1 00:00:00,000 --> 00:00:01,716 [Music] 2 00:00:01,716 --> 00:00:03,350 Our solar system is home 3 00:00:03,350 --> 00:00:06,350 to eight planets and nearly 300 known moons, 4 00:00:06,683 --> 00:00:11,283 but of those many worlds, only two are shaped by an active rain cycle: 5 00:00:11,766 --> 00:00:14,833 Earth and Saturn's largest moon, Titan. 6 00:00:15,550 --> 00:00:20,300 Now, NASA's James Webb Space Telescope has discovered a new molecule 7 00:00:20,316 --> 00:00:24,183 in Titan's atmosphere, one that may have implications for the future 8 00:00:24,250 --> 00:00:27,250 of this surprisingly Earthlike world. 9 00:00:27,250 --> 00:00:28,816 [Music] 10 00:00:28,816 --> 00:00:32,616 From space, Titan appears to be a featureless, orange globe, 11 00:00:32,616 --> 00:00:36,550 with its lower atmosphere and its surface hidden by an organic haze. 12 00:00:37,116 --> 00:00:40,366 But when we look at the moon in infrared, its features emerge: 13 00:00:40,966 --> 00:00:43,550 dark dune fields, circling the equator, 14 00:00:43,550 --> 00:00:47,550 vast plains in the mid-latitudes, and in the far north, 15 00:00:47,750 --> 00:00:51,433 lakes and seas rivaling the Great Lakes of North America. 16 00:00:52,366 --> 00:00:56,833 Unlike Earth, these bodies are not made of liquid water, but of hydrocarbons 17 00:00:56,833 --> 00:00:59,933 like methane and ethane chilled to cryogenic temperatures. 18 00:01:00,700 --> 00:01:04,750 From 2022 to 2023, my colleagues and I studied Titan 19 00:01:04,750 --> 00:01:08,516 with the Webb Telescope and the Keck Observatory on Mauna Kea. 20 00:01:08,850 --> 00:01:11,866 Their powerful infrared vision cut through Titan's haze 21 00:01:11,983 --> 00:01:14,983 to reveal its northern hemisphere during late summer. 22 00:01:15,383 --> 00:01:18,900 What we saw were two broad areas of methane cloud cover 23 00:01:18,933 --> 00:01:22,616 around 55 degrees north, close to the largest lakes and seas. 24 00:01:23,333 --> 00:01:28,450 In 2004, NASA's Cassini orbiter made its first close encounter with Titan 25 00:01:28,583 --> 00:01:32,450 while the southern hemisphere was in summer. Cassini witnessed rain clouds 26 00:01:32,450 --> 00:01:36,916 forming in the drier south polar regions due to seasonal heating and evaporation. 27 00:01:37,583 --> 00:01:41,783 Climate models predicted that as Titan's northern hemisphere entered summer 28 00:01:41,883 --> 00:01:46,383 beginning in 2017, methane would evaporate from its large lakes and seas, 29 00:01:46,516 --> 00:01:49,516 rising into the lower atmosphere to form rain clouds. 30 00:01:50,233 --> 00:01:54,733 Now, our study has confirmed that when Titan's northern hemisphere warms up, 31 00:01:54,783 --> 00:01:57,933 it also undergoes a seasonal cycle of cloud formation. 32 00:01:57,933 --> 00:01:59,733 [Music] 33 00:01:59,733 --> 00:02:01,883 In addition to taking pictures of Titan, 34 00:02:01,883 --> 00:02:04,933 we used the Webb Telescope’s Mid-Infrared Instrument, 35 00:02:05,116 --> 00:02:08,116 or MIRI, to study the makeup of its atmosphere. 36 00:02:08,216 --> 00:02:10,733 MIRI has both a camera and a spectrometer: 37 00:02:10,733 --> 00:02:12,616 it can break apart the light from an object 38 00:02:12,616 --> 00:02:15,383 to determine its chemical composition. 39 00:02:15,383 --> 00:02:19,250 Like Earth, Titan's atmosphere is made primarily of nitrogen, 40 00:02:19,516 --> 00:02:21,933 but it also has a substantial amount of methane, 41 00:02:21,933 --> 00:02:24,916 which plays a similar role to Earth's water vapor. 