The Japan Aerospace Exploration Agency (JAXA) successfully launched its Martian Moons eXploration (MMX) mission on October 19, sending a spacecraft toward Phobos to resolve a long-standing debate regarding the origin of Mars’ two moons.
While previous observations from the 1989 Soviet Phobos 2 mission and NASA’s Infrared Telescope Facility in the 2010s suggested the moons may be captured asteroids, the MMX mission aims to confirm whether they instead formed from debris following a giant impact on Mars, according to The Conversation.
The spacecraft, which lifted off atop an H3 rocket from the Tanegashima Space Center, is scheduled to arrive at the Red Planet in August 2027. It will spend several years analyzing Phobos and Deimos before collecting soil samples from the larger moon, Phobos, for a scheduled return to Earth in 2031, Stlawu reported.
Scientists currently hold two primary theories for how Phobos and Deimos came to orbit Mars. One hypothesis posits that the moons are D-type asteroids—primitive rocks from the outer Solar System that were captured by Martian gravity. However, researchers note that capturing two separate asteroids is statistically difficult to explain, leading some to propose that Mars instead captured fragments of a single asteroid that disintegrated near the planet.
The second theory suggests the moons formed from a cloud of debris ejected into orbit after a large object struck Mars.
A critical component of the MMX mission involves identifying "exogenous material"—rocks from Mars or other asteroids that have accumulated on the surface of Phobos over time. To prepare for this, scientists have conducted laboratory experiments, including firing projectiles at simulated soil to see how impact material behaves at low velocities.
While the mission is underway, several questions remain regarding the specific composition of the moons and the history of material transport in the Solar System. The research team is also investigating whether the spacecraft’s instruments can detect organic matter, which could provide further insight into the moon’s evolution, even if the compounds are not biological in origin.
Why is Phobos not spherical like Earth’s moon?
Phobos measures only 22km across, meaning its gravity is too weak to pull its mass into a spherical shape, according to NASA/JPL-Caltech/University of Arizona.
What does the name of the instrument MEGANE mean?
The name is the Japanese word for "glasses," reflecting its role as an instrument that will help scientists "see" the chemical elements present on the surface of Phobos, Stlawu reported.
What happens if the mission fails to find Martian material on Phobos?
If the instruments do not detect foreign material, scientists will still use the returned samples and spectral data to distinguish between the captured-asteroid and giant-impact theories, The Conversation noted.
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