1 00:00:05,000 --> 00:00:08,520 Lift off of Messenger on NASA'S mission to Mercury. 2 00:00:08,520 --> 00:00:10,280 MUSIC: The Void by Muse 3 00:00:10,280 --> 00:00:15,840 # They'll say no-one can see us 4 00:00:15,840 --> 00:00:22,320 # That we're estranged and all alone 5 00:00:23,720 --> 00:00:29,960 # They believe nothing can reach us 6 00:00:29,960 --> 00:00:34,080 # And pull us out of 7 00:00:34,080 --> 00:00:37,640 # The boundless gloom 8 00:00:37,640 --> 00:00:45,040 # They're wrong 9 00:00:45,040 --> 00:00:48,600 # They're wrong. # 10 00:01:08,320 --> 00:01:13,080 Our planetary neighbour, Mars, is a cold, barren rock. 11 00:01:16,960 --> 00:01:21,200 Its rusted surface covered in parched sand. 12 00:01:25,680 --> 00:01:27,520 But, beneath the dust, 13 00:01:27,520 --> 00:01:30,640 the planet bears the scars of a former life. 14 00:01:36,680 --> 00:01:40,480 Billions of years ago, Mars was just like Earth. 15 00:01:45,960 --> 00:01:48,440 A world with a thick atmosphere 16 00:01:48,440 --> 00:01:51,320 that supported oceans of water. 17 00:02:01,600 --> 00:02:04,480 But, today, that world is gone. 18 00:02:10,960 --> 00:02:14,200 Mars lies dead, 19 00:02:14,200 --> 00:02:16,840 while the Earth thrives. 20 00:02:20,840 --> 00:02:25,440 Why the two planets had such different fates is a mystery 21 00:02:25,440 --> 00:02:28,360 that we've only just begun to answer. 22 00:03:09,080 --> 00:03:13,120 You see that pale red point of light in the sky, 23 00:03:13,120 --> 00:03:14,760 just there? 24 00:03:14,760 --> 00:03:16,200 That's Mars. 25 00:03:16,200 --> 00:03:19,560 Through a small telescope, it appears almost Earth-like. 26 00:03:19,560 --> 00:03:23,520 Our sister world - polar ice caps and dark surface 27 00:03:23,520 --> 00:03:27,360 markings that 19th-century astronomers thought were vegetation, 28 00:03:27,360 --> 00:03:31,400 even canals bringing meltwater down from the poles 29 00:03:31,400 --> 00:03:34,240 to arid equatorial cities. 30 00:03:34,240 --> 00:03:36,640 Across the depths of space, 31 00:03:36,640 --> 00:03:42,600 the inhabitants watched us "with envious eyes", wrote HG Wells. 32 00:03:42,600 --> 00:03:45,640 We now know that there are no eyes looking back at us. 33 00:03:45,640 --> 00:03:50,120 Mars is a frozen, arid desert world. 34 00:03:50,120 --> 00:03:52,520 But a fleet of spacecraft have revealed 35 00:03:52,520 --> 00:03:54,840 that it hasn't always been that way. 36 00:03:57,760 --> 00:04:00,800 Mariner 4 was successfully launched on time 37 00:04:00,800 --> 00:04:04,000 for its historic 228-day journey to Mars. 38 00:04:05,320 --> 00:04:10,760 Picture information started to come in on July 15th, 1965. 39 00:04:12,200 --> 00:04:15,360 A revelation comparable to Galileo's first view 40 00:04:15,360 --> 00:04:18,120 of the moon through a telescope. 41 00:04:18,120 --> 00:04:19,960 During its brief flyby, 42 00:04:19,960 --> 00:04:24,000 Mariner 4 gave us our first close-up glimpses of Mars. 43 00:04:28,120 --> 00:04:31,560 When Mariner 9 was placed into an orbit around Mars, 44 00:04:31,560 --> 00:04:36,000 it saw a planet blanketed by a gigantic dust storm. 45 00:04:36,000 --> 00:04:38,240 In nearly a year of operation, 46 00:04:38,240 --> 00:04:41,320 they transmit more than 7,000 photographs. 47 00:04:41,320 --> 00:04:46,000 From orbit, Mariner 9 photographed 80% of the Martian surface. 48 00:04:47,240 --> 00:04:49,960 First of all, there are two eyes, not only in colour but also 49 00:04:49,960 --> 00:04:52,280 in stereo, and in the infrared part of the spectrum. 50 00:04:52,280 --> 00:04:54,760 It has a sense of touch, it has a sense of hearing, 51 00:04:54,760 --> 00:04:58,920 but by far the most important feature of the lander is its brain. 52 00:05:00,800 --> 00:05:03,640 The Viking programme took us down to the ground 53 00:05:03,640 --> 00:05:05,200 for the first time... 54 00:05:07,400 --> 00:05:09,240 Touchdown, we have touched down. 55 00:05:09,240 --> 00:05:11,160 ..and revealed Mars... 56 00:05:11,160 --> 00:05:12,760 Perfect set-down. 57 00:05:12,760 --> 00:05:14,560 ..like never before. 58 00:05:14,560 --> 00:05:17,240 There is the first piece of information coming in. 59 00:05:17,240 --> 00:05:19,280 Oh! Oh! 60 00:05:30,680 --> 00:05:35,120 The data gathered over the last 50 years has allowed us to create 61 00:05:35,120 --> 00:05:37,720 detailed maps of the Martian surface... 62 00:05:40,840 --> 00:05:43,840 ..and begin to piece together its past. 63 00:05:46,560 --> 00:05:49,000 Maps of Mars are like storybooks. 64 00:05:49,000 --> 00:05:51,560 You can read the history of the planet 65 00:05:51,560 --> 00:05:55,040 written across its surface, and the reason for that is that there's 66 00:05:55,040 --> 00:05:58,520 virtually no erosion, hasn't been for billions of years, 67 00:05:58,520 --> 00:06:03,120 so the scars of events that happened even four billion years ago 68 00:06:03,120 --> 00:06:05,000 can still be seen. 69 00:06:05,000 --> 00:06:08,520 This is a type of map called an elevation map. 70 00:06:08,520 --> 00:06:12,520 The colours correspond to difference in heights on the surface, 71 00:06:12,520 --> 00:06:14,720 so blue means low 72 00:06:14,720 --> 00:06:18,040 and red and whites are high. 73 00:06:18,040 --> 00:06:21,640 Now, this region here, which is much higher on average than the rest 74 00:06:21,640 --> 00:06:25,720 of Mars, is called Tharsis and it's covered in volcanoes, 75 00:06:25,720 --> 00:06:29,840 including the largest volcano in the solar system, Olympus Mons. 76 00:06:34,640 --> 00:06:39,200 At the other side of Tharsis is the great Valles Marineris, 77 00:06:39,200 --> 00:06:42,440 the Mariner Valley, and it is a canyon that dwarfs 78 00:06:42,440 --> 00:06:44,080 anything we see on Earth. 