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If I understand it correctly, boulders on the Moon are only found near fresh craters, because micrometeorites erode them over time. Asteroids are believed to have formed sometimes even earlier than the Moon, but some images show asteroids covered by boulders. And NASA is planning the ARM mission to go pick up a boulder from an asteroid.

Are boulders more frequent on asteroids than on the Moon, and if so, by what kind of mechanism? For example, it is not primarily micrometeorites, but temperature changes that erodes them on the Moon. Or don't microgravity objects attract as many micrometeorites as the Moon does?

Intact boulders on asteroid 25143 Itokawa: enter image description here

Eroded boulders on the Moon: enter image description here

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The moon does attract more particles. But more importantly, those particles hit the moon with velocities of the order of the Moon's escape velocity, 2.4 km/s. That's a very powerful sandblaster...

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  • $\begingroup$ But is it so much more than on an asteroid? The Moon's mass is only 1.2% of that of Earth. Shouldn't micrometeoroids destroy boulders (and ancient spacecrafts) over millions of years? Earth's orbital speed around the Sun is about 30 km/s. About the same for near Earth asteroids. 2 to 3 km/s seems slow in that context. Asteroids may have less impacts, but I don't think difference in orbital speed is a good explanation. $\endgroup$ – LocalFluff Oct 30 '15 at 22:48

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