by Chris Peterson » Fri Feb 12, 2010 8:26 pm
mark swain wrote:Is it possible that the Earth protected the Face of the Moon from the meteor bombardment long ago. Are there more Craters on the dark side of the Moon?
Most of the cratering on the Moon occurred during the
Late Heavy Bombardment about 4 billion years ago. That was before the Moon became tidally locked, so it wasn't keeping any one face directed towards the Earth. Since it became tidally locked, its distance has been such that the Earth was never larger in its sky than a couple of degrees. You could imagine that the part of the Moon directly under this small "shield" might get slightly less meteoroid activity, but the Earth also acts as a gravitational lens, focusing bodies slightly towards the Moon. So any effect by the Earth, either enhancing or reducing lunar impacts, is probably too small to detect.
Cratering is similar on the near and far sides of the Moon. The total number of craters is higher on the far side, but that's because that side was never flooded by the basalt plains we see. The cratering rate is about the same. Actually, the cratering rate is slightly higher in the western hemisphere, since that is the leading edge in the Moon's orbit around the Earth, and it therefore accumulates slightly more debris. The difference is subtle, however.
[quote="mark swain"]Is it possible that the Earth protected the Face of the Moon from the meteor bombardment long ago. Are there more Craters on the dark side of the Moon?[/quote]
Most of the cratering on the Moon occurred during the [url=http://en.wikipedia.org/wiki/Late_Heavy_Bombardment]Late Heavy Bombardment[/url] about 4 billion years ago. That was before the Moon became tidally locked, so it wasn't keeping any one face directed towards the Earth. Since it became tidally locked, its distance has been such that the Earth was never larger in its sky than a couple of degrees. You could imagine that the part of the Moon directly under this small "shield" might get slightly less meteoroid activity, but the Earth also acts as a gravitational lens, focusing bodies slightly towards the Moon. So any effect by the Earth, either enhancing or reducing lunar impacts, is probably too small to detect.
Cratering is similar on the near and far sides of the Moon. The total number of craters is higher on the far side, but that's because that side was never flooded by the basalt plains we see. The cratering rate is about the same. Actually, the cratering rate is slightly higher in the western hemisphere, since that is the leading edge in the Moon's orbit around the Earth, and it therefore accumulates slightly more debris. The difference is subtle, however.