WEBVTT FILE 1 00:00:00.334 --> 00:00:01.335 [Music] 2 00:00:01.335 --> 00:00:04.905 Early in its history, Mars had a far more hospitable climate than 3 00:00:04.905 --> 00:00:08.709 the one that we see today, with a thick atmosphere and abundant 4 00:00:08.709 --> 00:00:12.613 flowing water. So how did it evolve from warm and wet to cold 5 00:00:12.613 --> 00:00:17.084 and dry? Since 2015, NASA's MAVEN mission has been 6 00:00:17.084 --> 00:00:20.187 investigating this question by studying the red planet’s upper 7 00:00:20.187 --> 00:00:24.157 atmosphere. Now, it has mapped high-altitude global wind 8 00:00:24.157 --> 00:00:28.128 patterns at Mars for the first time. During the closest part of 9 00:00:28.128 --> 00:00:31.865 its orbit, MAVEN skims through the upper atmosphere, ingesting 10 00:00:31.865 --> 00:00:34.601 air molecules and determining their composition with an 11 00:00:34.601 --> 00:00:39.139 instrument called NGIMS. MAVEN can also rotate NGIMS back and 12 00:00:39.139 --> 00:00:42.643 forth to measure the air’s velocity. These measurements 13 00:00:42.643 --> 00:00:45.879 provide a snapshot of windspeed and direction along a track of 14 00:00:45.879 --> 00:00:50.117 MAVEN’s orbit. Because the orbit evolves over time, or precesses, 15 00:00:50.117 --> 00:00:53.553 the spacecraft’s closest approach to Mars drifts across 16 00:00:53.553 --> 00:00:56.323 the planet, allowing it to take snapshots at different 17 00:00:56.323 --> 00:01:00.460 locations. Over the past four years, MAVEN’s tracks have added 18 00:01:00.460 --> 00:01:04.665 up, crisscrossing Mars at many locations and at various seasons 19 00:01:04.665 --> 00:01:09.236 and times of day, wrapping the planet in a web of observations. 20 00:01:09.236 --> 00:01:12.239 The measurements reveal how the winds vary with location, and 21 00:01:12.239 --> 00:01:16.243 evolve throughout the Martian year. Now, scientists have used 22 00:01:16.243 --> 00:01:20.080 MAVEN data to build a global map wind currents roughly 200 23 00:01:20.080 --> 00:01:23.617 kilometers above Mars: the first time that winds have been mapped 24 00:01:23.617 --> 00:01:27.854 globally and at such high altitude anywhere beyond Earth. 25 00:01:27.854 --> 00:01:30.824 Within the new map, scientists discovered an unexpected 26 00:01:30.824 --> 00:01:34.828 feature: imprints of rugged terrain far below. As an 27 00:01:34.828 --> 00:01:38.298 example, during two of its orbits MAVEN saw winds above the 28 00:01:38.298 --> 00:01:41.735 Tharsis plateau diverting away from elevated terrain, driven by 29 00:01:41.735 --> 00:01:44.404 giant shield volcanoes reaching twice the height of Mount 30 00:01:44.404 --> 00:01:48.108 Everest. Here’s how the process works: Down at the Martian 31 00:01:48.108 --> 00:01:51.445 surface, winds are forced around and over obstacles when they 32 00:01:51.445 --> 00:01:55.048 encounter mountainous terrain. Disturbances in surface-level 33 00:01:55.048 --> 00:01:58.452 winds also disturb the air above, propagating up through 34 00:01:58.452 --> 00:02:01.989 the atmosphere as gravity waves. When they reach the upper 35 00:02:01.989 --> 00:02:05.158 atmosphere, the gravity waves block the high-altitude winds, 36 00:02:05.158 --> 00:02:08.795 causing them to alter course, and allowing MAVEN to sense the 37 00:02:08.795 --> 00:02:11.898 presence of mountains and valleys on the surface, while 38 00:02:11.898 --> 00:02:15.936 skimming the edge of space. High above Mars, MAVEN is studying 39 00:02:15.936 --> 00:02:19.973 the upper atmosphere, and reaching out to feel the breeze. 40 00:02:19.973 --> 00:02:22.809 It has now made the first measurement of high-altitude, 41 00:02:22.809 --> 00:02:25.946 global circulation patterns, and discovered a surprising 42 00:02:25.946 --> 00:02:29.683 connection to features on the surface. These measurements also 43 00:02:29.683 --> 00:02:33.387 shed new light on ancient Mars, with its thick atmosphere, and 44 00:02:33.387 --> 00:02:37.124 its warm, wet climate. By revealing how the climate of 45 00:02:37.124 --> 00:02:40.394 Mars works today, MAVEN is helping scientists piece 46 00:02:40.394 --> 00:02:43.296 together the early chapters of its dramatic history. 47 00:02:43.296 --> 00:02:53.707 [Music]