A cycle of moon formation could explain the slightly tilted orbit of Mars’ moon Deimos.
Mars has two moons circling the planet, called Phobos and Deimos. For many years, scientists supposed that both of these moons were captured asteroids, or space rocks. But new research shows the orbit of Deimos would not make that possible.
Deimos is very slightly tilted to the Martian equator, by only two degrees. Initially, the difference was so small that many scientists overlooked the matter.
“The fact that Deimos’ orbit is not exactly in plane with Mars’ equator was considered unimportant, and nobody cared to try to explain it,” study lead author Matija Cuk, a research scientist at the SETI Institute, said in a statement. “But once we had a big new idea and we looked at it with new eyes, Deimos’ orbital tilt revealed its big secret.”
The secret came from looking at the motions of Phobos, which orbits closer to the Martian surface and is slowly spiralling into the planet. Eventually, Phobos will drop so close to Mars that the gravity of the much larger planet will pull the moon into pieces — forming a ring.
Study co-authors David Minton, a professor at Purdue University, and Andrew Hesselbrock, who was his graduate student at the time of the research, suggest that Phobos’ future is not a one-off event. Instead, after the moon is pulled apart, eventually the pieces will reform into another moon. This not only will happen to Phobos, but has happened already other times in the Martian past.
This breaking up and reforming of moons would in turn explain how Deimos’ orbital tilt happened.