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Mystery Crash Into Mars

Way back in 1984, when the Berlin Wall was still erect and everyone felt obliged to read George Orwell, a few astrogeologists came up with a theory to explain why the northern side of Mars is smooth and flat, while the southern side is marred with craters and highly elevated.

They proposed that something really large slammed into Mars, creating a creating split almost down the middle of the planet. Their ideawas influenced by another theory circulating at the time; that the moon formed by a chunk of Mars breaking off after a massive impact.

The major crash theory didn't develop much beyond that. After sitting on some dusty academic shelf for the past 25 years it has finally been revived, thanks to new evidence from recent research. Scientists now believe that something similar to an asteroid or a comet smacked into Mars about 4 billion years ago.

Moreover, the giant crater left over from the impact may be the largest in our solar system, about the size of Asia, Europe, and Australia combined. The sheer size and shape of the crater provides conclusive evidence that Mars must have experienced a significant impact. A small part of the crater was actually uncovered in the 1980s (dubbed the Borealis Basin), but because a large portion is hidden under thick layers of lava, not one could map it entirely until now.

Researchers analyzed data from two Mars orbiters, studying crust thickness, surface elevations, and the gravitational pull. Using this information, they were able to reveal what lay beneath the lava. What they found was a huge scar that stretches between the two very different terrains of the planet. It covers about 40% of the surface.

A model simulation was also created to determine the size of the mystery asteroid or comet and exactly where it hit. Gaining clues into the impact, researchers figured out what happened in the aftermath. By bombarding a model simulation of Mars with various sized objects, they were able to pinpoint the conditions needed to result to in the formation of such a huge crater without melting the entire planetary crust.

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