Grazing asteroid impact may be behind two faces of Mars
From our Correspondent

http://www.dailyindia.com/show/12591...-faces-of-Mars

London, Mar 16: The two faces of Mars, the higher and heavily cratered southern hemisphere and a relatively flatter northern hemisphere, which is about five kilometres lower in elevation than the southern part, may be due to the impact of a giant asteroid, researchers say.

Researchers say computer simulations reveal an asteroid might have struck the planet with a glancing blow.

Earlier, in the 1980s, scientists had opined a giant impact by an asteroid about 300 kilometres across in Mars's early history could have led to a permanent indention in the planet's northern hemisphere.

Now, two teams of scientists have created the first computer simulations testing whether such an impact could have produced the observed differences.

Shawn Hart of the University of California in Santa Cruz, US, led one of the simulation teams.

His team found that such an impactor would produce huge amounts of lava, enough to cover the planet in an ocean of molten rock somewhere between 14 and 48 kilometres thick. That would have ended up erasing any record that an impact happened in the first place.

"We therefore consider it unlikely that you'll create the Martian crustal dichotomy utilising a single giant impact," Hart said.

Elsewhere, simulations carried out by the second team, led by Margarita Marinova of Caltech in Pasadena, US, revealed that a glancing blow by an impactor could leave a scar, but produce less heat, melting only a relatively small area around the impact site.

In this scenario, the total amount of lava produced is equivalent to a five-kilometre-deep layer distributed over the whole planet, fairly small enough to avoid erasing the depression, the researchers said.

"You can have a very large impact and not melt the whole planet and preserve some signature of this impact," New Scientist quoted Marinova as saying.

The results were presented this Wednesday at the Lunar and Planetary Science Conference in Houston, Texas, US.


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