1 00:00:00,000 --> 00:00:05,000 Using the NASA/ESA Hubble Space Telescope, astronomers have found the first clear evidence 2 00:00:05,000 --> 00:00:10,000 of high altitude haze or clouds in the atmosphere of an extrasolar planet. 3 00:00:10,000 --> 00:00:17,000 This discovery reveals a deeper understanding of the class of giant planets that astronomers call ‘hot Jupiters’. 4 00:00:40,000 --> 00:00:42,000 This is the Hubblecast! 5 00:00:42,000 --> 00:00:46,000 News and Images from the NASA/ESA Hubble Space Telescope. 6 00:00:46,000 --> 00:00:52,000 Travelling through time and space with our host Doctor J a.k.a. Dr Joe Liske. 7 00:00:52,000 --> 00:00:55,000 Hello and welcome to the Hubblecast. 8 00:00:55,000 --> 00:01:01,000 Over the last 15 years astronomers have discovered more than 270 planets around other stars. 9 00:01:01,000 --> 00:01:07,000 A burning question is naturally: What are these so called extrasolar planets like? 10 00:01:07,000 --> 00:01:16,000 Well, most of them are actually giant gaseous worlds several times the size of Jupiter which is our own Solar System’s largest planet. 11 00:01:16,000 --> 00:01:24,000 Others are smaller rocky or icy worlds that are still several times larger than our own home planet Earth. 12 00:01:24,000 --> 00:01:28,000 We have yet to discover a world that is similar to our own planet. 13 00:01:30,000 --> 00:01:34,000 Using the Advanced Camera for Surveys (or ACS), 14 00:01:34,000 --> 00:01:42,000 the Hubble Space Telescope has recently observed a fascinating large gaseous planet around the star HD 189733. 15 00:01:42,000 --> 00:01:50,000 Careful analysis of these very high precision observations by a team lead by Frédéric Pont from the Geneva University Observatory 16 00:01:50,000 --> 00:02:03,000 showed that this planet, designated HD 189733b, possesses a murky haze layer extending over an altitude range of about 1000 km in the planet’s upper atmosphere. 17 00:02:05,000 --> 00:02:09,000 The atmosphere of this gaseous planet is at around 800 degrees Celsius. 18 00:02:09,000 --> 00:02:17,000 This is due to its proximity to its parent star and is the reason that astronomers call this type of planet a ‘hot Jupiter’. 19 00:02:19,000 --> 00:02:25,000 These hazes are probably made of tiny condensed particles less that one-thousandth of a millimetre across, 20 00:02:25,000 --> 00:02:30,000 similar to those already known on Venus and Saturn’s moon, Titan. 21 00:02:30,000 --> 00:02:35,000 Their presence means that the sky over HD 189733b 22 00:02:35,000 --> 00:02:41,000 would look very much like a red hazy sunset viewed from an industrially polluted city on Earth. 23 00:02:44,000 --> 00:02:46,000 Today we have a special guest. 24 00:02:46,000 --> 00:02:51,000 This is Dr Bob Fosbury- he’s the leader of the European Hubble effort. 25 00:02:51,000 --> 00:02:55,000 So tell me Bob what’s so special about this particular star and its planet? 26 00:02:55,000 --> 00:03:00,000 Well this is a rather special planetary system because the star itself is quite small, 27 00:03:00,000 --> 00:03:06,000 it’s only about 75% the size of our Sun and yet the planet itself is larger than Jupiter. 28 00:03:06,000 --> 00:03:15,000 So when the planet transits in front of the star it obscures quite a large fraction of light from the star which enables a very accurate measurement. 29 00:03:15,000 --> 00:03:20,000 So what exactly made these observations so precise? Why was this only possible now? 30 00:03:20,000 --> 00:03:24,000 Well we have to do this from space because when we try and do this from the ground 31 00:03:24,000 --> 00:03:29,000 the atmosphere makes it very difficult to make precise measurements of brightness, so we do it from space. 32 00:03:29,000 --> 00:03:37,000 And the special thing about this particular observation is that the scientists spread the light out over many pixels in the detector. 33 00:03:37,000 --> 00:03:42,000 So rather than just having a little point of light representing the star on the detector 34 00:03:42,000 --> 00:03:49,000 the starlight was spread out into a spectrum using this so called ‘grism mode’ of the Advanced Camera for Surveys. 35 00:03:49,000 --> 00:03:56,000 Now, that enables a very precise measurement because you can measure over many many pixels a large area of detector 36 00:03:56,000 --> 00:04:06,000 but it also, by spreading out the colours, enables you to measure the brightness (or the reduction in brightness) of the starlight over many colours. 37 00:04:06,000 --> 00:04:14,000 So having these different measurements in different colours enables you to characterize the nature of the atmosphere. 38 00:04:15,000 --> 00:04:19,000 To detect the hazes astronomers actually had to do quite a bit of detective work. 39 00:04:19,000 --> 00:04:30,000 The reason why this work was possible at all was because from our vantage point the orbit of HD 189733b is seen almost exactly edge on. 40 00:04:30,000 --> 00:04:38,000 Now what that means is that every two days or so the planet actually moves across the face of its parent star as seen from here. 41 00:04:38,000 --> 00:04:48,000 Now when that happens some small fraction of the light from the star has to pass through the atmosphere of the planet in front of it in order to reach Earth. 42 00:04:48,000 --> 00:04:57,000 Because of this process the composition of the atmosphere of the planet is stamped onto the light like a unique fingerprint. 43 00:04:57,000 --> 00:05:02,000 Astronomers can then see this fingerprint in the spectrum of the star’s light. 44 00:05:04,000 --> 00:05:11,000 The astronomers were expecting to see clear signatures of sodium, potassium and water in the planet’s atmosphere. 45 00:05:11,000 --> 00:05:18,000 The fact that these were not seen led them to this conclusion that they were being masked by red-coloured high clouds or haze. 46 00:05:18,000 --> 00:05:26,000 According to the scientists the haze probably consists of tiny particles of condensates of iron and silicates. 47 00:05:30,000 --> 00:05:37,000 When extrasolar planets were first discovered about 15 years ago, little did we know how quickly we would begin to unravel their secrets. 48 00:05:37,000 --> 00:05:45,000 The new Hubble observations are an important new step towards a better understanding of these amazing planets outside our own Solar System. 49 00:05:45,000 --> 00:05:49,000 Who knows what we will discover in the next few years about these distant worlds? 50 00:05:49,000 --> 00:05:52,000 This is Dr J signing off for the Hubblecast. 51 00:05:52,000 --> 00:05:56,000 Once again nature has surprised us beyond our wildest imagination … 52 00:05:58,000 --> 00:06:03,000 Hubblecast is produced by ESA/Hubble at the European Southern Observatory in Germany. 53 00:06:03,000 --> 00:06:08,000 The Hubble mission is a project of international cooperation between NASA and the European Space Agency.