Mars had a bigger moon that formed a ring around the Red Planet billions of years ago, suggests new evidence
The study supports a 2017 theory: generations of Martian moons were destroyed into rings which would then give rise to a new, smaller moon to repeat the cycle all over again
Mars may have something odd going on with its moons. In the past, the Red Planet may have sported a ring around it, which many years later, disappeared to create the moons. Scientists predict that this piece of history will repeat itself in the future. A study adds weights to a 2017 theory proposed by the co-authors of this study: David Minton, a professor at Purdue University and Andrew Hesselbrock who was his graduate student at the time of the research.
They speculated that generations of Martian moons were destroyed into rings over the last billion years. Each time, the ring would then give rise to a new, smaller moon to repeat the cycle over again. Phobos, the inner moon, could be next as the team predicts that Mars' gravity will tear it apart to make a ring around the planet.
Currently, Mars has two moons: Phobos and Deimos. However, the latter circles around the planet differently, piquing the interest of the team. "The fact that Deimos' orbit is not exactly in-plane with Mars' equator was considered unimportant, and nobody cared to try to explain it," lead author Matija Ćuk, a research scientist at the SETI Institute, says 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 Japanese space agency JAXA will put this theory to test in 2024. The agency will send a spacecraft to Phobos to collect samples from the moon’s surface and bring them back to Earth. Ćuk is hopeful that this will give us firm answers about the murky past of the Martian moons: "I do theoretical calculations for a living, and they are good, but getting them tested against the real world now and then is even better."
What does the study say about the moons?
Deimos is a little distant and circles around Mars with a 2-degree tilt. Phobos, on the other hand, is a lot closer to the planet. For a long time, scientists believed that Mars' two moons, discovered in 1877, were captured asteroids. Realizing that their orbits are almost in the same plane as Red planet's equator, experts concluded that these bodies were indeed moons.
Deimos's tilt intrigued the team, leading them to speculate that a cycle of the moon breaking apart to form a ring, and then reforming into the Moon could be behind it. In other words, the ring around Mars may have resulted in the Moon's lopsided orbit. Under these conditions, a newly-formed moon would keep its distance from the ring and the planet, Ćuk and his colleagues explain.
This insight from a modest tilt of a humble moon’s orbit has some significant consequences for our understanding of Mars and its moon, says the team. The study implies that Mars possessed a prominent ring for much of its history, they add. The team presented their findings at the 236th Meeting of the American Astronomical Society, held virtually on June 1-3, 2020. It is accepted for publication in the Astrophysical Journal Letters.