WEBVTT - How did the moon get there? 0:00:00.520 --> 0:00:03.600 Welcome to brain Stuff from house stuff Works dot com 0:00:03.600 --> 0:00:14.640 where smart Happens. I am Marshall Brain with today's question, 0:00:15.040 --> 0:00:19.000 where did the Moon come from? This question became famous 0:00:19.040 --> 0:00:22.240 because of Bill O'Reilly, but it's a classic house stuff 0:00:22.280 --> 0:00:25.480 Works kind of question, so let's take a look at it. 0:00:25.480 --> 0:00:29.200 It's a basic tenet of science that everything in nature 0:00:29.280 --> 0:00:33.200 has some kind of explanation. So therefore, the moon has 0:00:33.240 --> 0:00:36.080 to have some kind of explanation. It had to come 0:00:36.200 --> 0:00:40.120 from somewhere or something. And scientists have been thinking about 0:00:40.159 --> 0:00:42.960 this and pondering this for a long time. They've come 0:00:43.040 --> 0:00:45.880 up with a number of theories that didn't really work 0:00:45.960 --> 0:00:49.480 when they looked at them deeper. So one example would 0:00:49.520 --> 0:00:53.279 be that the Earth and the Moon formed together when 0:00:53.320 --> 0:00:57.080 the Solar System was forming, there was an accretion process 0:00:57.200 --> 0:01:01.840 that allowed dust to accumulate into planets, and perhaps the 0:01:01.880 --> 0:01:04.640 Moon formed in the same way the Earth formed, and 0:01:04.720 --> 0:01:07.039 they formed next to each other and became this kind 0:01:07.080 --> 0:01:10.440 of orbiting system. There's a couple of reasons why we 0:01:10.480 --> 0:01:13.399 can say that isn't the case, but one really good 0:01:13.400 --> 0:01:16.199 reason is the fact that the Moon and the Earth 0:01:16.240 --> 0:01:19.480 have different compositions. The amount of iron in the cores 0:01:19.520 --> 0:01:23.000 of these two planets is remarkably different. If they had 0:01:23.040 --> 0:01:26.039 formed together, you'd expect them to be the same, So that, 0:01:26.120 --> 0:01:29.840 along with other things, kind of rules that out. Another 0:01:30.240 --> 0:01:34.480 theory that scientists came up with was the centrifugal force idea, 0:01:34.560 --> 0:01:38.600 the idea that the Earth formed with the Solar System, 0:01:38.680 --> 0:01:41.320 and it was much bigger than it is today, and 0:01:41.360 --> 0:01:45.720 it was spinning extremely quickly, and a chunk of it 0:01:46.080 --> 0:01:49.040 in the molten state just kind of flung off as 0:01:49.080 --> 0:01:53.560 a blob, and that became the Moon. So scientists looked 0:01:53.560 --> 0:01:55.400 at that and they thought about it, and they modeled 0:01:55.440 --> 0:01:57.960 it with computers. And there's a couple of problems with 0:01:58.000 --> 0:02:00.559 that theory, the main one being that the Earth would 0:02:00.600 --> 0:02:04.040 have to be spinning way too fast for it to 0:02:04.240 --> 0:02:06.920 fling a chunk of itself off, and it if it 0:02:07.000 --> 0:02:09.600 had been spinning that fast when the Moon was formed, 0:02:09.600 --> 0:02:12.680 then it would be spinning much faster than it is today. 0:02:12.680 --> 0:02:14.799 A day wouldn't be twenty four hours long, it would 0:02:14.840 --> 0:02:18.760 be much much shorter. Another theory is some kind of 0:02:18.919 --> 0:02:23.959 asteroid capture event. So an asteroid comes by and it 0:02:24.160 --> 0:02:28.320 somehow gets caught in Earth's gravitational field and it becomes 0:02:28.320 --> 0:02:31.760 our moon. The problem with this theory is that there 0:02:31.800 --> 0:02:34.840 would have to be something that would break the asteroid 0:02:34.960 --> 0:02:37.920 or slow it down once it approached Earth, and the 0:02:38.000 --> 0:02:40.720 atmosphere is one thing that could have done that. But 0:02:40.960 --> 0:02:43.639 because of the size of the Moon and the thickness 0:02:43.680 --> 0:02:46.959 of Earth's atmosphere and a couple other things, that theory 