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Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:01,209 --> 00:00:03,377 In the beginning, there was darkness... 2 00:00:03,420 --> 00:00:05,504 and then, bang... 3 00:00:05,547 --> 00:00:08,674 giving birth to an endless expanding existence... 4 00:00:08,717 --> 00:00:11,260 of time, space, and matter. 5 00:00:11,302 --> 00:00:14,013 Now, see further than we've ever imagined... 6 00:00:14,055 --> 00:00:16,015 beyond the limits of our existence... 7 00:00:16,057 --> 00:00:19,059 in a place we call "The Universe. " 8 00:00:23,064 --> 00:00:25,357 Lurking in the shadows of the solar system... 9 00:00:25,400 --> 00:00:28,318 are worlds so chemically active and misshapen... 10 00:00:28,361 --> 00:00:31,280 that they border on the bizarre. 11 00:00:31,322 --> 00:00:32,531 That I think the most shocking thing... 12 00:00:32,574 --> 00:00:37,661 was how very different the solar system is. 13 00:00:37,704 --> 00:00:38,829 These are the moons... 14 00:00:38,872 --> 00:00:41,373 surrounding the planets of the solar system... 15 00:00:41,416 --> 00:00:43,459 moons that were once either unknown... 16 00:00:43,501 --> 00:00:45,169 or considered afterthoughts... 17 00:00:45,211 --> 00:00:48,797 are now on the cutting edge of astronomical exploration. 18 00:00:48,840 --> 00:00:49,882 What was surprising... 19 00:00:49,924 --> 00:00:52,885 that they all didn't look like our moon. 20 00:00:52,927 --> 00:00:55,554 The so-called minor members of the solar systems... 21 00:00:55,597 --> 00:00:57,931 are not of minor interest. 22 00:00:57,974 --> 00:01:02,311 What surprises await us on these alien moons? 23 00:01:17,660 --> 00:01:20,662 Our solar system has always been fertile ground... 24 00:01:20,705 --> 00:01:23,082 for science fiction writers... 25 00:01:23,124 --> 00:01:26,919 but with exponential advances in telescopic technology... 26 00:01:26,961 --> 00:01:30,756 and close encounters by unmanned probes... 27 00:01:30,799 --> 00:01:35,969 the curtain has now been lifted on a new ballet of moons. 28 00:01:36,012 --> 00:01:37,429 Most of which are going one way around... 29 00:01:37,472 --> 00:01:39,848 some of which are going the other way around... 30 00:01:39,891 --> 00:01:42,059 all at different rates, passing one another... 31 00:01:42,102 --> 00:01:45,687 the inner ones passing the outer ones. 32 00:01:45,730 --> 00:01:47,272 For nearly half a century... 33 00:01:47,315 --> 00:01:51,985 it was believed the solar system was home to only 32 moons. 34 00:01:52,028 --> 00:01:54,279 They ranged in size from Jupiter's moon... 35 00:01:54,322 --> 00:01:57,950 Ganymede, larger than the planet Mercury... 36 00:01:57,992 --> 00:02:00,119 to small asteroid-shaped ones... 37 00:02:00,161 --> 00:02:05,207 like the Martian moons Phobos and Deimos. 38 00:02:05,250 --> 00:02:07,376 That number has exploded. 39 00:02:07,418 --> 00:02:10,462 In 2007 alone, scientists announced... 40 00:02:10,505 --> 00:02:14,174 the discovery of 20 new moons around Jupiter... 41 00:02:14,217 --> 00:02:15,717 one around Saturn... 42 00:02:15,760 --> 00:02:18,011 and three around Neptune. 43 00:02:18,054 --> 00:02:22,182 What happened is astronomical telescopes... 44 00:02:22,225 --> 00:02:26,603 had available to them what are called CCD cameras. 45 00:02:26,646 --> 00:02:28,147 These are digital cameras... 46 00:02:28,189 --> 00:02:31,859 that almost everybody has nowadays. 47 00:02:31,901 --> 00:02:34,111 It's difficult to hold astronomers... 48 00:02:34,154 --> 00:02:38,657 to an exact number of moons in the solar system. 49 00:02:38,700 --> 00:02:43,412 As cameras become more sensitive and telescopes more powerful... 50 00:02:43,454 --> 00:02:49,918 more moons reveal themselves. 51 00:02:49,961 --> 00:02:53,755 Moons are classified in two distinct ways. 52 00:02:53,798 --> 00:02:57,801 Those like our moon travel in nearly circular orbits... 53 00:02:57,844 --> 00:03:04,850 above their planet's equators and are called regular moons. 54 00:03:04,893 --> 00:03:06,810 While our moon formed from an impact... 55 00:03:06,853 --> 00:03:09,646 all other regular moons coalesced... 56 00:03:09,689 --> 00:03:11,148 from the gaseous stew... 57 00:03:11,191 --> 00:03:13,525 surrounding their parent planets... 58 00:03:13,568 --> 00:03:17,321 a process known as accretion. 59 00:03:17,363 --> 00:03:20,073 The classic example of regular moons... 60 00:03:20,116 --> 00:03:23,076 would be the Galilean moons of Jupiter... 61 00:03:23,119 --> 00:03:24,203 lo, Europa... 62 00:03:24,245 --> 00:03:26,914 Ganymede, and Callisto. 63 00:03:26,956 --> 00:03:28,916 The material that is going to form Jupiter, too... 64 00:03:29,250 --> 00:03:30,542 but extended a little bit... 65 00:03:30,585 --> 00:03:34,046 that material accumulates into the moons. 66 00:03:34,088 --> 00:03:36,548 Moons that follow elongated orbits... 67 00:03:36,591 --> 00:03:38,967 highly tilted to their planet's equators... 68 00:03:39,010 --> 00:03:41,553 are called irregular moons. 69 00:03:41,596 --> 00:03:43,889 Most of these move in retrograde orbits... 70 00:03:43,932 --> 00:03:48,477 clockwise if their planet rotates counterclockwise. 71 00:03:48,519 --> 00:03:51,688 Phoebe, the newly discovered moon orbiting Saturn... 72 00:03:51,731 --> 00:03:54,399 is a perfect example. 73 00:03:54,442 --> 00:03:56,276 She began her celestial life... 74 00:03:56,319 --> 00:03:59,363 as an independent traveler orbiting the sun... 75 00:03:59,405 --> 00:04:05,202 before being captured by the more massive Saturn. 76 00:04:05,245 --> 00:04:06,954 Whether regular or irregular... 77 00:04:06,996 --> 00:04:09,414 moons must fall within the gravitational reach... 78 00:04:09,457 --> 00:04:11,041 of their parent planet. 79 00:04:11,084 --> 00:04:15,963 The limit of these orbits is known as the Hill sphere. 80 00:04:16,005 --> 00:04:19,466 This phenomenon is named after George William Hill... 81 00:04:19,509 --> 00:04:24,263 an American astronomer from the mid-1800s. 82 00:04:24,305 --> 00:04:27,724 So a Hill sphere is this region around the planet... 83 00:04:27,767 --> 00:04:29,601 that moves along with the planet... 84 00:04:29,644 --> 00:04:32,229 inside of which the gravity of the planet... 85 00:04:32,272 --> 00:04:37,401 overwhelms the gravity of the sun. 86 00:04:37,443 --> 00:04:39,736 The moons of Mars, Deimos and Phobos... 87 00:04:39,779 --> 00:04:43,740 operate very differently within the Hill sphere. 88 00:04:43,783 --> 00:04:48,203 If the planet is rotating faster... 89 00:04:48,246 --> 00:04:51,832 than the moon it orbits, like Deimos... 90 00:04:51,874 --> 00:04:54,167 the tidal forces between the two... 91 00:04:54,210 --> 00:04:59,631 actually shove Deimos out further and further. 92 00:04:59,674 --> 00:05:01,091 Phobos, on the other hand... 93 00:05:01,134 --> 00:05:06,722 is rotating faster than Mars rotates. 94 00:05:06,764 --> 00:05:08,265 These small moons were discovered... 95 00:05:08,308 --> 00:05:13,312 by American astronomer Asaph Hall in 1877. 96 00:05:13,354 --> 00:05:16,481 He named Phobos after the Greek god of fear... 97 00:05:16,524 --> 00:05:21,445 and Deimos for the god of terror. 98 00:05:21,487 --> 00:05:25,115 Tom Duxbury was part of the Mariner 9 mission... 99 00:05:25,158 --> 00:05:28,493 that first photographed the two potato-shaped moons... 100 00:05:28,536 --> 00:05:32,831 in November of 1971. 101 00:05:32,874 --> 00:05:34,499 This was late at night... 102 00:05:34,542 --> 00:05:36,960 on a cold, rainy, dark, dreary day... 103 00:05:37,003 --> 00:05:38,003 and I looked at this... 104 00:05:38,046 --> 00:05:41,214 and I turned the picture sideways. 105 00:05:41,257 --> 00:05:52,976 It looked like a skull, and it was such an eerie thing. 106 00:05:53,019 --> 00:05:55,437 Phobos is in a death spiral. 107 00:05:55,480 --> 00:05:59,900 It orbits just 3,700 miles from the Martian surface... 108 00:05:59,942 --> 00:06:01,234 closer to its host planet... 109 00:06:01,277 --> 00:06:04,112 than any moon in our solar system. 110 00:06:04,155 --> 00:06:06,198 If our own moon were as close to the Earth... 111 00:06:06,240 --> 00:06:11,703 as Phobos is to Mars, it would look 20 times larger. 112 00:06:11,746 --> 00:06:14,039 Its orbital period would be in hours... 