1 00:00:01,129 --> 00:00:04,697 For as long as humans have known that the stars in the sky 2 00:00:04,697 --> 00:00:08,500 are other suns, they have been asking themselves: 3 00:00:08,500 --> 00:00:14,500 Are these suns orbited by other planets? Is there life out there? 4 00:00:14,500 --> 00:00:17,306 Are we alone in the Universe? 5 00:00:20,533 --> 00:00:25,500 Since the discovery of the first exoplanet only 25 years ago, 6 00:00:25,500 --> 00:00:27,600 Hubble is among the many instruments 7 00:00:27,600 --> 00:00:30,268 trying to answer these questions. 8 00:00:30,268 --> 00:00:34,919 And astronomers are using it to hunt for life on other worlds. 9 00:00:45,880 --> 00:00:50,469 Hubble, exoplanets and the hunt for life 10 00:00:53,000 --> 00:00:58,121 25 years have passed since the first exoplanet was discovered 11 00:00:58,121 --> 00:01:04,251 and eight years since Hubble made its first direct image of an alien world. 12 00:01:08,326 --> 00:01:13,272 While in the beginning we knew of only a few, very massive exoplanets 13 00:01:13,272 --> 00:01:16,076 — most often close to their parent star — 14 00:01:16,076 --> 00:01:19,742 today we know of more than 3000. 15 00:01:20,162 --> 00:01:22,309 They are of different sizes 16 00:01:22,309 --> 00:01:26,223 and orbit various types of stars at different distances. 17 00:01:27,495 --> 00:01:32,690 But one thing hasn’t been found so far: proof of life. 18 00:01:37,495 --> 00:01:41,033 Despite all the progress made in recent decades, 19 00:01:41,033 --> 00:01:44,951 the hunt for exoplanets is still a challenging one. 20 00:01:45,700 --> 00:01:51,400 They hide in the shadows, giving off no light of their own. 21 00:01:51,400 --> 00:01:54,005 Any starlight they reflect is swamped 22 00:01:54,005 --> 00:01:57,888 by the overwhelming brilliance of their parent star. 23 00:02:03,185 --> 00:02:07,389 This makes it especially difficult to find Earth-sized planets 24 00:02:07,389 --> 00:02:11,539 in the so-called habitable zone — the region around the star 25 00:02:11,539 --> 00:02:15,214 where liquid water can exist on the surface of a planet. 26 00:02:18,144 --> 00:02:22,443 And water is essential to all life as we know it. 27 00:02:24,363 --> 00:02:29,346 Water only remains liquid within a narrow range of temperatures. 28 00:02:29,346 --> 00:02:34,733 If a planet orbits too close to a star, the water evaporates. 29 00:02:34,733 --> 00:02:38,000 Too far away and it will freeze. 30 00:02:38,000 --> 00:02:42,378 The thin band between these extremes, the habitable zone, 31 00:02:42,378 --> 00:02:46,573 represents the most probable abode of alien life. 32 00:02:51,090 --> 00:02:53,576 So if we know where to look, 33 00:02:53,576 --> 00:02:58,573 how will we know if alien life exists on a faraway planet? 34 00:03:02,090 --> 00:03:05,257 No currently available or planned telescope 35 00:03:05,257 --> 00:03:08,605 is able to resolve the surface of a planet. 36 00:03:11,535 --> 00:03:14,908 But radio telescopes keep listening for messages 37 00:03:14,908 --> 00:03:21,080 from other civilisations, in the hope that they are as curious as we are. 38 00:03:21,080 --> 00:03:27,092 We could also be lucky and find signs of advanced civilisations. 39 00:03:27,092 --> 00:03:33,512 Something like a ringworld, a giant artificial structure built around a star. 40 00:03:33,512 --> 00:03:38,051 But the chances of such a discovery are rather low. 41 00:03:41,600 --> 00:03:45,947 In their search for life, optical and infrared telescopes 42 00:03:45,947 --> 00:03:50,047 focus on the analysis of exoplanet atmospheres. 43 00:03:50,047 --> 00:03:52,037 Life is capable of changing 44 00:03:52,037 --> 00:03:55,704 the composition of a planet’s atmosphere on a grand scale. 45 00:03:58,421 --> 00:04:01,600 The oxygen in the Earth’s atmosphere was released 46 00:04:01,600 --> 00:04:05,816 billions of years ago by microscopic organisms. 47 00:04:12,520 --> 00:04:15,959 If a similar process has occurred on other worlds, 48 00:04:15,959 --> 00:04:20,426 we may be able to detect it in the spectrum of the planet. 49 00:04:22,800 --> 00:04:25,050 From late 2016, 50 00:04:25,050 --> 00:04:29,543 European astronomers will use almost five hundred orbits of Hubble 51 00:04:29,543 --> 00:04:32,782 — corresponding to just over a month of observing time — 52 00:04:32,782 --> 00:04:36,800 to make a detailed study of the atmosphere of hundreds 53 00:04:36,800 --> 00:04:39,400 of already known exoplanets. 54 00:04:43,567 --> 00:04:46,900 Hubble has studied alien atmospheres before, 55 00:04:46,900 --> 00:04:50,060 but this programme offers an unrivalled chance 56 00:04:50,060 --> 00:04:53,379 to learn more about them than ever before. 57 00:04:57,100 --> 00:05:00,436 The data we gather in the next months from Hubble 58 00:05:00,436 --> 00:05:05,129 will be a fundamental database for further studies. 59 00:05:05,129 --> 00:05:06,800 And with the power of the upcoming 60 00:05:06,800 --> 00:05:10,551 next generation of telescopes in space and on the ground, 61 00:05:10,551 --> 00:05:13,971 astronomers may be closer than ever before 62 00:05:13,971 --> 00:05:18,705 to discovering life elsewhere in the Universe. 63 00:05:26,459 --> 00:05:37,617 Transcripted by ESA/Hubble. 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