Mars’ moon Phobos may actually be a comet – or at least part of one – that was captured long ago by the Red Planet’s gravity. This is suggested by a new preliminary study based on previously unpublished photos.
For years, researchers have puzzled over the origins of Phobos and its twin Deimos. Some have theorized that the moons are former asteroids that were Mars‘ Gravity, as their chemical composition is similar to that of certain rocks in the main asteroid belt between Mars and Jupiter. However, computer models that simulate this capture process were unable to reproduce the pair’s nearly circular orbits around Mars.
Another hypothesis is that a Huge impactlike what created us moondrove the duo away from the Red Planet; but Phobos has a different chemical composition than Mars, making this scenario unlikely as well.
Finding out exactly how Phobos was born is one of the goals of the Japan Aerospace Exploration Agency Mission Martian Moons eXploration (MMX).The market launch is planned for 2026. Sonia Fornasierprofessor of astronomy at Paris Cité University and lead author of the new study, is instrument scientist for the MMX mission. While she and other scientists analyzed images to refine the spacecraft’s planned path, Fornasier came across unpublished photos.
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Recorded by high-resolution cameras on board the Mars Express spacecraftA European Space Agency (ESA) orbiter that has been studying Mars and its moons since 2003, these approximately 300 images exquisitely document the features of Phobos. This also includes the 9 kilometer wide Stickney Crater, Phobos’ largest landmark.
Fornasier and her colleagues used the snapshots to analyze the intensity of sunlight that Phobos reflected from different angles. Using this technique, called photometry, they were able to determine how much light Phobos reflected when the sun was directly in front of it or at an offset angle.
The researchers discovered that Phobos’ surface did not reflect light evenly. Some regions, such as the northeastern rim of the crater, were highly reflective. However, the team’s analysis also showed that Phobos’ surface appeared significantly brighter overall when The sun was directly above us. This phenomenon, called an opposition wave, is characteristic of many airless objects in the solar system. The researchers also found that the surface of Phobos was porous, similar to sand. This led the team to believe that the lunar surface may be covered by a thick layer of dust with furrowed particles, whose shadows disappeared under direct illumination.
Both properties are also features of comets in the Jupiter family, which are comets whose orbits are gravitationally altered by Jupiter. These include the “Rubber Ducky” Comet 67P, developed by ESA Rosetta mission examined up close in 2016. In fact, the photometric properties of Phobos matched those of comet 67P almost exactly. The team concluded that Phobos may have been a comet captured by Mars.
The study’s findings also have implications for Deimos. Fornasier noted that if Phobos was once a comet, Deimos could have been one too. In fact, based on the study, her team suspects that the two moons may once have been together as a single two-lobed comet that was caught by Mars’ gravity and eventually torn apart. In other words, Mars’ twin moons may actually be two halves of a single whole.
“If the Mars satellites are indeed captured comets, this means that comets may also be captured by tellurium.” [terrestrial] Planets,” Fornasier added. She said some moons of gas giants like Saturn probably came from them Kuiper belt, the ring-shaped region that envelops the solar system and from which many comets form. However, astronomers have not yet identified a “comet moon” for terrestrial planets, making Phobos a possible first star.
However, there are also problems with comet interpretation. Some photometric parameters, such as the proportion of scattered light, do not match those of comets. In any case, Fornasier said, dynamic simulations – which take into account the movements of celestial objects, including Mars and Phobos – would help the team determine the likelihood of such a cometary inclusion. Ultimately, however, the MMX program, which will physically test parts of Phobos, is probably the best hope of shedding light on the obscure origins of this mysterious moon.
The new study will soon be published in the journal Astronomy and Astrophysics. available on the preprint server arXiv.