According to new research, the two tiny moons on the red planet, Phobos and Deimos, may have formed after an ancient collision. It’s an intriguing possibility, but not all evidence is convincing.
Phobos and Deimos look like potatoes (although they can actually be seen as an insult to potatoes). The origin of these malformed moons is not entirely clear, but their strange shape, combined with their tiny size, has led to speculation that they are captured asteroids. In fact, Phobos measures 23 miles wide and 11 miles wide in Deimos, so it’s not a completely extravagant idea.
Other factors need to be considered, however, such as their unusual compositions (they are very different from Mars from a geological perspective) and their unexpected orbits. In fact, captured asteroids should have elongated orbits and random tilt angles, none of which apply to Phobos or Deimos. In contrast, both moons have exceptionally circular orbits that are aligned above the equatorial plane of the red planet.
Another possibility is that the two moons are the shattered remains of an ancient collision, a hypothesis considered by Amirhossein Bagheri, a doctoral student at the ETH Zurich and lead author of a new Astronomy of Nature. paper on the subject.
Bagheri and his colleagues performed computer simulations of the two moons, but instead of running their models from a set budget of conditions, the scientists directed them backwards to track the historical movements of the moons. over time. Indeed, the simulations showed that Phobos and Deimos actually crossed paths.
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This implies that the “moons were very likely in the same place and therefore had the same origin,” explained Amir Khan, co-author of the study, a senior scientist at the University of Zurich and ETH Zurich, in statement. By “same origin,” Khan refers to a single parent object — a larger Martian moon that no longer exists — that separated after being struck by a celestial object, such as an asteroid or comet. Bagheri said that Phobos and Deimos “are the remnants of this lost moon,” arguing that they were in an almost synchronous orbit (that is, an orbital period that coincides with the planet’s rotational speed) around Mars. .
To run these simulations, however, the team had to figure out how Mars and the two moons interacted during the eons, including the tidal forces at play and the resulting energy dissipation.
Thanks to NASA’s InSight spacecraft and its ability to monitor seismic activity on Mars, scientists have a better understanding of what is happening beneath the Martian surface. The same cannot be said, however, for the Martian moons, but scientists have photos and measurements collected by remote sensing. Phobos and Deimos are probably like Swiss cheese, full of many cavities, some of which may contain water ice.
Equipped with their updated variables, the scientists executed the models, showing that the birth of the two moons occurred sometime between 1,000 and 2.7 billion years ago. The rather large discrepancy has to do with the uncertainties about the porosity of the two moons. Better data could clarify this and the good news is that the Japanese space agency is planning a mission to Phobos Exploration of the Martian moons, in which a probe will return surface samples sometime later in this decade.
Although the study offers an intriguing look at the history of the moons, Matija Ćuk, a researcher at the SETI Institute, was not convinced by the results.
“The authors have a detailed model of tides on Mars, but they really extend physics when it comes to tides on the moons,” he said in an email. “More importantly, their scenario makes no sense as they project that the orbits of Phobos and Deimos will overlap billions of years ago in [a very] relative high speed, much more than expected with the rupture of a combined body “.
Ćuk said that the idea of a single Martian moon in an almost synchronous orbit about 2,000 to 3 billion years ago “is probably not plausible, as the moon would quickly move away from this position and eventually.” it doesn’t help solve any of the questions people have about the olaugh at Phobos and Deimos, ”he said.
To this he added: “I am surprised that this document is accepted in a high-profile journal like Nature Astronomy.”
Ćuk, along with fellow David Minton of Purdue University, have their own ideas about Phobos and Deimos. In research published last year, scientists provided additional evidence that Phobos is trapped in a cycle of death and rebirth that periodically and temporarily produces rings around the red planet. These rings end up generating new moons, in an alternative explanation of how Mars reached its moons.