Some of the features of the orbits and the unusual location of Deimos and Phobos can be explained by the fact that they are fragments of a larger satellite of Mars. It could have collapsed about 3 billion years ago. These are the conclusions reached by Swiss paleontologists, whose article was published by the scientific journal Nature Astronomy.
"Traditionally, it is believed that Phobos and Deimos are asteroids that were captured by the planet's gravity. But this theory is contradicted by the fact that both satellites are in a perfectly circular equatorial orbit, and their rotation is not synchronized. These anomalies can be explained by the fact that Phobos and Deimos were part of the same object, which in the past was in the orbit of Mars, "the researchers write.
The diameters of Phobos and Deimos are 11 and 6 km, that is, in size and mass, they are comparable to large asteroids. Astronomers predict that Mars may lose both in the relatively near future.
In particular, Phobos in the next 20-40 million years can collapse under the influence of the attraction of the Red Planet. As a result, a gas-dust ring will form in the orbit of Mars, and a new satellite will appear in place of Phobos.
Deimos is constantly moving away from Mars. American scientists recently suggested that similar processes with both satellites could already occur in the past. This is indicated by some features of the angle of inclination of the orbits of the satellites of Mars.
A group of Swiss planetary scientists led by Domenico Giardini, professor at the Higher Polytechnic School in Zurich (Switzerland), found that these and many other unusual features of Deimos and Phobos can be explained by the fact that in the past they were part of the larger moon of Mars, studying another unusual anomaly in the behavior of the moons of Mars.
The fact is that Deimos and Phobos are on opposite sides of the so-called radius of the synchronous orbit. This is how astronomers call an imaginary line in the vicinity of Mars and other planets of the solar system, inside which a hypothetical satellite will orbit at the same speed with which the planet rotates around its axis, and behind it - lag behind.
In an effort to understand how Deimos ended up outside the radius of Mars' synchronous orbit, scientists have modeled how Mars has interacted with its satellites over the past several billion years.
The model showed that about 2.5-3 billion years ago, the position of the orbits of Deimos and Phobos almost perfectly coincided with each other. Then, due to gravitational interactions with Mars, Deimos moved away from Mars and crossed the radius of the synchronous orbit, and Phobos - as close as possible to the planet.
The similar nature of the movements of the satellites of Mars, as well as the elongated nature of their original orbits, according to scientists, suggests that Phobos and Deimos were fragments of a larger celestial body. It fell apart no later than 3 billion years ago. The different angle of inclination of the orbits of Phobos and Deimos shows that the reason for this was the collision of this object with some other.
In the coming years, it will be possible to test this theory: the Japanese MMX probe will go to study the satellites of Mars. With the help of his instruments, planetary scientists hope to enlighten the bowels of Phobos and Deimos and find traces of this ancient cataclysm there.