Why Are Craters on Saturn's Moons Vanishing?

[BoFox]

http://news.discovery.com/space/why-are-...151007.htm



The above pic is on Saturn's largest moon (Titan), bigger than Mercury and nearly as big as Mars. 

Even Mimas's massive crater is being rapidly "erased" (scroll the pictures with captions for more info).

Sexy image:


3-D rendered art


If "billion(s)-year-old" craters are vanishing within a matter of years, wouldn't the occurrence of cratering impacts have to be at least million times higher for there to still be craters, at that rate?

[SteelCrysis]

The craters in the first photo are not the same, the ridge lines near them are at different distances from the craters.

[BoFox]

Ahh, thanks for the correction. Well, it's still an enigma to the scientists as to Mimas, Tethys, and Dione:
http://www.sciencedirect.com/science/art...3511001734

BTW, the crater on Mimas (like the Death Star in Star Wars) seems far too large for the tiny moon to have remained intact if it were a head-on collision. Strange stuff.