79 00:06:48,680 --> 00:06:52,320 On the opposite side of the planet is an impact basin called Hellas. 80 00:06:55,480 --> 00:06:57,760 The height difference from the crater rim 81 00:06:57,760 --> 00:07:01,080 to the crater floor is 9km. 82 00:07:01,080 --> 00:07:04,280 That means you could fit Everest in the middle of there 83 00:07:04,280 --> 00:07:06,320 and look down on its summit. 84 00:07:10,520 --> 00:07:15,240 And the region surrounding the basin reveals Mars' former life. 85 00:07:18,920 --> 00:07:24,200 The Hellas basin is punched into the oldest-surviving terrain on Mars. 86 00:07:24,200 --> 00:07:26,440 It's called Noachis Terra 87 00:07:26,440 --> 00:07:29,040 or The Land Of Noah. 88 00:07:29,040 --> 00:07:33,160 And that's a wonderfully evocative name because its surface is sculpted 89 00:07:33,160 --> 00:07:34,680 by flowing water. 90 00:07:39,760 --> 00:07:44,320 All across the earliest Martian surface, we've glimpsed traces 91 00:07:44,320 --> 00:07:47,560 of what appear to have been lakes and rivers. 92 00:07:51,440 --> 00:07:55,960 And so a new generation of spacecraft has been sent to Mars, 93 00:07:55,960 --> 00:07:58,280 to investigate the existence of water... 94 00:08:01,280 --> 00:08:05,800 ..and what happened to the planet for it all to disappear. 95 00:08:16,200 --> 00:08:20,600 Led by the most audacious Mars mission ever attempted... 96 00:08:24,520 --> 00:08:26,720 INDISTINCT RADIO COMMUNICATION 97 00:08:26,720 --> 00:08:30,080 We have two-way Doppler and orbit around the planet Mars. 98 00:08:32,040 --> 00:08:36,120 ..to land a one-tonne rover on the Martian surface. 99 00:08:47,880 --> 00:08:52,760 Its final descent has become known as the "seven minutes of terror". 100 00:09:55,960 --> 00:09:59,920 Curiosity touched down in Gale crater, 101 00:09:59,920 --> 00:10:03,880 a 150-kilometre-wide impact basin, 102 00:10:03,880 --> 00:10:06,360 thought to have been home to an ancient lake. 103 00:10:17,480 --> 00:10:22,120 The rover is a $2.5 billion mobile chemistry lab... 104 00:10:25,200 --> 00:10:28,040 ..designed to take samples of the Martian surface 105 00:10:28,040 --> 00:10:30,040 and analyse its composition. 106 00:10:42,040 --> 00:10:47,080 As it explored the crater, Curiosity saw pebbles polished 107 00:10:47,080 --> 00:10:49,280 and rounded by running water 108 00:10:49,280 --> 00:10:52,280 in what had once been rivers and streams. 109 00:11:01,480 --> 00:11:06,920 Then, 61 days after landing, Curiosity identified the perfect 110 00:11:06,920 --> 00:11:09,440 spot to begin its primary mission. 111 00:11:15,800 --> 00:11:19,720 In a sandy area of the crater called the Rocknest, 112 00:11:19,720 --> 00:11:23,160 the rover took its first scoops of Martian soil. 113 00:11:39,240 --> 00:11:43,000 Chemical analysis of the fine, dusty sand revealed 114 00:11:43,000 --> 00:11:45,200 something quite unexpected. 115 00:11:49,760 --> 00:11:53,160 Even though the surface of Mars appears completely dry, 116 00:11:53,160 --> 00:11:58,200 2% of the soil is still made up of water. 117 00:12:05,120 --> 00:12:09,160 Curiosity had found evidence of just how wet a planet 118 00:12:09,160 --> 00:12:11,200 ancient Mars had been. 119 00:12:25,920 --> 00:12:28,640 Mars was a water world. 120 00:12:54,360 --> 00:12:56,680 Rains fell, 121 00:12:56,680 --> 00:12:59,160 rivers ran, 122 00:12:59,160 --> 00:13:01,560 and, in the northern hemisphere, 123 00:13:01,560 --> 00:13:03,640 water collected in a vast sea 124 00:13:03,640 --> 00:13:06,800 that covered a fifth of the Martian surface. 125 00:13:13,360 --> 00:13:17,280 The Red Planet was once blue. 126 00:13:28,000 --> 00:13:30,560 All the evidence suggests that there were large bodies 127 00:13:30,560 --> 00:13:34,480 of standing water on Mars around 4 billion years ago, 128 00:13:34,480 --> 00:13:38,760 and the atmospheric pressure was at least that of Earth today, 129 00:13:38,760 --> 00:13:40,200 perhaps even higher. 130 00:13:40,200 --> 00:13:45,880 Temperatures were around 25 degrees, so I could have sat on Mars 131 00:13:45,880 --> 00:13:48,720 all those years ago, admittedly with a mask to breathe, 132 00:13:48,720 --> 00:13:51,360 because there was very little oxygen, but I could have sat there 133 00:13:51,360 --> 00:13:54,600 and looked out over a view like that. 134 00:13:54,600 --> 00:14:00,080 So, you don't have to imagine what Mars was like in the past. 135 00:14:00,080 --> 00:14:02,080 You can experience it. 136 00:14:02,080 --> 00:14:04,240 It was pretty much like this. 137 00:14:12,280 --> 00:14:14,920 But, within a billion years, 138 00:14:14,920 --> 00:14:18,160 all Mars' lakes and seas had disappeared. 139 00:14:22,040 --> 00:14:26,280 In our solar system, only one blue planet survives... 140 00:14:28,560 --> 00:14:31,960 ..Mars' sister, Earth. 141 00:14:37,120 --> 00:14:41,320 70% of our planet's surface is covered by ocean. 142 00:14:47,000 --> 00:14:50,240 Under the waves, a million species thrive. 143 00:14:56,160 --> 00:15:00,360 While on land, the rains support Earth's delicate ecosystems... 144 00:15:07,360 --> 00:15:10,160 ..providing a home for an abundance of life. 145 00:15:15,760 --> 00:15:18,520 But it hasn't always been this way. 146 00:15:26,080 --> 00:15:30,080 The early Earth was unrecognisable from the planet we know today. 147 00:15:38,560 --> 00:15:42,640 Its atmosphere thick with carbon dioxide. 148 00:15:49,760 --> 00:15:52,160 And its oceans acidic. 149 00:15:58,120 --> 00:16:02,320 Four billions years ago, Earth was a troubled, toxic world... 