The age of Phobos and its largest crater, Stickney

We derived crater production functions and chronology functions of Phobos for two scenarios, which likely represent the end-members of its dynamical evolution. Case A assumes that Phobos has been in its current orbit about Mars since its formation. Case B assumes a recent capture of Phobos and the impact history of an average Main Belt Asteroid. We determined the age of an average surface to the west of the Stickney crater and of the interior of the Stickney crater. The results indicate (i) the formation or major collision of Phobos about 4.3 Ga (Case A) or 3.5 Ga (Case B) ago, (ii) the Stickney crater is about 4.2 Ga (Case A) or 2.6 Ga (Case B) old and (iii) grooves probably formed between 3.1 and 3.8 Ga (Case A) or 44 and 340 Ma (Case B). Thus, Stickney seems to be older than the investigated grooves on Phobos.