The Martian moons, Phobos and Deimos, may have been the result
of a giant impact that sent rocks and debris into orbit around
Mars, instead of asteroids that were captured by the planet’s
gravity as previously thought. After going into orbit, the
material from the giant impact aggregated and formed into small,
low-mass moons. This collision could also account for why Mars
spins on its axis. This theory is presented in an article by
Smithsonian scientist Robert Craddock at the Center for Earth
and Planetary Studies to be published in the Icarus
International Journal of Solar System Studies. Image right: A
double, oblique impact crater on the surface of Mars. Although
the origin of such elliptical impact craters on Mars is
uncertain, some scientists have determined that the nature of
these particular features is best explained by the impact of a
former Mars-orbiting moonlet. Potentially many such moonlets
were in orbit around Mars at one time, and Phobos and Deimos are
the only two surviving objects. In recent