Newly revealed photos of Mars’ moon Phobos suggest that this enigmatic satellite might actually be a captured comet, or at least a fragment of one, along with its twin moon Deimos.
### The Mystery of Phobos and Deimos
Mars’ moons Phobos and Deimos have long puzzled scientists. Some theories propose that the moons are former asteroids captured by Mars’ gravity, given their similarity to rocks in the asteroid belt. However, computer models have struggled to replicate the moons’ near-circular orbits. Another hypothesis suggests a giant impact on Mars created the moons, but Phobos’ differing composition from Mars challenges this idea.
### New Insights from Unpublished Photos
A new preprint study based on previously unpublished images may provide fresh insights. Sonia Fornasier, an astronomy professor at Paris Cité University and a key researcher in the Japan Aerospace Exploration Agency’s (JAXA) Martian Moons eXploration (MMX) mission, discovered the photos while preparing for the mission’s 2026 launch.
### Photometric Analysis
Taken by high-resolution cameras aboard the European Space Agency’s Mars Express spacecraft, these images document Phobos’ features in detail, including the prominent Stickney crater. Fornasier’s team used photometry to analyze the light reflected by Phobos, finding that the moon’s surface reflects light unevenly. They observed an opposition surge—a brightening when the sun is directly overhead—indicating a porous, dusty surface similar to that of comets.
### Phobos as a Comet
The photometric properties of Phobos closely matched those of Comet 67P, suggesting Phobos might be a captured comet. This theory could extend to Deimos, proposing that Mars’ moons are remnants of a single bilobed comet split by Mars’ gravity.
### Implications and Future Research
If Phobos and Deimos are indeed captured comets, it implies that comets can be trapped by terrestrial planets, a phenomenon not previously identified. However, some photometric parameters don’t entirely match those of known comets. Future dynamical simulations and the upcoming MMX mission, which will sample Phobos’ surface, will provide more definitive answers.
The new findings could potentially solve the long-standing mystery of Mars’ moons, shedding light on their true origins and the dynamic processes of our solar system.
