WEBVTT - What Is It Like In Our Asteroid Belt? 0:00:01.890 --> 0:00:07.930 Welcome to BrainStuff, a production of iHeartRadio. Hey, BrainStuff. Lauren 0:00:07.950 --> 0:00:13.290 Vogelbaum here. In the Star Wars film, The Empire Strikes Back, 0:00:13.780 --> 0:00:16.700 Han Solo and the crew escape from the planet Hoth, 0:00:17.000 --> 0:00:21.400 only to fly straight into an asteroid field. The field 0:00:21.540 --> 0:00:25.599 is densely packed, and with huge, spinning rocks careening around 0:00:25.640 --> 0:00:30.010 the Millennium Falcon, Han must deftly maneuver his spaceship to safety— 0:00:30.570 --> 0:00:36.090 the odds of which, calculated by C-3PO, are only 3,720 0:00:36.090 --> 0:00:40.570 to 1. Of course, Star Wars isn't known for its 0:00:40.830 --> 0:00:45.690 scientific realism. If a spaceship launched from Earth toward our 0:00:45.750 --> 0:00:48.710 solar system's asteroid belt and attempted to fly through it, 0:00:49.090 --> 0:00:52.240 would it look the same, with dangerous debris flying everywhere, 0:00:52.340 --> 0:00:56.320 putting the mission in jeopardy? As it turns out, navigating 0:00:56.380 --> 0:01:00.710 through our asteroid belt wouldn't be nearly as dramatic. Only 0:01:00.750 --> 0:01:03.110 a handful of asteroids are big enough to cause much 0:01:03.170 --> 0:01:06.369 damage to a spacecraft, and there's way more space between 0:01:06.430 --> 0:01:10.130 them than you might think. But that doesn't mean that 0:01:10.190 --> 0:01:13.730 our solar system's main asteroid belt, located between the orbits 0:01:13.830 --> 0:01:16.920 of Mars and Jupiter, is any less interesting than the 0:01:16.980 --> 0:01:22.280 field in Star Wars. The more astronomers study the composition, activity, 0:01:22.360 --> 0:01:25.220 and formation of asteroids in their orbit around the sun, 0:01:25.819 --> 0:01:28.720 the more we understand about how the entire solar system 0:01:28.780 --> 0:01:33.010 came to be. Some theories even suggest that life on 0:01:33.090 --> 0:01:36.350 Earth started with asteroids colliding with our planet in its 0:01:36.430 --> 0:01:40.970 early stages. And on the flip side, an asteroid's crash 0:01:41.030 --> 0:01:43.410 was a major factor in the mass extinction of the 0:01:43.430 --> 0:01:48.340 dinosaurs 65 million years ago. Today, let's talk about our 0:01:48.480 --> 0:01:53.690 asteroid belt. Asteroids are remnants of our solar system's early days, 0:01:53.850 --> 0:01:57.020 when the planets were still forming. Some are the oldest, 0:01:57.260 --> 0:02:01.300 most unchanged objects we know of, untouched by processes like 0:02:01.380 --> 0:02:06.060 volcanism that shaped larger bodies. There are several theories that 0:02:06.100 --> 0:02:09.200 attempt to explain how the solar system began, but the 0:02:09.240 --> 0:02:13.400 most widely accepted is known as the nebular theory. It 0:02:13.460 --> 0:02:16.540 goes that our solar system started as a large, shapeless 0:02:16.660 --> 0:02:21.060 cloud of gas, dust, and ice. But then something disrupted 0:02:21.100 --> 0:02:24.640 the mass and set things in motion, perhaps the explosion 0:02:24.680 --> 0:02:28.380 of a nearby star. If you've ever watched figure skating, 0:02:28.580 --> 0:02:31.690 you've seen how skaters can spin much faster if they 0:02:31.750 --> 0:02:35.630 pull their arms closer to their bodies. The more concentrated 0:02:35.669 --> 0:02:38.610 their body mass is, the faster they're able to rotate. 0:02:39.610 --> 0:02:43.540 The same thing happened with our solar system. the hypothetical 0:02:43.620 --> 0:02:48.169 explosion nearby squeezed the unformed gas and dust together, which 0:02:48.230 --> 0:02:51.970 began to spin faster and faster in a circle. As 0:02:52.010 --> 0:02:54.250 the sun formed in the middle, the cloud started to 0:02:54.370 --> 0:02:57.510 flatten out into a disk, sort of like a frisbee 0:02:57.650 --> 0:03:02.620 or a pancake made up of tiny grains of dust. Eventually, 0:03:02.860 --> 0:03:06.120 dust particles began to join together and form larger bodies 0:03:06.180 --> 0:03:11.060 called planetismals. Even more matter collided with these planetesimals and 0:03:11.120 --> 0:03:15.800 gravitationally stuck to them in a process called accretion. As 0:03:15.860 --> 0:03:19.010 the bodies orbited and rotated and gravity brought in more 0:03:19.070 --> 0:03:23.790 dust and gas, the planetesimals accreted into protoplanets, and then 0:03:23.950 --> 0:03:28.050 into the planets we currently know and love. The planets 0:03:28.190 --> 0:03:32.510 are wildly far apart. We measure this in astronomical units, 0:03:32.710 --> 0:03:36.090 or AUs. An astronomical unit is the distance between the 0:03:36.150 --> 0:03:39.430 Earth and the Sun, which is about 150 million kilometers. 