150 00:16:07,240 --> 00:16:10,240 ..while Mars was flourishing. 151 00:16:25,120 --> 00:16:28,080 But both planets were about to be engulfed 152 00:16:28,080 --> 00:16:30,120 by a cataclysm from space. 153 00:16:35,520 --> 00:16:38,160 To understand what happened, 154 00:16:38,160 --> 00:16:40,960 we have to look beyond our own world. 155 00:16:43,000 --> 00:16:45,880 You can't read the deep history of the Earth by looking 156 00:16:45,880 --> 00:16:50,120 at its surface because our planet is a geologically active world. 157 00:16:50,120 --> 00:16:55,000 The surface is constantly being reshaped by volcanic activity, 158 00:16:55,000 --> 00:17:00,160 weathering, and the actions of the oceans, but we have a companion, 159 00:17:00,160 --> 00:17:04,320 the moon, which has been inactive for many billions of years, 160 00:17:04,320 --> 00:17:08,400 and so the history of events that happened in this region 161 00:17:08,400 --> 00:17:12,240 of the solar system is written all over its surface. 162 00:17:17,840 --> 00:17:20,360 The most distinctive feature of the moon's surface 163 00:17:20,360 --> 00:17:24,840 are its craters - it is literally covered in a record of impacts 164 00:17:24,840 --> 00:17:28,840 from space, and that allows us to estimate the relative ages 165 00:17:28,840 --> 00:17:30,960 of different parts of the moon. 166 00:17:30,960 --> 00:17:33,240 Quite simply, if there are more craters, 167 00:17:33,240 --> 00:17:35,240 then that piece of the moon must be older. 168 00:17:35,240 --> 00:17:38,280 There's been more time for the impacts to build up. 169 00:17:38,280 --> 00:17:42,240 But we can do better than just measure the relative ages 170 00:17:42,240 --> 00:17:46,560 because we have rocks, the moon rocks brought back 171 00:17:46,560 --> 00:17:48,800 by the Apollo astronauts. 172 00:17:48,800 --> 00:17:52,080 We can estimate the ages of rocks very precisely by looking 173 00:17:52,080 --> 00:17:55,440 at the rates of decay of radioactive elements inside them. 174 00:17:55,440 --> 00:17:59,320 They're like little stopwatches that start ticking the moment 175 00:17:59,320 --> 00:18:04,600 the rocks are formed, in this case by the impacts from space. 176 00:18:04,600 --> 00:18:09,280 So, the moon rocks allow us to tie the number of craters 177 00:18:09,280 --> 00:18:11,800 in a particular region of the moon 178 00:18:11,800 --> 00:18:14,920 to an absolute age measured by the rocks. 179 00:18:24,360 --> 00:18:28,520 And this doesn't just allow us to date impacts on the lunar surface. 180 00:18:36,200 --> 00:18:38,040 It means that craters can be used 181 00:18:38,040 --> 00:18:41,160 to read the histories of worlds across the solar system. 182 00:18:46,600 --> 00:18:48,720 Including Mars. 183 00:18:54,640 --> 00:18:58,520 When we gathered all the data, we discovered something surprising. 184 00:18:58,520 --> 00:19:02,600 There was a peak in the crater formation rate, about 3.8 185 00:19:02,600 --> 00:19:04,680 to 3.9 billion years ago, 186 00:19:04,680 --> 00:19:09,720 which signified a period of intense violence in the solar system, 187 00:19:09,720 --> 00:19:13,080 and that is called the Late Heavy Bombardment. 188 00:19:40,400 --> 00:19:44,960 Countless asteroids fragmented in Mars' atmosphere, 189 00:19:44,960 --> 00:19:47,720 raining havoc across the planet. 190 00:20:23,200 --> 00:20:27,440 It's estimated that 53 tonnes of rock 191 00:20:27,440 --> 00:20:30,760 fell on every square metre of Mars. 192 00:20:41,280 --> 00:20:45,280 Over a third of the planet's surface was obliterated... 193 00:20:49,200 --> 00:20:52,280 ..and Mars was pushed to the brink of death. 194 00:21:05,080 --> 00:21:08,000 Whilst the evidence from the surface of the moon tells us 195 00:21:08,000 --> 00:21:11,960 that the Late Heavy Bombardment happened, it doesn't tell us why. 196 00:21:11,960 --> 00:21:15,000 For that, we have to resort to computer models of the evolution 197 00:21:15,000 --> 00:21:17,640 of the solar system, and, when we do that, 198 00:21:17,640 --> 00:21:20,040 they point the finger at Neptune. 199 00:21:23,720 --> 00:21:27,800 It's thought that Neptune migrated outwards into the Kuiper belt... 200 00:21:30,920 --> 00:21:33,400 ..a region of icy, rocky objects 201 00:21:33,400 --> 00:21:36,280 orbiting at the edge of the solar system. 202 00:21:40,200 --> 00:21:44,440 The resulting gravitational interactions disrupted those orbits 203 00:21:44,440 --> 00:21:48,320 and sent many of the objects inwards to the inner solar system, 204 00:21:48,320 --> 00:21:51,920 and that may have been the cause of the Late Heavy Bombardment. 205 00:22:03,120 --> 00:22:07,800 Earth also suffered the onslaught, 206 00:22:07,800 --> 00:22:11,880 and, for tens of millions of years, 207 00:22:11,880 --> 00:22:16,920 the fortunes of the two sister worlds hung in the balance. 208 00:22:41,880 --> 00:22:46,600 But, just when conditions appeared at their least promising, 209 00:22:46,600 --> 00:22:50,040 Earth's most precious characteristic emerged. 210 00:22:54,240 --> 00:22:55,600 Life. 211 00:22:58,840 --> 00:23:02,440 There is good evidence that life was present on Earth 212 00:23:02,440 --> 00:23:06,280 around 3.8 billion years ago, and discounting the - I think - 213 00:23:06,280 --> 00:23:08,840 remote possibility that life began elsewhere 214 00:23:08,840 --> 00:23:11,320 in the solar system and was transported to the Earth 215 00:23:11,320 --> 00:23:13,480 on meteorites or comets, 216 00:23:13,480 --> 00:23:17,080 that means that life must have begun here. 217 00:23:17,080 --> 00:23:20,120 So, somewhere on this planet there was a transition 218 00:23:20,120 --> 00:23:23,560 from geochemistry - the chemistry of Earth, 219 00:23:23,560 --> 00:23:26,560 to biochemistry - the chemistry of life. 220 00:23:42,680 --> 00:23:46,480 And whilst the precise details of how that transition occurred 221 00:23:46,480 --> 00:23:52,200 remain a mystery, it's thought that in warm volcanic pools 222 00:23:52,200 --> 00:23:56,680 or deep sea hydrothermal vents, conditions were right 223 00:23:56,680 --> 00:24:01,520 for the chemical building blocks of life to form spontaneously. 