42 00:02:24,916 --> 00:02:30,066 Trace gases are present as well, including heavier hydrocarbons like ethane. 43 00:02:30,266 --> 00:02:33,266 but the details of their formation are murky. 44 00:02:33,333 --> 00:02:38,266 Now, Webb's MIRI instrument has shed new light on how these hydrocarbons form. 45 00:02:38,750 --> 00:02:43,266 When MIRI measured Titan's spectrum, it saw a previously undetected spike 46 00:02:43,400 --> 00:02:45,783 indicating the presence of the methyl radical, 47 00:02:45,783 --> 00:02:48,366 the missing link to the heavier hydrocarbons. 48 00:02:48,366 --> 00:02:51,966 Here's how the process works: in Titan's upper atmosphere, 49 00:02:51,966 --> 00:02:55,333 UV radiation from the Sun and electrons from Saturn 50 00:02:55,350 --> 00:02:59,066 break apart methane into hydrogen atoms and methyl radicals. 51 00:02:59,383 --> 00:03:02,833 The hydrogen is lost to space, while the short-lived methyl 52 00:03:02,833 --> 00:03:06,100 radicals recombine into heavier molecules, like ethane. 53 00:03:06,666 --> 00:03:10,133 Ethane and methane eventually condense into droplets and rain 54 00:03:10,133 --> 00:03:13,700 out of the atmosphere, replenishing lakes and seas on the surface. 55 00:03:14,133 --> 00:03:17,333 Rainfall on Titan has yet to be directly observed, 56 00:03:17,516 --> 00:03:21,266 but the discovery of methyl radicals fills a gap in our observations, 57 00:03:21,500 --> 00:03:25,650 and it supports our understanding of this surprisingly Earthlike world. 58 00:03:25,650 --> 00:03:27,216 [Music] 59 00:03:27,216 --> 00:03:30,050 Further discoveries will come in 2034, 60 00:03:30,050 --> 00:03:34,633 when NASA's Dragonfly mission touches down near the equator during northern winter. 61 00:03:35,133 --> 00:03:39,683 Dragonfly will drill into the icy surface to look for complex molecules 62 00:03:39,766 --> 00:03:43,250 made from Titan's abundant methane, nitrogen and oxygen. 63 00:03:43,716 --> 00:03:46,833 Of particular interest to its search are amino acids, 64 00:03:47,016 --> 00:03:50,033 the building blocks of proteins that make up life on Earth. 65 00:03:50,966 --> 00:03:56,216 As spring slowly returns to the northern hemisphere, in the late 2030’s, Dragonfly 66 00:03:56,216 --> 00:03:59,933 may also become the first mission to witness rainfall on another world. 67 00:03:59,950 --> 00:04:02,050 [Music] 68 00:04:02,050 --> 00:04:05,116 Looking ahead to the far future, our study hints 69 00:04:05,116 --> 00:04:08,700 at an intriguing possibility for the evolution of Titan's climate. 70 00:04:09,266 --> 00:04:12,483 If the methane that is being broken apart in the upper atmosphere 71 00:04:12,550 --> 00:04:14,766 is not replenished from the moon's interior, 72 00:04:14,766 --> 00:04:17,766 it could eventually disappear from the environment. 73 00:04:17,933 --> 00:04:22,066 Over tens of millions of years, Titan's lakes and seas could dry up. 74 00:04:22,750 --> 00:04:26,200 Its shorelines could gradually give way to the encroaching desert. 75 00:04:26,950 --> 00:04:30,966 Its rain clouds and organic haze could vanish, leaving a dark blue sky. 76 00:04:31,716 --> 00:04:34,716 At last, Saturn would be visible from Titan's surface, 77 00:04:34,883 --> 00:04:40,633 gazing down upon a world of dry lakebeds, empty river channels, and endless dunes. 78 00:04:40,633 --> 00:04:43,483 [Dry wind blowing] [Music] 79 00:04:43,733 --> 00:04:55,566 [Music]