0:03:40.570 --> 0:03:44.030 For today's purposes, we're mostly interested in the area between 0:03:44.350 --> 0:03:47.690 Mars and Jupiter. Mars lies about 1.5 AU from the Sun, 0:03:47.700 --> 0:03:49.740 or 225 million kilometers away. Jupiter is about 5.2 AU 0:03:49.780 --> 0:03:59.580 from the Sun, or 780 million kilometers. That means that 0:03:59.620 --> 0:04:05.260 there's about 3.7 AU between Mars and Jupiter, or 555 0:04:05.260 --> 0:04:09.180 million kilometers. It seems like there's enough room there for 0:04:09.300 --> 0:04:13.770 another planet, right? So why isn't there? What happened in 0:04:13.790 --> 0:04:17.690 that area during the formation of the solar system? Some 0:04:17.730 --> 0:04:21.469 astronomers have suggested that a separate planet or protoplanet actually 0:04:21.589 --> 0:04:25.030 formed between them, but that the impact of a high-speed 0:04:25.110 --> 0:04:28.210 comet broke up and scattered this newly formed body to 0:04:28.310 --> 0:04:32.469 create what we now know as the main asteroid belt. Today, 0:04:32.650 --> 0:04:35.860 it's thought more likely that asteroids are leftover matter from 0:04:35.890 --> 0:04:39.660 the solar system's formation that never successfully came together as 0:04:39.820 --> 0:04:44.260 one planet. But if that's accurate, why did it never 0:04:44.300 --> 0:04:50.789 come together? Well, Jupiter is big. By big, I mean 0:04:50.850 --> 0:04:53.279 it's about two and a half times as massive as 0:04:53.339 --> 0:04:56.820 the rest of the planets put together. It's much closer 0:04:56.900 --> 0:04:58.920 to being like our sun than it is to being 0:04:58.960 --> 0:05:03.230 like Earth or Mars. Jupiter's mass is plenty enough to 0:05:03.290 --> 0:05:06.490 disturb any rocky matter that fell in between it and Mars. 0:05:07.150 --> 0:05:10.730 Its strong gravitational pull could have caused any potential protoplanets 0:05:10.790 --> 0:05:14.280 to collide and break apart. leaving us with this large, 0:05:14.440 --> 0:05:17.770 spread-out collection of stuff that orbits around the Sun in 0:05:17.830 --> 0:05:21.430 an elliptical pattern, mostly in the same direction as the planets. 0:05:22.750 --> 0:05:26.190 With its center around 2.7 AU from the Sun, the 0:05:26.210 --> 0:05:29.600 main asteroid belt separates the rocky inner planets from the 0:05:29.680 --> 0:05:34.260 massive gas giants farther out. The gravitational force of Jupiter 0:05:34.360 --> 0:05:37.920 still affects the asteroid belt to this day. Its giant 0:05:38.020 --> 0:05:42.000 mass disturbs the path of asteroids and creates large gaps 0:05:42.160 --> 0:05:46.680 known as Kirkwood gaps. This happens due to orbital resonance, 0:05:46.980 --> 0:05:50.680 which happens when orbiting bodies periodically line up and exert 0:05:50.720 --> 0:05:55.160 gravitational force on each other. For example, an asteroid might 0:05:55.240 --> 0:05:57.500 make two full orbits around the Sun in the time 0:05:57.560 --> 0:06:01.350 it takes Jupiter to make one. So, every other orbit, 0:06:01.640 --> 0:06:04.750 that asteroid would line up with Jupiter, and its orbit 0:06:04.810 --> 0:06:09.390 would display a slight change. This has caused several different 0:06:09.410 --> 0:06:13.029 groups of asteroids to cluster together over time, depending on 0:06:13.089 --> 0:06:16.480 how frequently they circle the sun. It also leaves several 0:06:16.560 --> 0:06:21.479 gaps where there aren't any asteroids. Due to orbital interactions 0:06:21.520 --> 0:06:24.620 with Jupiter, and even more occasional ones with Mars, Earth, 0:06:24.720 --> 