113 00:06:14,082 --> 00:06:16,666 not days like it is now, but hours. 114 00:06:16,709 --> 00:06:21,797 And at full moon, it would fill the sky. 115 00:06:21,839 --> 00:06:24,216 The daily tides, you know, would rise and fall... 116 00:06:24,258 --> 00:06:26,009 tens of feet if not hundreds of feet... 117 00:06:26,052 --> 00:06:27,177 and so the Earth's moon... 118 00:06:27,220 --> 00:06:30,263 would eventually crash into the Earth... 119 00:06:30,306 --> 00:06:35,811 in such a situation. 120 00:06:35,853 --> 00:06:38,563 Phobos' predicament is caused by a process... 121 00:06:38,606 --> 00:06:41,566 known as secular acceleration. 122 00:06:41,609 --> 00:06:44,903 As Phobos races faster than Mars rotates... 123 00:06:44,946 --> 00:06:48,657 a tidal bump is raised on the Martian surface. 124 00:06:48,908 --> 00:06:52,828 In the process, Mars yanks Phobos closer to its surface... 125 00:06:52,870 --> 00:06:57,374 with each orbit. 126 00:06:57,417 --> 00:06:59,418 The struggle between Mars and Phobos... 127 00:06:59,460 --> 00:07:04,381 is similar to the dynamics of a simple game of tetherball. 128 00:07:04,424 --> 00:07:08,927 Imagine the ball as the moon, the pole as the planet... 129 00:07:08,970 --> 00:07:11,346 and the rope between the pole and the ball... 130 00:07:11,389 --> 00:07:17,602 as the planet's gravitational pull. 131 00:07:17,645 --> 00:07:21,273 What we see is that the gravity... 132 00:07:21,315 --> 00:07:24,443 would pull the moon in such a way... 133 00:07:24,485 --> 00:07:25,694 that it speeds up. 134 00:07:25,736 --> 00:07:28,280 It goes faster and faster, and it works its way... 135 00:07:28,322 --> 00:07:31,450 until it eventually hits the pole. 136 00:07:31,492 --> 00:07:34,453 That's exactly what's happening to Phobos. 137 00:07:34,495 --> 00:07:38,748 Phobos is going around Mars faster than Mars rotates. 138 00:07:38,791 --> 00:07:40,083 That tidal interaction... 139 00:07:40,126 --> 00:07:43,044 is pulling Phobos in closer and closer... 140 00:07:43,087 --> 00:07:45,464 and speeding it up in its orbit. 141 00:07:45,506 --> 00:07:46,965 In about 50 million years... 142 00:07:47,008 --> 00:07:49,676 we expect Phobos to be pulled in so closely... 143 00:07:49,719 --> 00:07:56,558 it will impact Mars and disappear as a moon of Mars. 144 00:07:56,601 --> 00:07:59,895 On the other hand, Deimos, the further-out moon... 145 00:07:59,937 --> 00:08:02,481 is going slower than Mars rotates. 146 00:08:02,523 --> 00:08:06,651 And so it's unwinding the string in the opposite way... 147 00:08:06,694 --> 00:08:08,320 and what we see is Deimos... 148 00:08:08,362 --> 00:08:12,574 is going further and further away from Mars. 149 00:08:12,617 --> 00:08:13,742 And eventually... 150 00:08:13,784 --> 00:08:16,703 Deimos will be pulled away from Mars... 151 00:08:16,746 --> 00:08:18,872 by the gravity of the sun. 152 00:08:18,915 --> 00:08:22,918 So, over time, Mars will become moonless. 153 00:08:28,758 --> 00:08:32,177 Because Phobos outpaces the rotation of Mars... 154 00:08:32,220 --> 00:08:37,474 it appears to rise in the west and set in the east. 155 00:08:37,517 --> 00:08:40,060 Instead of the planet turning quickly under it... 156 00:08:40,102 --> 00:08:42,229 like our moon and most other moons... 157 00:08:42,271 --> 00:08:45,649 and thus having it rise in the east... 158 00:08:45,691 --> 00:08:46,691 and set in the west... 159 00:08:46,734 --> 00:08:49,528 it races ahead of the rotation of the planet. 160 00:08:49,570 --> 00:08:52,322 And so it comes up on the western horizon... 161 00:08:52,365 --> 00:08:59,996 and races ahead and sets on the eastern horizon. 162 00:09:00,039 --> 00:09:02,290 It will be another 50 millions years... 163 00:09:02,333 --> 00:09:06,336 before Phobos completely disappears. 164 00:09:06,379 --> 00:09:08,922 Before then, it may prove useful... 165 00:09:08,965 --> 00:09:12,300 for the eventual colonization of Mars. 166 00:09:12,343 --> 00:09:14,719 Science fiction writer Arthur C. Clarke... 167 00:09:14,762 --> 00:09:16,221 speculated on this idea... 168 00:09:16,264 --> 00:09:19,683 in his book "The Sands of Mars. " 169 00:09:19,725 --> 00:09:23,895 Although there is no real reason to colonize Phobos itself... 170 00:09:23,938 --> 00:09:29,276 its close proximity to Mars makes it a natural waystation. 171 00:09:29,318 --> 00:09:30,735 From a gravity standpoint... 172 00:09:30,778 --> 00:09:33,530 it's much easier to go to Phobos... 173 00:09:33,573 --> 00:09:34,906 which has no gravity... 174 00:09:34,949 --> 00:09:37,325 than it is to fight the gravity of Mars... 175 00:09:37,368 --> 00:09:40,829 to get down to this surface. 176 00:09:40,871 --> 00:09:43,081 From Galileo to Stanley Kubrick... 177 00:09:43,124 --> 00:09:45,750 the giant planets of the outer solar system... 178 00:09:45,793 --> 00:09:49,421 have tantalized our imagination with their enormity. 179 00:09:49,463 --> 00:09:54,342 But in reality, exploring them is tantamount to suicide. 180 00:09:54,385 --> 00:09:55,385 The overwhelming pressure... 181 00:09:55,428 --> 00:09:57,512 from Jupiter's massive atmosphere... 182 00:09:57,555 --> 00:10:02,100 would make it almost impossible to function. 183 00:10:02,143 --> 00:10:04,019 But the moons of these behemoths... 184 00:10:04,270 --> 00:10:06,104 may provide a more promising platform... 185 00:10:06,147 --> 00:10:11,276 for exploration and even future colonization. 186 00:10:11,319 --> 00:10:14,029 Are these prisoners of Jupiter's gravity... 187 00:10:14,071 --> 00:10:16,239 hostile worlds with little chance... 188 00:10:16,282 --> 00:10:18,783 of sustaining organic life? 189 00:10:18,826 --> 00:10:20,785 Or might they provide a safe haven... 190 00:10:20,828 --> 00:10:29,002 for future generations of planetary explorers? 191 00:10:29,045 --> 00:10:31,546 Until recently, very little was known... 192 00:10:31,589 --> 00:10:34,633 about the moons of the gas and ice giants. 193 00:10:34,675 --> 00:10:37,010 Most of them remained hidden in the glare... 194 00:10:37,053 --> 00:10:40,180 of their parent planets. 195 00:10:40,222 --> 00:10:43,975 Today, modern telescopes and unmanned space exploration... 196 00:10:44,018 --> 00:10:47,896 reveal a realm populated by a host of moons... 197 00:10:47,938 --> 00:10:50,065 from planet-like spherical worlds... 198 00:10:50,107 --> 00:10:56,446 to misshapen ones barely 30 miles across. 199 00:10:56,489 --> 00:10:59,115 Jupiter, the largest planet in the solar system... 200 00:10:59,158 --> 00:11:01,242 is a moon magnet. 201 00:11:01,285 --> 00:11:03,662 Nearly 4.5 billion years ago... 202 00:11:03,704 --> 00:11:09,167 it began as a massive gas cloud collapsing in on itself. 203 00:11:09,210 --> 00:11:11,211 This process, known as accretion... 204 00:11:11,253 --> 00:11:14,255 formed the beginnings of the Jovian system. 205 00:11:14,298 --> 00:11:16,758 While nearly all the gas and spinning material... 206 00:11:16,801 --> 00:11:19,094 went into forming Jupiter itself... 207 00:11:19,136 --> 00:11:22,263 a very small percentage clumped in small eddies... 208 00:11:22,306 --> 00:11:24,099 within Jupiter's orbit. 209 00:11:24,141 --> 00:11:25,392 These miniature accretions... 210 00:11:25,434 --> 00:11:26,851 solidified into Jupiter's regular moons... 211 00:11:26,894 --> 00:11:32,691 lo, Europa, Ganymede, and Callisto. 212 00:11:32,733 --> 00:11:35,151 As Jupiter coalesced, its massive gravity... 213 00:11:35,194 --> 00:11:39,364 began adding to its menagerie little remaining bits... 214 00:11:39,407 --> 00:11:43,243 from the birth of the early solar system. 215 00:11:43,285 --> 00:11:48,456 The giant planets formed early in a gas-rich environment... 216 00:11:48,499 --> 00:11:51,167 when there was lots of little flotsam and jetsam... 217 00:11:51,210 --> 00:11:56,131 around the solar system still to be captured into orbit. 218 00:11:56,173 --> 00:12:01,094 The number of Jupiter's moons ranges from 60 to over 200... 219 00:12:01,137 --> 00:12:05,974 depending on who's counting. 220 00:12:06,016 --> 00:12:07,267 What's clear is... 221 00:12:07,309 --> 00:12:08,727 if you could stand at the edge... 222 00:12:08,769 --> 00:12:10,895 of Jupiter's gaseous atmosphere... 223 00:12:10,938 --> 00:12:12,439 and look to the heavens... 