The Moon Feature crossword solutions are MARE (4 letters), CRATER (6 letters), RILL (4 letters), and RILLE (5 letters). A MARE is a large, dark area on the surface of the moon, which is caused by ancient lava flows. A CRATER is a bowl-shaped depression on the surface of the moon, created by an asteroid or comet impact. A RILL is a small, shallow channel on the surface of the moon, created by erosion. A rille is a long, narrow channel on the surface of the moon, also created by erosion.