00:41:06,079
optical system of of tpsc which is the

1094
00:41:16,710 --> 00:41:07,839
sort of instrument we would want to use

1095
00:41:19,270 --> 00:41:17,750
and

1096
00:41:21,510 --> 00:41:19,280
what i'm going to do here is just a

1097
00:41:23,190 --> 00:41:21,520
quick comparison of of what's involved

1098
00:41:25,109 --> 00:41:23,200
in doing polarimetric observations

1099
00:41:26,710 --> 00:41:25,119
compared with spectroscopic observations

1100
00:41:29,270 --> 00:41:26,720
which is the way people have normally

1101
00:41:30,550 --> 00:41:29,280
been thought of characterizing planets

1102
00:41:32,069 --> 00:41:30,560
and

1103
00:41:33,270 --> 00:41:32,079
what i've estimated here is that you

1104
00:41:35,430 --> 00:41:33,280
would need

1105
00:41:37,109 --> 00:41:35,440
to detect for example the rainbow signal

1106
00:41:40,230 --> 00:41:37,119
on the radius scattering signal you'd

1107
00:41:41,430 --> 00:41:40,240
need to measure maybe six

1108
00:41:42,790 --> 00:41:41,440
phase angles

1109
00:41:44,630 --> 00:41:42,800
and you'd need to measure measure the

1110
00:41:46,230 --> 00:41:44,640
polarization of each one to an accuracy

1111
00:41:47,670 --> 00:41:46,240
of about two percent completely

1112
00:41:49,670 --> 00:41:47,680
sufficient to

1113
00:41:51,190 --> 00:41:49,680
comfortably see these effects

1114
00:41:54,790 --> 00:41:51,200
and you can calculate that that needs

1115
00:41:58,470 --> 00:41:56,470
and if you look at what's required for

1116
00:41:59,510 --> 00:41:58,480
spectroscopic observations

1117
00:42:01,349 --> 00:41:59,520
um

1118
00:42:02,390 --> 00:42:01,359
capable of detecting the spectral

1119
00:42:05,510 --> 00:42:02,400
features

1120
00:42:08,630 --> 00:42:05,520
similar calculation gives around 18 000

1121
00:42:10,470 --> 00:42:08,640
photons so so doing this is is no more

1122
00:42:12,630 --> 00:42:10,480
difficult than doing the spectroscopic

1123
00:42:13,829 --> 00:42:12,640
observation that doesn't mean it's easy

1124
00:42:15,109 --> 00:42:13,839
both of these are really difficult

1125
00:42:17,270 --> 00:42:15,119
things to do

1126
00:42:19,109 --> 00:42:17,280
but but the

1127
00:42:20,790 --> 00:42:19,119
but an important point is that you don't

1128
00:42:23,750 --> 00:42:20,800
have to do one or the other you can do

1129
00:42:25,829 --> 00:42:23,760
both of these at the same time

1130
00:42:27,990 --> 00:42:25,839
because you can use an instrument that

1131
00:42:28,829 --> 00:42:28,000
is that is measuring both polarization

1132
00:42:31,510 --> 00:42:28,839
and

1133
00:42:33,990 --> 00:42:31,520
spectroscopy um so there's it's not

1134
00:42:35,430 --> 00:42:34,000
really um increasing the the time you

1135
00:42:37,270 --> 00:42:35,440
need to characterize these planets

1136
00:42:38,630 --> 00:42:37,280
although it doesn't mean you need to

1137
00:42:40,630 --> 00:42:38,640
think of it think a bit more about how

1138
00:42:42,069 --> 00:42:40,640
you plan the observations you can do

1139
00:42:45,990 --> 00:42:42,079
both of these in principle with the same

1140
00:42:51,670 --> 00:42:49,510
and in fact the the designs for for tpfc

1141
00:42:54,390 --> 00:42:51,680
already include splitting the light into

1142
00:42:57,030 --> 00:42:54,400
two different polarization channels um i

1143
00:42:59,430 --> 00:42:57,040
believe this is this is done um

1144
00:43:01,510 --> 00:42:59,440
in order to allow the coronagraphic

1145
00:43:03,829 --> 00:43:01,520
systems to work optimally but it

1146
00:43:05,270 --> 00:43:03,839
essentially means that it's already got

1147
00:43:07,030 --> 00:43:05,280
built into it the

1148
00:43:14,230 --> 00:43:07,040
um the main instrumental requirement for

1149
00:43:18,069 --> 00:43:16,069
okay so um

1150
00:43:20,309 --> 00:43:18,079
how do we

1151
00:43:22,390 --> 00:43:20,319
follow up this work um

1152
00:43:23,589 --> 00:43:22,400
we would like to get better observations

1153
00:43:25,109 --> 00:43:23,599
of what

1154
00:43:26,550 --> 00:43:25,119
polarization phase curve the earth

1155
00:43:27,910 --> 00:43:26,560
actually produces

1156
00:43:29,349 --> 00:43:27,920
and there's a couple of ways you can do

1157
00:43:31,109 --> 00:43:29,359
this

1158
00:43:33,349 --> 00:43:31,119
you can observe the the lunar earth

1159
00:43:34,790 --> 00:43:33,359
shine this is this is earth light

1160
00:43:36,790 --> 00:43:34,800
scattered off the

1161
00:43:39,430 --> 00:43:36,800
dark side of the moon and this

1162
00:43:41,030 --> 00:43:39,440
technique's been used

1163
00:43:43,670 --> 00:43:41,040
by a number of groups to look at the

1164
00:43:45,190 --> 00:43:43,680
spectrum of the earth from space but in

1165
00:43:46,790 --> 00:43:45,200
principle you can look at polarization

1166
00:43:49,510 --> 00:43:46,800
of the earth in this way and in fact

1167
00:43:51,349 --> 00:43:49,520
audran dolphus did this back in the 50s

1168
00:43:53,589 --> 00:43:51,359
he measures the polarization of this

