I'm the Moon
June 27, 2011 6:53 PM   Subscribe

Why isn't the earth (or our moon) being constantly bombarded with meteors, when it seems like pictures of all the other planets (and our moon) are fully pock marked from meteor hits?
posted by JenBBB to Science & Nature (16 answers total) 1 user marked this as a favorite
Best answer: Earth *is* being constantly bombarded. Our atmosphere just burns up most of them.

The Moon *is* being hit, we just aren't there to see it. Also (IANAP) maybe the gravity well of Earth pulls more meteors away from the Moon (citation needed!)

When you look at other planets and moons, the atmospheres are thinner or non-existent. Also, for many planets/moons, there's no erosion mechanism to smooth out the impacts, so they stay pockmarked for longer.
posted by Queen Sabium at 6:57 PM on June 27, 2011 [5 favorites]

Lots of reasons....first being that Earth is continually reshaped by geologic forces, and the moon has existed in a steady state for billions of years and so has had most of it's surface scarred already.
posted by dfriedman at 6:59 PM on June 27, 2011

What Queen Sabium said. The Earth doesn't really protect the Moon. Meteoroid impacts on the Moon have been filmed in recent years.
posted by lukemeister at 6:59 PM on June 27, 2011 [1 favorite]

The moon is, all the time! I mean, it's not constant or anything because there's lots of empty space out there between stuff, but it's happening often enough. If you give the moon a close look, you'll see craters everywhere. (Try Google Earth/Moon (Mars too!))

It happens less-so on Earth because the atmosphere burns up lots of the meteors that intersect Earth. The ones that make it through the burning friction of entering our atmostphere are called meteroites, and they show up every once in a while. Check your local planetarium.
posted by carsonb at 7:00 PM on June 27, 2011

There are several seasonal meteor showers - check out this calendar.
posted by jb at 7:00 PM on June 27, 2011

Also, I just learned that the first iron ever worked on earth was meteorite iron, because it is purer and thus doesn't need to be smelted and worked like earth iron ore.
posted by jb at 7:02 PM on June 27, 2011 [1 favorite]

This also is happening on a geologic time scale, the really huge impacts on the moon(s) don't occur every day.
posted by sammyo at 7:03 PM on June 27, 2011 [1 favorite]

All the other planets in the solar system help us out big time (or so my documentary watching has led me to believe). The other planets with a greater mass then us pulls them in their direction.
posted by Sweetmag at 7:03 PM on June 27, 2011

from the man himself

posted by One Thousand and One at 7:21 PM on June 27, 2011

The other half of the answer to this question is that large impacts were much more common a few billion years ago than they are now. You can see craters on the Moon because it has no geologic activity or atmosphere to eradicate them— the big craters are all ancient. There are still rocks out there smacking into things, including the Earth, but at nowhere near the same rate.
posted by hattifattener at 7:58 PM on June 27, 2011 [4 favorites]

In the early history of the solar system, there were a hell of a lot more rocks flying around, and a lot more impacts. As time went on, most of them hit things, and were gone. Most of the craters you see on the moon are very, very old, on the order of 3-4 billion years.

But areas of the moon (and other bodies in the solar system) where new surface has been created since then don't have a lot of impacts because that part of the surface dates from after the main bombardment period.

There are large parts of the surface of Mars which are heavily cratered and large parts which are nearly smooth. The latter are main low areas around the north pole, and during the bombardment period that part of Mars was a big ocean. Rocks which hit there caused splashes rather than craters. Eventually the ocean dried up.

There are parts of the near side of the Moon which are very smooth. The ancients called them "maria" ("oceans") because that's what they thought those areas were. Now we know that they are huge lava fields, and they formed after the bombardment primary bombardment period was over.

There are still rocks flying around, and there are still strikes. But the rate is really greatly reduced now.
posted by Chocolate Pickle at 8:10 PM on June 27, 2011

There definitely are some big impact craters on Earth... For example, I live near one of them. We call it "the Chesapeake Bay" (you may have heard of it). Water doesn't just erode down the top, it also fills up the bottom of the really big craters so that they look more like water features and less omg crater!
posted by anaelith at 8:30 PM on June 27, 2011 [3 favorites]

We had a near miss today
posted by hortense at 9:02 PM on June 27, 2011

The Earth has a nice atmosphere.
posted by bardic at 9:52 PM on June 27, 2011 [1 favorite]

Not if you ask the Discovery Channel meteors, who promotionally illustrate the concept at hand.
posted by bicyclefish at 10:18 PM on June 27, 2011

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