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[Music]

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yes it said and I'm going to be taking a

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small step outside the box of pigments

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and having a look at how fluorescents

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might be a potential bio signature for

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planets that experience higher UV

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radiation than more earth-like planets

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and so what I'm going to do today is to

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talk about how we came up with the idea

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of looking at fluorescents add a surface

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bio signature and so the main problem we

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had was that a lot of the first planets

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that we're going to be able to

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characterize in the habitable zones of

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stars are these n star planets that are

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very close in to their their host stars

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and these M star can be very active they

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can flare very frequently and these

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players can often in x-ray or extreme UV

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wavelengths or at the longer wavelength

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UV that can be detrimental to any

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surface life that might be exposed to it

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and so we want what we wanted to to do

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is to try and think of ways in which

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life could exist on these planets but

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actually still be detectable because it

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because if you live it on a UV bathed

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world in order to protect yourself your

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protection mechanisms like living

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underground or living underwater then

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don't lend themselves to us remotely

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detecting life and that's where we came

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up with the idea of fluorescence which

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could be used as a sort of UV protection

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method which has knock-on effect of

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actually if there's enough aversion

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that's bright enough could actually

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signal the presence of life on the

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surface compared to these other source

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UV protection mechanisms that life can

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use and so I'm going to start just by

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doing a brief overview of fluorescence

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in the natural world

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it is everywhere in some form the

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brightness of fluorescence changes from

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organism to organism it's especially

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prevalent in marine organisms for a

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variety of reasons there they use it for

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communication they use it for

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into in some coral species species they

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might be using this as a UV protection

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mechanism which is where we've got this

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idea from and and the idea of

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fluorescence being a globally detectable

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surface by a signature is illustrated

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quite well by chlorophyll fluorescence

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on earth so chlorophyll in surface

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vegetation fluorescence when it's

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exposed to UV wavelengths now this this

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fluorescence effect is happening at such

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a low level that it's completely drowned

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out by the ambient light environment on

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earth but if you take surface

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observations of the planet and you

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subtract the solar radiation component

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and this orbit the other reflectance

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features so that you just leave the

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fluorescence behind you get this very

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clear image of exactly where the

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vegetation is and then this fluorescent

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fluorescent signature provides a good

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indication of plant health you can see

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seasons changing as vegetation loses

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leaves and your regains the leaves in

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spring and so it's a very good marker

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for and what surface vegetation on earth

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is doing it just happens to be not a

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very bright effect but when it comes to

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defining potential bias signatures it's

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very good to start thinking outside the

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box slightly so if you can get this kind

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of detectable effect from fluorescence

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but at a low level how how much can we

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scale this up such that we could

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actually have a remote to the observable

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fluorescent bio signature and and so

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what we did is we took corals as an

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example so corals are some of the most

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well studied flores's in the animal

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kingdom and and we had a conversation

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with some coral biologists who are able

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to give us some measurements on how

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coral for proteins respond to UV and

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blue wavelengths and how all the

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absorption absorption and mission

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profiles change and so that the very

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basic overview of fluorescence is you're

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taking in high-energy photons they're

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absorbed by whatever molecule is

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absorbing them energy level of an

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electron is raised up and as that

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electron then relaxes back down a tree

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releases a photon at a longer wavelength

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and so this is why UV protection is one

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of these possibilities for corals and

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other organisms that are exposed to that

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there can be exposed to high UV because

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you can take in a UV photon which can be

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biologically damaging and you can shift

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it to a longer and safer wavelength

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protecting this is a biological material

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around the fluorescent pigments or in

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the case of flora corals protect

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potentially the symbiotic algae that

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live within the coral and so why why is

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this a problem for n star planets but as

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I mentioned they're very active stars or

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they can be very active stars and we

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know that certainly for the planet slick

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rocks would be at the plant and the trap

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is one planet their host stars are very

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active to a point that it earth-like

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planets an earth-like atmosphere would

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certainly be very affected by this and

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the flares in the e UV and x-ray x-ray

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wavelengths can have effects on a

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planet's atmosphere they can Road away

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atmospheres over time if the star is

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constantly flaring regularly and so you

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could end up which much with much

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thinner atmospheres you can destroy

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ozone in the atmosphere and and this all

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can lead to higher surface UV fluxes

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then we got on earth and in terms of UV

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and we need to start thinking about the

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biologically relevant UV so you can

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split UV into three different sort of

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wavelength bands and these in terms of

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the biological effects they have in

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terms of destroying DNA or causing

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mutations or various other kinds of

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biological damage the effects that

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different wavelengths of UV have on

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organisms some scales with decreasing

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wavelength so the UVA we

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which is most of the UV that reaches the

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surface on earth is fairly benign

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compared to UVB which can cause an order

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or two of magnitude more damage and I'm

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at the moment I'm a walking example of

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this because having spent three days in

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San Francisco in the Sun my UVB exposure

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is turning bright red if I had that

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length that same time exposure to UV see

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I wouldn't be here right now so these

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these effects really do scale up

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dramatically but on earth so if you see

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the drawing the UV surface cut off on

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earth ozone is very good at filtering

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out the worst of the UV for life so UVA

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UVB can still cause damage but the

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damage rate happens at the slope for a

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slow slow rate and it can easily be so

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the biological organisms can easily

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repair themselves using various various

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different methods but if you have an M

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style planet and that is letting in more

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of this UV either because it has less

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ozone or has a thinner atmosphere then

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the surface UV environment can make the

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surface a lot more inheritable for life

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and now life has various ways of

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protecting itself but as I said before

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these protection mechanisms like living

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underground or underwater aren't so good

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for us to then be able to checked

