Mars has two moons: Phobos and Deimos. Both are very different from our own Moon, which is large and mostly spherical. Martian moons have irregular shapes, almost as if they were terrestrial potatoes. Now a team of researchers has come up with an intriguing conclusion: the two moons were once a single moon.
The scientists used geophysical data and models on the Moon’s orbital motion to turn back the cosmic clock. And it turns out that billions of years ago (between 1,000 and 2,700 million years), Phobos and Deimos were in exactly the same place around Mars. Which suggests that they were once a single, much larger object.
A single moon orbiting the Red Planet?
The unusual profile of the moons of Mars led researchers to suspect that they looked more like asteroids than natural moons and therefore could actually be asteroids captured by the planet’s gravitational field.
The Martian moons are, therefore, two fragments of what was once a larger satellite that was destroyed by a large collision, possibly an asteroid, according to experts in their study published in the journal Nature Astronomy . This violent explosion with the wandering rock would have fragmented the enormous moon and two of its fragments would have been trapped in the orbit of Mars; those two fragments are Phobos and Deimos.
“The idea was to track the orbits and their changes in the past,” explains Amir Khan from the University of Zurich and the ETH Zurich Institute of Geophysics.
However, the orbits of the Martian moons are almost circular and move in the equatorial plane of Mars. So what is the explanation for the current orbits of Phobos and Deimos? To solve this problem, they relied on computer simulations. This led to the conclusion that “Phobos and Deimos are the remains of a lost moon.”
The key to this work has been the data collected by NASA’s InSight seismometer, whose instruments measure marsquakes and any vibrations that the red planet experiences. They combined these data with measurements taken by other Mars probes, which allowed them to model a phenomenon known as tidal forces , which states that each celestial body exerts some force on its neighbors.
It was these data that provided the key to allowing researchers to reconstruct the history of the moons and discover their violent origin .
Of course, the moons do not seem to have much future, at least, Phobos . Scientists hope that within less than 40 million years, Phobos will disappear, as it is slowly but surely approaching Mars, which could lead to an eventual collision with the planet . Here we could contemplate a scenario in which the moon would provide the planet with its own ring system, as Jupiter, Saturn, Uranus and Neptune have.
The names of the Martian moons
The moons of the red planet were discovered in 1877 by the American astronomer Asaph Hall. They owe their names to the Greek twin gods Phobos (panic) and Deimos (terror), sons of Ares, Mars in Roman mythology. Phobos is 22 kilometers wide and Deimos a little more than half.
Referencia: Amirhossein Bagheri et al. Dynamical evidence for Phobos and Deimos as remnants of a disrupted common progenitor, Nature Astronomy (2021). DOI: 10.1038/s41550-021-01306-2
