English subtitles for clip: File:Hubblecast 102.webm
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1 00:00:00,880 --> 00:00:07,260 No other topic fascinates both astronomers and the public quite like exoplanets. 2 00:00:07,260 --> 00:00:12,520 What do they look like? Could we breathe there? Is life possible on them? 3 00:00:12,520 --> 00:00:20,220 Answering these questions requires us to detect and study the thin atmospheres of these distant objects. 4 00:00:34,260 --> 00:00:38,780 The atmosphere of an exoplanet can reveal a wealth of information. 5 00:00:39,820 --> 00:00:43,740 By determining the composition and thickness of the atmosphere, 6 00:00:43,740 --> 00:00:49,900 astronomers can infer many other characteristics such as the planet's temperature, 7 00:00:49,900 --> 00:00:54,940 the air pressure, and whether the planet is suitable for life. 8 00:00:57,000 --> 00:01:02,320 But studying the atmospheres of exoplanets isn't an easy task. 9 00:01:02,320 --> 00:01:08,520 Planets don’t emit their own light and they are tiny compared to their host stars. 10 00:01:11,680 --> 00:01:17,840 The only way to study exoplanet atmospheres is by monitoring the host star's light 11 00:01:17,840 --> 00:01:23,500 as the exoplanet moves between Earth and the parent star — known as a transit. 12 00:01:24,900 --> 00:01:31,540 During the transit a tiny fraction of the star’s light passes through the atmosphere of the planet 13 00:01:31,540 --> 00:01:34,860 and interacts with the chemical elements therein. 14 00:01:35,580 --> 00:01:41,700 Each atom and molecule present in the atmosphere absorbs light at specific wavelengths, 15 00:01:41,700 --> 00:01:44,680 while allowing other wavelengths to pass. 16 00:01:49,660 --> 00:01:52,900 By observing the light of a star during a transit 17 00:01:52,900 --> 00:01:58,780 astronomers can find the fingerprint of the exoplanet's atmosphere in the spectrum of the star. 18 00:01:59,260 --> 00:02:04,500 Each element creates distinctive dark lines — absorption lines — in the spectrum. 19 00:02:05,000 --> 00:02:11,240 So these lines act as chemical fingerprints revealing the make-up of the atmosphere. 20 00:02:11,240 --> 00:02:16,960 Also, the stronger the line, the more of the corresponding element is present in the atmosphere. 21 00:02:19,480 --> 00:02:26,180 But even the strongest lines of the most abundant elements are incredibly weak and hard to detect: 22 00:02:27,180 --> 00:02:32,920 only a tiny fraction of the star’s light is interfering with the atmosphere of the exoplanet. 23 00:02:34,100 --> 00:02:40,720 Hubble is one of the few telescopes powerful enough to perform studies of exoplanet atmospheres. 24 00:02:40,720 --> 00:02:48,180 It also has instruments to collect spectra ranging from the ultraviolet, through the optical, to the near infrared. 25 00:02:49,620 --> 00:02:54,020 This is crucial to fully characterise these atmospheres. 26 00:02:58,820 --> 00:03:01,120 In spite of Hubble’s capacities, 27 00:03:01,120 --> 00:03:07,460 the analysis of exoplanet atmospheres pushes Hubble’s instrumentation to its limits. 28 00:03:08,040 --> 00:03:13,600 The telescope can only detect the strongest lines from an atmosphere in a given spectrum. 29 00:03:14,100 --> 00:03:19,940 It’s enough to give us an idea of the composition of an atmosphere and the appearance of a planet, 30 00:03:19,940 --> 00:03:23,760 but it is not possible to reveal the fine details. 31 00:03:26,560 --> 00:03:33,400 While Hubble will continue its studies and will help to advance our understanding of planetary atmospheres, 32 00:03:33,400 --> 00:03:37,240 astronomers need bigger and even more sensitive instruments 33 00:03:37,240 --> 00:03:41,100 to detect the weaker signatures in atmospheric spectra: 34 00:03:44,100 --> 00:03:51,900 the forthcoming NASA/ESA/CSA James Webb Space Telescope will deliver exactly that. 35 00:03:55,040 --> 00:03:57,040 Transcribed by ESO; Translated by —