Mars' Moons Might Have Formed from a Massive Asteroid Impact

Tuesday, 05 July 2016 - 5:45PM
Mars
Tuesday, 05 July 2016 - 5:45PM
Mars' Moons Might Have Formed from a Massive Asteroid Impact
Mars' moons, Phobos and Deimos, have long been thought to be asteroids captured by the planet's gravitational pull. Now, researchers have an alternative (and significantly more exciting) explanation: the bodies formed from a circle of debris following a massive asteroid impact that destroyed half of Mars' surface.

The moons' small size, oval-shaped appearance, and other properties such as density, electromagnetic activity, and surface reflectivity led researchers to conclude that they were captured asteroids. However, that theory wouldn't account for their circular orbits, as Mars' gravity isn't strong enough to produce that kind of trajectory. The other option is that the moons accreted from a disk of debris that surrounded Mars following a huge asteroid impact, and in a new paper published in Nature, researchers provide evidence that this theory is the most plausible.

For the study, a research team led by Pascal Rosenblatt of the Royal Observatory of Belgium ran a series of computer simulations that recreated the conditions immediately after an asteroid impact on Mars during that time period. They found that a huge disk of debris would form in just a few hours after impact, and that the inner disk coalesced into a large moon very quickly. Then, over time, Mars' gravity began to pull on the outer disk, causing small moons like Phobos and Deimos to form. 

According to this model, about five million years after impact, the large moons would fall towards Mars, while the smaller moons would become satellites with similar orbits to Phobos and Deimos. This accretion theory would explain many properties of Phobos and Deimos, including their orbits and their unusual composition, which is predicted to be a mixture of material from Mars and the asteroid that caused the initial impact.

Although this is still just a hypothesis, it's quickly becoming the most plausible explanation for the formation of these moons. And best of all, it's perfectly testable, as we would expect Mars to play host to the remains of the destroyed asteroid on its surface. So when NASA (and/or SpaceX) completes a mission to Mars in the next few decades, we'll most likely get the answer to this longstanding question.
Science
Space
Mars

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