A team of scientists from the SETI Institute and Purdue University (USA) have discovered that the only way to produce the unusually inclined orbit that one of the Martian moons, Deimos , presents is that Mars had a ring thousands ago of millions of years. While some of the most massive planets in our solar system have giant rings (Jupiter, Saturn …) and numerous large moons, Mars only has two small, warped moons, Phobos and Deimos. Although these moons are small, their rather peculiar orbits hide important secrets about their past.
For a long time, scientists believed that the two moons of Mars, discovered in 1877, were asteroids captured by the planet’s orbit. However, since their orbits are almost in the same plane as the equator of Mars, the moons must have formed at the same time as the red planet. But the orbit of the smallest and most distant moon, Deimos (which orbits the planet every 30 hours), is tilted about two degrees.
“The fact that Deimos’ orbit is not exactly in plane with the equator of Mars was not considered important,” said Matija Ćuk, leader of the work. “But once we had a different idea and looked at it with new eyes, Deimos’ orbital tilt revealed a great secret.”
Making a Martian Ring
Previous theories suggested that the moons of Mars formed from debris ejected when a giant impactor struck Mars between 100 and 800 million years after the planet was created. However, this recent twist in theory suggests that after the original collision and over the course of billions of years, generations of Martian moons have recycled into rings , which, in turn, were molded into newer moons. little. Thus, like a phoenix rising from its ashes, scientists believe that one of the current moons of Mars may have been born from a ring of dust left by earlier versions of itself.
And the only way to explain Deimos’s strange orbital tilt would be that the ring was pushing it away, moving into its outer orbit.
The oldest moon would have been about 20 times larger than Phobos and existed about 3 billion years ago. This ancient moon was eventually torn apart by the gravity of Mars, and two more ring-moon cycles followed.
Cyclical Moon Theory
Researchers already knew that Mars could develop a ring in the far future, as its fragile moon Phobos will be dragged towards the planet for millions of years and ripped apart by its tidal forces to form a ring of rocky particles that will surround it. This event will take place in approximately 70 million years. Experts suggest that it could be possible that it is a huge cycle in which the rocky matter that makes up the moon separates and rejoins, with Mars oscillating between having rings and moons or not having them. Because of what would have happened several times in the past, fitting the Deimos story.
This research remains theoretical, but we may have experimental evidence available within a few years if the Japanese Space Agency sends its spacecraft as planned, to Phobos in 2024. Phobos samples could reveal much more about the origin of the moons and the history of Mars. If it is not more than a couple hundred million years old, it would be enough to validate this prediction.
Reference: The study has been presented at the 236th meeting of the American Astronomical Society and accepted for publication in The Astrophysical Journal Letters. The study is available on arXiv. https://arxiv.org/abs/2006.00645
