The two small moons of the Red Planet – Phobos and Deimos – could have formed after an ancient collision, according to new research. This is an interesting possibility, but not everyone is convinced by the evidence.
Phobos and Deimos look like potatoes (although they can actually be considered an insult to potatoes). The origin of these malformed moons is not entirely clear, but their strange shape, combined with their small size, has led to speculation that they are trapped asteroids. Indeed, Phobos measures 23 kilometers wide and Deimos 11 kilometers wide, so this is not a completely strange idea.
However, other factors need to be considered, such as their unusual compositions (very different from Mars from a geological perspective) and their unexpected orbits. Captured asteroids must indeed have elongated orbits and random angles of inclination, which do not apply to Phobos or Deimos. Instead, both moons have extraordinary circular orbits that are equal above the equatorial plane of the Red Planet.
Another possibility is that the two moons are the crushed remains of an ancient collision, a hypothesis being considered by Amirhossein Bagheri, a doctoral student at the ETH Zurich and the lead author of a new Natural Astronomy. paper on the subject.
Bagheri and his colleagues did computer simulations of the two moons, but instead of running their models forward from a supposed set of conditions, the scientists ran them backwards to follow the historical movements of the moons over time. The simulations certainly showed that Phobos and Deimos actually did crosses.
G / O Media can get a commission
This implies that the “moons were most likely in the same place and therefore of the same origin”, study co-author Amir Khan, a senior scientist at the University of Zurich and ETH Zurich, explained in a statement statement. According to “the same origin”, Khan refers to a single-parent object – a larger Martian moon that no longer exists – that splinters after being hit by a celestial object, such as an asteroid or comet. Bagheri said Phobos and Deimos ‘are the remnants of this lost moon’, which they say was in an almost-synchronous orbit (ie an orbital period corresponding to the rotation speed of the planet) around Mars.
To perform these simulations, however, the team had to figure out how Mars and the two moons had interacted over the centuries, including the tidal forces played and the resulting distribution of energy.
Thanks to NASA’s InSight probe and its ability to monitor seismic activity on Mars, scientists have a better understanding of what is happening below the Martian surface. The same cannot be said for the Martians, however, but scientists do have photographs and measurements collected by remote sensing. Phobos and Deimos are probably like Swiss cheese, filled with many cavities, some of which may contain water ice.
Equipped with their updated variables, the scientists performed the models and showed that the birth of the two moons took place at some point between 1 billion and 2.7 billion years ago. The rather large difference has to do with uncertainties about the porosity of the two moons. Better data could clear it up, and the good news is that the Japanese space agency is planning a mission to Phobos Martian exploration, in which a probe will return surface samples at some point later this decade.
While the study provides an intriguing look at the history of the moons, Matija Ćuk, a researcher at the SETI Institute, was not convinced by the findings.
“The authors do have a detailed model for tides within Mars, but the physics really stretch when it comes to tides in the moon,” he said in an email. “What is even more important is that their scenario makes no sense because they project the paths of Phobos and Deimos to overlap billions of years ago. [a very] high relative velocity – much more than expected by breaking up a combined body. ”
Ćuk said that the idea of a single Martian moon in an almost synchronous orbit about 2 billion to 3 billion years ago is ‘probably not plausible’, as the moon would quickly move away from such a position and ultimately ‘nothing helps’ not of the questions people have about the oguideline of Phobos and Deimos, ”he said.
To which he added: “I am amazed that this article was accepted in a high-profile journal such as Nature Astronomy.”
Ćuk, along with colleague David Minton of Purdue University, have their own ideas about Phobos and Deimos. In research published last year, the scientists provided further evidence that Phobos is trapped in a cycle of death and rebirth that periodically and temporarily produces rings around the Red Planet. These rings eventually cultivate brand new moons, which is an alternative explanation for how Mars got its moons.