1169
00:43:56,230 --> 00:43:53,599
earth shine and he detected the rayleigh

1170
00:43:58,230 --> 00:43:56,240
scattering signal from the earth

1171
00:43:59,589 --> 00:43:58,240
the reflection of the moon complicates

1172
00:44:01,589 --> 00:43:59,599
things because that introduces

1173
00:44:03,190 --> 00:44:01,599
polarization effects of its own

1174
00:44:05,349 --> 00:44:03,200
um

1175
00:44:08,710 --> 00:44:05,359
it actually reduces the polarization to

1176
00:44:09,589 --> 00:44:08,720
about a third of the original amount

1177
00:44:12,069 --> 00:44:09,599
and

1178
00:44:13,910 --> 00:44:12,079
polarization observations are

1179
00:44:15,430 --> 00:44:13,920
now being attempted of the earthshine

1180
00:44:16,790 --> 00:44:15,440
particularly

1181
00:44:18,230 --> 00:44:16,800
at the

1182
00:44:20,630 --> 00:44:18,240
um

1183
00:44:23,510 --> 00:44:20,640
in the canary islands the iac is looking

1184
00:44:25,510 --> 00:44:23,520
at this the other way you can do it is

1185
00:44:26,790 --> 00:44:25,520
to observe the earth from space

1186
00:44:27,750 --> 00:44:26,800
and there's been

1187
00:44:29,910 --> 00:44:27,760
um

1188
00:44:31,829 --> 00:44:29,920
suggestions for simple space missions

1189
00:44:33,829 --> 00:44:31,839
that do this um

1190
00:44:36,630 --> 00:44:33,839
a couple of these were discussed at the

1191
00:44:38,950 --> 00:44:36,640
the recent pep cyclone meeting by nick

1192
00:44:40,710 --> 00:44:38,960
wolfe and maggie turnbull so one idea

1193
00:44:41,990 --> 00:44:40,720
was to have have something that would

1194
00:44:43,589 --> 00:44:42,000
actually operate from the surface of the

1195
00:44:45,910 --> 00:44:43,599
moon that the astronauts would take with

1196
00:44:49,910 --> 00:44:45,920
them and point at the earth

1197
00:44:51,510 --> 00:44:49,920
or you can have a spacecraft in

1198
00:44:58,630 --> 00:44:51,520
in space near the moon looking back at

1199
00:45:02,150 --> 00:45:00,069
and then the other thing i'm looking at

1200
00:45:05,109 --> 00:45:02,160
is is improved modeling of the

1201
00:45:06,710 --> 00:45:05,119
polarization effects um

1202
00:45:08,870 --> 00:45:06,720
most of the models i described early

1203
00:45:10,790 --> 00:45:08,880
were earlier were only using single

1204
00:45:12,230 --> 00:45:10,800
scattering models

1205
00:45:14,230 --> 00:45:12,240
but i have a

1206
00:45:15,510 --> 00:45:14,240
radio transfer model for plant free

1207
00:45:17,109 --> 00:45:15,520
atmospheres that i use to produce

1208
00:45:19,190 --> 00:45:17,119
planetary spectra

1209
00:45:21,990 --> 00:45:19,200
i've used successfully for more than the

1210
00:45:23,670 --> 00:45:22,000
spectra of earth mars venus and titan

1211
00:45:25,910 --> 00:45:23,680
shown here

1212
00:45:27,589 --> 00:45:25,920
and i'm planning to incorporate

1213
00:45:29,510 --> 00:45:27,599
polarization into this so that i have a

1214
00:45:31,829 --> 00:45:29,520
model capable of predicting uh

1215
00:45:32,950 --> 00:45:31,839
polarization of a planet at any

1216
00:45:35,349 --> 00:45:32,960
wavelength

1217
00:45:37,910 --> 00:45:35,359
and this will enable accurate estimates

1218
00:45:39,270 --> 00:45:37,920
of the rainbow and glint effects for a

1219
00:45:46,630 --> 00:45:39,280
range of different possible

1220
00:45:50,390 --> 00:45:47,589
so

1221
00:45:52,790 --> 00:45:50,400
um polarization could provide important

1222
00:45:53,829 --> 00:45:52,800
information about a planet's atmosphere

1223
00:45:56,550 --> 00:45:53,839
the presence

1224
00:45:58,470 --> 00:45:56,560
or absence of clouds cloud composition

1225
00:46:00,150 --> 00:45:58,480
the atmospheric pressure

1226
00:46:02,069 --> 00:46:00,160
and and even the presence of surface

1227
00:46:04,630 --> 00:46:02,079
oceans although this i think is

1228
00:46:06,630 --> 00:46:04,640
currently is difficult with a mission on

1229
00:46:08,470 --> 00:46:06,640
the scale of tpfc

1230
00:46:10,790 --> 00:46:08,480
probably needs an even bigger telescope

1231
00:46:12,309 --> 00:46:10,800
than that

1232
00:46:14,470 --> 00:46:12,319
polarimetric and spectroscopic

1233
00:46:15,910 --> 00:46:14,480
techniques are complementary for

1234
00:46:17,510 --> 00:46:15,920
planetary characterization they give

1235
00:46:19,190 --> 00:46:17,520
very different information about the

1236
00:46:21,109 --> 00:46:19,200
planet

1237
00:46:23,510 --> 00:46:21,119
and the observations should be feasible

1238
00:46:24,950 --> 00:46:23,520
with emission like tpfc

1239
00:46:27,750 --> 00:46:24,960
in similar integration times to

1240
00:46:30,710 --> 00:46:27,760
spectroscopic observations

1241
00:46:33,190 --> 00:46:30,720
so the recommendations are that when

1242
00:46:34,390 --> 00:46:33,200
the tpfc mission or something similar is

1243
00:46:35,670 --> 00:46:34,400
continued

1244
00:46:37,670 --> 00:46:35,680
because the uh

1245
00:46:40,630 --> 00:46:37,680
that mission is uh is effectively on

1246
00:46:43,589 --> 00:46:40,640
