Phobos grooves formation from Stickney impact ejecta: a simulation
Résumé
Although grooves are common on asteroids, on
Phobos the grooves have been the subject of many
various formation hypotheses for two reasons: the
fact that Phobos is orbiting around Mars close to
the Roche limit that implies an unusual gravity
environment, and also the fact that the huge crater
impact, Stickney, seems to be related at least to a
family of grooves radial to this crater. However,
some authors claim that these grooves could have
been formed not from the Stickney impact, but
from martian crater ejecta hitting Phobos.
The present study explores the first idea by
computing the trajectory of a test mass gliding on
the surface of Phobos for any initial position and
velocity. An ellipsoidal model of Phobos is used
for both the gravity and surface geometry.
Depending on these initial conditions a gliding
mass stay gliding or can take off after some
distance. Generally the trajectories are not ‘down
hill’ as the motion is strongly dependent on the
velocity. Then the main objections to the
hypothesis that gliding or rolling blocks could
have dug these grooves fail.
As the Stickney impact occurred at larger
distances from Mars, the study is extended to the
ancient Phobos in its drift towards Mars and then
the various hypotheses for the grooves formation
are discussed.