Hello sOOner!
Just a couple of late points to make on some of your earlier questions.
The sun is not shrinking but is in reality expanding. In a few billions years it will become a red giant and engulf mercury, venus, and earth.
There are a couple of reasons why the moon has a thin layer of dust.
1) Its younger than the earth
2) Well this one is the biggie. The moon has weak gravity and little or no atmoshphere. So when an object comes near the moon it is not going to be pulled into the moon do to the moons weak gravitational pull, nor will it burn up in an atmoshpere, it will just keep flying by. When a comet or asteroid does hit the moon it creates a huge explosion and ejects debris. Now on earth, the debris ejected from the surface floats around the atmosphere for awhile and eventually settles back to the earth. It doesn't leave the earth do to the earth's strong gravitational pull. The problem with the moon is that its gravity is too week to keep the debree from leaving the moon. The debris has an escape velocity cannot be overpowered by the moons weak gravity, so all of the debris flies of into space. I believe the moons gravity is about 1/10th that of earths so if you weigh 200lbs here you would only weigh 20lbs on the moon. That is why the Astronaughts could leap 30-40ft at a time.
NASA has tons of info on the moon and the sun so if you have any questions check out NASA's sites.