hold it's not not funded at the moment

1247
00:46:45,430 --> 00:46:43,599
it must include polarimetry capabilities

1248
00:46:46,470 --> 00:46:45,440
in the instrument design and observing

1249
00:46:48,550 --> 00:46:46,480
plan

1250
00:46:52,630 --> 00:46:48,560
and polarization needs to be included in

1251
00:46:54,390 --> 00:46:52,640
models for extrasolar planet

1252
00:46:56,470 --> 00:46:54,400
atmospheres

1253
00:46:58,390 --> 00:46:56,480
such as those that the vpl team is

1254
00:47:00,390 --> 00:46:58,400
working on

1255
00:47:01,910 --> 00:47:00,400
now do i have a bit of time to

1256
00:47:03,670 --> 00:47:01,920
just say a bit about the hot jupiter

1257
00:47:04,470 --> 00:47:03,680
work okay

1258
00:47:05,190 --> 00:47:04,480
yep

1259
00:47:09,829 --> 00:47:05,200
so

1260
00:47:11,829 --> 00:47:09,839
we may be able to do way in the future

1261
00:47:13,750 --> 00:47:11,839
with missions like tpf

1262
00:47:14,950 --> 00:47:13,760
but there is actually um one type of

1263
00:47:16,630 --> 00:47:14,960
planet that we might be able to detect

1264
00:47:18,950 --> 00:47:16,640
polarization from now and that's that's

1265
00:47:20,950 --> 00:47:18,960
these hot jupiter type systems

1266
00:47:24,790 --> 00:47:20,960
where you have a planet orbiting very

1267
00:47:26,790 --> 00:47:24,800
close to the star a giant planet

1268
00:47:28,230 --> 00:47:26,800
um

1269
00:47:29,510 --> 00:47:28,240
and these are

1270
00:47:31,270 --> 00:47:29,520
these these are likely to be the

1271
00:47:32,309 --> 00:47:31,280
brightest planets in scattered light

1272
00:47:33,589 --> 00:47:32,319
because they're big planets and they're

1273
00:47:35,750 --> 00:47:33,599
very close to the stars so they're

1274
00:47:37,750 --> 00:47:35,760
receiving a lot of light from the star

1275
00:47:40,069 --> 00:47:37,760
and the idea is that

1276
00:47:41,589 --> 00:47:40,079
looking at the combined light the star

1277
00:47:43,670 --> 00:47:41,599
and planet

1278
00:47:45,670 --> 00:47:43,680
light from the star is unpolarized the

1279
00:47:46,950 --> 00:47:45,680
planet's light might be polarized at a

1280
00:47:49,190 --> 00:47:46,960
few percent

1281
00:47:51,510 --> 00:47:49,200
10 percent or so

1282
00:47:53,589 --> 00:47:51,520
but it's but it's only one ten thousand

1283
00:47:55,270 --> 00:47:53,599
the total light of the system

1284
00:47:56,870 --> 00:47:55,280
if you look at the combined light and

1285
00:47:57,990 --> 00:47:56,880
can measure the polarization accurately

1286
00:47:59,990 --> 00:47:58,000
enough should be able to see a

1287
00:48:02,150 --> 00:48:00,000
polarization

1288
00:48:03,910 --> 00:48:02,160
at a fractional level of something like

1289
00:48:06,550 --> 00:48:03,920
ten to the minus five or less probably a

1290
00:48:08,550 --> 00:48:06,560
few times ten to minus six

1291
00:48:11,430 --> 00:48:08,560
and this this was actually modeled by uh

1292
00:48:12,950 --> 00:48:11,440
sega whitney and sassaloth in 2000 and

1293
00:48:15,589 --> 00:48:12,960
they produced the sort of polarization

1294
00:48:17,750 --> 00:48:15,599
curves you might expect to see from a

1295
00:48:19,589 --> 00:48:17,760
for one of these planetary systems

1296
00:48:20,870 --> 00:48:19,599
and they concluded that the polarization

1297
00:48:23,270 --> 00:48:20,880
signatures are well under the current

1298
00:48:25,510 --> 00:48:23,280
limits of detectability which are a few

1299
00:48:27,510 --> 00:48:25,520
times 10 to the minus 4 in fractional

1300
00:48:29,270 --> 00:48:27,520
polarization

1301
00:48:30,710 --> 00:48:29,280
and that was probably true for

1302
00:48:32,950 --> 00:48:30,720
astronomical polarimeters that were

1303
00:48:35,190 --> 00:48:32,960
available at the time

1304
00:48:37,829 --> 00:48:35,200
but um we knew that it's possible to do

1305
00:48:39,910 --> 00:48:37,839
polarization much better than that

1306
00:48:40,950 --> 00:48:39,920
in particular from the work of james

1307
00:48:42,630 --> 00:48:40,960
kemp

1308
00:48:44,790 --> 00:48:42,640
who'd developed

1309
00:48:47,109 --> 00:48:44,800
polarometric techniques using a device

1310
00:48:48,309 --> 00:48:47,119
called a photoelastic modulator and he'd

1311
00:48:49,270 --> 00:48:48,319
actually measured the polarization of

1312
00:48:53,510 --> 00:48:49,280
the sun

1313
00:48:56,950 --> 00:48:54,710
so um

1314
00:48:58,950 --> 00:48:56,960
together with the the group at

1315
00:49:00,950 --> 00:48:58,960
university of hartfordshire uh jim huff

1316
00:49:02,470 --> 00:49:00,960
and phil lucas

1317
00:49:04,870 --> 00:49:02,480
we came up with a design for a

1318
00:49:06,390 --> 00:49:04,880
polarimeter that could measure stellar

1319
00:49:08,549 --> 00:49:06,400
polarizations

1320
00:49:10,549 --> 00:49:08,559
to an accuracy of about one part in a

1321
00:49:13,030 --> 00:49:10,559
million and this is using these things

1322
00:49:15,829 --> 00:49:13,040
called photoelastic modulators which are

