1 00:00:04,000 --> 00:00:10,000 Twenty five years ago not a single planet outside the Solar System had been detected. 2 00:00:10,000 --> 00:00:18,000 But, remarkably, we now know of thousands and have studied many in surprising detail. 3 00:00:19,000 --> 00:00:25,000 ESO’s observatories in Chile have been at the forefront of this enormous expansion in knowledge. 4 00:00:25,000 --> 00:00:29,000 And their state-of-the-art instruments are continuing to discover 5 00:00:29,000 --> 00:00:34,000 and study the extraordinary diversity of exoplanets. 6 00:00:38,000 --> 00:00:49,000 This is the ESOcast! Cutting-edge science and life behind the scenes at ESO, the European Southern Observatory. 7 00:01:01,000 --> 00:01:06,000 Looking up at the night sky, people throughout history have wondered if there are planets 8 00:01:06,000 --> 00:01:10,000 — and especially planets bearing life — beyond the Solar System. 9 00:01:11,000 --> 00:01:16,000 Astronomers have also asked themselves these questions, and many more. 10 00:01:17,000 --> 00:01:19,000 Are planets common? Or very rare? 11 00:01:19,000 --> 00:01:24,000 Do they resemble planets in the Solar System, or are they totally different? 12 00:01:25,000 --> 00:01:28,000 Frustratingly, until very recently, 13 00:01:28,000 --> 00:01:34,000 observational techniques were not advanced enough to be able to answer any of these questions. 14 00:01:35,000 --> 00:01:39,000 But in 1995, this changed overnight. 15 00:01:39,000 --> 00:01:43,000 The first exoplanet orbiting a Sun-like star was detected. 16 00:01:44,000 --> 00:01:51,000 The monumental discovery was made by Geneva-based astronomers Michel Mayor and Didier Queloz 17 00:01:51,000 --> 00:01:54,000 around the star 51 Pegasi. 18 00:01:56,000 --> 00:02:01,000 The exoplanet, named 51 Pegasi b, has around half the mass of Jupiter 19 00:02:01,000 --> 00:02:06,000 and travels around its parent star in just over four Earth days. 20 00:02:07,000 --> 00:02:09,000 But this was only the beginning. 21 00:02:09,000 --> 00:02:13,000 The initial trickle of discoveries became a flood. 22 00:02:13,000 --> 00:02:20,000 Thousands of exoplanets have since been detected in a huge variety of sizes and orbits. 23 00:02:21,000 --> 00:02:27,000 Many of these discoveries have been made by ESO’s observatories in Chile. 24 00:02:28,000 --> 00:02:32,000 But the hunt for exoplanets is a challenging one. 25 00:02:32,000 --> 00:02:38,000 These alien worlds hide in the shadows, giving off little or no light of their own. 26 00:02:38,000 --> 00:02:44,000 Any light that they do emit is swamped by the overwhelming brilliance of their parent star. 27 00:02:45,000 --> 00:02:51,000 However, advanced observational methods can be used to spot these elusive exoplanets. 28 00:02:52,000 --> 00:03:00,000 The weak gravitational pull of an exoplanet in orbit causes its parent star to wobble back and forth. 29 00:03:00,000 --> 00:03:04,000 This tiny motion causes a small shift in the star’s spectrum, 30 00:03:04,000 --> 00:03:11,000 which extremely sensitive spectrographs such as ESO’s HARPS can detect through radial velocity tracking. 31 00:03:12,000 --> 00:03:18,000 HARPS, installed on the ESO 3.6-metre telescope at the La Silla Observatory, 32 00:03:18,000 --> 00:03:21,000 is the world's foremost exoplanet hunter. 33 00:03:21,000 --> 00:03:26,000 It’s the most successful finder of low-mass exoplanets to date. 34 00:03:27,000 --> 00:03:33,000 In 2010, the instrument discovered the richest planetary system yet. 35 00:03:33,000 --> 00:03:41,000 The system, located over 120 light-years away around the Sun-like star HD 10180, 36 00:03:41,000 --> 00:03:45,000 contains at least five exoplanets. 