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"Hubble Science"

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"Exoplanets: Alien Atmospheres"

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Exoplanets are very difficult to detect  

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because they are tiny little 
objects orbiting very bright stars.

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Other telescopes are designed to 
be better detectors of exoplanets,  

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but what Hubble is used for is to find, for 
some of them, the atmospheric composition  

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of these exoplanets. It has to be a system 
that just by chance has to be aligned so  

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that the planet is orbiting its star along the 
line of sight of the Hubble Space Telescope.

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[ MUSIC ]

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For doing a lot of the exoplanet observations, 
you have to catch what's known as a "transit,"  

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one the orbit of the exoplanet has to be such that  

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it's going to go between you 
and the star it's going around.

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And then you have to do the timing. We can't just  

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do an exoplanet observation whenever 
we want or whenever it's convenient.  

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We have to do an exoplanet observation when 
it's first starting to go into the star.  

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So they have to know, very accurately, the timing 
of that. We have to schedule it ahead of time. This  

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is not something that, you know, Hubble can get 
around to when it wants to. We have to say, 

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"No, at this point in time, on this date, you have to 
be pointed here, and you have to be looking here."

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When that planet passes in front of its star, the 
starlight, some of it is blocked by the planet.  

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But some of it comes through the outer ridge, the 
outer rims of the atmosphere of that planet on its  

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way to the Hubble telescope. Some of that light 
is absorbed by whatever is in that atmosphere,  

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and it is absorbed at very particular frequencies 
that correspond to the atoms and molecules that  

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are in the atmosphere of that exoplanet. Then when 
the Hubble telescope receives that light, and we  

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take it in, usually with a spectrograph, we get 
the light, we spread it out into its constituent  

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colors or wavelengths of light, and we can tell 
which of those wavelengths have been absorbed.  

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And that tells us, by the pattern of spectroscopy, 
what are the elements and molecules that are found  

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in the atmosphere of that planet. Hubble has 
detected things like sodium and hydrogen, and  

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even evidence of methane and water vapor, by using 
transit observations of exoplanets, and measuring,  

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not only that composition, but also the height of 
the atmosphere, which can tell us something about  

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how heavy the atmosphere is, and that tells 
us something about its composition as well.  

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Hubble was the pioneer in doing 
that, and now other observatories  

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are also using the transit technique to 
analyze the atmospheres of exoplanets.

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[ MUSIC ]