1323
00:49:17,589 --> 00:49:15,839
polarization modulators where you have a

1324
00:49:19,750 --> 00:49:17,599
um

1325
00:49:21,349 --> 00:49:19,760
a piece of optical material and you make

1326
00:49:24,710 --> 00:49:21,359
it oscillate as it's its natural

1327
00:49:26,390 --> 00:49:24,720
frequency by piezo transducers

1328
00:49:28,309 --> 00:49:26,400
attached to it and it produces

1329
00:49:33,430 --> 00:49:28,319
polarization modulations at high

1330
00:49:35,670 --> 00:49:33,440
frequencies um 20 kilohertz in our case

1331
00:49:37,670 --> 00:49:35,680
and these devices have been used

1332
00:49:39,190 --> 00:49:37,680
for both in astronomy and in

1333
00:49:41,990 --> 00:49:39,200
laboratory conditions for doing

1334
00:49:44,230 --> 00:49:42,000
polarization with very high accuracy

1335
00:49:45,750 --> 00:49:44,240
so this is the

1336
00:49:47,829 --> 00:49:45,760
schematic of the

1337
00:49:49,430 --> 00:49:47,839
device we built it as photoelastic

1338
00:49:51,990 --> 00:49:49,440
modulators

1339
00:49:54,390 --> 00:49:52,000
a walliston prism which splits the light

1340
00:49:56,150 --> 00:49:54,400
into two polarization beams

1341
00:49:58,630 --> 00:49:56,160
and the detectors are

1342
00:50:00,390 --> 00:49:58,640
avalanche photodiodes

1343
00:50:02,470 --> 00:50:00,400
which we chose because they

1344
00:50:04,390 --> 00:50:02,480
they're linear up to very high photon

1345
00:50:06,549 --> 00:50:04,400
rates and to do polarization to this

1346
00:50:08,390 --> 00:50:06,559
accuracy to to measure ten to the minus

1347
00:50:09,990 --> 00:50:08,400
six polarization effects basically the

1348
00:50:12,870 --> 00:50:10,000
ten to the twelve photons so you need to

1349
00:50:13,990 --> 00:50:12,880
work at very high photon levels

1350
00:50:15,190 --> 00:50:14,000
and so

1351
00:50:17,270 --> 00:50:15,200
so this is the instrument it's just an

1352
00:50:22,309 --> 00:50:17,280
aperture polarimeter just measures the

1353
00:50:27,349 --> 00:50:23,190
and

1354
00:50:29,349 --> 00:50:27,359
said it was sitting on the back of the

1355
00:50:36,630 --> 00:50:29,359
willie herschel telescope

1356
00:50:39,990 --> 00:50:38,470
and this is the the sort of results that

1357
00:50:41,670 --> 00:50:40,000
come out of it this is this is looking

1358
00:50:44,069 --> 00:50:41,680
at the

1359
00:50:46,390 --> 00:50:44,079
what we call the the second stage

1360
00:50:48,549 --> 00:50:46,400
chopping signal so we actually we

1361
00:50:50,630 --> 00:50:48,559
modulate the

1362
00:50:53,109 --> 00:50:50,640
light using the rapidly using the

1363
00:50:55,349 --> 00:50:53,119
photoelastic modulator but then we also

1364
00:50:56,790 --> 00:50:55,359
rotate um optical elements within the

1365
00:50:59,829 --> 00:50:56,800
system to reverse the sign of that

1366
00:51:01,190 --> 00:50:59,839
modulation um every um

1367
00:51:02,950 --> 00:51:01,200
every uh

1368
00:51:05,349 --> 00:51:02,960
couple of minutes or so

1369
00:51:07,910 --> 00:51:05,359
so this

1370
00:51:10,470 --> 00:51:07,920
square wave pattern is the uh

1371
00:51:11,430 --> 00:51:10,480
the polarized signal we're seeing from

1372
00:51:13,270 --> 00:51:11,440
the

1373
00:51:17,510 --> 00:51:13,280
two

1374
00:51:18,870 --> 00:51:17,520
avalanche photodiodes

1375
00:51:23,030 --> 00:51:18,880
and that

1376
00:51:24,470 --> 00:51:23,040
polarization of

1377
00:51:26,230 --> 00:51:24,480
i can't read that from here but it's

1378
00:51:27,349 --> 00:51:26,240
something like ten to the minus four

1379
00:51:28,630 --> 00:51:27,359
it's a

1380
00:51:29,829 --> 00:51:28,640
it's what would have been about the

1381
00:51:31,510 --> 00:51:29,839
limit of what you could measure with

1382
00:51:33,750 --> 00:51:31,520
previous astronomical instruments and it

1383
00:51:37,109 --> 00:51:33,760
gives a huge signal without system

1384
00:51:39,910 --> 00:51:37,119
and then these are smaller polarizations

1385
00:51:42,069 --> 00:51:39,920
between 20 times 10 to the minus 6

1386
00:51:44,069 --> 00:51:42,079
and 12 times 10 to the minus 6 that show

1387
00:51:46,470 --> 00:51:44,079
we can fairly easily see

1388
00:51:48,870 --> 00:51:46,480
polarizations at this 10 to the minus 6

1389
00:51:53,750 --> 00:51:50,470
we also have to remove telescope

1390
00:51:55,910 --> 00:51:53,760
polarization which we do by

1391
00:51:57,670 --> 00:51:55,920
using the fact that it's an an altamis

1392
00:51:58,950 --> 00:51:57,680
telescope and we can see

1393
00:52:05,270 --> 00:51:58,960
the

1394
00:52:07,829 --> 00:52:05,280
different hour angles

1395
00:52:09,510 --> 00:52:07,839
so we've observed a number of stars

1396
00:52:13,430 --> 00:52:09,520
this is

1397
00:52:15,670 --> 00:52:13,440
data of bright stars

1398
00:52:18,069 --> 00:52:15,680
nearby bright stars so most of the stars

1399
00:52:19,270 --> 00:52:18,079
and the size of the the disc here is is

1400
00:52:20,710 --> 00:52:19,280
a measure of the

1401
00:52:24,150 --> 00:52:20,720