224 00:24:06,080 --> 00:24:08,880 And that means that if similar conditions 225 00:24:08,880 --> 00:24:11,560 were to be found elsewhere in the solar system, 226 00:24:11,560 --> 00:24:15,080 it might be possible that life began there too. 227 00:24:20,840 --> 00:24:26,480 Ignition, and lift off of the Atlas V rocket with MRO. 228 00:24:28,120 --> 00:24:30,200 Surveying for the deepest insights 229 00:24:30,200 --> 00:24:32,360 into the mysterious evolution of Mars. 230 00:24:35,080 --> 00:24:39,520 So, in 2005, NASA embarked on a mission to look 231 00:24:39,520 --> 00:24:43,560 for those same environments on Mars. 232 00:24:57,800 --> 00:25:01,280 For more than a decade, the Mars Reconnaissance Orbiter 233 00:25:01,280 --> 00:25:04,080 has been our eyes on the Red Planet... 234 00:25:09,560 --> 00:25:12,040 ..sending back more data 235 00:25:12,040 --> 00:25:15,040 than all the other Mars missions combined. 236 00:25:21,280 --> 00:25:26,040 MRO has made more than 60,000 orbits, 237 00:25:26,040 --> 00:25:30,080 mapping over 99% of the planet's surface. 238 00:25:36,160 --> 00:25:41,640 Its high-resolution cameras have revealed Mars as never before, 239 00:25:41,640 --> 00:25:46,600 discovering polar avalanches, 240 00:25:46,600 --> 00:25:48,800 shifting sand dunes... 241 00:25:52,760 --> 00:25:58,720 ..and what could be seasonal flows of sand or even liquid meltwater. 242 00:26:03,480 --> 00:26:08,320 Then, in 2017, MRO turned its gaze 243 00:26:08,320 --> 00:26:12,280 to one of the Red Planet's oldest features, 244 00:26:12,280 --> 00:26:14,160 the Eridania Basin. 245 00:26:18,680 --> 00:26:23,400 3.8 billion years ago, the basin was a vast sea... 246 00:26:26,920 --> 00:26:29,000 ..holding ten times more water 247 00:26:29,000 --> 00:26:32,040 than the Great Lakes of North America. 248 00:26:37,560 --> 00:26:41,600 And it was here that MRO found the evidence it was looking for. 249 00:26:44,240 --> 00:26:49,960 400-metre-thick deposits of minerals that, on Earth, 250 00:26:49,960 --> 00:26:53,320 form in deep sea hydrothermal vents. 251 00:27:00,720 --> 00:27:05,800 In the Eridania Basin, MRO revealed that conditions on Mars 252 00:27:05,800 --> 00:27:09,080 had once been ripe for the emergence of life. 253 00:27:33,400 --> 00:27:37,920 We won't know for sure whether life began or even perhaps still exists 254 00:27:37,920 --> 00:27:41,520 on Mars until we go there and find physical evidence - 255 00:27:41,520 --> 00:27:46,000 so, microbes buried deep below the soil in oases of liquid water, 256 00:27:46,000 --> 00:27:49,640 or maybe microbe fossils - but what we do know is that, 257 00:27:49,640 --> 00:27:53,480 when life began here on Earth, 3.8 billion years ago, 258 00:27:53,480 --> 00:27:55,760 the conditions on Mars were very similar. 259 00:27:55,760 --> 00:27:58,400 There were seas, there was volcanic activity, 260 00:27:58,400 --> 00:28:02,440 there were even hydrothermal vent systems on the floors of its oceans. 261 00:28:02,440 --> 00:28:06,120 So, it is at least possible that Earth is not the only world 262 00:28:06,120 --> 00:28:08,720 in the solar system where life began. 263 00:28:15,480 --> 00:28:18,280 The habitable conditions during what's known 264 00:28:18,280 --> 00:28:23,360 as Mars' Noachian era persisted for hundreds of millions of years. 265 00:28:32,560 --> 00:28:37,560 But then, prospects for life on the Red Planet changed dramatically. 266 00:28:43,880 --> 00:28:48,120 Around 3.5 billion years ago, the Noachian era drew to a close 267 00:28:48,120 --> 00:28:53,040 and Mars entered a more frozen, arid phase, known as the Hesperian. 268 00:28:53,040 --> 00:28:57,080 The water that flowed freely over the surface during the age of Noah 269 00:28:57,080 --> 00:29:01,560 became locked away in giant reservoirs of ice. 270 00:29:01,560 --> 00:29:05,840 But, around the same time, Mars became more volcanically active, 271 00:29:05,840 --> 00:29:08,880 and the volcanic eruptions and sub-surface lava flows 272 00:29:08,880 --> 00:29:13,440 occasionally melted the ice, leading to catastrophic flooding. 273 00:29:13,440 --> 00:29:16,440 They must have been some of the most spectacular sights 274 00:29:16,440 --> 00:29:18,800 in the history of the solar system. 275 00:29:25,880 --> 00:29:29,960 As molten rock pushed upwards through the crust, 276 00:29:29,960 --> 00:29:33,080 meltwater poured out onto the surface. 277 00:29:37,160 --> 00:29:39,680 It raged down from the southern highlands... 278 00:29:44,240 --> 00:29:49,680 ..until, in a place known as Echus Casma, it plunged 279 00:29:49,680 --> 00:29:52,280 over cliffs 4km high... 280 00:30:02,360 --> 00:30:05,520 ..creating the largest waterfall 281 00:30:05,520 --> 00:30:08,520 the solar system has ever seen. 282 00:30:49,240 --> 00:30:53,480 Echus Casma would have been like no waterfall ever seen on Earth. 283 00:30:53,480 --> 00:30:58,080 350 cubic kilometres of water flowed over it. 284 00:30:58,080 --> 00:31:02,960 That's like a cube 70km by 70km by 70km. 285 00:31:02,960 --> 00:31:06,280 It all entered into a canyon 10km wide 286 00:31:06,280 --> 00:31:11,120 and 100km long, and that happened in a few weeks. 