Did a Giant Impact Make the Martian Moons?

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by Ken Croswell

The Martian moons look like asteroids—dark, crater-pocked, and potato-shaped—suggesting Mars had snatched them from the nearby asteroid belt. But now planetary scientists have conducted the first computer simulations that bolster a controversial alternative idea: The satellites formed as our own moon did, after a big object smashed into the planet and kicked up debris.

Full story: ScienceNOW
 

Answers and Replies

  • #3
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by Ken Croswell

The Martian moons look like asteroids—dark, crater-pocked, and potato-shaped—suggesting Mars had snatched them from the nearby asteroid belt. But now planetary scientists have conducted the first computer simulations that bolster a controversial alternative idea: The satellites formed as our own moon did, after a big object smashed into the planet and kicked up debris.

Full story: ScienceNOW
There are four different hypotheses being proposed:
  1. Phobos and Deimos were captured asteroids; or
  2. Phobos and Deimos formed during the accretion process that created Mars; or
  3. Phobos and Deimos are second-generation Solar System objects that coalesced in orbit after Mars formed, rather than forming concurrently out of the same birth cloud as Mars; or
  4. Phobos and Deimos are debris from a large impactor on Mars (similar to the Terra/Theia impact that created our moon).
The near-circular orbits of the two moons are very near to Mars' equator, which makes it difficult to reconcile in the capture theory. The problem with option #2 is that both Phobos and Deimos are spectroscopically different from Mars. Furthermore, Phobos is spectroscopically different from the asteroids in the asteroid belt. Deimos is spectroscopically similar to D-Class asteroids in the asteroid belt. If Phobos and Deimos were the debris from a large impactor on Mars, then they should both be chemically similar, but they are not. With regard to the second-generation object theory, I was not able to find a paper on the subject, just a quotation from Dr. Martin Pätzold, from the University of Cologne, Germany, and Principal Investigator of the Mars Radio Science (MaRS) experiment: http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Phobos_flyby_success

See also:
Capture of Phobos and Deimos by Photoatmospheric Drag - Icarus, Volume 37, Issue 1, January 1979, Pages 113–123 (paid subscription)
http://[URL [Broken]']Formation of Phobos and Deimos via a Giant Impact[/URL] - Icarus, Volume 252, May 2015, Pages 334-338 (paid subscription) (arXiv free reprint)
 
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