polarization

1402
00:52:25,990 --> 00:52:24,160
so these big ones here are about 200

1403
00:52:27,990 --> 00:52:26,000
times 10 to the minus six so everything

1404
00:52:29,349 --> 00:52:28,000
in units at ten to the minus six

1405
00:52:31,510 --> 00:52:29,359
so these are

1406
00:52:33,990 --> 00:52:31,520
what we're seeing up here is is a region

1407
00:52:35,750 --> 00:52:34,000
where we're getting far enough um out to

1408
00:52:37,829 --> 00:52:35,760
see interstellar polarization effects to

1409
00:52:38,630 --> 00:52:37,839
see interstellar dust

1410
00:52:40,309 --> 00:52:38,640
but

1411
00:52:42,230 --> 00:52:40,319
um most of these other stars have very

1412
00:52:44,390 --> 00:52:42,240
low polarizations

1413
00:52:45,670 --> 00:52:44,400
except for a couple of cases which we

1414
00:52:47,750 --> 00:52:45,680
think have

1415
00:52:49,589 --> 00:52:47,760
um intrinsic polarization regulus is

1416
00:52:52,069 --> 00:52:49,599
actually a rapidly rotating flattened

1417
00:52:53,670 --> 00:52:52,079
star and vega has a dust disc around it

1418
00:52:55,589 --> 00:52:53,680
so they're both cases that are probably

1419
00:52:58,549 --> 00:52:55,599
producing polarization

1420
00:53:00,390 --> 00:52:58,559
where does the sun come in there

1421
00:53:01,589 --> 00:53:00,400
the sun well it's not on the diagram but

1422
00:53:02,790 --> 00:53:01,599
it would be uh

1423
00:53:05,190 --> 00:53:02,800
it would be it's less than ten to the

1424
00:53:08,150 --> 00:53:05,200
minus six so the the smallest dots on

1425
00:53:12,710 --> 00:53:11,109
um okay well there's

1426
00:53:14,309 --> 00:53:12,720
the basic result so far is that we've

1427
00:53:16,309 --> 00:53:14,319
looked at one of these subject systems

1428
00:53:17,990 --> 00:53:16,319
and we've we've failed to detect the

1429
00:53:19,190 --> 00:53:18,000
polarization signature that was

1430
00:53:21,109 --> 00:53:19,200
predicted

1431
00:53:23,510 --> 00:53:21,119
but we probably chose star which was not

1432
00:53:25,109 --> 00:53:23,520
the best one for a number of reasons

1433
00:53:28,870 --> 00:53:25,119
so we're continuing observations of

1434
00:53:32,950 --> 00:53:30,790
and

1435
00:53:36,230 --> 00:53:32,960
we have found various other interesting

1436
00:53:41,510 --> 00:53:38,150
we've

1437
00:53:42,790 --> 00:53:41,520
nearby stars have very low polarization

1438
00:53:46,230 --> 00:53:42,800
which is helpful for detecting the

1439
00:53:49,270 --> 00:53:47,030
um

1440
00:53:51,750 --> 00:53:49,280
we don't yet see the expected

1441
00:53:54,230 --> 00:53:51,760
polarization signature of a hot jupiter

1442
00:53:56,150 --> 00:53:54,240
planet but we may be able to

1443
00:53:57,829 --> 00:53:56,160
do so by looking at other systems we've

1444
00:53:59,109 --> 00:53:57,839
also discovered interesting things about

1445
00:54:00,790 --> 00:53:59,119
polarization effects in the earth's

1446
00:54:02,630 --> 00:54:00,800
atmosphere um

1447
00:54:04,470 --> 00:54:02,640
at the la palma site frequently gets to

1448
00:54:06,230 --> 00:54:04,480
horror and dust blowing over and we've

1449
00:54:07,589 --> 00:54:06,240
found that that's a horrendous produces

1450
00:54:09,030 --> 00:54:07,599
lots of polarization or lots of

1451
00:54:10,549 --> 00:54:09,040
polarization of the levels we're looking

1452
00:54:12,390 --> 00:54:10,559
at which is actually tells us

1453
00:54:13,829 --> 00:54:12,400
interesting things about

1454
00:54:15,109 --> 00:54:13,839
what how does particles behave in the

1455
00:54:19,589 --> 00:54:15,119
earth's atmosphere because it implies

1456
00:54:29,349 --> 00:54:20,549
okay

1457
00:54:33,670 --> 00:54:31,430
uh it seems like you could use the

1458
00:54:36,069 --> 00:54:33,680
requirement of having the correct

1459
00:54:39,030 --> 00:54:36,079
phase angle to actually calculate the

1460
00:54:41,829 --> 00:54:39,040
angle of inclination um

1461
00:54:44,230 --> 00:54:41,839
is that something worthwhile have you

1462
00:54:45,829 --> 00:54:44,240
thought about that

1463
00:54:49,349 --> 00:54:45,839
um which are you talking about the hot

1464
00:54:51,109 --> 00:54:49,359
jupiters or the oh sorry the the planet

1465
00:54:53,109 --> 00:54:51,119
um

1466
00:54:55,829 --> 00:54:53,119
well yeah for example the phase the

1467
00:54:57,589 --> 00:54:55,839
required phasing of blind

1468
00:54:59,430 --> 00:54:57,599
you could maybe use to figure out the

1469
00:55:01,349 --> 00:54:59,440
inclination between the

1470
00:55:02,870 --> 00:55:01,359
planet's orbit and the

1471
00:55:04,470 --> 00:55:02,880
star which

1472
00:55:06,549 --> 00:55:04,480
i don't know if the glint tells you that

1473
00:55:08,630 --> 00:55:06,559
but polarization angles in general will

1474
00:55:10,069 --> 00:55:08,640
do that because

1475
00:55:12,390 --> 00:55:10,079
the polarization

1476
00:55:15,190 --> 00:55:12,400
tells you the

1477
00:55:16,790 --> 00:55:15,200
the vector to the star effectively

1478