287 00:31:19,680 --> 00:31:22,960 Once the flood subsided, the water disappeared... 288 00:31:26,040 --> 00:31:30,400 ..leaving the evidence of the falls etched into the face of the planet. 289 00:31:39,040 --> 00:31:43,040 We don't know precisely why the climate of Mars changed 290 00:31:43,040 --> 00:31:45,680 from warm and wet to cold and arid. 291 00:31:45,680 --> 00:31:48,120 We're talking about events that happened 292 00:31:48,120 --> 00:31:51,560 three and a half billion years ago on a planet hundreds of millions 293 00:31:51,560 --> 00:31:55,680 of kilometres away, so it is a hard problem. 294 00:31:55,680 --> 00:31:58,880 But we do strongly suspect that changes happening 295 00:31:58,880 --> 00:32:01,160 on the planet's surface were driven 296 00:32:01,160 --> 00:32:04,480 at least in part by changes in the planet's interior. 297 00:32:11,680 --> 00:32:13,920 Deep within Mars' core, 298 00:32:13,920 --> 00:32:17,160 something was causing the planet to die... 299 00:32:18,600 --> 00:32:23,680 ..and the evidence can be found in Mars' atmosphere. 300 00:32:23,680 --> 00:32:28,560 T-minus ten, nine, eight, seven, six, 301 00:32:28,560 --> 00:32:31,040 five, four, three, 302 00:32:31,040 --> 00:32:33,040 two, one. 303 00:32:33,040 --> 00:32:36,880 Main engine start, ignition, and lift-off 304 00:32:36,880 --> 00:32:39,640 of the Atlas V with MAVEN, 305 00:32:39,640 --> 00:32:42,320 looking for clues about the evolution of Mars 306 00:32:42,320 --> 00:32:44,000 through its atmosphere. 307 00:32:49,680 --> 00:32:53,720 In September 2014, NASA'S MAVEN probe made its final 308 00:32:53,720 --> 00:32:56,040 approach to the Red Planet. 309 00:33:10,800 --> 00:33:14,600 Its mission - to understand what drove the planet's 310 00:33:14,600 --> 00:33:16,280 dramatic climate change. 311 00:33:28,880 --> 00:33:32,720 MAVEN is equipped with an array of instruments designed to measure 312 00:33:32,720 --> 00:33:36,960 the behaviour of the atoms and molecules in Mars' atmosphere. 313 00:34:28,720 --> 00:34:32,240 The spacecraft circles Mars in an elliptical orbit... 314 00:34:41,320 --> 00:34:43,600 ..allowing it to measure the full profile 315 00:34:43,600 --> 00:34:45,840 of the planet's upper atmosphere. 316 00:34:54,240 --> 00:34:55,800 At its lowest point, 317 00:34:55,800 --> 00:34:59,160 it's just 150km above the surface. 318 00:35:02,280 --> 00:35:05,560 At its highest, a little over 6,000 kilometres. 319 00:35:09,880 --> 00:35:14,080 And it was at the very top of Mars' atmosphere that MAVEN found 320 00:35:14,080 --> 00:35:17,520 the key to the mystery of what happened to Mars. 321 00:35:23,640 --> 00:35:27,200 Detailed measurements revealed gas is being lost 322 00:35:27,200 --> 00:35:29,480 from the Martian atmosphere, 323 00:35:29,480 --> 00:35:31,960 escaping to space 324 00:35:31,960 --> 00:35:35,280 at a rate of about two kilograms every second. 325 00:35:40,240 --> 00:35:45,760 Over time, it's thought this gradual stripping away of Mars' atmosphere 326 00:35:45,760 --> 00:35:50,320 has slowly thinned the insulating layer surrounding the planet... 327 00:35:53,120 --> 00:35:56,120 ..causing surface temperatures to plummet. 328 00:36:14,440 --> 00:36:18,440 But what was it that caused Mars to lose its atmosphere 329 00:36:18,440 --> 00:36:21,200 while Earth clung on to hers? 330 00:36:29,880 --> 00:36:34,080 150 million kilometres away in that direction is the setting sun, 331 00:36:34,080 --> 00:36:36,960 a giant nuclear fusion reactor. 332 00:36:36,960 --> 00:36:39,040 You can fit one million Earths inside it. 333 00:36:39,040 --> 00:36:41,240 Now, the surface temperature 334 00:36:41,240 --> 00:36:43,800 is only around 6,000 degrees Celsius, 335 00:36:43,800 --> 00:36:46,280 but the sun's atmosphere, known as its corona, 336 00:36:46,280 --> 00:36:47,920 is at one million degrees. 337 00:36:47,920 --> 00:36:51,080 And that means it's in the form of what's known as a plasma, a soup 338 00:36:51,080 --> 00:36:53,400 of electrically charged particles. 339 00:36:53,400 --> 00:36:57,160 Some of those particles are moving around so fast that they can escape, 340 00:36:57,160 --> 00:37:00,440 and they stream away in what's known as the solar wind. 341 00:37:00,440 --> 00:37:04,200 They reach the Earth travelling at a few hundred kilometres per second. 342 00:37:04,200 --> 00:37:07,600 And, if we weren't protected, they would strip away our atmosphere. 343 00:37:17,600 --> 00:37:20,400 And when the sun dips below the horizon... 344 00:37:22,880 --> 00:37:27,720 ..there are times when that protective force field is revealed. 345 00:37:47,000 --> 00:37:48,960 Just look at that! 346 00:37:48,960 --> 00:37:51,280 I mean, there is the aurora. 347 00:37:55,600 --> 00:37:59,240 It's the laws of nature, all of them, written across the sky. 348 00:38:03,160 --> 00:38:06,760 Electrically-charged particles have been driven away from the sun, 349 00:38:06,760 --> 00:38:11,640 ultimately from nuclear fusion reactions in the core of a star. 350 00:38:11,640 --> 00:38:15,680 They're crossing the solar system, hitting the Earth's magnetic field, 351 00:38:15,680 --> 00:38:19,480 stretching it out on the dark side of the planet. 352 00:38:19,480 --> 00:38:23,200 The field then snaps back like an elastic band, 353 00:38:23,200 --> 00:38:27,200 accelerating all of those charged particles up and down 354 00:38:27,200 --> 00:38:30,440 the field lines to the poles, which is here in the skies 355 00:38:30,440 --> 00:38:34,160 over Iceland, and they hit nitrogen 356 00:38:34,160 --> 00:38:37,160 and oxygen molecules in the atmosphere. 