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exoplanets are very difficult to detect

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because they are tiny little objects

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other telescopes are designed to be

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better detectors of exoplanets

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but what hubble is used for is to find

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for some of them the atmospheric

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composition of these exoplanets

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[Music]

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it has to be a system that just by

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chance has to be aligned so that the

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planet is orbiting its star

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along the line of sight of the hubble

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[Music]

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for doing a lot of the exoplanet

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observations you have to catch what's

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known as a transit one the orbit of the

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exoplanet has to be such that it's going

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to go between you and the star it's

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and then you have to do the timing we

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can't just do an exoplanet observation

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whenever we want or whenever it's

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convenient we have to do an exoplanet

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observation when it's first starting to

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go into the star

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so they have to know very accurately the

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timing of that we have to schedule it

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ahead of time this is not something that

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you know hubble can get around to when

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it wants to we have to say no at this

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point in time on this date you have to

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be pointed here and you have to be

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when that planet passes in front of its

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star the starlight some of it is blocked

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by the planet but some of it comes

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through the outer

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ridge the outer rims of the atmosphere

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of that planet on its way to the hubble

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telescope

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some of that light is absorbed by

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whatever is in that atmosphere

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and it is absorbed at very particular

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frequencies that correspond to the atoms

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and molecules that are in the atmosphere

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of that exoplanet then when the hubble

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telescope receives that light and we

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take it in usually with a spectrograph

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we get the light we spread it out into

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its constituent colors or wavelengths of

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light and we can tell which of those

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wavelengths have been absorbed and that

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tells us by the pattern of spectroscopy

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what are the elements and molecules that

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are found in the atmosphere of that

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planet hubble has detected things like

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sodium and hydrogen and even evidence of

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methane and water vapor by using transit

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observations of exoplanets and measuring

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not only that composition but also the

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height of the atmosphere which can tell

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us something about how heavy the

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atmosphere is and that tells us

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something about its composition as well

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hubble was the pioneer in doing that and

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now other observatories are also using