00:55:18,150 --> 00:55:16,800
polarization is always orthogonal to the

1479
00:55:19,430 --> 00:55:18,160
stars vectors so if you can see how that

1480
00:55:22,710 --> 00:55:19,440
rotates around the object you can get

1481
00:55:26,630 --> 00:55:24,870
i'm curious if you if the glint can

1482
00:55:28,309 --> 00:55:26,640
allow you to distinguish between uh

1483
00:55:29,829 --> 00:55:28,319
water ice or some other liquid if

1484
00:55:31,190 --> 00:55:29,839
there's characteristics

1485
00:55:32,870 --> 00:55:31,200
it'll tell you what uh but it's actually

1486
00:55:34,470 --> 00:55:32,880
collecting

1487
00:55:37,510 --> 00:55:34,480
i don't think you can easily tell that

1488
00:55:39,190 --> 00:55:37,520
all you can tell is that you've got a

1489
00:55:41,190 --> 00:55:39,200
reflecting surface and i think you

1490
00:55:43,109 --> 00:55:41,200
probably have to figure out from other

1491
00:55:45,109 --> 00:55:43,119
um properties of the atmosphere what

1492
00:55:46,230 --> 00:55:45,119
that is likely to be so i guess other

1493
00:55:54,390 --> 00:55:46,240
other information on the atmosphere

1494
00:55:58,789 --> 00:55:55,990
how long did you look at it so you can

1495
00:55:59,910 --> 00:55:58,799
just describe the observations and

1496
00:56:03,589 --> 00:55:59,920
how

1497
00:56:05,510 --> 00:56:03,599
predictions and so forth

1498
00:56:08,150 --> 00:56:05,520
well well this is this is what we're

1499
00:56:09,670 --> 00:56:08,160
seeing for tomato okay so we got a

1500
00:56:11,750 --> 00:56:09,680
reasonable coverage of the phase

1501
00:56:12,549 --> 00:56:11,760
although there's a few gaps

1502
00:56:14,870 --> 00:56:12,559
um

1503
00:56:16,950 --> 00:56:14,880
and we did seem to see some polarization

1504
00:56:18,950 --> 00:56:16,960
but the curve is completely wrong for

1505
00:56:20,870 --> 00:56:18,960
what we would expect

1506
00:56:22,309 --> 00:56:20,880
if it was a it was a clear atmosphere

1507
00:56:24,390 --> 00:56:22,319
for example we'd expect peak

1508
00:56:27,349 --> 00:56:24,400
polarization to be around 90 degrees

1509
00:56:28,829 --> 00:56:27,359
which is probably where we're seeing

1510
00:56:30,870 --> 00:56:28,839
low

1511
00:56:32,710 --> 00:56:30,880
polarizations we seem to be seeing high

1512
00:56:35,349 --> 00:56:32,720
polarizations here where we wouldn't

1513
00:56:37,270 --> 00:56:35,359
expect to see to see much polarization

1514
00:56:39,430 --> 00:56:37,280
so we don't really know what's going on

1515
00:56:41,589 --> 00:56:39,440
but what we suspect is that what we're

1516
00:56:43,030 --> 00:56:41,599
seeing is probably not due to the planet

1517
00:56:44,309 --> 00:56:43,040
it's probably due to what's going on on

1518
00:56:45,910 --> 00:56:44,319
the staff

1519
00:56:47,910 --> 00:56:45,920
because that that's consistent with

1520
00:56:50,069 --> 00:56:47,920
what's come out of the

1521
00:56:51,589 --> 00:56:50,079
the the canadian most satellite has been

1522
00:56:53,910 --> 00:56:51,599
observing this thing as well looking for

1523
00:56:55,349 --> 00:56:53,920
the for the light curve

1524
00:56:56,789 --> 00:56:55,359
that you'd expect from scaling off the

1525
00:56:58,390 --> 00:56:56,799
planet and they don't see anything like

1526
00:56:59,589 --> 00:56:58,400
that but they do see bigger effects

1527
00:57:00,870 --> 00:56:59,599
which they think are coming from the

1528
00:57:04,309 --> 00:57:00,880
star

1529
00:57:05,670 --> 00:57:04,319
active

1530
00:57:08,230 --> 00:57:05,680
which means there there might be some

1531
00:57:10,150 --> 00:57:08,240
polarization coming from magnetic zeeman

1532
00:57:11,349 --> 00:57:10,160
effects and so that might be confusing

1533
00:57:13,990 --> 00:57:11,359
us

1534
00:57:18,470 --> 00:57:14,000
but is each of these data points

1535
00:57:20,630 --> 00:57:18,480
just looking once or did you have many

1536
00:57:23,109 --> 00:57:20,640
many times

1537
00:57:25,270 --> 00:57:23,119
we followed it over well several cycles

1538
00:57:27,670 --> 00:57:25,280
but but with incomplete coverage on all

1539
00:57:29,349 --> 00:57:27,680
of them because we listen

1540
00:57:31,829 --> 00:57:29,359
well you missed you missed the daytime

1541
00:57:34,230 --> 00:57:31,839
party anyway it's the periods only

1542
00:57:36,470 --> 00:57:34,240
three point something days

1543
00:57:48,789 --> 00:57:36,480
and we generally missed some bits due to

1544
00:57:48,799 --> 00:57:52,829
each data point is plotted there though

1545
00:57:57,190 --> 00:57:55,589
yes what

1546
00:57:59,270 --> 00:57:57,200
excuse me

1547
00:58:00,470 --> 00:57:59,280
those uh

1548
00:58:01,750 --> 00:58:00,480
sorry

1549
00:58:04,230 --> 00:58:01,760
the uh

1550
00:58:05,430 --> 00:58:04,240
the tpf integration times you were

1551
00:58:07,510 --> 00:58:05,440
talking about there i think are around

1552
00:58:09,270 --> 00:58:07,520
the order of a week or two so i was

1553
00:58:12,230 --> 00:58:09,280