357 00:38:38,800 --> 00:38:42,720 And you're seeing quantum mechanics - they're exciting the 358 00:38:42,720 --> 00:38:45,520 molecules so that they emit light in characteristic colours. 359 00:38:58,280 --> 00:39:00,800 And, if you think about it, this is the only time 360 00:39:00,800 --> 00:39:04,040 that we really see the Earth's magnetic field. 361 00:39:05,440 --> 00:39:08,440 It's one of the reasons why life on Earth 362 00:39:08,440 --> 00:39:11,520 has been able to persist for four billion years. 363 00:39:14,440 --> 00:39:17,600 In a sense, that's the reason that you exist. 364 00:39:22,920 --> 00:39:26,560 It's Earth's magnetic field that protects our atmosphere 365 00:39:26,560 --> 00:39:29,640 from the ravages of the solar wind, 366 00:39:29,640 --> 00:39:32,840 and that protective shield has its origins deep 367 00:39:32,840 --> 00:39:34,600 in the planet's interior. 368 00:39:36,920 --> 00:39:40,360 Thousands of kilometres down below my feet, 369 00:39:40,360 --> 00:39:43,840 actually below your feet now, is the Earth's outer core, 370 00:39:43,840 --> 00:39:47,080 which is a seething mass of molten iron. 371 00:39:47,080 --> 00:39:51,160 Convection currents cause the molten iron to rise, 372 00:39:51,160 --> 00:39:55,040 and then the Earth's rotation causes it to spiral around. 373 00:39:55,040 --> 00:39:57,640 Now, a spiralling, circling flow 374 00:39:57,640 --> 00:40:01,360 of an electrically conducting liquid is a dynamo. 375 00:40:01,360 --> 00:40:06,080 A dynamo generates a magnetic field and the Earth's field rises up, 376 00:40:06,080 --> 00:40:09,640 not just to the surface here, but out into space, 377 00:40:09,640 --> 00:40:11,720 forming our protective shield. 378 00:40:11,720 --> 00:40:14,600 And that is what you see there. 379 00:40:21,600 --> 00:40:23,880 And just like Earth, 380 00:40:23,880 --> 00:40:27,440 ancient Mars was also shielded from the sun. 381 00:40:33,840 --> 00:40:36,640 Aurora once danced above its poles... 382 00:40:39,920 --> 00:40:44,800 ..keeping guard over the Martian atmosphere and seas below. 383 00:41:00,600 --> 00:41:04,240 But between 3.5 and 4 billion years ago, 384 00:41:04,240 --> 00:41:06,760 Mars' dynamo switched off. 385 00:41:09,760 --> 00:41:13,800 The aurora surrounding the poles slowly faded away 386 00:41:13,800 --> 00:41:15,960 as the magnetic field diminished... 387 00:41:18,480 --> 00:41:21,520 ..allowing the atmosphere to be stripped away 388 00:41:21,520 --> 00:41:23,160 by the solar wind. 389 00:41:33,040 --> 00:41:38,320 Without protection, seas evaporated, the surface froze, 390 00:41:38,320 --> 00:41:41,840 and Mars was transformed. 391 00:41:50,400 --> 00:41:54,240 At the same time, the fortunes of Mars' sister world 392 00:41:54,240 --> 00:41:56,640 were about to take a very different turn. 393 00:42:01,160 --> 00:42:04,840 For the next billion years or so, Earth was indistinguishable 394 00:42:04,840 --> 00:42:07,200 from those landscapes of early Mars - 395 00:42:07,200 --> 00:42:10,480 barren continents surrounded by ocean. 396 00:42:10,480 --> 00:42:15,040 But in Earth's oceans, life was beginning to transform the planet. 397 00:42:18,840 --> 00:42:23,080 Primitive algae started to neutralise the ocean's acidity 398 00:42:23,080 --> 00:42:27,000 and replace the dense red fog of Earth's methane-rich 399 00:42:27,000 --> 00:42:29,160 atmosphere with oxygen. 400 00:42:32,840 --> 00:42:37,320 Around 600 million years ago, that oxygen-rich atmosphere allowed 401 00:42:37,320 --> 00:42:41,560 complex life to evolve in the oceans, colonise the land, 402 00:42:41,560 --> 00:42:46,000 and ultimately produce this almost-infinitely rich living world 403 00:42:46,000 --> 00:42:48,480 today, of which we are a part. 404 00:43:00,280 --> 00:43:04,280 While Mars died, Earth flourished. 405 00:43:10,640 --> 00:43:15,400 To understand why the two sisters had such different destinies, 406 00:43:15,400 --> 00:43:18,080 you have to go right back 407 00:43:18,080 --> 00:43:21,520 to the time the planets were forming. 408 00:43:26,440 --> 00:43:28,680 When Mars and Earth were born, 409 00:43:28,680 --> 00:43:32,760 the solar system was a chaotic vortex of gas and rock. 410 00:43:37,440 --> 00:43:43,520 Material clumped together and grew, only to be smashed apart. 411 00:43:51,800 --> 00:43:55,120 Over time, some of the objects became large enough to survive 412 00:43:55,120 --> 00:43:58,560 at least the smaller impacts, and continued to grow, 413 00:43:58,560 --> 00:44:01,960 including the embryonic planets Earth and Mars. 414 00:44:10,760 --> 00:44:15,240 But there was one crucial difference between the young planets. 415 00:44:21,880 --> 00:44:24,760 Mars formed in a region of the solar system 416 00:44:24,760 --> 00:44:27,360 with considerably less rocky material. 417 00:44:28,480 --> 00:44:31,680 And that had a profound impact on the planet's growth. 418 00:44:37,320 --> 00:44:41,200 Mars is a significantly smaller world - it's about half the diameter 419 00:44:41,200 --> 00:44:43,880 of the Earth, and that makes all the difference. 420 00:44:43,880 --> 00:44:47,440 Although the details are not yet fully understood, 421 00:44:47,440 --> 00:44:51,720 it seems clear that Mars' smaller size meant that its dynamo switched 422 00:44:51,720 --> 00:44:54,040 off many billions of years ago. 423 00:44:57,840 --> 00:45:02,120 Being smaller meant Mars' core cooled more quickly than Earth's. 424 00:45:04,960 --> 00:45:08,080 And this is certainly part of the reason why Mars 425 00:45:08,080 --> 00:45:09,840 lost its magnetic field. 