Mars’ 9-mile-wide moon Deimos imaged on Feb. 21, 2009 by HiRISE (Credit: NASA/JPL-Caltech/University of Arizona)
(News from SETI)
Scientists from the SETI Institute and Purdue University have found that the only way to produce Deimos’s unusually tilted orbit is for Mars to have had a ring billions of years ago. While some of the more massive planets in our solar system have giant rings and numerous big moons, Mars only has two small, misshapen moons, Phobos and Deimos. Although these moons are small, their peculiar orbits hide important secrets about their past.
This insight from a modest tilt of a humble moon’s orbit has some significant consequences for our understanding of Mars and its moons… It implies that for much of its history, Mars possessed a prominent ring.
For a long time, scientists believed that Mars’s two moons, discovered in 1877, were captured asteroids. However, since their orbits are almost in the same plane as Mars’s equator, that the moons must have formed at the same time as Mars. But the orbit of the smaller, more distant moon Deimos is tilted by two degrees.
“The fact that Deimos’s orbit is not exactly in plane with Mars’s equator was considered unimportant, ...