224 00:12:12,481 --> 00:12:16,943 you'd see a magnificent dance of lunar objects. 225 00:12:16,986 --> 00:12:19,779 It would look pretty cool to be able to see the moons. 226 00:12:19,822 --> 00:12:22,240 Every so often, you'd see lo come by. 227 00:12:22,283 --> 00:12:24,576 Every second time lo comes by... 228 00:12:24,618 --> 00:12:27,704 you'd see Europa at the same time. 229 00:12:27,747 --> 00:12:29,497 And every four times lo comes by... 230 00:12:29,540 --> 00:12:31,541 you'd see Ganymede. 231 00:12:31,584 --> 00:12:33,293 One member of this Jovian cast... 232 00:12:33,335 --> 00:12:36,129 is so battered by Jupiter's great mass... 233 00:12:36,172 --> 00:12:41,551 that it is literally bursting from the inside out. 234 00:12:41,594 --> 00:12:45,597 In February of 2007, the New Horizons spacecraft... 235 00:12:45,639 --> 00:12:47,640 eventually bound for Pluto... 236 00:12:47,683 --> 00:12:50,769 focused its cameras on lo. 237 00:12:50,811 --> 00:12:52,437 About the size of Earth's moon... 238 00:12:52,480 --> 00:12:57,942 it orbits 263,000 miles from Jupiter's surface. 239 00:12:57,985 --> 00:13:02,197 What sets lo apart from the other Jovian moons... 240 00:13:02,239 --> 00:13:05,700 is its spectacular volcanism. 241 00:13:05,743 --> 00:13:07,202 New Horizons' cameras... 242 00:13:07,244 --> 00:13:10,079 captured detailed photos of glowing lava... 243 00:13:10,122 --> 00:13:13,500 scattered across lo's surface. 244 00:13:13,876 --> 00:13:18,213 A huge 200-mile-high dust plume rose above the surface... 245 00:13:18,255 --> 00:13:22,550 of the molten moon. 246 00:13:22,593 --> 00:13:25,261 lo, like all Jupiter's regular moons... 247 00:13:25,304 --> 00:13:27,889 is named after a lover of the god Jupiter... 248 00:13:27,932 --> 00:13:30,308 from Roman mythology. 249 00:13:30,351 --> 00:13:33,978 It was discovered by Galileo in 1610... 250 00:13:34,021 --> 00:13:37,982 first photographed by Pioneer I in 1974... 251 00:13:38,025 --> 00:13:41,361 and again by Voyager I in 1979. 252 00:13:41,403 --> 00:13:44,155 Its pulsating activity has puzzled... 253 00:13:44,198 --> 00:13:47,826 and intrigued scientists for decades. 254 00:13:47,868 --> 00:13:51,830 Leaving lo is about a ton per second of material... 255 00:13:51,872 --> 00:13:53,373 every second of every day. 256 00:13:53,415 --> 00:13:56,417 It's a phenomenal machine. 257 00:13:56,460 --> 00:13:57,544 I would like to go to lo... 258 00:13:57,586 --> 00:13:59,420 even though it would be very dangerous... 259 00:13:59,463 --> 00:14:04,175 and hot and sulfurous. 260 00:14:04,218 --> 00:14:07,512 lo is too small to have maintained a molten core... 261 00:14:07,555 --> 00:14:09,430 since its formation. 262 00:14:09,473 --> 00:14:11,182 Another mysterious process... 263 00:14:11,225 --> 00:14:14,644 must be responsible for its heating. 264 00:14:14,687 --> 00:14:17,772 lo's entire interior may be molten... 265 00:14:17,815 --> 00:14:21,568 because it's squeezed so much as it's orbiting around Jupiter. 266 00:14:21,610 --> 00:14:24,988 This process is known as tidal heating. 267 00:14:25,030 --> 00:14:26,739 The massive gravity of Jupiter... 268 00:14:26,782 --> 00:14:32,787 is causing friction at the inner core of lo. 269 00:14:32,830 --> 00:14:38,459 Much like a sculptor kneads a cold lump of clay... 270 00:14:38,502 --> 00:14:46,217 Jupiter is endlessly creating its own masterpiece. 271 00:14:46,260 --> 00:14:49,554 If a moon gets a little bit of tidal heating... 272 00:14:49,597 --> 00:14:51,556 it becomes malleable. 273 00:14:51,599 --> 00:14:54,058 It can be stretched out like clay... 274 00:14:54,101 --> 00:14:57,395 and deformed by the gravity of the parent planet. 275 00:14:57,438 --> 00:14:59,272 The surface of the moon is cold. 276 00:14:59,315 --> 00:15:03,067 It breaks like pulling clay apart quickly. It'll break. 277 00:15:03,110 --> 00:15:05,069 But the interior, where it's warm... 278 00:15:05,112 --> 00:15:07,864 can literally flow and stretch... 279 00:15:07,907 --> 00:15:14,162 and be kneaded by the gravity of the parent planet. 280 00:15:14,204 --> 00:15:17,916 Most regular moons have circular orbits. 281 00:15:17,958 --> 00:15:19,542 To produce tidal heating... 282 00:15:19,585 --> 00:15:22,086 a moon must be in a more oblong orbit... 283 00:15:22,129 --> 00:15:23,796 where the distance from the host planet... 284 00:15:23,839 --> 00:15:27,884 changes radically during a single revolution. 285 00:15:27,927 --> 00:15:30,595 The only way to produce these eccentric orbits... 286 00:15:30,638 --> 00:15:34,515 is if another moon's gravity disrupts it. 287 00:15:34,558 --> 00:15:37,310 When a moon is in an eccentric orbit... 288 00:15:37,353 --> 00:15:38,770 a non-round orbit... 289 00:15:38,812 --> 00:15:43,107 it gets closer and farther from its parent planet. 290 00:15:43,150 --> 00:15:44,776 When it does, it gets squeezed. 291 00:15:44,818 --> 00:15:49,322 It gets pulled apart when it's closer. 292 00:15:49,365 --> 00:15:51,532 lo is in orbital resonance... 293 00:15:51,575 --> 00:15:55,203 with its companion moons Europa and Ganymede. 294 00:15:55,245 --> 00:15:57,330 While Jupiter and lo struggle to find... 295 00:15:57,373 --> 00:15:59,624 a synchronistic relationship... 296 00:15:59,667 --> 00:16:01,000 Europa and Ganymede... 297 00:16:01,043 --> 00:16:04,128 are yanking lo in opposite directions. 298 00:16:04,171 --> 00:16:05,630 Jupiter yanks back... 299 00:16:05,673 --> 00:16:10,343 and lo gets stretched and squeezed in the process. 300 00:16:10,386 --> 00:16:12,011 The tidal heating on lo... 301 00:16:12,054 --> 00:16:15,139 which is responsible for its prodigious volcanoes... 302 00:16:15,182 --> 00:16:17,642 has a secondary side effect. 303 00:16:17,935 --> 00:16:20,728 It creates the largest stationary visible object... 304 00:16:20,771 --> 00:16:22,647 in the solar system... 305 00:16:22,690 --> 00:16:30,488 a massive gas cloud 500 times the size of Jupiter. 306 00:16:30,531 --> 00:16:33,032 In 1990, Professor Michael Mendillo... 307 00:16:33,075 --> 00:16:35,368 and his team from Boston University... 308 00:16:35,411 --> 00:16:39,163 discovered a large gas cloud spanning the huge distance... 309 00:16:39,206 --> 00:16:42,625 from one side of Jupiter to the other. 310 00:16:42,668 --> 00:16:44,669 They were the first to photograph... 311 00:16:44,712 --> 00:16:47,588 the entire nebula, discover its origins... 312 00:16:47,631 --> 00:16:51,009 and the mechanism that keeps it growing. 313 00:16:51,051 --> 00:16:52,635 Now, lo is small... 314 00:16:52,678 --> 00:16:54,887 so it doesn't have much of an atmosphere. 315 00:16:54,930 --> 00:16:55,930 But these volcanoes... 316 00:16:55,973 --> 00:16:59,183 are continually providing material... 317 00:16:59,226 --> 00:17:00,560 that could be an atmosphere. 318 00:17:00,602 --> 00:17:01,853 But you might ask... 319 00:17:01,895 --> 00:17:04,188 "Well, why doesn't it have tremendous atmosphere... 320 00:17:04,231 --> 00:17:07,191 if all the volcanoes have been going on for eons?" 321 00:17:07,234 --> 00:17:10,528 Well, it's because the material escapes. 322 00:17:10,571 --> 00:17:12,864 The key gas is sodium. 323 00:17:12,906 --> 00:17:15,241 Even though it only makes up five percent... 324 00:17:15,284 --> 00:17:17,744 of lo's ejected materials... 325 00:17:17,786 --> 00:17:21,497 it is easily detectable by telescopes on Earth. 326 00:17:21,540 --> 00:17:24,042 Sodium emits an orange glow. 327 00:17:24,084 --> 00:17:28,087 In fact, sodium is commonly used to illuminate streetlights... 328 00:17:28,130 --> 00:17:32,550 in many cities across the world. 329 00:17:32,593 --> 00:17:34,802 The sodium and the other gas molecules... 330 00:17:34,845 --> 00:17:36,846 are pelted by light from the sun... 331 00:17:36,889 --> 00:17:41,184 and electrons in Jupiter's powerful magnetic field. 332 00:17:41,226 --> 00:17:43,561 Electrons and protons are knocked off... 333 00:17:43,604 --> 00:17:46,814 some of these particles and ionized. 334 00:17:46,857 --> 00:17:48,399 Now in plasma form... 335 00:17:48,442 --> 00:17:50,526 these ions are taken on a ride... 336 00:17:50,569 --> 00:17:54,072 by Jupiter's powerful magnetosphere. 337 00:17:54,114 --> 00:17:56,574 Its speed increases dramatically... 