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Recent research has proposed a compelling theory regarding the formation of Mars’ moons, Phobos and Deimos, suggesting they could be relics of an asteroid that ventured too close to the planet. This hypothesis, outlined in the January edition of Icarus, may provide insights into the unusual characteristics of these small, irregularly shaped moons.
Unlike typical moons that are often round and large, Mars’ moons resemble small, lumpy potatoes, raising questions about their origins. Two primary theories have emerged to explain how these moons formed. One theory posits that they were originally asteroids that fell under Mars’ gravitational influence. However, this explanation struggles to account for the stable, circular orbits of the moons relative to Mars’ equator.
The second theory suggests that Phobos and Deimos might have been created similarly to Earth’s moon, which formed from debris resulting from a colossal impact. Jacob Kegerreis, a planetary scientist at NASA’s Ames Research Center, highlights that such an impact scenario is one of the few methods capable of producing a significant amount of material to form a moon.
Nevertheless, Kegerreis and his team have developed a hybrid theory. They propose that while Mars may have captured an asteroid, its gravity could have subsequently disintegrated the asteroid, creating a transient ring around the planet. The moons could have then formed from the remnants of this ring, already possessing their current stable orbits.
To evaluate this new hypothesis, Kegerreis and his team conducted numerous computer simulations examining the interactions between asteroids and Mars. They discovered that varying the size, speed, and rotation of the asteroids significantly influenced the formation of rings, ultimately leading to the creation of substantial material capable of forming a disk around Mars.
The upcoming Mars Moons Exploration mission, scheduled to launch in 2026 by the Japanese space agency, could provide crucial evidence to support one of the competing theories. This mission aims to gather samples from Phobos and return them to Earth for analysis.
If the samples reveal that the moons’ compositions closely resemble that of Mars, it would bolster the argument for the giant impact model. Conversely, if they show similarities to asteroids or contain volatile materials that would have been lost during a heat-filled impact, then the hypothesis of a shredded asteroid becomes more compelling.
Investigating the origins of these Martian moons may also extend our understanding of moon formation around exoplanets. Kegerreis notes that even if the proposed model does not specifically apply to Mars, it could illuminate processes applicable to moons formed around other planetary bodies. With the growing discovery of exoplanets and the possibilities of exomoons, exploring these formation mechanisms becomes increasingly relevant.
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