MOSCOW, May 11 — RIA Novosti. Data from the European probe "Mars Express" show that in the depths of one of the moons of Mars, Phobos is a giant cave, occupying about one-third of its volume, causing reject the theory that the satellite — an asteroid captured by Mars, the scientists write in an article published in the journal Geophysical Research Letters.
The research team, led by Thomas Anderta (Thomas Andert) from the German Air Force University studied the Doppler distortion of radio signals from the machine "Mars Express" during his encounters with Phobos. These distortions can accurately detect changes in speed of the probe and, therefore, to measure the gravitational influence of the moons of Mars. The data analysis has helped to get more accurate values of the mass and density, as well as to draw conclusions about the internal structure of Phobos.
"The new values of the gravitational parameter … and the density of Phobos (1876 plus or minus 20 kilograms per cubic meter) provide new data on the porosity of the celestial body (30% plus or minus 5%), and the basis for a new understanding of its internal structure. We concluded that the subsoil of Phobos is likely to contain large voids "- the scientists write.
Around the turn of Mars two moons: Phobos and Deimos (from the Greek words "fear" and "horror"). Size larger satellite, Phobos is about 20 kilometers. In the 1950s and 60s features of the motion of Phobos led astronomers to assume that within the satellite may be void. The idea was immediately picked up by science fiction writers who have made the conclusion that this celestial body was created alien civilization.
However, the beginning of interplanetary expeditions and images taken by the spacecraft, "killed" this hypothesis — Phobos was a giant "cobblestone" irregular shape, covered with craters. Now, however, new, more accurate measurements of forced scientists to return to the idea of a hollow Phobos.
These "Mars-Express", the scientists say, could also force to review the current ideas on the origin of the satellite. It was believed that Phobos — an asteroid captured by Mars. In favor of this hypothesis showed spectral characteristics of the surface, which were similar to certain types of asteroids.
New data on the porosity of the satellite forced to reject this hypothesis, because such an internal structure can only be the result of destruction and a new "assembly" of the resulting debris.
However, the assumption is that Phobos formed from rocks, "airborne," from the surface of Mars after hitting a giant cosmic body also "fails" due to the fact that the composition of Phobos is not like the composition of Martian matter.
Andert and his colleagues conclude that Phobos formed from the cluster of fragments that have arisen after the collision of ancient Martian moon of an asteroid.
"This scenario explains how high the emptiness of Phobos, and the spectral characteristics of the surface," — the authors conclude the article.