338 00:17:56,617 --> 00:18:03,081 because it's been picked up by the magnetic field. 339 00:18:03,123 --> 00:18:07,960 It's like they're taking a ride on a cosmic carousel. 340 00:18:08,003 --> 00:18:11,589 The magnetic field lines are the poles here. 341 00:18:11,632 --> 00:18:12,882 And then every now and then... 342 00:18:12,925 --> 00:18:16,677 a sodium atom gets picked up along with this electron. 343 00:18:16,720 --> 00:18:19,889 And now, I'm in the Jupiter plasma chorus... 344 00:18:19,932 --> 00:18:21,682 with all the other ions and electrons... 345 00:18:21,725 --> 00:18:23,976 that have been captured previously... 346 00:18:24,019 --> 00:18:26,395 and the ions and the electrons recombine. 347 00:18:26,438 --> 00:18:29,774 The neutral is not confined by the magnetic field... 348 00:18:29,817 --> 00:18:32,318 and it goes off at a much higher speed... 349 00:18:32,361 --> 00:18:35,113 and that's enough to escape from Jupiter. 350 00:18:35,155 --> 00:18:37,615 And they form the largest visible cloud of gas... 351 00:18:37,658 --> 00:18:42,537 that's permanently in the solar system. 352 00:18:42,579 --> 00:18:44,914 If we could see the nebula with the naked eye... 353 00:18:44,957 --> 00:18:49,585 it would be the size of 12 moons in the night sky. 354 00:18:49,628 --> 00:18:51,629 It is so enormous that to view it... 355 00:18:51,672 --> 00:18:56,467 Mendillo and his team created their own specialized telescope. 356 00:18:56,510 --> 00:18:59,220 Well, as it turns out, to get a big field of view... 357 00:18:59,263 --> 00:19:01,139 all you need is a small lens... 358 00:19:01,181 --> 00:19:05,476 like a pair of binoculars gives you a big field of view. 359 00:19:05,519 --> 00:19:09,939 Even in 1991, the telescope may have seemed ordinary... 360 00:19:09,982 --> 00:19:12,733 but its camera was highly sophisticated... 361 00:19:12,776 --> 00:19:16,821 and, at the time, revolutionary... 362 00:19:17,114 --> 00:19:18,948 the digital camera. 363 00:19:18,991 --> 00:19:20,992 Once you've got a picture that's in numbers... 364 00:19:21,034 --> 00:19:23,494 you can do all kinds of things with it. 365 00:19:23,537 --> 00:19:24,829 Mendillo and his team knew... 366 00:19:24,872 --> 00:19:27,707 that sodium existed in the nebula. 367 00:19:27,749 --> 00:19:34,088 Sodium also exists in the Earth's atmosphere. 368 00:19:34,131 --> 00:19:36,424 They were able to compare digital photographs... 369 00:19:36,466 --> 00:19:39,093 of both Jupiter and Earth's atmospheres... 370 00:19:39,136 --> 00:19:43,181 and bring forth an image of the nebula. 371 00:19:43,223 --> 00:19:44,640 Well, that was very difficult to do... 372 00:19:44,683 --> 00:19:47,226 if you just had two photographs and pieces of paper. 373 00:19:47,269 --> 00:19:49,353 But now that we have these digital cameras... 374 00:19:49,396 --> 00:19:55,026 we've revolutionized the way that we can process images. 375 00:19:55,068 --> 00:19:57,111 Though lo would be a fascinating... 376 00:19:57,154 --> 00:20:00,031 scientific and aesthetic destination... 377 00:20:00,073 --> 00:20:03,659 its hostile environment probably precludes that. 378 00:20:03,702 --> 00:20:06,579 Even landing an unmanned probe would be difficult... 379 00:20:06,622 --> 00:20:11,083 among lo's convulsing fissures. 380 00:20:11,126 --> 00:20:13,044 But there's another moon orbiting Jupiter... 381 00:20:13,086 --> 00:20:16,464 which may not only support human exploration... 382 00:20:16,506 --> 00:20:20,468 but possibly support its own alien life forms. 383 00:20:20,510 --> 00:20:22,261 Europa is one of the most fascinating... 384 00:20:22,304 --> 00:20:25,806 and enigmatic objects in our solar system... 385 00:20:25,849 --> 00:20:29,310 really unlike anyplace else in the solar system... 386 00:20:29,353 --> 00:20:34,190 and for that matter, unlike anything on Earth. 387 00:20:34,233 --> 00:20:36,067 The surface features are such... 388 00:20:36,109 --> 00:20:37,526 that there are cracks in the surface... 389 00:20:37,569 --> 00:20:40,696 there's mottled terrain, there's chaotic terrain... 390 00:20:40,739 --> 00:20:44,659 and it looks like icebergs in some areas. 391 00:20:44,701 --> 00:20:48,412 We know Europa is an alien moon. 392 00:20:48,455 --> 00:20:51,999 Could it be home to alien life forms as well? 393 00:20:54,711 --> 00:20:58,965 Europa orbits 400,000 miles from Jupiter's surface... 394 00:20:59,007 --> 00:21:01,676 about double the distance of lo. 395 00:21:01,718 --> 00:21:03,761 And like its convulsive cousin... 396 00:21:03,804 --> 00:21:09,517 it too is molded by gravitational tides. 397 00:21:09,559 --> 00:21:11,560 Jupiter has the greatest effect. 398 00:21:11,603 --> 00:21:13,896 Its mass, like a persistent lover... 399 00:21:13,939 --> 00:21:17,400 pulls the reluctant moon toward its surface. 400 00:21:17,442 --> 00:21:19,443 Europa resists with its own gravity... 401 00:21:19,486 --> 00:21:21,821 and they form a kind of symbiosis... 402 00:21:21,863 --> 00:21:25,992 hundreds of thousands of miles above the gas giant. 403 00:21:26,034 --> 00:21:28,953 But it's not just Jupiter tugging at Europa. 404 00:21:28,996 --> 00:21:31,622 Little lo and larger cousin Ganymede... 405 00:21:31,665 --> 00:21:34,625 pull at Europa from different directions. 406 00:21:34,668 --> 00:21:36,627 It's the same orbital resonance... 407 00:21:36,670 --> 00:21:41,048 that has such a dramatic effect on lo. 408 00:21:41,091 --> 00:21:44,468 However, the results are far different on Europa. 409 00:21:44,511 --> 00:21:46,637 Europa's surface is cold... 410 00:21:46,680 --> 00:21:50,850 minus 550 degrees fahrenheit in some places... 411 00:21:50,892 --> 00:21:52,476 yet there is heating. 412 00:21:52,519 --> 00:21:54,812 And what rises to the surface of Europa... 413 00:21:54,855 --> 00:22:01,694 is also what makes the moon so exciting: water. 414 00:22:01,737 --> 00:22:04,947 This water, actually a kind of glacial ice... 415 00:22:04,990 --> 00:22:07,158 is rising from an underground ocean... 416 00:22:07,200 --> 00:22:09,660 and oozing out onto the surface... 417 00:22:09,703 --> 00:22:13,831 repaving it as a Zamboni does an ice rink. 418 00:22:13,874 --> 00:22:16,250 Europa's ocean is thought to be shallow... 419 00:22:16,293 --> 00:22:23,132 only about 10 or 15 miles below the surface. 420 00:22:23,175 --> 00:22:26,177 Water was the cradle of life on Earth. 421 00:22:26,219 --> 00:22:31,474 Could the same be true on Europa or other moons? 422 00:22:31,767 --> 00:22:35,144 Icy satellite oceans could be the most common habitat... 423 00:22:35,187 --> 00:22:37,521 that exists in the universe. 424 00:22:37,564 --> 00:22:39,940 Earths might be relatively rare... 425 00:22:39,983 --> 00:22:44,695 but icy satellites are probably plentiful. 426 00:22:44,738 --> 00:22:49,200 In February of 2007, the New Horizons spacecraft... 427 00:22:49,242 --> 00:22:50,451 on its way to Pluto... 428 00:22:50,494 --> 00:22:52,870 and the outer reaches of the solar system... 429 00:22:52,913 --> 00:22:55,206 managed to fly close enough to Europa... 430 00:22:55,248 --> 00:22:59,085 to send back some startling pictures. 431 00:22:59,127 --> 00:23:02,963 Seen only as the sun is rising or setting behind Europa... 432 00:23:03,006 --> 00:23:05,633 are enormous geological patterns... 433 00:23:05,675 --> 00:23:08,803 that have been dubbed crop circles. 434 00:23:08,845 --> 00:23:10,888 They are very large. 435 00:23:10,931 --> 00:23:11,972 If you were to, you know... 436 00:23:12,015 --> 00:23:14,392 try to drive across one of the circles... 437 00:23:14,434 --> 00:23:17,478 you would very, you know, gently go in and travel down... 438 00:23:17,521 --> 00:23:21,232 to a location that's a few hundred feet lower... 439 00:23:21,274 --> 00:23:23,025 than the surface you came up from... 440 00:23:23,068 --> 00:23:25,528 and then rise back up. 441 00:23:25,570 --> 00:23:27,780 The resemblance of Europa's crop circles... 442 00:23:27,823 --> 00:23:31,409 to the mysterious ones that dot the countryside here on Earth... 443 00:23:31,451 --> 00:23:33,911 ends when you consider their size. 444 00:23:33,954 --> 00:23:39,125 Each one is 2,000 to 3,000 miles in diameter. 445 00:23:39,167 --> 00:23:42,503 They're too shallow and uniform to be impact craters. 