wondering to get eighteen thousand or

1554
00:58:13,589 --> 00:58:12,240
whatever you need yeah but it's gonna be

1555
00:58:14,870 --> 00:58:13,599
for something like

1556
00:58:17,750 --> 00:58:14,880
earth

1557
00:58:20,150 --> 00:58:17,760
which has both these water and cloud

1558
00:58:22,390 --> 00:58:20,160
systems and it's gonna be but also land

1559
00:58:24,309 --> 00:58:22,400
how much is the the rotation

1560
00:58:25,510 --> 00:58:24,319
of the planet in that

1561
00:58:27,270 --> 00:58:25,520
ten days

1562
00:58:30,630 --> 00:58:27,280
if you will gonna smear out some of

1563
00:58:34,390 --> 00:58:32,390
um

1564
00:58:35,589 --> 00:58:34,400
it's it's obviously gonna have some

1565
00:58:36,390 --> 00:58:35,599
effect

1566
00:58:37,510 --> 00:58:36,400
um

1567
00:58:39,349 --> 00:58:37,520
yeah i mean

1568
00:58:41,030 --> 00:58:39,359
well the not just the rotation but the

1569
00:58:42,630 --> 00:58:41,040
fact that the cloud cover is

1570
00:58:44,789 --> 00:58:42,640
edging all the time

1571
00:58:46,789 --> 00:58:44,799
um

1572
00:58:48,309 --> 00:58:46,799
i think it's

1573
00:58:49,270 --> 00:58:48,319
i think these are these are on the whole

1574
00:58:50,789 --> 00:58:49,280
big enough

1575
00:58:52,230 --> 00:58:50,799
certainly the rainbows and the rainy

1576
00:58:54,150 --> 00:58:52,240
scattering effects are big enough that

1577
00:58:56,390 --> 00:58:54,160
they should show up i'm not sure about

1578
00:58:57,670 --> 00:58:56,400
blind i mean obviously the blood spot

1579
00:59:00,870 --> 00:58:57,680
can disappear completely if a cloud

1580
00:59:03,190 --> 00:59:02,230
yes

1581
00:59:05,430 --> 00:59:03,200
so

1582
00:59:07,750 --> 00:59:05,440
but um um

1583
00:59:09,349 --> 00:59:07,760
i mean enric poller has been looking for

1584
00:59:11,109 --> 00:59:09,359
to see if you can see the rotation of

1585
00:59:13,670 --> 00:59:11,119
the earth in the

1586
00:59:15,510 --> 00:59:13,680
um earthshite data and i think he's

1587
00:59:17,190 --> 00:59:15,520
found it quite difficult to pick it out

1588
00:59:21,270 --> 00:59:17,200
so rotation effect doesn't seem to be

1589
00:59:24,470 --> 00:59:22,950
so i was talking to bill sparks at the

1590
00:59:27,430 --> 00:59:24,480
apps icon

1591
00:59:29,829 --> 00:59:27,440
and it was in looking at

1592
00:59:33,270 --> 00:59:29,839
being able to detect various color that

1593
00:59:35,030 --> 00:59:33,280
might be involved in photosynthesis

1594
00:59:37,589 --> 00:59:35,040
and not just

1595
00:59:38,870 --> 00:59:37,599
you know green plants but perhaps

1596
00:59:40,789 --> 00:59:38,880
red plants

1597
00:59:43,510 --> 00:59:40,799
and

1598
00:59:45,030 --> 00:59:43,520
is there a possibility of using

1599
00:59:47,670 --> 00:59:45,040
polarization that

1600
00:59:49,270 --> 00:59:47,680
not necessarily look at color from

1601
00:59:52,950 --> 00:59:49,280
photosynthesis

1602
00:59:54,870 --> 00:59:52,960
color that might be associated with

1603
00:59:57,190 --> 00:59:54,880
a chemical signal

1604
00:59:59,910 --> 00:59:57,200
organic or inorganic signal for example

1605
01:00:01,910 --> 00:59:59,920
the dark coloration on the leads of

1606
01:00:04,630 --> 01:00:01,920
europa for example could that be

1607
01:00:06,950 --> 01:00:04,640
detected with polarization and could we

1608
01:00:13,670 --> 01:00:06,960
actually find a way to delineate what

1609
01:00:18,150 --> 01:00:16,630
well i mean the reason the reason

1610
01:00:20,390 --> 01:00:18,160
bill sparks is able to detect

1611
01:00:21,829 --> 01:00:20,400
polarization signatures is is because

1612
01:00:27,829 --> 01:00:21,839
these are

1613
01:00:29,589 --> 01:00:27,839
so so things like chlorophylls

1614
01:00:31,510 --> 01:00:29,599
do produce a circular polarization

1615
01:00:33,910 --> 01:00:31,520
signature

1616
01:00:36,630 --> 01:00:35,109
organic

1617
01:00:39,829 --> 01:00:36,640
in principle any

1618
01:00:43,349 --> 01:00:39,839
any organic molecule will do that but

1619
01:00:45,349 --> 01:00:43,359
in most molecules the circular dichroism

1620
01:00:48,309 --> 01:00:45,359
effects are more in the uv so you might

1621
01:00:50,150 --> 01:00:48,319
have to go far into the uv to to see to

1622
01:00:51,910 --> 01:00:50,160
see strong effects

1623
01:00:52,870 --> 01:00:51,920
but all of these are very small signals

1624
01:00:54,710 --> 01:00:52,880
i mean

1625
01:00:55,829 --> 01:00:54,720
the effects bill is seeing is sort of

1626
01:00:57,910 --> 01:00:55,839
0.2

1627
01:00:59,670 --> 01:00:57,920
polarization at best

1628
01:01:01,510 --> 01:00:59,680
so we're looking for something sort of

1629
01:01:03,190 --> 01:01:01,520
100 times down on the

1630
01:01:05,030 --> 01:01:03,200
sort of atmospheric polarizations i'm

1631
01:01:06,309 --> 01:01:05,040
talking about here

1632
01:01:11,910 --> 01:01:06,319
so

1633
01:01:13,990 --> 01:01:11,920
be feasible

1634
01:01:16,069 --> 01:01:14,000
is there a future for

1635
01:01:19,589 --> 01:01:16,079