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surface biosignatures because you get so

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the reflectance spectrum as they sound

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or water mixed in with whatever it is

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that's living on the surface or near the

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surface but threatens is potentially one

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way of getting around this and so what

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we wanted to do is just do this with

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first order of magnitude let's have a

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look at how fluorescence or how much

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fluorescence we could we would need

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based on these coral proteins to cause a

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detectable signature so we'd have the

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reflectance spectrum of whatever

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organism with modeling our surface

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biosphere on which in this case we use

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corals because we're working with coral

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biologists

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and we had all the spectra from them but

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this could equally work with any other

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kind of organism that could potentially

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evolve and then we added a fluorescence

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effect based on the coral fluorescent

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proteins which gives you an increased

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emission to add on to the surface

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reflectance feature which which could

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then cause a detectable spike in a

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certain wavelength and and so this is

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what we did so we used them as a global

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coverage of this model biosphere of

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corals we added in atmosphere as

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earth-like atmosphere over the top but

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adapted so as an earth-like atmosphere

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would appear around an M star and then

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we looked at different fractions of

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coverage on the surface so we started

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with a whole biosphere and then we split

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it up into fractions of open ocean and

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with different cloud coverage over the

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top to investigate how detectable this

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feature would be and so we we will have

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free reign with deciding how strong a

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fluorescence could be and so what we

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modeled initially as a best-case

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scenario was fluorescence that is 100%

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efficient so it's taking every photon

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that is absorbed it really and then we

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assumed we had a very dense coverage and

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that effect so that such as quenching

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which can turn there which students

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effectively destroy a fluorescent

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pigments could be reversible which is

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something you can see in certain certain

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fluorescent proteins and so we ran that

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through a model and as you can see at

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the bottom there the these reflectance

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spectra are slowly adapting based once

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we start adding layers of land of

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surface of clouds and the sort of spike

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you can see just after 500 so we were

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looking so the ones I'm showing here are

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green fluorescence proteins this is the

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sort of sort of like a bit like the

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vegetation red edge a very large very

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sudden spike in reflectance at a given

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wavelength and

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but we could then do is plot this onto

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the color diagram color color diagram

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which is effectively just comparing the

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strengths of reflectance at certain

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wavelength bands and so Sid is our

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resident color colored diagram expert at

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the Carl Sagan Institute and so here

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we'll go into these these diagrams in a

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lot more detail next I think and but the

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the main thing here is to see how

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fluorescence affects the surface

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reflectance of our model planets so when

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the coral biosphere is not fluorescing

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so we took four different example

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species of coral labeled A to D which

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are the gray squares on this diagram and

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then when fluorescence turns on so you

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can imagine this so say a large flare

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hits the planet the UV levels spike the

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biosphere then starts fluorescing in

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response to this huge UV flux increase

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and then as it fluorescence it moves its

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position in the in color space fairly

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significantly and and so this is the

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sort of detectable effect we wanted to

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start thinking about so a planet is

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would effectively be turning itself into

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sort of a lighthouse like beacon as this

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surface biosphere lights up and so what

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I've shown here is the best case so this

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is where we just have an entire planet

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clear sky is covered in a fluorescent

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biosphere and obviously the effect of

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this or the magnitude of this change

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will change depending on the fraction of

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the surface coverage and the brightness

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of the effect but this illustrates it

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quite nicely and so there are other

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things that for us so of all sorts of

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things fluoresce as long as you've got

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the right structure you can have

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something that will fluoresce and one of

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the things we wanted to compare to here

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is threatened minerals but so we a lot

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of the fluorescent minerals that

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fluoresced at the same wavelength as the

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sort of various coral fluorescent

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proteins that we investigated we're all

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roughly in that area of this diagram so

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they were all fairly separate

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and when they were and we're not

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fluorescing they hardly moved at all

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because the strength of the fluorescence

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effect was so low and so we're sort of

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using the argument here that if if

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fluorescence evolved as a UV protection

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mechanism in whatever surface biases

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lives on these planets bright

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fluorescence would be favored by

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evolution if this is an effective

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protection mechanism whereas these

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fluorescent minerals

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would not be subject to some Darwinian

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evolutionary rules and so they would

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just be fluorescing as they're naturally

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low levels and so in a way it could be

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distinguishable from false positives

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like that and there other possibilities

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such as irori

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but if you had know something about the

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chemical composition of an atmosphere

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then if you detect an auroral emission

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and you know that a certain molecule is

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present that causes that color of

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emission then you could argue that we

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can say that's not fluorescence at

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Aurora so they it could potentially be

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distinguished distinguishable from other

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false positives and so this is just a

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quick illustration of how high the UV

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levels can get during the flare so this

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is for a very active M star ad Leo and

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gray line there is the top of the

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atmosphere solar UV emission that we get

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on earth and so the star is normally

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giving a planet Earth's equivalent

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distance a much lower flux the moon get

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on earth and but when it flares it can

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jump up by an order of magnitude or more

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in terms of the UV flux that could reach

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these planets so we could get very high

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UV fluxes and one thing we've done

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recently Lisa and I at the Carl Sagan

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Institute we wrote a quick paper for the

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proximate Eid for the Trappist one

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planet to look at what UV levels they

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would get and we look to nurse-like

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atmosphere and an earth-like atmosphere

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that's been eroded so much thinner and

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then a then a completely anoxic

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oxygen-free atmosphere and so in all of

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these cases this is the oxygen-free

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atmosphere you get a lot more UVC coming

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to the planet so the really damaging

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wavelength

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but they're still at a much lower lower

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level than I and so UV protection

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mechanisms like for essence could

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potentially work without UVC completely

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destroying everything and and so I'll