New Clues About the Origins of Mars’ Moons Phobos and Deimos
Researchers from a French university have presented fresh evidence that sheds light on how Mars’ two small moons, Phobos and Deimos, might have formed. The findings, published and archived in open scientific repositories, come after a detailed analysis of a large set of images and data derived from the Mars Express mission.
For decades, scientists have debated the origins of Phobos and Deimos. One widely discussed possibility suggests that both moons are captured asteroids drawn into Mars’s gravitational field. This theory gains some support from the moons’ chemical signatures, which show similarities to objects in the asteroid belt between Mars and Jupiter. Yet computer simulations have struggled to recreate a scenario in which Mars merely captured objects from this belt as moons, casting doubt on the capture hypothesis.
Another longstanding idea proposes that Phobos and Deimos originated from debris ejected by a colossal impact on Mars long ago. If true, the moons would be fragments of a once much larger object. However, Phobos carries chemical distinctions from Mars that complicate the impact-origin model and invite further investigation.
The latest study analyzes more than 300 photographs captured by the Mars Express orbiter since 2003. Scientists carefully examined how sunlight reflects off the surface of Phobos from multiple viewing angles. The results reveal an irregular and unstable reflection pattern, suggesting complex surface properties that influence how light is absorbed and scattered across the satellite.
Another important finding concerns the surface texture of Phobos. The data indicate high porosity, with a loose, sand-like composition that could host a substantial layer of fine dust. This dust would create shadows that fade when exposed to direct sunlight, a feature consistent with certain dusty, low-density bodies rather than solid rock surfaces alone.
These observational traits align with a family of comet-like bodies that orbit near the giant planet Jupiter. In particular, the photometric behavior of Phobos bears a close resemblance to the known properties of comet 67P/Churyumov-Gerasimenko, as observed in its surrounding population. The resemblance suggests a wider connection to a population of icy remnants that travel through the outer solar system and occasionally interact with the inner planets when gravitational dynamics allow.
The researchers propose a scenario in which Phobos and Deimos may have originated as part of a single, larger comet that became bound to Mars. Under the influence of Mars’s gravity, this primordial subscriber could have split, producing two separate moons that then settled into their current orbits. While this model aligns with some observational aspects, it also prompts questions about the exact processes that would lead to a stable, double-moon configuration around Mars over billions of years. The new evidence adds to a growing body of work examining whether small, irregular satellites around inner planets can be remnants of more complex, past interactions with distant celestial bodies.
Overall, the study emphasizes how modern observational data, combined with careful analysis of light scattering and surface texture, can refine theories about the origins of Mars’ moons. By comparing the photometric properties of Phobos with those of known cometary bodies and dusty, low-density surfaces, researchers are building a more nuanced picture of where these moons may have come from and how they have evolved under the influence of Mars’s gravity. The findings underscore that the story of Phobos and Deimos is likely tied to a broader history of solar system dynamics, rather than a single, simple origin scenario.
Previous research and ongoing analyses continue to explore related questions, including whether other small satellites around Mars or neighboring planets share similar histories. The work also highlights how high-resolution imaging from space missions, aligned with laboratory-based interpretations of surface materials, can unlock clues about the complex evolutionary paths of these enigmatic moons. While no single theory fully resolves the question, the accumulation of diverse lines of evidence brings scientists closer to understanding the true origins of Phobos and Deimos and their place in the solar system’s grand narrative. These insights contribute to a broader effort to map how small bodies form, migrate, and interact within planetary systems, both in the past and in the present era of planetary exploration. Notes from the research team indicate that ongoing observations, data reanalysis, and comparative studies with other irregular satellites will continue to refine the proposed scenarios and may reveal new facets of Mars’s captivating moons.