37 00:03:47,000 --> 00:03:52,000 There is also tantalising evidence that two more planets may be present in this system, 38 00:03:52,000 --> 00:03:56,000 one of which would have the lowest mass ever found. 39 00:03:59,000 --> 00:04:06,000 Planetary transits can also be utilised by astronomers to indirectly detect distant worlds. 40 00:04:06,000 --> 00:04:11,000 When an exoplanet passes in front of its parent star — as seen from the Earth — 41 00:04:11,000 --> 00:04:16,000 it blocks a small fraction of the star's light from our view. 42 00:04:16,000 --> 00:04:21,000 This creates a dip in the brightness of the star which can be measured. 43 00:04:22,000 --> 00:04:26,000 In addition to determining the size of an exoplanet, 44 00:04:26,000 --> 00:04:32,000 planetary transits can reveal the composition of an exoplanet’s atmosphere. 45 00:04:33,000 --> 00:04:36,000 The atmosphere around a super-Earth exoplanet 46 00:04:36,000 --> 00:04:42,000 was analysed for the first time by astronomers using the Very Large Telescope. 47 00:04:43,000 --> 00:04:47,000 The planet, which is known as GJ 1214b, 48 00:04:47,000 --> 00:04:54,000 was studied as it passed in front of its parent star and starlight passed through the planet’s atmosphere. 49 00:04:55,000 --> 00:05:01,000 This starlight revealed that the planet’s atmosphere is either mostly water in the form of steam, 50 00:05:01,000 --> 00:05:05,000 or is dominated by thick clouds or hazes. 51 00:05:06,000 --> 00:05:13,000 Directly observing an exoplanet is a monumental feat, but one that was first achieved by ESO. 52 00:05:14,000 --> 00:05:21,000 The Very Large Telescope obtained the first-ever image of a planet outside the Solar System. 53 00:05:21,000 --> 00:05:26,000 2M1207b is five times more massive than Jupiter. 54 00:05:26,000 --> 00:05:35,000 It orbits a failed star — a brown dwarf — at a distance 55 times larger than the Earth to the Sun. 55 00:05:36,000 --> 00:05:41,000 ESO’s telescopes are equipped with state-of-the-art instruments, 56 00:05:41,000 --> 00:05:44,000 but to remain at the forefront of exoplanet research, 57 00:05:44,000 --> 00:05:50,000 ESO has recently commissioned two new instruments for the VLT. 58 00:05:50,000 --> 00:05:58,000 SPHERE is able to find and study faint planets masked by the glare of their host stars. 59 00:05:58,000 --> 00:06:06,000 And in the near future, the ESPRESSO spectrograph will arrive at the VLT, where it will surpass HARPS. 60 00:06:08,000 --> 00:06:13,000 The European Extremely Large Telescope, which is currently under construction in Chile, 61 00:06:13,000 --> 00:06:17,000 will take the hunt for exoplanets even further. 62 00:06:17,000 --> 00:06:23,000 Once operational, this 39-metre telescope could detect Earth-like planets 63 00:06:23,000 --> 00:06:27,000 and possibly evidence of alien biospheres. 64 00:06:29,000 --> 00:06:35,000 The search for planets outside the Solar System constitutes a key element of what is possibly 65 00:06:35,000 --> 00:06:41,000 the greatest question of all: is there life elsewhere in the Universe? 66 00:06:41,000 --> 00:06:47,000 Over the past 20 years, our knowledge of exoplanets has advanced dramatically. 67 00:06:47,000 --> 00:06:51,000 But the quest for Earth-like planets and those that harbour life 68 00:06:51,000 --> 00:06:55,000 remains one of the great frontiers of astronomy. 69 00:06:56,000 --> 00:07:03,000 Are we alone? We do not know, but the answer is almost within reach. 70 00:07:06,000 --> 00:07:12,000 Transcription by ESO; translation by —