WEBVTT FILE 1 00:00:00.030 --> 00:00:05.400 [ music ] 2 00:00:05.420 --> 00:00:08.980 From a distance, everything in our solar system appears to be in its place. 3 00:00:09.000 --> 00:00:13.560 However, if you take a closer look, sometimes you can find asteroids, like Bennu, 4 00:00:13.580 --> 00:00:17.680 leaving their home in the inner asteroid belt and passing very close to Earth. 5 00:00:17.700 --> 00:00:24.480 Most other asteroids tend to stay grouped together in a few regions of our solar system, yet some still end up in our backyard. 6 00:00:24.500 --> 00:00:30.480 So once these asteroids get close, what makes the difference between a near-miss, and a potential hit? 7 00:00:30.500 --> 00:00:34.380 NASA's OSIRIS-REx mission will help better answer this question when it visits Bennu, 8 00:00:34.400 --> 00:00:39.250 but scientists think that a force called the Yarkovsky effect might be an important part of the answer. 9 00:00:39.270 --> 00:00:46.680 So how does this effect work? Well, like Earth, most asteroids rotate slowly as they move through space. 10 00:00:46.700 --> 00:00:52.420 During the day, the surface of the asteroid is illuminated by the Sun, so it absorbs heat and grows warmer. 11 00:00:52.440 --> 00:00:57.910 During the night, however, the surface cools down, emitting the heat it absorbed as radiation. 12 00:00:57.930 --> 00:01:05.550 This radiation exerts a force on the asteroid, acting as a sort of mini-thruster that can slowly change the asteroid's direction over time. 13 00:01:05.570 --> 00:01:12.480 On larger asteroids this doesn't amount to much, but on small ones it can make a pretty large change over time. 14 00:01:12.500 --> 00:01:15.630 Because the surface emits the most heat radiation at the end of the day, 15 00:01:15.650 --> 00:01:20.380 the direction the asteroid rotates can ultimately determine what happens in the long run. 16 00:01:20.400 --> 00:01:29.080 Other factors, such as composition, asteroid shape, and surface features, can modify the magnitude and direction of the Yarkovsky thrust. 17 00:01:29.100 --> 00:01:32.830 By studying the Yarkovsky effect on Bennu with the OSIRIS-REx spacecraft, 18 00:01:32.850 --> 00:01:36.820 NASA scientists hope to better predict how an asteroid might move through the solar system, 19 00:01:36.840 --> 00:01:40.320 and whether it poses any danger to us here on Earth. 20 00:01:40.340 --> 00:01:47.580 So the next time an asteroid starts gradually moving into our neighborhood, we'll have a better idea of exactly where it will end up. 21 00:01:47.600 --> 00:01:49.530 22 00:01:49.550 --> 00:02:03.470 [ satellite beeping ]