426 00:45:16,960 --> 00:45:20,360 Even though the planet is further away from the sun than we are, 427 00:45:20,360 --> 00:45:23,360 that meant that the solar wind stripped away its atmosphere 428 00:45:23,360 --> 00:45:25,440 and Mars died. 429 00:45:25,440 --> 00:45:30,560 So, even though Earth and Mars are so similar in so many ways, 430 00:45:30,560 --> 00:45:34,520 the difference in position and size in the solar system 431 00:45:34,520 --> 00:45:37,000 led to very different fates. 432 00:45:47,640 --> 00:45:51,320 Long ago, two sister worlds were born. 433 00:45:56,120 --> 00:45:59,800 In childhood, Mars was warm and wet... 434 00:46:05,320 --> 00:46:09,360 ..whilst the Earth was inhospitable and toxic. 435 00:46:17,480 --> 00:46:20,320 Both young planets survived the violence 436 00:46:20,320 --> 00:46:24,800 of the Late Heavy Bombardment, 437 00:46:24,800 --> 00:46:28,880 emerging as mature worlds, 438 00:46:28,880 --> 00:46:32,720 primed with all the ingredients for life. 439 00:46:42,280 --> 00:46:47,000 But deep inside, the smaller of the two was dying. 440 00:46:53,400 --> 00:46:55,680 Mars' seas dried up. 441 00:47:07,840 --> 00:47:14,360 And as the planet's interior cooled, one by one her fires went out. 442 00:47:19,240 --> 00:47:23,720 Olympus Mons, the largest volcano in the solar system, 443 00:47:23,720 --> 00:47:27,040 last erupted around 25 million years ago. 444 00:47:36,080 --> 00:47:39,520 As the lava turned to stone, 445 00:47:39,520 --> 00:47:42,600 Mars was frozen in time. 446 00:47:57,240 --> 00:48:03,760 And so, today, her surface lies rusted and gathering dust. 447 00:48:11,440 --> 00:48:14,880 But that might not be the end of Mars' story. 448 00:48:22,840 --> 00:48:27,280 Because the next generation of spacecraft are already on their way. 449 00:48:35,840 --> 00:48:40,040 NASA Orion - currently in advanced testing. 450 00:49:10,360 --> 00:49:13,160 ESA ExoMars - 451 00:49:13,160 --> 00:49:17,440 a fleet of spacecraft designed to search for signs of life. 452 00:49:27,640 --> 00:49:31,880 And the most ambitious private space mission ever conceived. 453 00:49:43,040 --> 00:49:48,720 A launch vehicle developed to take humans to the surface of Mars. 454 00:50:06,120 --> 00:50:09,080 Mars is, in a sense, a failed world, 455 00:50:09,080 --> 00:50:13,920 a faded ember etched with the memories of a more enticing past, 456 00:50:13,920 --> 00:50:18,920 but there may have been, and may still be, life on Mars. 457 00:50:18,920 --> 00:50:22,560 And the discovery of a second genesis in our solar system 458 00:50:22,560 --> 00:50:27,160 would have profound philosophical, scientific and cultural consequences 459 00:50:27,160 --> 00:50:30,320 because it would mean there is a sense of inevitability 460 00:50:30,320 --> 00:50:32,200 about the origin of life, 461 00:50:32,200 --> 00:50:34,560 and that would mean that the universe 462 00:50:34,560 --> 00:50:38,840 is most likely teeming with life - that we are not alone. 463 00:50:44,400 --> 00:50:48,400 But equally importantly, I think, is the role that a planet 464 00:50:48,400 --> 00:50:52,320 with a history like Mars could play in our future. 465 00:50:52,320 --> 00:50:56,800 Mars is rich in resources, it has vast reservoirs of frozen 466 00:50:56,800 --> 00:50:59,240 water below the surface, and minerals - 467 00:50:59,240 --> 00:51:02,840 iron, nitrogen, carbon, oxygen - all the things 468 00:51:02,840 --> 00:51:05,120 you need to support a civilisation. 469 00:51:07,360 --> 00:51:10,000 And that's why I think that, in my lifetime, 470 00:51:10,000 --> 00:51:14,080 there will be Martians, but the Martians will be us. 471 00:51:14,080 --> 00:51:17,200 We will go to Mars and make it our home, 472 00:51:17,200 --> 00:51:20,680 and that old red world will become our first step 473 00:51:20,680 --> 00:51:24,200 beyond the cradle, and out to the stars. 474 00:51:56,400 --> 00:51:59,120 Mars really captures 475 00:51:59,120 --> 00:52:02,160 our imagination, 476 00:52:02,160 --> 00:52:05,280 partly because it's so close. 477 00:52:05,280 --> 00:52:09,880 I think people are really interested in Mars because it actually 478 00:52:09,880 --> 00:52:12,160 is so similar to Earth. 479 00:52:12,160 --> 00:52:17,040 It's close by, it's easy to travel there with robots 480 00:52:17,040 --> 00:52:21,280 and space missions, and so we've done a lot of exploration. 481 00:52:21,280 --> 00:52:24,720 And, every time you go and look, you discover something new. 482 00:52:28,600 --> 00:52:33,080 NASA Curiosity launched on the 26th of November, 2011. 483 00:52:36,160 --> 00:52:38,720 But the biggest obstacle facing the mission team 484 00:52:38,720 --> 00:52:40,400 wasn't leaving the Earth. 485 00:52:44,000 --> 00:52:45,680 Mars has a unique set of challenges 486 00:52:45,680 --> 00:52:48,320 compared to other places we go with spacecraft. 487 00:52:48,320 --> 00:52:52,040 Mars has an atmosphere but it's thin, so it's not enough 488 00:52:52,040 --> 00:52:53,280 to really slow you down, 489 00:52:53,280 --> 00:52:56,160 but it is enough to actually burn you up as you're trying to land. 490 00:52:58,880 --> 00:53:01,760 Curiosity reached the top of the Martian atmosphere, 491 00:53:01,760 --> 00:53:04,320 travelling at 20,000km per hour. 492 00:53:07,240 --> 00:53:10,040 Curiosity is a big rover. It weighs a metric ton, 493 00:53:10,040 --> 00:53:12,480 and so landing that required every trick in the book 494 00:53:12,480 --> 00:53:14,960 of how we've learned to land on Mars with previous missions. 