446 00:23:42,546 --> 00:23:46,715 Asteroids and comets come in different sizes and shapes. 447 00:23:46,758 --> 00:23:50,886 Europa's crop circles are remarkably similar geologically. 448 00:23:50,929 --> 00:23:52,555 Although nothing has been proven... 449 00:23:52,597 --> 00:23:54,890 it seems the great mass of Jupiter... 450 00:23:54,933 --> 00:23:58,978 may once again be the culprit. 451 00:23:59,020 --> 00:24:00,104 The speculation is... 452 00:24:00,147 --> 00:24:02,940 that the icy covering surrounding Europa... 453 00:24:02,983 --> 00:24:05,651 is not tethered to the core of the moon. 454 00:24:05,694 --> 00:24:08,612 Rather, it's floating above the subsurface ocean... 455 00:24:08,655 --> 00:24:11,574 like a spherical iceberg. 456 00:24:11,616 --> 00:24:14,994 The polar region may be somehow shaped by Jupiter... 457 00:24:15,036 --> 00:24:17,830 and then over hundreds of thousands of years... 458 00:24:17,873 --> 00:24:20,791 slowly tugged toward the equator. 459 00:24:20,834 --> 00:24:23,377 This forms a line of small circle depressions... 460 00:24:23,420 --> 00:24:27,965 dropping from the polar region toward the equator. 461 00:24:28,008 --> 00:24:29,216 If Europa's ice crust... 462 00:24:29,259 --> 00:24:32,136 has similar structure to icebergs on Earth... 463 00:24:32,179 --> 00:24:36,182 most of it would be under the ocean's surface. 464 00:24:36,224 --> 00:24:40,352 This has huge implications for future exploration. 465 00:24:40,395 --> 00:24:42,354 It means there has to be something like eight... 466 00:24:42,397 --> 00:24:46,150 or nine times that amount of ice underneath them to allow... 467 00:24:46,193 --> 00:24:50,237 that kind of a large-scale topography to exist. 468 00:24:50,280 --> 00:24:53,073 The iceberg theory lays to rest the belief... 469 00:24:53,116 --> 00:24:56,577 that Europa's subsurface ocean can be easily tapped... 470 00:24:56,620 --> 00:24:58,162 through a thin crust. 471 00:24:58,205 --> 00:25:00,372 Radar mapping and ultraviolet data... 472 00:25:00,415 --> 00:25:02,541 will prove to be even more important... 473 00:25:02,584 --> 00:25:03,792 before a Europa lander... 474 00:25:03,835 --> 00:25:07,171 can make its way down to the surface. 475 00:25:07,214 --> 00:25:09,965 Future explorers will have to search out hot spots... 476 00:25:10,008 --> 00:25:12,009 in places where this mysterious ocean... 477 00:25:12,052 --> 00:25:14,512 has welled up through the surface... 478 00:25:14,554 --> 00:25:20,476 and from there try to find a way to dip into it. 479 00:25:20,519 --> 00:25:22,770 Those explorers may choose instead... 480 00:25:22,812 --> 00:25:25,689 to set up a base of operations on Ganymede... 481 00:25:25,732 --> 00:25:27,858 Jupiter's largest moon. 482 00:25:27,901 --> 00:25:30,277 As Phobos might serve Martian exploration... 483 00:25:30,320 --> 00:25:31,737 as a waystation... 484 00:25:32,030 --> 00:25:36,534 Ganymede might do the same for the Jovian system. 485 00:25:36,576 --> 00:25:38,410 Larger than the planet Mercury... 486 00:25:38,453 --> 00:25:40,829 its gravity is closer to that of Earth's... 487 00:25:40,872 --> 00:25:44,500 than any of Jupiter's moons. 488 00:25:44,543 --> 00:25:46,126 And though it's in orbital residence... 489 00:25:46,169 --> 00:25:48,295 with both lo and Europa... 490 00:25:48,338 --> 00:25:51,507 it's far enough away from Jupiter to be less affected... 491 00:25:51,550 --> 00:25:55,636 by the gas giant's relentless tides. 492 00:25:55,679 --> 00:25:57,263 And at Ganymede, you could, say... 493 00:25:57,305 --> 00:25:58,597 park in some nice, big crater... 494 00:25:58,640 --> 00:26:01,559 and build your domed, protected region... 495 00:26:01,601 --> 00:26:04,353 protected from the charged particles... 496 00:26:04,396 --> 00:26:05,896 in the Jovian system... 497 00:26:05,939 --> 00:26:08,816 and make a pretty safe place to study... 498 00:26:08,858 --> 00:26:11,986 not just Ganymede itself and its magnetic field... 499 00:26:12,028 --> 00:26:14,238 and its interior and its geology... 500 00:26:14,281 --> 00:26:17,575 but the Jupiter system as a whole. 501 00:26:17,617 --> 00:26:20,369 Ganymede is the only moon in the solar system... 502 00:26:20,412 --> 00:26:22,413 with its own magnetic field. 503 00:26:22,455 --> 00:26:23,622 To have this distinction... 504 00:26:23,665 --> 00:26:25,332 Ganymede must have sufficient mass... 505 00:26:25,875 --> 00:26:27,543 and a hot inner core. 506 00:26:27,961 --> 00:26:29,420 Its mass is obvious... 507 00:26:29,462 --> 00:26:30,963 but where the heat is coming from... 508 00:26:31,006 --> 00:26:35,175 is a bit of a mystery. 509 00:26:35,218 --> 00:26:39,597 Ganymede is affected by both lo and Europa's tidal forces. 510 00:26:39,639 --> 00:26:42,099 But the measurements on its orbit indicate... 511 00:26:42,142 --> 00:26:45,269 that it's round enough to avoid the squashing and stretching... 512 00:26:45,312 --> 00:26:48,731 that its smaller cousins endure from Jupiter. 513 00:26:48,773 --> 00:26:50,065 The thought is... 514 00:26:50,108 --> 00:26:52,860 maybe something happened in Ganymede's past... 515 00:26:52,902 --> 00:26:55,112 to change its orbit slightly... 516 00:26:55,155 --> 00:26:59,033 and maybe its eccentricity got kind of haywire... 517 00:26:59,075 --> 00:27:00,159 for a little while... 518 00:27:00,201 --> 00:27:02,911 and generated a lot of heat within Ganymede... 519 00:27:02,954 --> 00:27:04,705 and caused the core to be hot. 520 00:27:04,748 --> 00:27:05,831 We don't really know. 521 00:27:05,874 --> 00:27:07,458 What we do know... 522 00:27:07,500 --> 00:27:09,460 is that New Horizons' recent flyby... 523 00:27:09,502 --> 00:27:10,878 of the Jovian system... 524 00:27:10,920 --> 00:27:13,881 gave us a tantalizing glimpse of the wonders that await us... 525 00:27:13,923 --> 00:27:16,717 on Jupiter's alien moons. 526 00:27:16,760 --> 00:27:18,594 Scientists look forward to the day... 527 00:27:18,637 --> 00:27:21,138 a lander touches down on one of these moons... 528 00:27:21,181 --> 00:27:23,599 and starts to uncover the secrets... 529 00:27:23,642 --> 00:27:28,145 of these mysterious worlds. 530 00:27:28,188 --> 00:27:31,649 Another icy moon orbits the gas giant Saturn. 531 00:27:31,691 --> 00:27:34,818 It's too small to hold onto its own atmosphere... 532 00:27:34,861 --> 00:27:35,986 but that doesn't stop it... 533 00:27:36,029 --> 00:27:40,366 from sapping the atmosphere of its parent planet. 534 00:27:40,408 --> 00:27:42,660 Enceladus, even though quite small... 535 00:27:42,702 --> 00:27:46,538 is named after a tribe of giants in Greek mythology. 536 00:27:46,581 --> 00:27:48,499 Like lo and Europa... 537 00:27:48,541 --> 00:27:50,167 Enceladus has an eccentric orbit... 538 00:27:50,210 --> 00:27:52,878 around its parent planet Saturn. 539 00:27:52,921 --> 00:27:54,338 The tidal forces of Saturn... 540 00:27:54,381 --> 00:27:57,007 squeeze and knead this tiny moon... 541 00:27:57,050 --> 00:28:01,053 and create heat at its core. 542 00:28:01,346 --> 00:28:02,304 But unlike lo... 543 00:28:02,347 --> 00:28:04,640 it doesn't regurgitate molten material... 544 00:28:04,683 --> 00:28:07,935 it coalesces into a massive gas cloud. 545 00:28:07,977 --> 00:28:09,687 Water doesn't well up to the surface... 546 00:28:09,729 --> 00:28:11,939 as it does on icy Europa. 547 00:28:11,981 --> 00:28:16,276 No, Enceladus actually spits plumes of icy water... 548 00:28:16,319 --> 00:28:18,487 into the atmosphere of Saturn. 549 00:28:18,530 --> 00:28:19,905 So we don't call it a volcano. 550 00:28:19,948 --> 00:28:21,532 It's more like a geyser. 551 00:28:21,574 --> 00:28:24,410 The water vapor is then in orbit... 552 00:28:24,452 --> 00:28:26,078 around the little tiny moon... 553 00:28:26,121 --> 00:28:28,455 or because it's near Saturn... 554 00:28:28,498 --> 00:28:31,959 Saturn's gravity can pull it into the planet. 555 00:28:32,001 --> 00:28:35,045 Interested by their work on the torus of lo... 556 00:28:35,088 --> 00:28:37,715 Michael Mendillo and his team at Boston University... 557 00:28:37,757 --> 00:28:40,134 began to consider Enceladus' effect... 558 00:28:40,176 --> 00:28:42,761 on Saturn's atmosphere. 559 00:28:42,804 --> 00:28:45,556 And it turns out that water is a wonderful catalyst... 560 00:28:45,598 --> 00:28:49,768 to have the ions and electrons recombine. 