According to new research, the Red Planet’s two small moons – Phobos and Deimos – could have formed after an ancient collision. It’s an intriguing possibility, but not everyone is convinced by the evidence.
Phobos and Deimos are similar to potatoes (although this can actually be seen as an insult to potatoes). The origin of these misshapen moons is unclear, but their strange shape, combined with their small size, has led to speculation that they are asteroids. Phobos is indeed 23 kilometers wide and Deimos 11 kilometers wide, so this is not entirely a strange idea.
However, other factors must be taken into account, such as their unusual compositions (they look very different to Mars from a geological perspective) and their unexpected orbits. Indeed, trapped asteroids should have elongated orbits and arbitrary lean angles, neither of which applies to Phobos or Deimos. Instead, both moons have exceptionally circular orbits aligned above the Red Planet’s equatorial plane.
Another possibility is that the two moons are the shattered remains of an ancient collision, a hypothesis being considered by Amirhossein Bagheri, a doctoral student at ETH Zurich and the lead author of a new Nature Astronomy. paper about the subject.
Bagheri and his colleagues ran computer simulations of the two moons, but instead of running their models forward from a supposed set of conditions, the scientists left them back to track the moons’ historical movements over time. Sure enough, the simulations showed that Phobos and Deimos did indeed cross each other.
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This implies that the “moons were very likely in the same place and therefore have the same origin,” explained study co-author Amir Khan, a senior scientist at the University of Zurich and ETH Zurich in a pronunciationWith ‘the same origin’, Khan refers to a single parent object – a larger Mars moon that no longer exists – that shattered after being hit by a celestial body, such as an asteroid or comet. Bagheri said that Phobos and Deimos are “the remnants of this lost moon,” which they claim were in a nearly synchronous orbit (ie, an orbital period corresponding to the planet’s rotational speed) around Mars.
However, to run these simulations, the team had to figure out how Mars and the two moons interact over the course of the eons, including the tidal forces at play and the resulting dissipation of energy.
Thanks to NASA’s InSight probe and its ability to track seismic activity on Mars, scientists have a better understanding of what is happening beneath the surface of Mars. However, the same cannot be said for the moons of Mars, but scientists have collected pictures and measurements through 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 ran the models, showing that the birth of the two moons happened somewhere between 1 billion and 2.7 billion years ago. The fairly large discrepancy has to do with uncertainties about the porosity of the two moons. Better data could clear this up, and the good news is that the Japanese space agency is planning a mission to Phobos called Martian moon research, in which a probe will return surface samples sometime later this decade.
While the study provides an intriguing look at the history of the moons, Matija Ćuk, a research scientist at the SETI Institute, was not convinced of the findings.
“The authors have a detailed model for tides on Mars, but the physics is really expanding when it comes to tides within the moons,” he said in an email. More importantly, their scenario makes no sense as they project the orbits of Phobos and Deimos to overlap billions of years ago. [a very] high relative speed – much more than expected from the disintegration of a combined body. “
Ćuk said the idea of a single Mars moon in a near-synchronous orbit some 2 billion to 3 billion years ago is “ probably not plausible, ” since the moon would soon move away from such a position, eventually “ not helping. in solving the questions people have about the oorigin of Phobos and Deimos, ”he said.
To which he added, “I’m surprised this article has been accepted in a high-profile journal like Nature Astronomy.”
Ćuk, along with colleague David Minton from Purdue University, have their own ideas about Phobos and Deimos. In Research Published last year, the scientists provided further evidence that Phobos is caught in a cycle of death and rebirth that periodically and temporarily produces rings around the Red Planet. These rings eventually spawn brand new moons, which is an alternate explanation for how Mars got its moons.