Are Mars’ moons the remnants of a massive planetary impact?

Space · Published 18 October 2026 Swipe more like this →

In short: For decades, astronomers have debated whether Phobos and Deimos are captured asteroids or the debris of a colossal collision. A new international mission aims to settle the score by bringing Martian moon dust back to Earth, potentially rewriting the history of our solar system.

The origin of Mars’ two moons, Phronos and Deimos, remains one of the great mysteries of the inner solar system. Scientists are currently divided between two primary theories: that the moons are ancient asteroids captured by Martian gravity billions of years ago, or that they are the fragments left behind after a massive impact struck the Red Planet. Determining which is true could illuminate the early era when Earth and other inner planets may have acquired essential water and organic compounds.

To solve this, the Japan Aerospace Exploration Agency (JAXA) is leading the MMX (Martian Moons eXploration) mission, with significant support from NASA. The mission's spacecraft is scheduled to arrive at Mars in August 2027. A critical component of this effort is the MEGANE spectrograph, developed by the Johns Hopkins Applied Physics Laboratory. This instrument will measure gamma rays and neutrons to determine the chemical elemental composition of Phobos' surface, providing vital clues about its makeup.

The mission also features a technological demonstration of NASA’s Pneumatic Sampler (P-Sampler), developed by Honeybee Robotics, a Blue Origin company. This system uses high-pressure nitrogen gas bursts to collect surface material. Following a detailed survey, the spacecraft intends to collect a sample from Phames no earlier than December 2028, with a planned return to Earth in 2031. NASA will curate approximately 15% of the total returned sample at the Johnson Space Center Astromaterials Lab in Houston, ensuring the material is available for research for decades.

While missions like MMX focus on the Martian system, other space endeavors, such as the STS-134 mission involving Commander Mark Kelly, have utilized instruments like the Alpha Magnetic Spectrometer to unlock broader secrets of the universe.

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