561 00:28:49,811 --> 00:28:53,188 Before Cassini, scientists relied on computer models... 562 00:28:53,231 --> 00:28:57,818 to determine atmospheric conditions surrounding Saturn. 563 00:28:57,861 --> 00:28:59,653 They indicated that Saturn should have... 564 00:28:59,696 --> 00:29:02,197 a very robust ionosphere. 565 00:29:02,240 --> 00:29:05,159 Surprisingly, Cassini's data indicated... 566 00:29:05,201 --> 00:29:07,327 that Saturn's ionosphere was only 10 percent... 567 00:29:07,370 --> 00:29:10,122 of what computer models had predicted. 568 00:29:10,165 --> 00:29:13,584 It seems that the icy water ejected from Enceladus... 569 00:29:13,626 --> 00:29:15,794 is neutralizing the charged particles... 570 00:29:15,837 --> 00:29:18,839 in Saturn's ionosphere. 571 00:29:18,882 --> 00:29:23,427 Commence liftoff. 572 00:29:23,470 --> 00:29:25,929 Scientists had learned quite by accident... 573 00:29:25,972 --> 00:29:31,143 the effect water can have on Earth's atmosphere. 574 00:29:31,186 --> 00:29:35,773 In 1973, when Nasa launched its Skylab workshop... 575 00:29:35,815 --> 00:29:39,193 it launched its last gigantic Saturn V rocket... 576 00:29:39,235 --> 00:29:40,694 the moon rocket. 577 00:29:40,737 --> 00:29:42,613 And it had never had a launch... 578 00:29:42,655 --> 00:29:44,531 that allowed the space vehicle... 579 00:29:44,574 --> 00:29:47,785 to keep its engine burning as high as the ionosphere. 580 00:29:47,827 --> 00:29:49,369 Well, this gigantic engine... 581 00:29:49,412 --> 00:29:51,872 dumped a ton per second of water vapor... 582 00:29:51,915 --> 00:29:54,124 which comes out of a giant rocket motor... 583 00:29:54,167 --> 00:29:55,292 into the ionosphere. 584 00:29:55,335 --> 00:29:59,129 And the ionosphere nearly vanished on that day. 585 00:29:59,172 --> 00:30:02,007 It blew a gaping hole in Earth's ionosphere... 586 00:30:02,050 --> 00:30:04,301 the top layer of the atmosphere... 587 00:30:04,344 --> 00:30:07,346 a hole that took the sun's ionizing radiation... 588 00:30:07,388 --> 00:30:11,058 24 hours to repair. 589 00:30:11,100 --> 00:30:13,060 However, on Saturn... 590 00:30:13,102 --> 00:30:14,478 where Enceladus continuously dumps... 591 00:30:14,521 --> 00:30:18,106 six tons of water per minute into its atmosphere... 592 00:30:18,149 --> 00:30:23,362 the long-term effects have been significant. 593 00:30:23,404 --> 00:30:25,322 There's no worry that Enceladus will strip away... 594 00:30:25,365 --> 00:30:28,826 its parent planet's ionosphere completely... 595 00:30:28,868 --> 00:30:32,621 but this tiny moon, only 300 miles in diameter... 596 00:30:32,664 --> 00:30:35,791 has gotten the attention of the scientific community... 597 00:30:35,834 --> 00:30:39,461 and Saturn itself. 598 00:30:39,504 --> 00:30:42,297 While we prepare probes to Phobos and Europa... 599 00:30:42,340 --> 00:30:45,342 and study data from Enceladus and lo... 600 00:30:45,385 --> 00:30:47,344 an entirely new set of moons... 601 00:30:47,387 --> 00:30:50,597 has literally just come into the picture. 602 00:30:53,518 --> 00:30:57,020 Before the 1990s, most astronomers agreed... 603 00:30:57,063 --> 00:31:00,482 that there were only 34 moons in the solar system. 604 00:31:00,525 --> 00:31:03,694 Most of those were regular moons like our own... 605 00:31:03,736 --> 00:31:06,530 spherical bodies that orbit their host planet... 606 00:31:06,573 --> 00:31:08,532 in the same direction it rotates. 607 00:31:08,575 --> 00:31:10,367 But a handful of these satellites... 608 00:31:10,410 --> 00:31:14,955 were what's known as irregular moons. 609 00:31:14,998 --> 00:31:17,916 These freakish moons follow elongated orbits. 610 00:31:17,959 --> 00:31:19,668 Their orbits are often tilted... 611 00:31:19,711 --> 00:31:21,545 and they rotate in the opposite direction... 612 00:31:21,588 --> 00:31:24,006 of their host planets. 613 00:31:24,048 --> 00:31:28,176 They look like flying potatoes or splinters or misshapen lumps. 614 00:31:28,219 --> 00:31:30,804 They've been hard to find before now... 615 00:31:30,847 --> 00:31:32,180 because they're very small... 616 00:31:32,223 --> 00:31:38,103 and they're also usually very dark. 617 00:31:38,146 --> 00:31:40,647 The advent of digital photography... 618 00:31:40,690 --> 00:31:42,482 and the use of light-sensitive optics... 619 00:31:42,525 --> 00:31:46,737 changed the lunar terrain within a decade. 620 00:31:46,779 --> 00:31:48,447 Dr. Brett Gladman... 621 00:31:48,489 --> 00:31:50,908 from the University of British Columbia... 622 00:31:50,950 --> 00:31:54,328 discovered his first irregular moon in 1997... 623 00:31:54,370 --> 00:31:57,247 at the Palomar Observatory. 624 00:31:57,290 --> 00:32:00,042 Since then, Dr. Gladman has brought to light... 625 00:32:00,084 --> 00:32:05,213 17 previously hidden objects in the solar system. 626 00:32:05,256 --> 00:32:07,925 So you detect objects in the outer solar system... 627 00:32:07,967 --> 00:32:09,885 by observing them move... 628 00:32:09,928 --> 00:32:12,179 relevant to the background stars and galaxies... 629 00:32:12,221 --> 00:32:13,931 which are stationary. 630 00:32:13,973 --> 00:32:16,391 So if you take a picture of the sky... 631 00:32:16,434 --> 00:32:17,601 and you wait an hour... 632 00:32:17,644 --> 00:32:19,519 and you take another picture of the sky... 633 00:32:19,604 --> 00:32:22,648 none of the stars in the galaxy will have moved... 634 00:32:22,690 --> 00:32:26,026 but distant objects in the outer solar system... 635 00:32:26,069 --> 00:32:28,946 will displace by a visible amount... 636 00:32:28,988 --> 00:32:30,864 between the two pictures. 637 00:32:30,907 --> 00:32:32,157 And so by comparing the two pictures... 638 00:32:32,200 --> 00:32:38,080 you can see, as we have here, a moving target. 639 00:32:38,122 --> 00:32:41,166 The object could be a comet or an asteroid... 640 00:32:41,209 --> 00:32:44,294 or, if it orbits a planet in a retrograde fashion... 641 00:32:44,337 --> 00:32:47,798 a new irregular moon. 642 00:32:47,840 --> 00:32:50,467 Another important distinction between regular moons... 643 00:32:50,510 --> 00:32:53,095 and their irregular counterparts... 644 00:32:53,137 --> 00:32:55,681 irregular moons are captured. 645 00:32:55,723 --> 00:32:57,432 That is, they formed... 646 00:32:57,475 --> 00:32:59,017 independently of their host planet... 647 00:32:59,060 --> 00:33:00,978 and most likely were part of the debris... 648 00:33:01,020 --> 00:33:05,440 that originally formed our solar system. 649 00:33:05,483 --> 00:33:08,735 Phoebe, the largest irregular moon orbiting Saturn... 650 00:33:08,778 --> 00:33:11,405 is a classic example. 651 00:33:11,447 --> 00:33:14,783 Phoebe orbits Saturn very far out. 652 00:33:14,826 --> 00:33:17,577 It has a very elliptical and very inclined orbit. 653 00:33:17,620 --> 00:33:21,498 It orbits in a retrograde direction. 654 00:33:21,541 --> 00:33:23,750 Voyager images suggested... 655 00:33:23,793 --> 00:33:25,961 that this thing looks like it could be an asteroid... 656 00:33:26,004 --> 00:33:29,423 and so people thought maybe it is a captured asteroid. 657 00:33:29,465 --> 00:33:34,052 Now we know from Cassini it's a very waterized-rich body. 658 00:33:34,095 --> 00:33:36,847 That pretty much rules out the asteroid belt. 659 00:33:36,889 --> 00:33:39,850 The thinking is that Phoebe could very well have come... 660 00:33:39,892 --> 00:33:41,018 from the Kuiper Belt... 661 00:33:41,060 --> 00:33:45,981 way out in the outer reaches of the solar system. 662 00:33:46,274 --> 00:33:49,234 The Kuiper Belt is thought to be the debris left over... 663 00:33:49,277 --> 00:33:51,069 after the solar system formed. 664 00:33:51,112 --> 00:33:54,990 It revolves around the sun beyond the orbit of Pluto. 665 00:33:55,033 --> 00:33:56,867 However, another theory... 666 00:33:56,909 --> 00:34:02,748 suggests something altogether different. 667 00:34:02,790 --> 00:34:05,375 It's much more likely that Phoebe formed... 668 00:34:05,418 --> 00:34:07,586 in an independent orbit around the sun... 669 00:34:07,628 --> 00:34:11,798 and then was captured into orbit around Saturn... 670 00:34:11,841 --> 00:34:13,383 whereas most of the other objects... 