Unraveling Mars

Theories on Moon Formation

There are two main ideas regarding the formation of Mars’ moons:

• One theory suggests that the moons were actually asteroids caught by Mars’ gravity.

• Another theory proposes that Phobos and Deimos formed out of the debris of a giant impact, similar to how our own moon was formed.

A Shredded Asteroid Origin

A new idea put forth by planetary scientist Jacob Kegerreis suggests something in between: Maybe Mars captured an asteroid, but its gravity ripped it apart. The remains could have formed a short-lived ring around the Red Planet. From this ring, the potato moons could form with circular orbits already in place.

Computer Simulations

Kegerreis and his colleagues ran hundreds of computer simulations to test this idea. They found that across various conditions, the asteroids’ sizes, speeds, and spins made a significant difference in how the rings formed. However, they consistently observed material forming a disk that could give rise to moons.

The Upcoming Mars Moons Exploration Mission

An upcoming mission by the Japanese space agency may help determine which idea is correct. This mission will provide valuable insights into the formation of Phobos and Deimos.

Shredded Asteroid Hypothesis

A recent study published in Icarus suggests that Phobos and Deimos could be the remains of an asteroid that was shredded as it passed close to Mars. Supercomputer simulations showed how an asteroid could break apart into a ring of debris, eventually forming moons around the Red Planet.

Evidence Supporting the Shredded Asteroid Hypothesis

An upcoming mission by the Japanese space agency, Mars Moons Exploration, will collect surface material from Phobos and bring it back to Earth. If the samples have compositions similar to Mars, it would support the giant impact hypothesis. However, if they are more similar to an asteroid or contain water and other compounds that would evaporate in a giant impact, the shredded asteroid hypothesis becomes more likely.

Implications for Exoplanet Moons

Studying the origin of Phobos and Deimos could provide insights into how moons form around extrasolar planets. Even if the shredded asteroid hypothesis is not the correct explanation for Mars’ moons, it could be relevant to other solar systems.

Related Articles

• Planets without stars might have moons suitable for life (April 2, 2023)

• The tiny dot in this image may be the first look at exomoons in the making (July 28, 2021)

References

• Kegerreis et al. Origin of Mars’s moons by disruptive partial capture of an asteroid. Icarus, January 1, 2025, p. 116337.

• Swissinfo.ch. Traces of water on Mars dated back to 4.45 billion years ago (November 20, 2024)