0:02:47.000 --> 0:02:50.120 doesn't really work very well either. But it probably is 0:02:50.160 --> 0:02:53.320 what happened with the little moons that are surrounding Mars 0:02:53.440 --> 0:02:56.880 right now. A fourth theory is the one that most 0:02:56.919 --> 0:03:00.840 scientists are currently pretty comfortable with, and the basic idea 0:03:00.919 --> 0:03:04.800 here is pretty easily stated. A planet like object with 0:03:04.840 --> 0:03:09.040 a size roughly equal to Mars hit planet or shortly 0:03:09.120 --> 0:03:12.359 after these two bodies formed, you know, maybe fifty million 0:03:12.440 --> 0:03:15.680 years after these two bodies formed, and the Moon was 0:03:15.800 --> 0:03:20.600 formed by matter that was ejected into orbit by that collision. 0:03:20.960 --> 0:03:23.440 So it would have been a massive collision with a 0:03:23.520 --> 0:03:27.800 lot of energy, and these objects would have formed into 0:03:27.840 --> 0:03:31.960 another molten ball in a chunk just was blasted out 0:03:32.000 --> 0:03:34.960 into orbit, and it would have been blasted out into orbit. 0:03:35.040 --> 0:03:38.840 Probably is is bits and pieces that would have formed 0:03:38.960 --> 0:03:43.440 or aggregated together to create the Moon that we have today. 0:03:43.640 --> 0:03:47.000 Science is based on evidence. So what evidence do we 0:03:47.120 --> 0:03:50.640 have to support this view of the Moon's origin. One 0:03:50.680 --> 0:03:53.680 piece of evidence came back from the Apollo Moon missions. 0:03:53.960 --> 0:03:58.160 The moon rocks collected by the Apollo astronauts support this theory. 0:03:58.840 --> 0:04:02.160 Another thing that support is the size of the core 0:04:02.200 --> 0:04:05.040 of the Moon. Is mentioned earlier. The core of the Moon, 0:04:05.560 --> 0:04:08.480 being of iron, is much smaller than the core of 0:04:08.520 --> 0:04:13.520 the Earth, and that fact is easily explained by some 0:04:13.600 --> 0:04:17.400 kind of collision event. In that event, mostly mantle would 0:04:17.400 --> 0:04:21.279 have been ejected into the uh into orbit around Earth 0:04:21.400 --> 0:04:24.360 rather than the iron core, it's thought, and so the 0:04:24.400 --> 0:04:28.200 Moon would therefore have less iron in its core as 0:04:28.240 --> 0:04:32.160 a result. Another piece of evidence is the canting of 0:04:32.200 --> 0:04:36.279 the Earth's rotational axis. You know, the fact that the 0:04:36.320 --> 0:04:38.880 axis is tilted, and this is what gives us our 0:04:39.000 --> 0:04:43.040 seasons and the length of the Earth day. And another 0:04:43.320 --> 0:04:45.800 is the distance of the Moon from the Earth and 0:04:45.839 --> 0:04:49.479 the increase in that distance over time. So you take 0:04:49.640 --> 0:04:53.320 pieces of evidence like this and they work together with 0:04:53.360 --> 0:04:56.839 each other to support the theory that the Moon was 0:04:56.880 --> 0:04:59.800 created by a collision event. There's a great deal of 0:05:00.040 --> 0:05:02.880 cheerill available through Google if you'd like to increase your 0:05:02.920 --> 0:05:06.400 scientific understanding of the Moon's origin. It really is an 0:05:06.400 --> 0:05:09.280 interesting question. If you think about it and you know 0:05:09.360 --> 0:05:12.039 in theory, you could come up with another idea for 0:05:12.080 --> 0:05:14.719 where the moon came from, and if you have the evidence, 0:05:14.800 --> 0:05:18.680 you could bring it forward and create another scientific discovery. 0:05:19.000 --> 0:05:23.520 That's How Science Works. Be sure to check out our 0:05:23.560 --> 0:05:26.960 new video podcast, Stuff from the Future. Join how Stuff 0:05:26.960 --> 0:05:29.880 Work staff as we explore the most promising and perplexing 0:05:29.960 --> 0:05:34.880 possibilities of tomorrow. The house Stuff Works iPhone app has arrived. 0:05:35.000 --> 0:05:36.919 Download it today on iTunes.