The Martian lunar month Phobos and Deimos are tiny compared to our own or the peachy satellites of the outer Solar System . Nevertheless , with Venus and Mercury having no moons at all , astronomers have long mull their origins . Now two astrophysicists are confident the answer lies in the collision between Mars and an aim the size of the largest asteroid .
It ’s now by and large believed our own Moon was organize from material shake off into orbit when an aim the size of Mars slammed into the early Earth , althoughone theoryproposes a serial of many smaller events . Between them , Phobos and Deimos have just one-50 - millionth of Mars ' muckle , in stark dividing line to the Moon , which has around 1 percent of the mass of the Earth . With Mars being closer to the asteroid belt , many people have assumed the moons are captured former asteroids .
However , Dr Robin CanupandDr Julien Salmonof the South - West Research Institute argue inScience Advances , “ Intact seizure is difficult to conciliate with the moon ’ most circular and coplanar orbits , which , rather , suggest that they accreted from an equatorial disk around Mars . ”
However , when multitude have tried to pose the event that could have led to their introduction , they ’ve mark the large size of it of the Borealis Basin , proposed as a likely impingement site , intimate whatever strike Mars had a mass at least a thousandth of that of the satellite it ran into , and perhaps as much as several percent of Mars ' passel . This would have fuddle up far more material than now makes up the moons , but the possibility ran that instead of form into one satellite , numerous diminished moons accreted , with the inmost ones spiraling down until they land back on the major planet .
Canup and Salmon have ladder what they claim is a more sophisticated exemplar , incorporating interactions between the moons , rather than cover each as an autonomous body pretend only by Mars . They also use a much fine mass resolution for their models ' particles .
“ The outer portion of the magnetic disc accumulate[d ] into Phobos and Deimos , while the inner fate of the disk accumulate[d ] into prominent moons that finally spiral in and are assimilate into Mars , ” Dr Salmon said in astatement .
To produce objects of the correct size and locating , the pair conclude an object between the masses of Vesta and Ceres was take ( 520 - 940 kilometers/330 - 590 miles ) , with the accurate size of it depend on the impact angle and speed . Such an object might have produced one of Mars ' low watershed , rather than Borealis .
The Japanese Aerospace Exploration Agency design to launcha missionto the two moons in 2024 , bringing back a sample distribution from Phobos , potentially revealing if Canup and Salmon are right .
Robin Canup Southwest Research Institute
