How long would a footprint last on the moon?

[corky]

Now we all know the moon isn't made of spare ribs...

These photos have been going around the internets today.  And they are super-duper awesome cool.  You can actually see the tracks of astronauts walking (and driving!) on the moon.  Hooray science!

Anyway, the question I want to consider (when I have time) is this:  How long will the astronauts footprints last?

My first thought would be to find the rate of meteoroid impact as a function of crater size.  From that I could find the expected amount of time until the footprints are covered.

Maybe posting this up here will motivate me to work on the problem before someone else figures it out...

[corky]

Took long enough, but here's my stab at it.