Mars’ Moons Formed from Giant Impact
Southwest Research Institute scientists posit a violent birth of the tiny Martian moons Phobos and Deimos, but on a much smaller scale than the giant impact thought to have resulted in the Earth-Moon system. Their work shows that an impact between proto-Mars and a dwarf-planet-sized object likely produced the two moons, as detailed in a paper published today in Science Advances.
The origin of the Red Planet’s small moons has been debated for decades. The question is whether the bodies were asteroids captured intact by Mars gravity or whether the tiny satellites formed from an equatorial disk of debris, as is most consistent with their nearly circular and co-planar orbits. The production of a disk by an impact with Mars seemed promising, but prior models of this process were limited by low numerical resolution and overly simplified modeling techniques.
Credit: Southwest Research Institute
SwRI scientists modeled a Ceres-sized object crashing into Mars at an oblique angle. These four frames from the 3-D simulation show that the impact initially produces a disk of orbiting debris primarily derived from Mars (bottom right frame). The outer portions of the disk later accumulate into Mars’ small moons, Phobos and Deimos. The inner portions of the disk accumulate into larger moons that eventually spiral inward and are assimilated into Mars.
![Four frames from the Mars impact 3-D simulation](https://i0.wp.com/www.swri.org/sites/default/files/styles/facebook_image/public/media-resources/mars-impact-model-crop.jpg?ssl=1)
While they formed in the same timeframe, Deimos and Phobos are very small, with diameters of only 7.5 miles and 14 miles respectively, and orbit very close to Mars. The proposed Phobos-Deimos forming impactor would be between the size of the asteroid Vesta, which has a diameter of 326 miles, and the dwarf planet Ceres, which is 587 miles wide.
This composite image compares how big the moons of Mars appear, as seen from the surface of the Red Planet, in relation to the size that our Moon appears from Earth’s surface. While Earth’s Moon is 100 times bigger than the larger Martian moon Phobos, the Martian moons orbit much closer to their planet, making them appear relatively larger in the sky. Deimos, at far left, and Phobos, beside it, are shown together as photographed by NASA’s Mars rover Curiosity on Aug. 1, 2013.
“A primary objective of the MMX mission is to determine the origin of Mars’ moons, and having a model that predicts what the moons compositions would be if they formed by impact provides a key constraint for achieving that goal,” Canup said.
The “Origin of Phobos and Deimos by the impact of a Vesta-to-Ceres-sized body with Mars,” is published in the April 18, 2018, issue of Science Advances. The research was funded by NASA’s Solar System Exploration Research Virtual Institute (SSERVI) in Silicon Valley, and by NASA’s Emerging Worlds program. The research was conducted as part of the Institute for the Science of Exploration Targets (ISET), a SSERVI team from SwRI’s Boulder, Colorado, office.
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Deb Schmid
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Robert Beatty
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It would be nice to know where Mars and the Asteroid belt came from before we draw conclusion about the origin of Deimos and Phobos.
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jerry krause
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Hi Robert,
Do you consider that Worlds in Collision by Immanuel Velikovsky and first published April 3, 1950 should be a required read for anyone commenting upon the moon’s of Mars?
Have a good day, Jerry
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Robert Beatty
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Having a good ANZAC day in this sunny part of the southern hemisphere.
No, I would not recommend this book. Wiki comment says it all “Many of the book’s claims are completely rejected by the established scientific community as they are not supported by any available evidence.”
My advice would be to spend time reading http://www.bosmin.com/PSL/PlanetsSatellitesLandforms.pdf
Well he would say that wouldn’t he!
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jerry krause
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Hi Robert,
“the book’s claims are completely rejected by the established scientific community as they are not supported by any available evidence.”
Depends upon what one wants to believe.
Have a good day, Jerry
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