Are striations on Phobos evidence for tidal stress?

Abstract

VIKING orbiter photographs of Phobos, the inner satellite of Mars, reveal a curious series of striations or grooves over much of the surface¹. These features cross over large eroded craters but are in turn interrupted by very small well defined craters, which indicate an origin substantially later than the time of formation of the satellite itself when the large scale cratering presumably occurred. The grooves have no obvious connection with the ‘crater chains’ also seen in Phobos, and their nearly parallel spacing seems to rule out an origin due to primary or secondary impacts. We suggest that some of these features are related to readjustment of the satellite's figure with increasing tidal stress as the orbit evolves inwards under the action of tidal friction.