WEBVTT FILE 1 00:00:02.336 --> 00:00:05.205 The OSIRIS-REx spacecraft was launched with a clear mission: 2 00:00:05.205 --> 00:00:07.975 collect a sample from an asteroid called Bennu, and send 3 00:00:07.975 --> 00:00:11.011 it back to Earth. But with the number of known asteroids in our 4 00:00:11.011 --> 00:00:13.947 solar system reaching into the hundreds of thousands, why was 5 00:00:13.947 --> 00:00:18.585 Bennu chosen? What made it the best target? The first set of 6 00:00:18.585 --> 00:00:22.489 selection criteria was proximity to Earth. The most accessible 7 00:00:22.489 --> 00:00:27.895 asteroids are located around 74 to 153 million miles away. And 8 00:00:27.895 --> 00:00:30.564 in that group, the most ideal targets are ones with an 9 00:00:30.564 --> 00:00:33.901 Earth-like circular orbit and a low degree of tilt, due to 10 00:00:33.901 --> 00:00:38.322 spacecraft maneuverability. At the time of selection in 2008, 11 00:00:38.322 --> 00:00:40.874 that brought the number of known near-Earth objects down from 12 00:00:40.874 --> 00:00:45.696 seven-thousand to one-hundred ninety-two. From there, the size 13 00:00:45.696 --> 00:00:48.799 of the asteroid became a factor. Bigger meant better in this 14 00:00:48.799 --> 00:00:52.352 case, because asteroids with smaller diameters rotate faster, 15 00:00:52.352 --> 00:00:55.656 and material on their surface are more easily ejected. Not 16 00:00:55.656 --> 00:00:58.959 ideal conditions for safely grabbing a sample. So, mission 17 00:00:58.959 --> 00:01:03.030 scientists wanted the target to have a diameter larger than 200 18 00:01:03.030 --> 00:01:05.449 meters. That brought the candidates down from one-hundred 19 00:01:05.449 --> 00:01:09.469 ninety-two to twenty-six. The chemical composition of the 20 00:01:09.469 --> 00:01:12.506 asteroid was the next factor, because we want our return 21 00:01:12.506 --> 00:01:15.092 sample to help us learn more about the history of our solar 22 00:01:15.092 --> 00:01:18.845 system and life on Earth. That dropped our target list to 23 00:01:18.845 --> 00:01:22.349 twelve asteroids with a known composition. And from there, 24 00:01:22.349 --> 00:01:25.035 only five of those were ideal for sampling because they are 25 00:01:25.035 --> 00:01:29.439 known from Earth observations to be carbon-rich. This matters, 26 00:01:29.439 --> 00:01:33.010 because a carbon-rich asteroid may contain organic molecules, 27 00:01:33.010 --> 00:01:36.113 volatiles, and amino acids that may have been the precursors to 28 00:01:36.113 --> 00:01:40.350 life on Earth. So now it’s decision time. Of these five 29 00:01:40.350 --> 00:01:44.121 contenders, why Bennu? Quite simply, it’s because there was 30 00:01:44.121 --> 00:01:47.291 more information about it available to scientists. It was 31 00:01:47.291 --> 00:01:50.661 the only object of the five that had been observed with radar. 32 00:01:50.661 --> 00:01:53.046 This provided not just an accurate measurement of its 33 00:01:53.046 --> 00:01:56.800 size, dimensions, and shape, but also suggested it has a smooth 34 00:01:56.800 --> 00:01:59.987 surface with an ample amount of material to sample, and few 35 00:01:59.987 --> 00:02:03.907 large boulders to get in the way. We didn’t have this level 36 00:02:03.907 --> 00:02:06.827 of detail with the others, which put the ability to safely get a 37 00:02:06.827 --> 00:02:11.264 surface sample in doubt. Sorry fellas! The material we gather 38 00:02:11.264 --> 00:02:14.001 from asteroid Bennu will help generations of scientists better 39 00:02:14.001 --> 00:02:16.653 understand how the planets formed and the source of the 40 00:02:16.653 --> 00:02:20.507 organic materials and water that helped spawn life on Earth. And 41 00:02:20.507 --> 00:02:23.760 beyond learning about the past, studying Bennu can help us plan 42 00:02:23.760 --> 00:02:27.164 for the future – everything from space travel, to utilizing 43 00:02:27.164 --> 00:02:30.017 natural resources, and better understanding the risks of 44 00:02:30.017 --> 00:02:33.937 asteroids. And this is why we chose Bennu.