0:06:29.670 and other objects, the asteroid belt is always changing. Asteroids 0:06:29.710 --> 0:06:32.170 can get knocked or pulled out of the belt and 0:06:32.290 --> 0:06:37.080 flung through space, even towards us. A network of observatories 0:06:37.240 --> 0:06:41.320 and space telescopes, wrangled by organizations like NASA's Planetary Defense 0:06:41.360 --> 0:06:46.210 Coordination Office, keeps track of near-Earth objects, that is, asteroids 0:06:46.250 --> 0:06:49.490 and other things like comets that graze Earth's orbit and 0:06:49.610 --> 0:06:53.790 pose a potential hazard. But large impacts are thought to 0:06:53.850 --> 0:06:56.980 be extremely few and far between, on the scale of 0:06:57.300 --> 0:07:00.380 hundreds of thousands, if not hundreds of millions, of years. 0:07:01.680 --> 0:07:04.260 Most asteroids in the main belt are only the size 0:07:04.279 --> 0:07:07.390 of a pebble. Despite the vast amount of space that 0:07:07.410 --> 0:07:10.670 it takes up, astronomers estimate the total mass of the 0:07:10.710 --> 0:07:13.990 entire belt to be less than 1,000th the mass of 0:07:14.010 --> 0:07:16.380 the Earth, or less than half of the mass of 0:07:16.420 --> 0:07:19.300 our moon, and even that might be a generous estimate. 0:07:20.720 --> 0:07:23.760 The largest object in the belt is the dwarf planet Ceres, 0:07:24.060 --> 0:07:27.840 which has a diameter of about 600 miles or 1,000 kilometers. 0:07:28.620 --> 0:07:31.970 Only another 15 asteroids or so have a diameter over 0:07:32.010 --> 0:07:35.180 a quarter of that. The largest object in the belt 0:07:35.250 --> 0:07:38.260 currently defined as an asteroid is Vesta, which is a 0:07:38.280 --> 0:07:42.280 little over half the size of Ceres. The majority of 0:07:42.300 --> 0:07:47.760 the asteroids in the main belt fall under three main categories, carbonaceous, silicaceous, 0:07:48.140 --> 0:07:53.820 or metallic. Carbonaceous, or C-type asteroids, make up about 75% 0:07:53.820 --> 0:07:57.860 of all known asteroids. They're carbon-rich, made up of clay 0:07:57.920 --> 0:08:01.610 and silicate rocks, like Earth's crust, very dark because they 0:08:01.640 --> 0:08:04.540 absorb light, and are found on the outer edges of 0:08:04.580 --> 0:08:10.000 the belt. Silicaceous or S-type asteroids make up about 17% 0:08:10.000 --> 0:08:14.150 of all known asteroids. Their composition is mainly stony, and 0:08:14.170 --> 0:08:17.390 they're found along the inner edge of the belt. The 0:08:17.410 --> 0:08:21.730 remaining 8% of asteroids are metallic or M-type. These are 0:08:21.770 --> 0:08:25.400 made mostly of denser metals like iron and nickel, and 0:08:25.440 --> 0:08:28.150 are found in the middle region of the belt. the 0:08:28.170 --> 0:08:30.590 different types may have formed up due to their distance 0:08:30.610 --> 0:08:34.230 from the sun, or from actions like dense planetismals getting 0:08:34.270 --> 0:08:39.380 their mantles stripped away by early collisions. Note that any 0:08:39.420 --> 0:08:43.380 given asteroid can contain different types of material. Many have 0:08:43.460 --> 0:08:46.980 smashed into each other over time, and a few, like Vesta, 0:08:47.400 --> 0:08:52.270 even formed layers like Earth did. NASA's Dawn mission visited 0:08:52.290 --> 0:08:56.400 Vesta from 2011 to 2012, and found evidence that objects 0:08:56.520 --> 0:08:59.340 like Vesta were able to form a core, mantle, and 0:08:59.400 --> 0:09:03.350 crust because of radioactive materials that they had created early on, 0:09:03.780 --> 0:09:06.250 which basically melted the rest of the stuff they were 0:09:06.290 --> 0:09:09.609 made up of, allowing the materials of different densities to 0:09:09.710 --> 0:09:14.449 separate out, with metals sinking to the core. In case 0:09:14.490 --> 0:09:17.290 you're planning a trip, don't worry. The internal radiation on 0:09:17.330 --> 0:09:22.110 Vesta seems to have decayed since then. Many asteroids contain 0:09:22.270 --> 0:09:26.189 water ice as well. We only discovered that asteroids currently 0:09:26.250 --> 0:09:29.770 contain water ice about 20 years ago in the early 2000s, 0:09:30.070 --> 0:09:33.150 when researchers