making this technique

1636
01:01:21,990 --> 01:01:19,599
more sensitive than it is right now

1637
01:01:25,430 --> 01:01:22,000
is there a mechanism to make it 100

1638
01:01:26,870 --> 01:01:25,440
times more sensitive

1639
01:01:28,390 --> 01:01:26,880
well if we're talking about exoplanets

1640
01:01:29,829 --> 01:01:28,400
the way you make it 100 times more

1641
01:01:33,190 --> 01:01:29,839
sensitive is make your telescope 100

1642
01:01:36,230 --> 01:01:34,710
if you talk about looking for things in

1643
01:01:37,510 --> 01:01:36,240
the solar system

1644
01:01:39,750 --> 01:01:37,520
then we

1645
01:01:41,670 --> 01:01:39,760
i guess we ought to be able to

1646
01:01:43,589 --> 01:01:41,680
push circular polarization measurements

1647
01:01:44,390 --> 01:01:43,599
down to these sort of ten to the minus

1648
01:01:46,549 --> 01:01:44,400
six

1649
01:01:47,829 --> 01:01:46,559
levels we're achieving with with

1650
01:01:49,829 --> 01:01:47,839
planetfall

1651
01:01:51,670 --> 01:01:49,839
principle which is

1652
01:01:53,670 --> 01:01:51,680
which is better than anybody's actually

1653
01:01:58,309 --> 01:01:53,680
used in a solar system observations so

1654
01:02:03,829 --> 01:02:00,150
how much you you showed the plots that

1655
01:02:05,750 --> 01:02:03,839
show basically the the peak migrating at

1656
01:02:06,950 --> 01:02:05,760
a single wavelength if i if i understood

1657
01:02:08,309 --> 01:02:06,960
correctly with the different

1658
01:02:09,990 --> 01:02:08,319
compositions how much additional

1659
01:02:11,990 --> 01:02:10,000
diagnostic information you get by

1660
01:02:14,470 --> 01:02:12,000
looking at the migration of a peak

1661
01:02:16,870 --> 01:02:14,480
so it's definitely the rainbow peak yeah

1662
01:02:17,829 --> 01:02:16,880
essentially the radial peak yeah

1663
01:02:20,390 --> 01:02:17,839
if you're looking at different

1664
01:02:22,150 --> 01:02:20,400
wavelengths and can you does it buy you

1665
01:02:23,829 --> 01:02:22,160
a whole lot more diagnostics yes yes it

1666
01:02:25,750 --> 01:02:23,839
does help a bit because you get not just

1667
01:02:27,829 --> 01:02:25,760
the refractive index of one wavelength

1668
01:02:29,030 --> 01:02:27,839
but you get part of the refractive index

1669
01:02:30,870 --> 01:02:29,040
curve

1670
01:02:33,430 --> 01:02:30,880
as a function of wavelengths and james

1671
01:02:35,030 --> 01:02:33,440
hudson actually used that in the venus

1672
01:02:36,390 --> 01:02:35,040
rainbow measurements that was part of

1673
01:02:39,910 --> 01:02:36,400
the information that tight tightened

1674
01:02:43,670 --> 01:02:41,510
um so if you want to

1675
01:02:45,109 --> 01:02:43,680
verify this for the earth the

1676
01:02:47,990 --> 01:02:45,119
polarization

1677
01:02:49,430 --> 01:02:48,000
why can't you use a

1678
01:02:51,109 --> 01:02:49,440
satellite that stays pretty close to the

1679
01:02:52,470 --> 01:02:51,119
earth why do you have to get so far away

1680
01:02:54,470 --> 01:02:52,480
couldn't you just kind of stare at the

1681
01:02:57,190 --> 01:02:54,480
ground at different angles and

1682
01:02:59,190 --> 01:02:57,200
get all the information you need

1683
01:03:00,870 --> 01:02:59,200
well effectively we have we have that

1684
01:03:04,150 --> 01:03:00,880
sort of information from polder so we

1685
01:03:07,589 --> 01:03:06,069
we know these polarization

1686
01:03:09,510 --> 01:03:07,599
effects are there

1687
01:03:10,470 --> 01:03:09,520
um in principle yeah i guess you could

1688
01:03:12,230 --> 01:03:10,480
try and

1689
01:03:13,750 --> 01:03:12,240
use a whole lot of satellite data and

1690
01:03:14,870 --> 01:03:13,760
combine it together to get some idea of

1691
01:03:17,109 --> 01:03:14,880
what the

1692
01:03:18,470 --> 01:03:17,119
total earth signal would look like

1693
01:03:20,309 --> 01:03:18,480
but you don't usually get quite the same

1694
01:03:22,390 --> 01:03:20,319
thing because for example the satellites

1695
01:03:23,829 --> 01:03:22,400
usually look straight down

1696
01:03:24,710 --> 01:03:23,839
whereas when

1697
01:03:27,029 --> 01:03:24,720
if you're actually looking at the

1698
01:03:28,789 --> 01:03:27,039
integrated

1699
01:03:29,910 --> 01:03:28,799
view of the earth from a distance you're

1700
01:03:30,870 --> 01:03:29,920
looking straight down in the center of

1701
01:03:32,789 --> 01:03:30,880
the planet and you're looking at

1702
01:03:34,470 --> 01:03:32,799
different angles as you go go to near

1703
01:03:35,670 --> 01:03:34,480
the limb

1704
01:03:37,670 --> 01:03:35,680
but there certainly may be some

1705
01:03:39,109 --> 01:03:37,680
potential for using existing sunlight

1706
01:03:40,710 --> 01:03:39,119
data to get some of this information i

1707
01:03:42,630 --> 01:03:40,720
mean if you just convince them to not

1708
01:03:45,750 --> 01:03:42,640
look straight down convince them to like

1709
01:03:49,589 --> 01:03:45,760
look look at the edge look towards the