671 00:34:13,426 --> 00:34:15,469 that formed near Saturn's distance... 672 00:34:15,511 --> 00:34:17,012 were either accreted by Saturn... 673 00:34:17,055 --> 00:34:20,599 or ejected from the solar system. 674 00:34:20,641 --> 00:34:23,477 Phoebe would then be made of the planetary debris... 675 00:34:23,519 --> 00:34:26,480 that was floating around Saturn at the time of its birth. 676 00:34:26,522 --> 00:34:29,775 And possibly it;s made up of different material... 677 00:34:29,817 --> 00:34:33,028 than some of the irregular moons orbiting Jupiter. 678 00:34:33,071 --> 00:34:34,404 If this is the case... 679 00:34:34,447 --> 00:34:38,158 astrogeologists may be able to discern and compare... 680 00:34:38,201 --> 00:34:39,367 the different ingredients... 681 00:34:39,410 --> 00:34:42,954 that birthed these two gas giants. 682 00:34:42,997 --> 00:34:45,624 Three main theories currently exist... 683 00:34:45,666 --> 00:34:48,835 as to how Phoebe and its other irregular counterparts... 684 00:34:48,878 --> 00:34:50,587 lost their independence. 685 00:34:50,630 --> 00:34:52,923 Two suggest the irregulars were captured... 686 00:34:52,965 --> 00:34:55,300 as the solar system was still forming... 687 00:34:55,343 --> 00:34:57,302 and the planets were still an accreting blob... 688 00:34:57,345 --> 00:34:59,429 of gas and debris. 689 00:34:59,472 --> 00:35:02,390 The gas-drag theory is the most straightforward. 690 00:35:02,433 --> 00:35:06,144 Thick gases were swirling around the accreting planet... 691 00:35:06,187 --> 00:35:08,188 when a comet, asteroid... 692 00:35:08,231 --> 00:35:10,315 or a shattered combination of both... 693 00:35:10,358 --> 00:35:13,777 passed through the gaseous mixture. 694 00:35:13,820 --> 00:35:15,529 We know that the giant planets... 695 00:35:15,571 --> 00:35:18,031 built their regular satellite systems... 696 00:35:18,074 --> 00:35:21,910 in a large accretion disc around each of the planets... 697 00:35:21,953 --> 00:35:23,745 sort of like a mini little solar system... 698 00:35:23,788 --> 00:35:25,789 forming around each planet. 699 00:35:25,832 --> 00:35:28,458 And the gas and dust that was in that disc... 700 00:35:28,501 --> 00:35:31,628 can also serve in its outer regions... 701 00:35:31,671 --> 00:35:33,547 as a source of friction... 702 00:35:33,589 --> 00:35:37,008 where passing planetesimals formed independently... 703 00:35:37,051 --> 00:35:41,096 are slowed down a little bit and captured into orbit. 704 00:35:41,139 --> 00:35:44,266 The second theory is really a variation on the first. 705 00:35:44,308 --> 00:35:47,310 It's sometimes called the pull-down theory. 706 00:35:47,353 --> 00:35:49,312 Here, instead of an object being caught... 707 00:35:49,355 --> 00:35:52,482 by simply passing through the accreting gases... 708 00:35:52,525 --> 00:35:54,317 it is unsuspectingly pulled... 709 00:35:54,360 --> 00:35:56,194 into the forming planet's orbit... 710 00:35:56,237 --> 00:35:59,948 by its growing gravitational pull. 711 00:35:59,991 --> 00:36:01,992 The gas-drag and the pull-down theories of capture... 712 00:36:02,034 --> 00:36:04,661 work well for both Jupiter and Saturn... 713 00:36:04,704 --> 00:36:06,872 because their mixture of ingredients... 714 00:36:06,914 --> 00:36:13,879 was massive enough to slow down these passing objects. 715 00:36:13,921 --> 00:36:18,341 But what about the icy giants Neptune and Uranus? 716 00:36:18,384 --> 00:36:22,179 Because of the extreme cold, they formed much more slowly... 717 00:36:22,221 --> 00:36:23,763 and it's difficult to believe... 718 00:36:23,806 --> 00:36:26,558 that their icy accretion mixture contained enough mass... 719 00:36:26,601 --> 00:36:31,813 to snare a passing piece of the solar system. 720 00:36:31,856 --> 00:36:36,318 Yet both icy giants have their own irregular moons... 721 00:36:36,360 --> 00:36:41,740 hence, a third theory: three-body interaction. 722 00:36:41,991 --> 00:36:43,033 We discover that many of the objects... 723 00:36:43,075 --> 00:36:44,701 are actually more than one object. 724 00:36:44,744 --> 00:36:46,453 They're usually two objects... 725 00:36:46,495 --> 00:36:50,165 often that because they're both more or less the same size... 726 00:36:50,208 --> 00:36:53,210 as the other in a binary relationship. 727 00:36:53,252 --> 00:36:54,711 Instead of being a big object... 728 00:36:54,754 --> 00:36:58,298 with a small object going in an orbit around it like this... 729 00:36:58,341 --> 00:37:00,759 it's two more or less similar-sized objects... 730 00:37:00,801 --> 00:37:02,677 going around a common orbit. 731 00:37:02,720 --> 00:37:05,805 Between the two of them is called the barycenter. 732 00:37:05,848 --> 00:37:07,390 A binary pair exists... 733 00:37:07,433 --> 00:37:09,559 when two objects of the same size... 734 00:37:09,602 --> 00:37:11,519 are tight enough to the barycenter... 735 00:37:11,562 --> 00:37:16,149 to prevent a third larger object from splitting them apart. 736 00:37:16,192 --> 00:37:17,734 But when one of the binary pair... 737 00:37:17,777 --> 00:37:20,278 is significantly larger than the other... 738 00:37:20,321 --> 00:37:22,155 the more massive third object... 739 00:37:22,198 --> 00:37:25,784 has a greater chance of separating them. 740 00:37:25,826 --> 00:37:28,411 The smaller one will tend to have the much bigger orbit... 741 00:37:28,454 --> 00:37:30,872 swing out further. 742 00:37:30,915 --> 00:37:32,540 This brings the smaller object... 743 00:37:32,583 --> 00:37:35,168 close enough to the planet to be captured... 744 00:37:35,211 --> 00:37:41,508 while its partner is slung out into an independent orbit. 745 00:37:41,550 --> 00:37:45,553 One bizarre moon seems to defy classification. 746 00:37:45,596 --> 00:37:49,057 Triton orbits Neptune in a retrograde fashion... 747 00:37:49,100 --> 00:37:51,268 counter to Neptune's rotation. 748 00:37:51,310 --> 00:37:53,436 That would make it an irregular moon... 749 00:37:53,479 --> 00:37:55,146 except that it's spherical... 750 00:37:55,189 --> 00:37:57,357 and orbits close to the equator... 751 00:37:57,400 --> 00:38:00,277 with an almost perfectly round circumference... 752 00:38:00,319 --> 00:38:07,033 a classical description of a regular moon. 753 00:38:07,076 --> 00:38:10,203 It also spews out mysterious icy plumes... 754 00:38:10,246 --> 00:38:12,372 with some indication that it once was... 755 00:38:12,415 --> 00:38:16,334 or possibly still is volcanically active. 756 00:38:20,381 --> 00:38:23,967 Before Voyager 2 ventured into the outer solar system... 757 00:38:24,010 --> 00:38:26,636 Neptune's moon Triton was assumed to be... 758 00:38:26,679 --> 00:38:28,972 a geologically dead ball of rock... 759 00:38:29,015 --> 00:38:32,475 about the size of our own moon. 760 00:38:32,518 --> 00:38:34,811 When Voyager beamed back photographs... 761 00:38:34,854 --> 00:38:36,771 revealing a world with mountains... 762 00:38:36,814 --> 00:38:39,983 fault lines, and fissures... 763 00:38:40,026 --> 00:38:42,152 indicative of tectonic movement... 764 00:38:42,194 --> 00:38:45,697 as well as a surprisingly thick atmosphere... 765 00:38:45,740 --> 00:38:49,326 scientists were amazed. 766 00:38:49,368 --> 00:38:51,244 Geologic forces usually associated... 767 00:38:51,287 --> 00:38:54,080 with much warmer and larger planets... 768 00:38:54,123 --> 00:38:56,416 might be occurring on a frozen moon... 769 00:38:56,459 --> 00:38:59,002 slightly smaller than our own. 770 00:38:59,045 --> 00:39:02,881 Voyager detected no active volcanoes in 1989. 771 00:39:02,923 --> 00:39:05,842 However, like Saturn's moon Enceladus... 772 00:39:05,885 --> 00:39:10,972 geysers periodically erupted from the planet's surface. 773 00:39:11,015 --> 00:39:12,682 What's really stunning about Triton... 774 00:39:12,725 --> 00:39:14,225 is not just that it has... 775 00:39:14,268 --> 00:39:16,936 some unique geological processes occurring... 776 00:39:16,979 --> 00:39:18,355 but the fact that they're happening... 777 00:39:18,397 --> 00:39:22,108 even though Triton is an irregular moon. 778 00:39:22,151 --> 00:39:24,444 Most large moons in the solar system... 779 00:39:24,487 --> 00:39:26,696 are regular satellites... 780 00:39:26,739 --> 00:39:29,532 with the very important exception of Triton... 