observed tails coming off of asteroids in the 0:09:33.170 --> 0:09:37.360 main belt, similar to comets' tails. Heat from the sun 0:09:37.460 --> 0:09:40.559 causes the ice in them to evaporate, and a trail 0:09:40.620 --> 0:09:43.179 of gas and dust is left behind as the object 0:09:43.260 --> 0:09:48.950 moves through space. These are called main belt comets. We've 0:09:48.990 --> 0:09:51.960 since learned that some asteroid tails are not made of water, 0:09:52.280 --> 0:09:55.580 but of other materials shed due to small collisions or 0:09:55.600 --> 0:09:59.209 a rapid rotation. These are part of a broader category 0:09:59.309 --> 0:10:04.660 called activations. asteroids. The biggest revelation coming from the discovery 0:10:04.720 --> 0:10:08.060 of so-called main belt comets is the possibility that icy 0:10:08.200 --> 0:10:11.060 asteroids may have crashed into Earth and provided us with 0:10:11.120 --> 0:10:15.970 our water, or even with life. Astronomers used to think 0:10:16.020 --> 0:10:19.230 that ice from regular comets provided the Earth with its water. 0:10:19.790 --> 0:10:23.170 But recent observations have shown that comet water doesn't tend 0:10:23.190 --> 0:10:26.590 to have much in common with our planet's water. If 0:10:26.750 --> 0:10:30.810 asteroidal water is anything like ours, icy asteroids may provide 0:10:30.870 --> 0:10:34.430 us with important insights into the Earth's formation and even 0:10:34.550 --> 0:10:39.360 our own existence. And our main asteroid belt isn't unique. 0:10:40.580 --> 0:10:44.020 Farther out, beyond Neptune, the Kuiper Belt exists some 30 0:10:44.020 --> 0:10:48.580 to 50 AU from the Sun. It's another, even larger 0:10:48.640 --> 0:10:52.190 belt of small objects left over from the solar system's formation. 0:10:53.010 --> 0:10:55.790 It contains what's now recognized as the dwarf planet Pluto. 0:10:57.130 --> 0:10:59.689 Just as Jupiter may have prevented a full planet from 0:10:59.790 --> 0:11:03.360 forming where the main asteroid belt lies, Neptune may have 0:11:03.400 --> 0:11:06.439 caused the creation of these small icy bodies that make 0:11:06.500 --> 0:11:10.020 up the Kuiper Belt. Astronomers estimate the Kuiper Belt to 0:11:10.080 --> 0:11:13.400 contain a total mass of about one-tenth the mass of Earth. 0:11:14.100 --> 0:11:17.540 and it's slowly eroding out of orbit, with bodies flying 0:11:17.640 --> 0:11:20.880 either out into space or deeper into the solar system 0:11:21.080 --> 0:11:25.720 to become comets or asteroids. The idea of the Kuiper 0:11:25.740 --> 0:11:30.319 Belt was first proposed by astronomer Gerard Kuiper in 1951, 0:11:30.320 --> 0:11:35.080 but its existence wasn't confirmed until 1992, when astronomers observed 0:11:35.280 --> 0:11:40.430 the first smaller Kuiper Belt objects. But what about outside 0:11:40.450 --> 0:11:44.090 of our solar system? Having a sample size of one 0:11:44.170 --> 0:11:46.690 solar system to look at around us means that we 0:11:46.730 --> 0:11:50.650 can't assume anything here is universally normal, but we have 0:11:50.730 --> 0:11:55.320 found asteroid belts around several other stars. Observing them may 0:11:55.360 --> 0:11:58.880 help us better understand the process of planetary formation overall. 0:12:00.140 --> 0:12:05.300 Even here, although over 1.56 million asteroids have already been discovered, 0:12:05.940 --> 0:12:09.700 new-to-us asteroids are being identified all the time, presenting us 0:12:09.740 --> 0:12:12.990 with new opportunities to learn, and Maybe in the future, 0:12:13.210 --> 0:12:17.480 even visit, mine for materials, or use as ready-made platforms 0:12:17.620 --> 0:12:25.660 for further exploration. Today's episode is based on the article 0:12:25.800 --> 0:12:29.380 How Asteroid Belts Work on HowStuffWorks.com, written by John Fuller. 0:12:30.059 --> 0:12:32.720 BrainStuff is a production of iHeart Podcasts in partnership with 0:12:32.740 --> 0:12:36.520 HowStuffWorks.com and is produced by Tyler Klang. For more shows 0:12:36.540 --> 0:12:40.439 from iHeart Podcasts, visit the iHeartRadio app. Apple Podcasts, or 0:12:40.520 --> 0:12:42.270 wherever you listen to your favorite shows.