495 00:53:18,080 --> 00:53:21,040 To land safely, the rover had to be slowed 496 00:53:21,040 --> 00:53:23,480 to less than 4km per hour. 497 00:53:31,360 --> 00:53:33,760 You end up arriving at Mars going really fast, 498 00:53:33,760 --> 00:53:35,960 so you actually have to slow down, 499 00:53:35,960 --> 00:53:38,800 and we do that using a heat shield, 500 00:53:38,800 --> 00:53:42,240 which burns off a lot of energy and creates a lot of heat, 501 00:53:42,240 --> 00:53:45,160 so you have to absorb that somehow and not damage the spacecraft. 502 00:53:45,160 --> 00:53:47,160 Then a parachute comes out. 503 00:53:51,400 --> 00:53:54,160 The biggest parachute we've ever used in a planetary mission. 504 00:53:56,560 --> 00:53:59,280 And that even doesn't slow Curiosity down enough, 505 00:53:59,280 --> 00:54:02,640 because Mars' atmosphere is quite thin, so then rockets carry 506 00:54:02,640 --> 00:54:05,400 the spacecraft and guide the spacecraft to the surface. 507 00:54:11,440 --> 00:54:14,400 There's nothing you can do at that point to ensure its success 508 00:54:14,400 --> 00:54:16,040 or prevent its crashing... 509 00:54:18,280 --> 00:54:21,280 ..and yet you've invested so much in the outcome. 510 00:54:24,000 --> 00:54:27,840 All I could do was sort of curl up in a ball and wait for the 511 00:54:27,840 --> 00:54:30,240 green light that Curiosity was safely on Mars. 512 00:54:33,760 --> 00:54:37,560 Seven years and $2.5 billion in the making, 513 00:54:37,560 --> 00:54:40,280 Curiosity finally touched down 514 00:54:40,280 --> 00:54:45,280 at 6.32 Universal Time, on the 6th of August, 2012. 515 00:54:50,600 --> 00:54:53,200 I was sitting in the control room watching the engineers, 516 00:54:53,200 --> 00:54:56,280 who were actually monitoring the signals coming in from Curiosity, 517 00:54:56,280 --> 00:54:58,960 and so they were reading out the data that they were getting 518 00:54:58,960 --> 00:55:01,960 and they detected the wheels touching the soil. 519 00:55:01,960 --> 00:55:05,000 Then a few seconds went by when cables had to be cut 520 00:55:05,000 --> 00:55:07,040 and the rocket jet pack had to fly away. 521 00:55:08,480 --> 00:55:11,280 And, only then, they understood that Curiosity was safe 522 00:55:11,280 --> 00:55:14,600 on the ground, and the whole room just erupted in celebration. 523 00:55:19,680 --> 00:55:24,080 Since it landed, Curiosity has been exploring Gale Crater 524 00:55:24,080 --> 00:55:25,680 for more than six years. 525 00:55:29,160 --> 00:55:33,640 Curiosity is a roving laboratory. 526 00:55:33,640 --> 00:55:38,720 We actually collect samples by scooping it or by drilling, 527 00:55:38,720 --> 00:55:41,120 or just by sucking in some of the atmospheric gas. 528 00:55:43,440 --> 00:55:48,160 And it's that type of data that allows us to pick apart 529 00:55:48,160 --> 00:55:50,280 the story that those things hold. 530 00:55:52,960 --> 00:55:58,440 In 2015, we made our first identification of organic molecules 531 00:55:58,440 --> 00:56:00,640 that we think were coming from the Martian materials. 532 00:56:02,080 --> 00:56:04,720 And that is a turning point for us. 533 00:56:07,960 --> 00:56:10,520 What we found in those rocks 534 00:56:10,520 --> 00:56:14,120 is what we expected of natural organic matter. 535 00:56:14,120 --> 00:56:16,280 It's what you would expect to find on Earth. 536 00:56:19,160 --> 00:56:23,000 Finding the organic matter is the clue to searching for life. 537 00:56:25,640 --> 00:56:28,280 What everybody wants to know is whether or not Mars 538 00:56:28,280 --> 00:56:31,520 once had life, and the short answer is - we don't know. 539 00:56:33,120 --> 00:56:35,600 The somewhat longer answer is - 540 00:56:35,600 --> 00:56:40,080 we see all the signs of materials that could have supported life. 541 00:56:40,080 --> 00:56:42,680 We have evidence for lots of water early on. 542 00:56:44,560 --> 00:56:48,360 We see the nutrients, we see carbon, we see oxygen, 543 00:56:48,360 --> 00:56:50,600 we see nitrogen, we see phosphorus, 544 00:56:50,600 --> 00:56:52,880 we see all the stuff that life needs 545 00:56:52,880 --> 00:56:57,240 in order to reproduce and survive as simple microorganisms. 546 00:57:01,520 --> 00:57:05,280 For me personally, I find it might actually 547 00:57:05,280 --> 00:57:08,000 be more surprising if we never found evidence of life on Mars. 548 00:57:08,000 --> 00:57:11,080 Everything we've found suggests that Mars was such a friendly, 549 00:57:11,080 --> 00:57:14,000 supportive place for life in its early history, 550 00:57:14,000 --> 00:57:17,640 and there should be a lot of planets like that around other stars, 551 00:57:17,640 --> 00:57:19,680 and lots of life in the universe. 552 00:57:19,680 --> 00:57:22,880 So, maybe we're getting to the point where it'll be more surprising 553 00:57:22,880 --> 00:57:24,920 if we never find other life. 554 00:57:31,080 --> 00:57:35,280 And so, thanks to Curiosity's discoveries, the latest wave 555 00:57:35,280 --> 00:57:38,840 of spacecraft might finally answer the question - 556 00:57:38,840 --> 00:57:41,520 has there ever been life on Mars? 557 00:57:47,760 --> 00:57:49,040 Next time... 558 00:57:51,400 --> 00:57:54,160 ..we enter the realm of the gas giants... 559 00:57:57,160 --> 00:58:01,720 ..to discover how the largest and oldest of the planets 560 00:58:01,720 --> 00:58:04,320 sculpted the entire solar system. 561 00:58:09,600 --> 00:58:12,360 Jupiter, the godfather. 562 00:58:19,000 --> 00:58:22,240 Journey through our solar system with this free poster produced 563 00:58:22,240 --> 00:58:26,680 by the Open University, and discover more about its planets and moons. 564 00:58:28,480 --> 00:58:31,240 Order your free copy by calling... 565 00:58:35,040 --> 00:58:38,320 ..or go to... 566 00:58:41,440 --> 00:58:43,760 ..and follow the links to the Open University.