Mars' mysterious moon Phobos may be a captured comet

Deimos and Phobos are natural satellites orbiting Mars. Scientists have spent years investigating their origins but have not yet been able to determine with complete certainty their history. Some theories suggest that Mars' gravity may have captured the twin moons due to their chemical composition, which is believed to be similar to that of rocks in the asteroid belt between Mars and Jupiter.

Another hypothesis about the presence of these satellites near Mars posits that a giant impact might have ejected both Phobos and Deimos from the Red Planet. However, scientists often reject this idea due to differences in the composition of the two objects.

The Martian Moons eXploration (MMX) mission, conducted by the Japanese Space Agency and led by Sonia Fornasier from Université Paris Cité, aims to analyse Deimos and Phobos thoroughly. The researchers examined 300 unpublished images from a high-resolution camera mounted on the Mars Express spacecraft, focusing on the specific features of Phobos visible in the photographs.

Fornasier's team used the images to study the intensity of Phobos' reflected sunlight from different angles. This technique, known as photometry, allows scientists to determine precisely how much light Phobos reflects. Through this method, they observed that Phobos' surface did not reflect light evenly, as reported by Live Science.

Some areas of the moon were highly reflective, and its surface appeared significantly brighter at certain angles to the Sun. Researchers point out that this phenomenon is characteristic of airless objects in the Solar System.

Additionally, the photos revealed that Phobos' surface is porous. This led to suspicions that the surface might be covered with a layer of dust with specifically arranged grooves, whose shadows disappear when illuminated.

The current findings are valuable because Mars' satellite's properties resemble those of comets from the Jupiter family. The research team suggests that Phobos might have been a comet captured by Mars. Although the discovery mainly concerns Phobos, Fornasier points out that if Phobos was originally a comet, it is possible that Deimos was also.

Moreover, the team proposes that both moons might have been a single comet torn apart by Mars' gravity. This implies that the twin moons are potentially the two halves of one comet. More precise studies will be possible when the MMX mission collects samples from fragments of Phobos for examination.