The small, misshapen moons of Mars, Phobos, and Deimos have long puzzled and fascinated planetary scientists, though Phobos has caught the most attention. Scientists assume that in a few tens of million of years, the moon is expected to be pulled apart by Mars’ gravity, and when that happens, a ring will develop around the Red Planet.
Phobos, one of the moons of Mars, is getting closer to the planet. According to the model, after reaching the Roche limit, Phobos will break apart and become a set of rings in approximately 70 million years. Depending on where the Roche limit is, Minton and Hesselbrock assume that this cycle could have been replicated between three and seven times over billions of years.
Every time the moon broke apart and emerged from the resulting ring, its successor moon would be five times smaller than the previous, according to the model, and the debris would have rained down on the earth, probably explaining the mysterious sedimentary deposits found near the Mars’s equator.
“You could have had kilometer-thick piles of moon sediment raining down on Mars in the early parts of the planet’s history, and there are enigmatic sedimentary deposits on Mars with no explanation as to how they got there,” Minton said. “And now it’s possible to study that material.”
As children, we have learned about the planets in our solar system through certain characteristics — Jupiter is the largest, Saturn has rings, Mercury is the closest to the sun. Mars is red, but it’s probable that one of our closest neighbors had rings at one point, too, and might have rings again someday.
A new research study discussed at the 236th meeting of the American Astronomical Society (AAS) held on June 1-3 and accepted for publication in the Astrophysical Journal Letter is a step forward. The team believes that Mars had rings in the past, and this happened several times during the cycle of formation and destruction between rings and the moons.
Evidence reveals that this doesn’t come from Phobos but from the smaller and more distant Deimos. Unlike Phobos, the orbit of Deimos is tilted by 2 degrees with respect to the plane of Mars’ equator. Researchers at the SETI Institute and Purdue University have attempted to model this and have reached the conclusion that the influence of something around Mars must have caused a shift, although with some caveats. The properties of Deimos would make much more sense if a much larger moon than Phobos was being pushed outward.
Other theories suggest that the impact with Mars that created the North Polar Basin led to the creation of Phobos 4.3 billion years ago, but Minton said it was unlikely that the moon would have lasted all that time. Additionally, Phobos would have had to form far from Mars and would have had to cross through the resonance of Deimos, the outer two moons of Mars.
Resonance happens when two moons exert gravitational influence on each other on a periodic basis, as do the major moons of Jupiter. By going through its resonance, Phobos would have altered the orbit of Deimos. But Deimos ‘orbit is within one degree of Mars’ equator, suggesting that Phobos had no impact on Deimos.
“Not much has happened to Deimos’ orbit since it formed,” Minton said. “Phobos passing through these resonances would have changed that.”
“This research highlights even more ways that major impacts can affect a planetary body,” said Richard Zurek of NASA’s Jet Propulsion Laboratory, Pasadena, California. It is a project scientist for NASA’s Mars Reconnaissance Orbiter, whose gravity mapping supported the hypothesis that the northern lowlands had a significant impact.
This resulted in a suggestion for a ring system. The ring could force an object 20 times the mass of Phobos outward, forcing Deimos into its current trajectory. But where did the moon go? It’s possible that the material in the ring fell on Mars, as did the moon, ultimately being ripped apart and creating a new ring system. Experts suggest that it took two more ring-moon cycles to reach the current Phobos, and this may have happened just 200 million years ago.
“The fact that Deimos’s orbit is not exactly in-plane with Mars’s equator was considered unimportant, and nobody cared to try to explain it,” lead author Matija Ćuk, 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’s orbital tilt revealed its big secret.”