The re-processed data from the Mars Global Surveyor provided new arguments to support the hypothesis that Phobos was once part of the Red Planet.
Mars has two large moons - Phobos and Deimos. Their origin is unclear: much darker than Mars itself, both bodies in the visible and near-infrared regions are most similar to dark carbon class C asteroids. Therefore, there is a version that Phobos and Deimos are asteroids captured by the gravity of the Red Planet. This scenario, however, does not correspond to the outlines and orbits of the satellites; rather, they indicate that both bodies were once part of Mars and were separated by a collision with a large object. The Martian origin of the satellites was confirmed this year by mathematical modeling.
Re-processed data from the interplanetary station Mars Global Surveyor (1997-2006) provided new arguments to support the theory that the satellites of Mars Phobos and Deimos were once part of Mars. The study is published in the Journal of Geophysical Research: Planets.
The authors of the new study drew attention to the spectrum of Phobos in the rarely considered near-infrared region of the spectrum (in which the human body and objects similar in temperature radiate heat). No new measurements were required: the spectrometer of the Mars Global Surveyor collected data in 1998 while flying between Phobos and Mars before entering low Martian orbit.
The satellite's near-infrared spectrum was compared with the spectrum of a meteorite that fell to Earth near Lake Tagish in Canada, the remnant of a class D asteroid that burned up in the atmosphere and other minerals rich in carbon. To do this, the meteorite and other samples were placed in a vacuum chamber and created conditions that simulate a sharp transition from day to night on Phobos.
It turned out that in the near-infrared range, the Phobos spectrum was not at all similar to the spectrum of a carbonaceous meteorite, but it practically coincided with the spectrum of basalt, a volcanic rock that mainly consists of the crust of Mars. The authors of the study do not claim that all of Phobos is composed of Martian matter, but spectral data indicate that at least some part of the satellite is Martian basalt. It is possible that the satellite also includes the substance of the body, the collision with which gave rise to Phobos.
It is too early to draw final conclusions: critics of the new work note that Phobos, devoid of atmosphere, is subject to strong erosion, which, among other things, forms its spectrum, and the effect of cosmic radiation and solar wind is difficult to recreate in a laboratory. In addition, the Lake Tagish meteorite is not the most typical sample of the D-class asteroid, and it is not entirely correct to compare its radiation and the radiation of Phobos. The opportunity to refine the results will appear when the OSIRIS-Rex and Hayabusa-2 spacecraft deliver samples of the material of the asteroids Bennu and Ryugu to Earth in 2023 and 2020, respectively.
Ksenia Malysheva
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