781 00:39:29,825 --> 00:39:31,242 Neptune's largest moon... 782 00:39:31,285 --> 00:39:33,620 which orbits the wrong way. 783 00:39:33,662 --> 00:39:37,999 So Triton is thought to have been a captured object. 784 00:39:38,042 --> 00:39:41,252 A captured moon that acts like a regular one. 785 00:39:41,295 --> 00:39:43,296 How did an object the size of Triton... 786 00:39:43,339 --> 00:39:44,672 slow down enough... 787 00:39:44,715 --> 00:39:47,884 not to either pass through Neptune's atmosphere... 788 00:39:47,927 --> 00:39:52,514 or collide directly into the icy planet? 789 00:39:57,436 --> 00:39:58,770 There's no sure bet... 790 00:39:58,813 --> 00:40:02,190 but some theories carry better odds. 791 00:40:02,233 --> 00:40:04,859 Much like gamblers at the roulette wheel... 792 00:40:04,902 --> 00:40:06,986 Triton and Neptune played the odds... 793 00:40:07,029 --> 00:40:10,573 and trusted to luck. 794 00:40:10,616 --> 00:40:12,742 Place your bets. Get lucky now. 795 00:40:12,785 --> 00:40:15,078 In roulette, there are several ways to bet. 796 00:40:15,121 --> 00:40:17,163 Each one carries different odds. 797 00:40:17,206 --> 00:40:18,957 And like most games of chance... 798 00:40:18,999 --> 00:40:22,335 the longer the odds, the greater the payoff. 799 00:40:22,378 --> 00:40:24,629 20 black, 20 black even. 800 00:40:24,672 --> 00:40:26,631 There are at least three possible ways... 801 00:40:26,674 --> 00:40:29,300 Triton could've been captured by Neptune. 802 00:40:34,515 --> 00:40:37,058 All three hypotheses are physically possible... 803 00:40:37,101 --> 00:40:40,228 but the first one, the idea of gas drag... 804 00:40:40,271 --> 00:40:41,271 is the least likely... 805 00:40:41,313 --> 00:40:43,690 simply because the period of time... 806 00:40:43,732 --> 00:40:46,734 which Neptune had a disc of gas and dust... 807 00:40:46,777 --> 00:40:49,612 which could've captured a proto Triton object... 808 00:40:49,655 --> 00:40:51,781 it was a very short period of time... 809 00:40:51,824 --> 00:40:54,868 and so the window of opportunity was very small. 810 00:40:54,910 --> 00:40:56,995 So that's like betting on the green zero... 811 00:40:57,037 --> 00:40:59,998 on the roulette table. 812 00:41:00,040 --> 00:41:03,251 More likely is the possibility that the proto Triton... 813 00:41:03,294 --> 00:41:04,961 sometime in the solar system history... 814 00:41:05,004 --> 00:41:08,965 crashed into a set of a regular... 815 00:41:09,008 --> 00:41:10,341 middle-sized icy satellites... 816 00:41:10,384 --> 00:41:13,678 and it was the collision which gave us Triton. 817 00:41:13,721 --> 00:41:16,764 And that's like betting on the first third... 818 00:41:16,807 --> 00:41:18,057 of the numbers on the roulette table... 819 00:41:18,100 --> 00:41:19,642 so you have, like, a one-in-three chance... 820 00:41:19,685 --> 00:41:22,729 of that taking place. 821 00:41:22,771 --> 00:41:26,316 Your best bet is to bet on the even numbers. 822 00:41:26,358 --> 00:41:27,609 There you have a one-in-two chance... 823 00:41:27,651 --> 00:41:28,818 of things happening. 824 00:41:28,861 --> 00:41:32,447 And the best bet for the capture of Triton right now... 825 00:41:32,490 --> 00:41:35,116 is this binary capture hypothesis because there... 826 00:41:35,159 --> 00:41:38,161 we know there are probably thousands of objects... 827 00:41:38,204 --> 00:41:40,538 that had existed in the Kuiper Belt... 828 00:41:40,581 --> 00:41:42,165 that would have the right size... 829 00:41:42,208 --> 00:41:46,044 and be partnered with another even larger object... 830 00:41:46,086 --> 00:41:50,840 and Neptune could capture one of them. 831 00:41:50,883 --> 00:41:52,842 No one knows for sure which number paid... 832 00:41:52,885 --> 00:41:55,136 in the early days of the solar system... 833 00:41:55,179 --> 00:41:57,222 when Neptune captured Triton. 834 00:41:57,264 --> 00:42:00,016 However, once Triton began orbiting Neptune... 835 00:42:00,059 --> 00:42:01,726 in an irregular fashion... 836 00:42:01,769 --> 00:42:05,813 it started obliterating anything that got in its way. 837 00:42:05,856 --> 00:42:10,318 Neptune doesn't have a very regular system of satellites. 838 00:42:10,361 --> 00:42:11,861 It's thought that the capture of Triton... 839 00:42:11,904 --> 00:42:14,405 disrupted what would've otherwise been... 840 00:42:14,448 --> 00:42:16,449 a nice regular system... 841 00:42:16,492 --> 00:42:19,827 like the other large planets have. 842 00:42:20,120 --> 00:42:22,872 It's as if Triton was angry at losing its freedom... 843 00:42:22,915 --> 00:42:26,376 and took it out on Neptune's other hapless moons. 844 00:42:26,418 --> 00:42:31,089 But where did this headstrong moon come from? 845 00:42:31,131 --> 00:42:33,091 Data from Voyager 2 indicates... 846 00:42:33,133 --> 00:42:36,427 that Triton's density nearly matches Pluto's. 847 00:42:36,470 --> 00:42:37,804 This suggests a kinship... 848 00:42:37,846 --> 00:42:41,808 that no other regular moon can claim. 849 00:42:41,850 --> 00:42:43,768 It's suspected that Pluto and Triton... 850 00:42:43,811 --> 00:42:48,106 are both objects that originated in the Kuiper Belt. 851 00:42:48,148 --> 00:42:49,148 The outer solar system... 852 00:42:49,191 --> 00:42:50,775 consisted of these large objects... 853 00:42:50,818 --> 00:42:53,278 going every which way, essentially. 854 00:42:53,320 --> 00:42:56,281 And some of them formed giant planets themselves... 855 00:42:56,323 --> 00:42:58,032 and some of them were tossed out further... 856 00:42:58,075 --> 00:43:01,786 where they sit today in the Kuiper Belt. 857 00:43:01,829 --> 00:43:03,580 Collisions, accretions... 858 00:43:03,622 --> 00:43:05,206 and even captures have diminished... 859 00:43:05,249 --> 00:43:07,500 what was once a major thoroughfare... 860 00:43:07,543 --> 00:43:10,753 of planetary building materials. 861 00:43:10,796 --> 00:43:11,921 Early in solar system history... 862 00:43:11,964 --> 00:43:14,716 the Kuiper Belt had far more larger objects... 863 00:43:14,758 --> 00:43:16,884 that may have once had a cumulative mass... 864 00:43:16,927 --> 00:43:18,845 of 50 Earths... 865 00:43:18,887 --> 00:43:20,597 whereas the current Kuiper Belt mass... 866 00:43:20,639 --> 00:43:23,016 is much less than one Earth. 867 00:43:23,058 --> 00:43:24,767 What's left of the Kuiper Belt... 868 00:43:24,810 --> 00:43:27,103 is as old as the solar system itself. 869 00:43:27,146 --> 00:43:29,522 The material that makes up the binary objects... 870 00:43:29,565 --> 00:43:32,650 shards of collisions, and even some alien moons... 871 00:43:32,693 --> 00:43:36,613 hasn't changed in over four billion years. 872 00:43:36,655 --> 00:43:37,989 It's amazing how really different... 873 00:43:38,032 --> 00:43:40,950 all the moons of the outer solar system are. 874 00:43:40,993 --> 00:43:42,368 When I first got interested in astronomy... 875 00:43:42,411 --> 00:43:43,494 as a kid in the 1960s... 876 00:43:43,537 --> 00:43:45,038 we hadn't seen any of these moons. 877 00:43:45,080 --> 00:43:46,914 They were little dots in your telescope... 878 00:43:46,957 --> 00:43:48,333 and so we had no idea... 879 00:43:48,375 --> 00:43:50,126 how radically different they could be. 880 00:43:50,169 --> 00:43:51,461 But I think the most shocking thing... 881 00:43:51,503 --> 00:43:52,754 was how, you know, much variety there is... 882 00:43:52,796 --> 00:43:54,088 in the solar system. 883 00:43:54,131 --> 00:43:56,132 I think that blew me and everybody else away... 884 00:43:56,175 --> 00:43:59,719 who lived through that period. 885 00:43:59,762 --> 00:44:01,095 As we travel back home... 886 00:44:01,138 --> 00:44:04,182 from the frigid outskirts of our solar system... 887 00:44:04,224 --> 00:44:06,726 awed by the vastness of the universe... 888 00:44:06,769 --> 00:44:08,978 and the majesty of the planets... 889 00:44:09,021 --> 00:44:11,439 it's worth it to pause and take notice... 890 00:44:11,482 --> 00:44:14,108 of the small worlds in the shadows. 891 00:44:14,151 --> 00:44:18,154 Those alien moons that were once considered afterthoughts... 892 00:44:18,197 --> 00:44:20,156 hold mysteries just waiting... 893 00:44:20,199 --> 00:44:24,202 for human curiosity to solve. 71280

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