© Tokyo Institute of TechnologyMars, Phobos, and Deimos.
International collaboration finds that two small satellites (Phobos and Deimos) orbiting Mars can also be
formed by a giant impact like the origin of our Moon. The research is reported in
Nature Geoscience, July 2016.
An international team of researchers from Royal Observatory of Belgium, Institut de Physique du Globe, Universite de Rennes 1, Kobe University, and Tokyo Institute of Technology (Earth-Life Science Institute: ELSI) investigated the formation process of a disk produced by a potential giant impact on Mars, and satellites' formation process from this disk.
A huge satellite is quickly formed from this disk first, and it enhances the accretion of Phobos and Deimos in the outer region. After their formation, the huge satellite falls into Mars due to the strong tidal interaction with Mars, and eventually disappears. Only two tiny satellites, that is, Phobos and Deimos were left behind.
Researchers also found that about a half of the disk produced by a giant impact originally come from Mars, so that Phobos and Deimos should contain Martian materials. Recently, Japan Aerospace Exploration Agency (JAXA) has just started to plan a sample return mission from Martian satellite(s). Returned samples from Martian satellites are expected to have Martian materials.
Enigmatic origin of Martian satellitesPhobos and Deimos are orbiting on the Martian equatorial plane with very circular orbits. They are very small satellites and their masses are less than 10-7 of Mars mass. Because of their irregular shapes and spectral features, many researchers have thought that they were captured objects by Mars coming from the asteroid belt. However, the capture origin cannot easily explain their current circular and coplaner orbits, because captured satellites should have eccentric and randomly oriented orbits like many captured satellites found around Jovian planets.
On the other hand, Mars has the largest crater in our solar system on its northern hemisphere, which is called Borealis. A huge impact can create this crater and also eject a lot of materials around Mars, which may form a disk around Mars. Although formation of Martian satellites from this disk was proposed, little is known about the detailed process of disk formation and satellites' formation.
Comment: The fact that the author calls noctilucent clouds common and rare in the same paragraph isn't the strangest thing about their article.
Space.com has previously published an article on the actual cause of these clouds which the author ignores, and it's an ominous cause that those of you who read our 'Fire in the Sky' section will be well aware of: