The moons of Saturn are generally tide locked. Iapetus is dark on one side and bright on the other side. In it's orbit around Saturn, the leading hemisphere is one color, and the trailing hemisphere is another color. And, these moons of Saturn have more craters on their leading hemisphere than their trailing hemisphere.
The Earth's Moon is also tide-locked. We see the near side. One would expect that the leading hemisphere would have more craters than the trailing hemisphere as it plows into stuff. But when i look at the Moon, one half doesn't seem to be more cratered than the other side. I mean, if one side is more cratered, it's not obvious. Why not?
And, if I'm in the Northern hemisphere on Earth, which side is the leading hemisphere of the Moon - the left or the right?
2009-01-04T19:03:25Z
The leading hemispheres of the moons of Saturn are more heavily cratered than the trailing hemispheres. Why not the Earth's Moon?
2009-01-04T19:37:57Z
The Moon is only recently tidally locked? Where'd you hear that? And that would beg the question of why the lunar far side looks so different.
2009-01-04T20:20:51Z
Brant is getting warm here, falling just short of an explanation.
DLM2009-01-04T20:54:43Z
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I suspect this might be a bit of a stretch, but does the difference in the earth-moon orbital period around the sun vs. the Saturn-Iapetus orbital period around the sun potentially play any role in this?
One of the respondents almost got the lunar orientation correct. If the moon is due south of you (and you are in the northern hemisphere) the left (west) side is the leading hemisphere. When the moon is rising, however, the leading hemisphere can be nearly straight down, and when it is setting the leading hemisphere can be nearly straight up.
Sometime look at the moon when it's rising, and note the darker markings on it. then, six hours later look again. The markings are in the same place, but appear to have rotated, because the orbit of the moon and the surface of Earth is curved.
As for the cratering, statistically you are correct in thinking that there should be more craters on the leading hemisphere (the moon would tend to run into some meteoroids that otherwise would miss the moon). However, there is something else at play.
The moon is only recently tidally locked with Earth. In the past the rotational time of the moon was faster than it's period of revolution. Tidal influences eventually slowed its rotation and locked the two together, but that occurred after the majority of impact craters were formed. Hence, the even distribution (except for the Maria) of the craters we see today.
Also, the formation of the Maria have overrun many craters which must have existed before the formation of the Maria. Maria material itself is denser than the lighter colored highlands, and that's likely the reason most of the maria are pointed toward Earth.
I would bet that more meteoroids are impacting the western hemisphere of the moon now, at least statistically. Relative to long ago (billions of years), however, fewer meteoroids are around to hit the moon.
The leading side of the moon IS more cratered. That would be the far side for us because it is the leading side when it's ahead of the earth. When you compare images of the near and far sides of the moon, you can see a definite difference in the cratering.
The near side is the leading side when it is trailing the earth and bets less exposure to impacts because the earth attracts much of the debris that would hit the moon.
Now what I would be interested in is how the moon looks when photographed at the two in between positions, (which would be new moon and full moon positions. Those sides should be more heavily cratered than the side facing directly toward us and less cratered than the side facing away. Of course, these views are the combination of the left and right halves of the other two views. In other words, if the theory is correct, the leading side at new and full moon should be just about as cratered as the far side. We should be able to see an increase in the number of craters as we look westward or eastward from the center.
Edit: I've looked at several images of the moon and to tell the truth, it doesn't look like it is more heavily cratered as you look east and west from the center. SO, maybe the apparent difference in cratering between the near side and the far side is due to some other reason. I don't know.
The vast majority of the craters on the Moon were formed well over 3 billion years ago, very early in the Moon's history. I would hypothesize that this was before the Moon's rotation became tidally locked to the Earth, though I have no proof of this. This would result in the craters being randomly distributed. Astronomers seem to have a lot harder time accounting for the dark stuff on Iapetus, and seem to think it's because Saturn, with its rings, has a lot more "stuff" in orbit around it than other planets. In the pictures of Iapetus, this dark "stuff" seems like a coat of paint over the cratered surface, rather than consisting of craters itself.
If you're standing facing south and looking up at the moon, the left side (toward the east) is the leading side. It's true that the moon is tidally locked to the Earth so that it always keeps the same face toward Earth. I don't think this would make a difference in regard to the leading face having more craters since the tangential velocity of the moon in its orbit around the Earth is smaller that the velocity of incoming (or outgoing) asteroids and comets.