Scars on Mars: Giant impact by asteroids caused the massive spots on red planet, says NASA study

The ancient surfaces of Mars, similar to those found on the Moon and Mercury, are covered with five giant scars that were caused by asteroid impacts, scientists have revealed. A NASA-funded study has revealed that the giant impacts on Mars were ten times fewer than some estimates made previously.

The early bombardment history of Mars and the timing of giant impacts have been investigated by Scientists Bill Bottke from the Southwest Research Institute, or SwRI, and Jeff Andrews-Hanna from the University of Arizona.

The five scars caused by giant impacts on Mars include the ancient giant Borealis basin (top of globe), Hellas (bottom right), and Argyre (bottom left). The team, funded by NASA, at SwRI found that a 400-million-year lull was experienced by Mars in impacts between the formation of Borealis and the younger basins.

The new study suggests that 4.5 billion years ago, the Borealis basin carved out the northern lowlands. It was followed by a lull of 400-million-years. During this period, no giant impacts occurred. This culminated in a shower of impacts between 4.1 and 3.8 billion-years-ago. Four giant basins and countless smaller craters formed during this period, says a release by NASA.

Borealis, which is nearly 6,000 miles wide, is the largest and most ancient giant impact basin on the Red Planet. It encompasses most of the northern hemisphere of Mars. Hellas, a smaller giant basin, is 1,200 miles wide and five miles deep.

Data was collected and models were run by Bottke and Andrews-Hanna in order to support their discovery that the rim of Borealis was excavated by only one later giant basin, called Isidis.

“This sets strong statistical limits on the number of giant basins that could have formed on Mars after Borealis”, said Bottke, principal investigator of the Institute for the Science of Exploring Targets, or ISET, team with NASA’s Solar System Exploration Research Virtual Institute or SSERVI.

“The number and timing of such giant impacts on early Mars has been debated, with estimates ranging from four to 30 giant basins formed in the time since Borealis. Our work shows that the lower values are more likely.”

In order to completely understand the implications of this bombardment, the team analysed the timing of the impacts responsible for other giant basins and compare their preservation state.

The preservation state of the four youngest giant basins on Mars - Hellas, Isidis, Argyre, and the now-buried Utopia basins were found to be strikingly similar to the larger and older Borealis basin.

Similar preservation of Borealis and these younger basins points out that any basins formed during this time interval should be similarly preserved. The study was published in Nature Geoscience.

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