Mars has two small moons, Phobos and Deimos, whose origin is debated—long thought to be captured asteroids but also plausibly formed from debris after impacts—making them intriguing targets for study
Observations from missions
Phobos and Deimos are small, irregularly shaped satellites that have been imaged and measured by orbiters and landers. Their surfaces are heavily cratered and their compositions and orbits provide key clues about how they formed.
Why it looks blue
Scientists debate whether the moons were captured asteroids or formed from a circum‑Martian debris disk produced by a large impact, with recent analyses and reviews arguing for impact‑related origins as a viable alternative to simple capture scenarios.
Recent evidence and imagery
Computer simulations and new observational constraints have produced models in which disrupted or tidally fragmented bodies evolve into collisional proto‑satellite disks that can accrete into small moons, offering pathways that match some physical and orbital properties seen today.
Implications for science
Understanding the moons’ origin informs Mars’s early impact history, the dynamics of satellite formation around terrestrial planets and the selection of landing or sampling sites for future missions that could directly test formation hypotheses.
Takeaway
Phobos and Deimos remain scientifically important: Phobos is gradually spiralling inward and may either break up into a ring or collide with Mars over tens of millions of years, and resolving whether these moons are captured bodies or products of an impact will refine our knowledge of planetary system evolution.