New Evidence Points to Mars' Two Moons Forming From a Massive Asteroid Impact

Wednesday, 18 April 2018 - 6:54PM
Space
Mars
Wednesday, 18 April 2018 - 6:54PM
New Evidence Points to Mars' Two Moons Forming From a Massive Asteroid Impact
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NASA
The idea that Mars' moons, Phobos and Deimos (named after the Greek gods of Fear and Panic respectively), were created by an enormous meteor crashing into Mars has been suggested before. If true, it'd be a violent and pretty apt origin story for the scarily named moons.

Unlike previous models explaining Mars and its moons, a new series of collision models from the Southwest Research Institute (SwRI) are among the most detailed yet in terms of explaining precisely what sort of asteroid could kick out enough materials to form Phobos and Deimos. In short, the ancient asteroid in question could have been around the size of an entire dwarf planet like Ceres, which is 587 miles (945 kilometers) in diameter.

At minimum, this asteroid would have been as large as Vesta, which is a couple hundred less miles in diameter but still nothing to brush off. Ceres and Vesta are still the two largest known objects in the Asteroid Belt.



Previous attempts to explain Phobos and Deimos included the much less exciting theory that Mars simply pulled in two objects from the nearby asteroid belt, which has a wide range of bodies inside it.

But since Phobos and Deimos orbit close to Mars' surface and are both quite small, being 7.5 and 14 miles (12 and 22.5 km) respectively, it'd be pretty easy for them to form in an impact scenario, and the math matches up with the potential asteroid sizes in the model.

According to Robin Canup from the SwRI Space Science and Engineering Division, who said the following in a press statement:

Opening quote
"A key result of the new work is the size of the impactor; we find that a large impactor - similar in size to the largest asteroids Vesta and Ceres - is needed, rather than a giant impactor. The model also predicts that the two moons are derived primarily from material originating in Mars, so their bulk compositions should be similar to that of Mars for most elements. However, heating of the ejecta and the low escape velocity from Mars suggests that water vapor would have been lost, implying that the moons will be dry if they formed by impact."
Closing quote


Since Japan's space agency JAXA is planning to send a probe to Phobos soon, this type of information is going to be extremely helpful. 

Phobos is a weird little moon, and could be dangerous to ever land astronauts on, but we might be solving its mysterious very soon.
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