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US News Mars's Two Tiny Moons Were Formed After an Asteroid Hit the Planet, New Theory Suggests

09:00  19 april  2018
09:00  19 april  2018 Source:   europe.newsweek.com

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One suggests that the moons were tiny asteroids trapped by Mars ’ s gravity. The other argues that they formed after some giant object crashed into the planet and created a bunch of debris, some of which clumped into the two moons . But that giant object may not have been so giant after all, according to new calculations presented in a paper published Wednesday in the journal Science Advances.

The two moons of Mars are Phobos and Deimos. They are irregular in shape. Both were discovered by American astronomer Asaph Hall in August 1877 and are named after the Greek mythological twin characters Phobos (fear) and Deimos (panic) who accompanied their father Ares into battle.

a close up of the moon: 04_18_mars_phobos_deimos © Provided by IBT Media (UK) 04_18_mars_phobos_deimos Mars has two tiny moons, Phobos and Deimos, whose names mean fear and terror in ancient Greek. Maybe mystery would have been the better term to choose, since the origins of the two satellites has stumped scientists for decades.

There are two leading theories. One suggests that the moons were tiny asteroids trapped by Mars's gravity. The other argues that they formed after some giant object crashed into the planet and created a bunch of debris, some of which clumped into the two moons. But that giant object may not have been so giant after all, according to new calculations presented in a paper published Wednesday in the journal Science Advances.

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Mars is the darling of many planetary scientists, who continue to visit it through increasingly advanced robotic explorers. But don’t forget that our planetary neighbor is adorned with two moons : puny Phobos, a lumpy mass 17 miles across; and diminutive Deimos, just 9 miles long. We don’t know where the moons came from because they look like asteroids foreign to the red planet but behave like byproducts of Mars ’ early, impact-laden history. And if that Japanese mission manages to grab some samples and decode the chemistry of the mangled moons , we might be able to discover their origins.

Mars has two small, funky-looking moons with strange orbits, and they may suggest that the red planet once had rings, like some of the larger planets in our solar system. The two lumpy moons , Phobos and Deimos, were both discovered in 1877 and named after the sons of Ares from Greek mythology ( Mars is named after the Roman god of war, which is Ares in Greek). Phobos means fear or panic and Deimos means dread. They were long thought to actually be asteroids captured by the planet ' s gravity.

That paper argues that the impactor would have been about 30 times smaller than previous estimates—the size of a large asteroid. "This is a very different scale of forming moons from an impact than we've ever considered before because these moons are so tiny," lead author Robin Canup, a planetary scientist at the Southwest Research Institute in Colorado, told Newsweek.

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Canup and her co-author had a few different constraints to balance as they tried to piece together the crime scene, like the moons' small size and their current distance from Mars. Then they modeled dozens of different collisions, looking for what moons resulted and comparing them to what really orbits Mars.

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The prevailing theory supported by the scientific community, the giant impact hypothesis suggests that the moon formed when an object smashed into early Earth. Like the other planets , Earth formed from the leftover cloud of dust and gas orbiting the young sun. In 2012, researcher Robin Canup, of the Southwest Research Institute in Texas, proposed that Earth and the moon formed at the same time when two massive objects five times the size of Mars crashed into each other. " After colliding, the two similar-sized bodies then re-collided, forming an early Earth surrounded by a disk of material that

Mars is the fourth planet from the Sun and the second-smallest planet with a thin atmosphere, having the surface features reminiscent both of the impact craters of the Moon , and the valleys, deserts and polar ice caps of Earth. It is named after the Roman god of war due to its red appearance. In different cultures, Mars represents masculinity, youth and its symbol is used as the symbol for the male gender. Due to the effects of the iron oxide prevalent on Mars ’ s surface, it has a reddish appearance distinctive among the astronomical bodies visible to the naked eye.

Those models showed that a truly giant impact didn't work. That size collision would have resulted in very big moons, big enough that they would absorb anything as small as Phobos and Deimos. "You don't actually end up with any little moons out where they are," Canup said of these models.

So she and her colleague started thinking a bit less giant, and that turned out to be the sweet spot for these small moons. The models worked best for an impactor that was between the size of Vesta and twice the size of Ceres—those are two of the largest asteroids in the belt of rocks that falls between Mars and Jupiter.

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Canup says that what's most exciting about these smaller impacts is that it helps overturn the old belief that moons are hard to make. "Over decades of simulations now we're actually finding the opposite," Canup said. "A huge fraction of those impacts would have produced at least transient moons from their debris."

And that in turn means scientists may have been thinking about moons formed by impacts across the solar system in the wrong way: The weird thing isn't that so many exist but that so few remain. "Instead of this being an unusual event, we think now it should have been commonplace," Canup said. "Moon formation we now think was rampant during planet formation and the early stages of the solar system."

That points to even more intriguing mysteries, she says. After all, Earth's other neighbor Venus has definitely been knocked about a bunch as well—but there are no moons to be found. Fortunately, after tackling Phobos and Deimos, scientists aren't likely to be scared off by more moon mysteries.

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