Mars has two moons – the larger one called Phobos and the smaller one named Deimos. Scientists believe that Deimos holds clues regarding Mars’ ancient past which includes a ring around the planet.
The moons were discovered by American astronomer Asaph Hall in August of 1877. They are two of the smallest moons in our solar system with Phobos measuring 14 miles across and Deimos being just 8 miles across. Phobos orbits Mars extremely close at just 3,700 miles away. In fact, it is so close that it orbits the Red Planet three times a day. Deimos, on the other hand, orbits at a distance of 12,470 miles and it takes approximately 30 hours to make a full trip around the planet.
It’s been long believed that both moons were space rocks or asteroids that got caught in Mars’ orbit. However, new research has indicated that it’s not possible because of Deimos’ slightly tilted orbit of just two degrees. In fact, those two degrees have changed some scientists’ thoughts in a big way regarding the Red Planet’s past.
Matija Cuk, who is a research scientist at the SETI Institute as well as the lead author of the study (which can be read here), described the significance of this new analysis in a statement, “The fact that Deimos' orbit is not exactly in plane with Mars' equator was considered unimportant, and nobody cared to try to explain it,” adding, “But once we had a big new idea and we looked at it with new eyes, Deimos' orbital tilt revealed its big secret.”
They first looked at Phobos which is slowly moving towards Mars and will eventually get so close that it will be pulled apart, causing a ring to form around the planet. In fact, the researchers said that after it is pulled apart, it will eventually form into another moon. And what’s even more incredible is that they claimed that this has already happened several times and it explains the reason why Deimos has a slight orbital tilt.
According to a statement released by the SETI Institute, “This cyclic Martian moon theory has one crucial element that makes Deimos’ tilt possible: a newborn moon would move away from the ring and Mars ... in the opposite direction from the inward spiral Phobos is experiencing due to gravitational interactions with Mars.”
The statement went on to read, “An outward-migrating moon just outside the rings can encounter a so-called orbital resonance, in which Deimos' orbital period is three times that of the other moon." "We can tell that only an outward-moving moon could have strongly affected Deimos, which means that Mars must have had a ring pushing the inner moon outward.”
If true, this would be exciting news as there are currently four planets in our solar system that have rings around them – Saturn, Jupiter, Uranus, and Neptune.
The outward-moving moon would have been around 20 times larger than Phobos and would have broken up and came back together on two occasions with the second time creating Phobos. And while Deimos is billions of years old, Phobos is only about 200 million years old.
More research needs to be conducted to know for sure, but the Japanese Aerospace Exploration Agency (JAXA) is planning a mission to Phobos in the year 2024 to hopefully collect samples from the moon Then they will hopefully get a better understanding of the moons as well as Mars’ potentially ringed past.