Behold the strange physics of double-acting asteroids

The best candidate for a binary crater on Earth today is the Lockne crater in Sweden and a smaller crater nearby called Målingen. “We dated these structures very precisely and found that they formed at the same degree,” said Jens Ormö from the Center for Biology in Spain, who led the analysis of the craters. age”. published in 2014. Another pair of promising candidates are known to be the Kamensk and Gusev craters, but their location – on the border between Russia and Ukraine – makes them difficult to study in the current global climate.

On Mars, craters can remain visible for billions of years. So, using high-resolution images of the surface taken by Mars orbiters, Vavilov and his colleagues examined nearly 32,000 craters larger than 4 kilometers across. to look for pairs of craters.

Their results show that 150 pairs appear to be the result of binary impacts, totaling 300 individual craters. These estimates come from finding pairs of crater shapes expected after a binary asteroid collision. These include teardrop-shaped craters where two craters overlap; peanut craters, where they are connected at their edges; and double craters, where there is a gap between the two craters. The orientation of the two craters depends on the position of the two asteroids at the time of impact.

“We don’t know how many people are on Mars,” said Katarina Milijkovic at Curtin University in Australia, who performed. original model in 2013 to show what crater shapes could be expected but did not participate in this latest work. “Someone had to do an exhaustive study to find all of them. I think that’s great.”

When two asteroids strike the surface simultaneously, it can lead to some gravitational physics. Elliot Sefton-Nash, deputy project scientist on ESA’s ExoMars show delayed, the shock waves from the collisions can collide, creating a raised trench between two craters or some high-pressure site. “It’s like going in the opposite direction on a highway,” he said. “You can see the difference in minerals that only form under very high pressure.”

In total, the number of binary craters found on Mars represents only about 0.5% of the total number of craters larger than 4 km wide on the planet – much lower than most estimates of the number of asteroids. double planets in the solar system. It could be the result of natural weathering that erased some of the impact, or it could be that pairs of smaller craters exist less than 4 km across. “There are more than 100 million impact craters larger than 100 meters,” said Anthony Lagain from Curtin University in Australia, co-author of the study. “If you start making smaller craters, you have to spend a lot of time looking at all of them.”

Many pairs of craters are similar in size, which contradicts the leading theory of how binary asteroids are formed. Such systems are thought to be formed by light from the sun hitting an asteroid, which can push matter off its surface and into its orbit. As the asteroid rotates, this material forms over millions of years into a small companion, as evidenced by the composition of most of the twins observed to date.

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