NASA Picture of the day- Serina Aridi C-ODD

"The Missing Craters of Asteroid Itowaka"
After the Japanese robot probe Hayabusa photographed an asteroid whose surface was entirely free from craters, astronomers have been trying to figure out where the missing craters on Asteroid Itowaka are. These craters are surprisingly and unexpectedly missing. Astronomers have developed various hypotheses to come to possible conclusions. Itowaka is a pile of rubble held together by a small amount of gravity. Itowaka is made of rocks and ice chunks, consequently disabling craters to form easily. The formation of craters is also disrupted by meteors or passing planets that might touch the asteroid and ultimately fill in the crater. Hayabusa not only took pictures, but also returned with samples of soil which can lead to a more accurate hypothesis of the missing creators on Itowaka. Itowaka has proven to be an unusual asteroid because of this, and the Hayabusa mission thus helps to further develop astronomers' information about the solar system. 
Because the missing crater explanation is not fully proven, this consequently brings about the questions of why the craters do not develop on Itowaka, and if it poses any sort of threat or alteration to the atmosphere in the solar system and how this may be harmful to Earth.

http://apod.nasa.gov/apod/astropix.html