Mercury/Pits

Rimless irregular pits that cluster around to form patchy deposits on some crater floors. These may be evidence of a recent volatile emission, such as a sulfur compound.

Clusters of Pits Resolved on Crater Floor Bottoms (Jun 2011)

 * http://www.nasa.gov/home/hqnews/2011/jun/HQ_11-186_MESSENGER_Update.html