According to new research, the two tiny telescopes of the Red Planet – Phobos and Deimos – could have formed after an old collision. It is an interesting possibility, but not everyone is convinced by the evidence.
Phobos and Deimos look like potatoes (although this can actually be seen as an insult to potatoes). The origin of these malformed months is not entirely clear, but their strange shape, combined with their diminutive size, has led to speculation that they are captured asteroids. Indeed, Phobos is 23 kilometers wide and Deimos is 7 miles (11 kilometers) wide, so this is not a completely strange idea.
However, other factors need to be considered, such as their unusual compositions (they are very different from Mars from a geological perspective) and their unexpected orbits. Indeed, captured asteroids should have elongated orbits and random tilt angles, none of which apply to Phobos or Deimos. Instead, both months have exceptionally circular orbits, which are aligned above the equatorial plane of the Red Planet.
Another possibility is that the two months will be the broken remains of an ancient collision, a hypothesis considered by Amirhossein Bagheri, PhD student at ETH Zurich and lead author of a new Astronomy of Nature paper on the subject.
Bagheri and his colleagues ran computer simulations of the two months, but instead of targeting their models from a supposed set of conditions, scientists led them back to track the historical movements of the months over time. . Sure enough, the simulations showed that Phobos and Deimos actually crossed paths.
G / O Media may receive a commission
This implies that “the months were most 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 statement. By “same origin” Khan refers to a single parent object – a larger Martian moon that no longer exists – that split after being hit by a celestial object, such as an asteroid or a comet. Bagheri said that Phobos and Deimos “are the remnants of this lost moon,” which they claim is in an almost synchronous orbit (ie an orbital period that matches the planet’s rate of rotation) around Mars.
However, to run these simulations, the team had to find out how Mars and the two months interacted over eons, including the tidal forces at play and the resulting dissipation of energy.
Thanks to NASA’s InSight probe and its ability to monitor seismic activity on Mars, scientists have an improved understanding of what is happening beneath the Martian surface. The same cannot be said, however, for the Martian months, but scientists have photos and measurements collected by remote sensing. Phobos and Deimos are probably Swiss cheese, filled with lots of cavities, a portion of which may contain water ice.
Equipped with their updated variables, the scientists ran the models, showing that the birth of the two months took place at some point between 1 billion and 2.7 billion years ago. The rather large discrepancy is related to the uncertainties regarding the porosity of the two months. Better data could clarify this, and the good news is that the Japanese space agency is planning a mission to Phobos, called Exploring the Martian months, in which a probe will return surface samples at some point at the end of this decade.
While the study offers an interesting look at the history of the months, Matija Ćuk, a researcher at the SETI Institute, was not convinced by the findings.
“The authors have a detailed model for the tides on Mars, but they really stretch physics when it comes to the tides of the moon,” 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 at [a very] high relative speed – much more than expected by breaking 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 not “probably plausible,” because the moon would quickly move away from such a position and, in the latter, “does not help to solve the questions that people have about arigin of Phobos and Deimos, “he said.
To which he added: “I am surprised that this paper was accepted in a profile journal such as Nature Astronomy.”
Ćuk, together with his colleague David Minton from Purdue University, have their own ideas about Phobos and Deimos. In the research published last year, scientists have 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 eventually produce new moons, which is an alternative explanation for how Mars received its moons.