Did Mars steal its moons from the asteroid belt? | Smart News


The dark gray object lurking above the Herschel crater on Mars is the Martian moon Phobos, seen by the Viking Orbiter 1 in 1977
NASA / JPL / Michael Benson / Kinetikon Pictures / Corbis

The two moons that orbit Mars are tiny, dark, and lumpy like two scorched potatoes. These seemingly non-lunar features led researchers to believe that Phobos and Deimos were originally asteroids in the asteroid belt that had been grabbed by the Red Planet. But now researchers argue they could have formed much more like Earth’s Moon likely did – after a planet-shattering impact.

For ScienceKen Croswell reports that this impact hypothesis is not new, but that the researcher who proposed it decades ago has been met with contempt. Croswell writes:

“It was embarrassing how much people resented me,” said geologist Robert Craddock of the National Air and Space Museum at the Smithsonian Institution in Washington, DC, who presented the idea at a conference. in 1994. “The general tone was that it couldn’t work.” He has submitted a scientific article to several journals, including Nature and Science, which, he says, all rejected him.

But now, new computer simulations from one research team and calculations from another show how Craddock’s idea works. The scenario could have unfolded as follows.

An object 10 times larger than Ceres, the largest asteroid currently in the belt, may have catapulted into ancient Mars during the formation of the solar system. It has rotated the planet enough so that its rotation is now faster than expected by scientists. It marked the surface of Mars with one of its largest craters – the Borealis Basin in the northern hemisphere, which covers 40 percent of the planet. And it sent enough debris into space to form a disk around the planet. This disc of debris came closer and eventually gave rise to three moons.

So what happened to this third moon? She was taller than Phobos and Deimos, although she was still only a tenth the size of Earth’s Moon. In this version of cosmic history, this third moon was eventually shot down to crash into Mars. “It probably only lasted a few hundred million years,” said Robin Canup, one of the researchers who worked on the simulations. Science.

However, Croswell reports that other researchers are still skeptical. He writes:

Scott Murchie, a planetary scientist at Johns Hopkins University in Baltimore, Maryland, who has studied Martian moons for more than a quarter of a century, says the new work is valuable. But, he adds, “I think the interpretation by far the most consistent with observable characteristics of moons outside of their orbits—[their] density, spectral properties, [dark color]- would be that they are captured asteroids. The new simulations do not address the composition of the moons, but only their sizes and orbits.

One way to resolve the debate is to send landers to the moons of Mars to verify their makeup. But if they want to go down this route, the researchers had better get down to it quickly: Phobos will crash one day on Mars, while Deimos will eventually drift out of orbit. Fortunately, they are at least a few million years old.


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