More than two million years ago, a giant asteroid hit Mars, creating a large crater and approximately two billion smaller craters on the surface. These secondary craters appear across 1,000 miles (1,800 kilometers), making this asteroid event one of the largest impacts seen on the Red Planet in relatively recent history.
It is estimated that asteroids large enough to cause widespread destruction like this will hit Mars only every 3 million years.
The impact occurred at Mars’ equator, in a region humanity calls Elysium Planitia; It left behind a main crater called Corinto, 8.6 miles (13.9 km) wide and 0.62 mi (1 km) deep. On the other hand, secondary craters from the impact range in size from 656 feet (200 meters) to 0.8 miles (1.3 km) across and extend outward in a large “ray system,” according to the scientists behind the results.
Although 2.3 million years old, the crater and its secondary fragments (some carved into lava flows originating from the summit of the extinct volcano Elysium Mons on Mars) are considered extremely young by the team.
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“The Corinto crater is a new impact crater on Elysium Planitia that produced one of the most extensive thermal beam systems and secondary craters on Mars, extending approximately 2,000 km to the south and occupying an approximately 180-degree arc on Mars.” the team wrote in a related study.
The authors described how they used both thermal and visible imaging data collected by NASA’s Mars Reconnaissance Orbiter to identify the crater and the debris blanket, or “ejection,” that was expelled into the Martian atmosphere by the impact. Ejecta refers to any material “ejected” from the crater by an impact. In this case, what is ejected are pieces of Mars that were ejected from the huge main crater cavity formed by the asteroid’s impact.
This data, collected by the spacecraft’s High Resolution Imaging Experiment (HiRISE) and Context Camera (CTX) instruments, was fed to a machine learning program that distinguished the craters resulting from this impact ejection from other Martian craters specifically resulting from asteroid impact events. This information was then used to estimate the age of the impact and the total number of secondary craters created by the initial impact.
By measuring the distribution of secondary craters extending from Corinto, the team found that the largest concentrations were south and southwest of the main impact crater.
There is a lack of ejecta north of the crater, and scientists think this indicates that the asteroid that caused this destruction entered the Red Planet’s atmosphere from the north or northeast at an angle of about 30 to 45 degrees.
The most distant secondary craters found by researchers showed that some of the ejecta from the impact was thrown as far as 1,150 miles (1,850 km). This is approximately four times the length of the Grand Canyon.
However, secondary craters differed not only in their distance and size from the main impact site. The team behind the findings also classified them based on their shape. Some were round and semicircular, while others appeared “flattened circular” or “elliptical.”
The researchers determined that the shape, or “morphology,” of secondary craters depends on the speed at which the pieces that form them are ejected, the size of those pieces, and the surface composition of the area of Mars they hit. While secondary craters close to Corinto have a semicircular shape, elliptical-shaped craters have also been found further away from the main impact site.
“The numerous secondary craters formed by Corinto are consistent with most of the ejected material being strong and competent basalt,” the team wrote.
Basalts are volcanic rocks formed by the rapid cooling of lava rich in magnesium and iron; Therefore, the pieces probably represent lava gushing from the volcano that was previously hit by the asteroid.
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The combination of this asteroid impact and some ejections from the Martian surface suggests that the space rock hit water or ice. This is also illustrated by the “pits” spread across the floor of the Corinto crater; This implies the drainage of water or gas released by the action of impact on ice-rich materials.
The team’s results were presented at the 55th annual Lunar and Planetary Science Conference in Texas in early March.