by More than two million years ago, a giant asteroid crashed into Mars, splitting the surface with one giant crater and about two billion smaller individual craters. These secondary craters are visible over 1,000 miles (1,800 kilometers), making this asteroid incident one of the largest impacts seen on the Red Planet in recent times.
It is estimated that asteroids massive enough to cause widespread destruction like this will impact Mars once every 3 million years.
The impact that occurred at the equator of Mars in a region that mankind named Elysium Planitia; it left behind a main crater, an 8.6-mile (13.9-km) wide and 0.62-mile (1-km) deep crater called Corinto. On the other hand, the secondary craters from the impact range from 656 feet (200 meters) to 0.8 miles (1.3 km) in diameter and spread out in a large “ray system,” according to the scientists behind the findings.
Despite being 2.3 million years old, the team considers the crater and its secondary parts – some carved in lava flows from the summit of the extinct Martian volcano Elysium Mons – to be extremely young.
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“The Corinto crater in Elysium Planitia is a new impact crater that produced one of the most extensive systems of thermal jets and secondary craters on Mars, extending approximately 1,243 miles (2,000 km) to the south and covering a nearly 180° arc on Mars,” the team wrote in a related study.
The authors explained how they used thermal and visible imaging data collected by NASA’s Mars Reconnaissance Orbiter to describe a crater and a blanket of debris, or “ejecta,” thrown into the Martian atmosphere by the impact. Ejecta refers to any material that has been “ejected” from a crater as a result of some impact. In this case, the ejecta are pieces of Mars shot out of the huge, main crater cavity formed by the accident of the asteroid.
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 separated these ejecta-charged craters from other Martian craters specifically caused by asteroid strike events. This information was then used to estimate the age of the impact and the total number of secondary craters generated by the initial impact.
Measuring the distribution of secondary craters extending out from Corinto, the team found the largest concentrations to the south and southwest of the main impact crater.
There is a lack of ejecta north of the crater, which scientists think indicates the asteroid that caused this devastation entered the Red Planet’s atmosphere at an angle of about 30 to 45 degrees from the north or northeast.
The longest secondary craters the researchers found showed that some of the ejecta from the impact was sent as far as 1,150 miles (1,850 km). That’s about four times the length of the Great Canyon.
The secondary craters were not exactly different in distance from the main impact zone and in size, however. The team behind the results classified them according to their shape. Some were round and semicircular, while others looked “flattened circular,” or “elliptical.”
The researchers determined that the shape, or “morphology,” of the secondary craters was related to the speed with which the fragments that created them were ejected, the size of those fragments, and the surface composition of the Martian region on which they fell. Near Corinto, secondary craters were semicircular, and elliptical craters were found further from the main impact zone.
“The large number of secondary craters formed at Corinto is consistent with most of the ejected material being strong, competent basalt,” the team wrote.
Basalt are volcanic rocks formed by the rapid cooling of magnesium- and iron-rich lava, so the fragments are likely to be lava spewed by the previous volcano that the asteroid hit.
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The composition of some of the ejecta sent from the surface of Mars by this asteroid impact shows that the space rock was slammed down into water or ice. This is also shown by “pits” scattered throughout the floor of the Corinto crater, which suggests the drainage of water or gas released by the effect of the impact on materials rich in ice.
The team’s findings were presented at the 55th annual Lunar and Planetary Science Conference in Texas earlier in March.
