MarkBour wrote:I would assume meteor strikes have the same bias as meteor showers, and I wonder if a similar bias can be found in some way on the Moon, though it might be a bias that you could plot in spacetime, but that would not show up simply in space (as in the distribution of craters on the surface of the Moon). That is, if the Moon is picking up more meteors the same times the Earth is, that effect would get scattered about as the Moon would be "leading" with a different part of its face at different times, when the Earth was "leading" with its northern hemisphere.
Meteor strikes (really, meteorites) on the Earth are unrelated to showers. There is no observed geographical bias in the distribution of meteorites. On the Earth, all meteor strikes are produced by sporadics- bodies not associated with showers. On the Moon, nearly all strikes are probably shower members. However, almost all meteorites on Earth had parent bodies in low inclinations, and there is theoretical support that this leads to a polar bias for those with higher initial velocities.
There is definitely a bias with both showers and sporadics favoring the leading orbital edge of the Earth or the Moon. But since that edge rotates- once every 24 hours for the Earth, once every 29 days for the Moon, there is no overall geographic bias on either body created by this effect.
Meanwhile, for the Moon, I imagine it would have its own (stronger?) bias of motion. It would seem that it would probably have the highest number of collisions when it is outside of the Earth's orbit, coming around us, as it would be travelling fastest then.
The difference in velocity with lunar phase is insignificant. For all practical purposes, the Moon is in a circular orbit around the Sun at the same velocity as the Earth. That is, each travels around the Sun at 30 km/s, with the Moon's orbit around Earth changing its own solar orbital speed by ±1 km/s.
I know that Earth is approaching perihelion when the southern hemisphere is leading along the path, and approaching aphelion when the northern hemisphere is leading, if I have that correct, but I don't see how that could account for the bias. I'm guessing that most comets orbit the Sun in the same direction as the Earth does, and most of them are going to experience most damage at closest approach, and leave a lot more debris on the way out, but that still doesn't "ring a bell" for me as to why the northern hemisphere would be collecting more dust than the southern.
New and long period comets have a uniform distribution of inclinations- that is, as many are in retrograde orbits as prograde. This is part of the strong evidence for a spherical Oort Cloud. Short period comets, however, have a strong prograde bias (80%), and a bias towards lower (more ecliptic) inclinations. This may be explained by a more toroidal structure of the inner Oort Cloud.