Unusual channels on the surface of Phobos were "carved" by giant boulders ejected from its surface after the fall of a large asteroid. This is the conclusion reached by planetary scientists who published an article in the journal Planetary and Space Science.
“We have been debating how these furrows originated in Phobos for nearly 40 years. We assume that we managed to find the first rational explanation for their existence and the appearance of those anomalous features of this moon of Mars, which are associated with these stripes, - said Ken Ramsley from Brown University in Providence (USA).
The Death Star
Today, two small irregular satellites revolve around Mars - Phobos and Deimos. Their diameter is only 22 and 12 kilometers, and the distance between them and the surface of the red planet does not exceed 10 and 23 thousand kilometers. Many scientists suggest that both of these moons are not planets, but asteroids captured by the gravity of Mars in the distant past.
Interestingly, Phobos is approaching Mars and will be destroyed and turned into a giant dust ring in 20-40 million years, while Deimos, on the contrary, is moving away from it and in the distant future it will "escape" from the red planet.
Scientists now have difficulty explaining why this is happening, and how Deimos and Phobos could have ended up in their current orbits. Recently, astronomers have suggested that in the past, Mars may have had three moons, one of which has already fallen to its surface and showered two other objects with a large number of fragments.
Ramsley and his colleague James Head, one of the most famous planetary scientists of the Earth, have been trying for many decades to understand how one of its most mysterious features appeared on the surface of Phobos - a set of several giant parallel lines - "channels" that almost completely encircle this moon of the red planet.
Promotional video:
Unlike Mars or Earth, Phobos never had an atmosphere or liquid water, and therefore such structures could not arise on its surface as a result of the movement of rivers or due to other forms of erosion. These "trenches" were opened on the surface of Phobos back in the 1970s by probes of the "Mariner" and "Viking" series, and since then scientists have been arguing about what they are.
More than 40 years ago, Head suggested that these lines could have been "drawn" on the surface of the moon of Mars by asteroid debris or rock fragments "catapulted" from the surface of Phobos during the formation of Stickney Crater. It is the largest structure of its kind on its surface and makes Phobos look like the "Death Star" from Star Wars.
Cosmos creators
This idea has not convinced all planetary scientists, since the "channels" adjacent to the crater diverge from it not radially, as is usually the case with traces of asteroid "road accidents", but parallel to each other. In addition, some of them are superimposed on each other or even pass through the Stickney itself, while others break off in an incomprehensible way. Therefore, they believed that these notches were left on Phobos by fragments of Mars.
Head and Ramsley found an explanation for all these oddities by creating a computer model of Phobos colliding with a large asteroid. Changing the size, mass, density and angle of incidence of the asteroid, scientists tried to understand whether such oddities could appear or they are excluded.
As it turned out, "channels" on Phobos could appear if its collision with an asteroid occurred in a slightly higher orbit, in which it is now, at an altitude of about 12 thousand kilometers from the surface of Mars.
In this case, the gravitational interactions between the red planet and its moon will cause some of the boulders to draw parallel lines and then "fly away" into space after they have reached the largest mountain range on Phobos. Other stones, respectively, had to fly around the entire moon and dig similar channels inside Stickney crater.
If these calculations are correct, then the mysterious stripes on Phobos appeared relatively recently, about 150 million years ago, when this moon of Mars was in a higher orbit. Calculating the exact age of Stickney crater, Head concludes, will help test his theory and see if it really is.
