1 00:00:00,000 --> 00:00:07,394 "Hubble Science" 2 00:00:07,394 --> 00:00:14,480 "Exoplanets: Alien Atmospheres" 3 00:00:14,480 --> 00:00:17,600 Exoplanets are very difficult to detect   4 00:00:17,600 --> 00:00:21,680 because they are tiny little  objects orbiting very bright stars. 5 00:00:25,360 --> 00:00:32,400 Other telescopes are designed to  be better detectors of exoplanets,   6 00:00:32,400 --> 00:00:38,720 but what Hubble is used for is to find, for  some of them, the atmospheric composition   7 00:00:38,720 --> 00:00:45,360 of these exoplanets. It has to be a system  that just by chance has to be aligned so   8 00:00:45,360 --> 00:00:51,840 that the planet is orbiting its star along the  line of sight of the Hubble Space Telescope. 9 00:00:51,840 --> 00:00:57,760 [ MUSIC ] 10 00:00:57,760 --> 00:01:02,160 For doing a lot of the exoplanet observations,  you have to catch what's known as a "transit,"   11 00:01:02,160 --> 00:01:05,280 one the orbit of the exoplanet has to be such that   12 00:01:05,280 --> 00:01:08,400 it's going to go between you  and the star it's going around. 13 00:01:10,800 --> 00:01:13,040 And then you have to do the timing. We can't just   14 00:01:13,040 --> 00:01:16,880 do an exoplanet observation whenever  we want or whenever it's convenient.   15 00:01:16,880 --> 00:01:21,840 We have to do an exoplanet observation when  it's first starting to go into the star.   16 00:01:21,840 --> 00:01:26,560 So they have to know, very accurately, the timing  of that. We have to schedule it ahead of time. This   17 00:01:26,560 --> 00:01:30,783 is not something that, you know, Hubble can get  around to when it wants to. We have to say,  18 00:01:30,783 --> 00:01:35,120 "No, at this point in time, on this date, you have to  be pointed here, and you have to be looking here." 19 00:01:38,720 --> 00:01:44,160 When that planet passes in front of its star, the  starlight, some of it is blocked by the planet.   20 00:01:44,160 --> 00:01:50,800 But some of it comes through the outer ridge, the  outer rims of the atmosphere of that planet on its   21 00:01:50,800 --> 00:01:57,760 way to the Hubble telescope. Some of that light  is absorbed by whatever is in that atmosphere,   22 00:01:57,760 --> 00:02:04,320 and it is absorbed at very particular frequencies  that correspond to the atoms and molecules that   23 00:02:04,320 --> 00:02:09,680 are in the atmosphere of that exoplanet. Then when  the Hubble telescope receives that light, and we   24 00:02:09,680 --> 00:02:14,880 take it in, usually with a spectrograph, we get  the light, we spread it out into its constituent   25 00:02:14,880 --> 00:02:20,640 colors or wavelengths of light, and we can tell  which of those wavelengths have been absorbed.   26 00:02:20,640 --> 00:02:27,120 And that tells us, by the pattern of spectroscopy,  what are the elements and molecules that are found   27 00:02:27,120 --> 00:02:32,880 in the atmosphere of that planet. Hubble has  detected things like sodium and hydrogen, and   28 00:02:32,880 --> 00:02:39,920 even evidence of methane and water vapor, by using  transit observations of exoplanets, and measuring,   29 00:02:39,920 --> 00:02:44,720 not only that composition, but also the height of  the atmosphere, which can tell us something about   30 00:02:44,720 --> 00:02:49,840 how heavy the atmosphere is, and that tells  us something about its composition as well.   31 00:02:51,280 --> 00:02:54,960 Hubble was the pioneer in doing  that, and now other observatories   32 00:02:54,960 --> 00:03:00,853 are also using the transit technique to  analyze the atmospheres of exoplanets. 33 00:03:00,867 --> 00:03:17,322 [ MUSIC ]