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Tornado Winds on Ancient Mars Created Mysterious Streaks

Tornado-like winds resulting from impacts on ancient Mars might explain the presence of mysterious marks observed near large impact craters on the red planet. The new findings are published in the journal Icarus.

Streaks of unknown origin seen in the vicinity of large Martian craters were apparently created in the aftermath of important collisions. What exactly created these marks? According to the new study, conducted by researchers from Brown University, they might have been formed from vapour plumes—emanating from impacts—resulting in 800 km/h tornado-like winds which would account for the streaks.

It all started a few years ago when Brown University’s geologist Peter Schultz, upon contemplating NASA images of the red planet, observed a series of bright streaks coming from a number of large impact craters on the Martian surface. The possibility of the streaks—which can only be seen in thermal infrared images captured at (Martian) night—being ejecta patterns was ruled out because they covered a longer distance from the craters than the usual ejecta.

Schultz and graduate student Stephanie Quintana, therefore, looked into the origin of the streaks using simulations combined with geological and laboratory impact experiments. Their findings show that massive collisions into Mars’ surface would have created large craters, all the while generating tornado-like wind vortices moving at over 800 km/h; Schultz resembles these to an F8 tornado. These winds, never to happen again unless a major impact occurs, would have wiped the surface of the planet, removing dust and small rocks, thereby revealing the underlying surfaces.

These streaks cannot be seen in images taken in visible wavelengths, explains Schultz. On the other hand, infrared images retain differences in heat stored on the surface: regions appearing brighter during Martian nighttime are a sign of a greater heat retention from the previous day. According to Schultz, brightness under infrared shows blockier surfaces which are able to save more heat than surfaces with dust and debris; this implies that some event happened whereby those surfaces were cleaned from their materials, leaving them bare. This something would be the tornado-like winds caused from huge impacts.

What happens during large impact events? A heavenly body, such as an asteroid, colliding into a planet at high velocity causes a great chunk of materials from both objects to become instantaneously vaporised. Vapour plumes thus generated would travel outwardly from the impact point at great speeds, as shown by Schultz’s impact experiments. These vapour plumes would have supersonic speeds, creating powerful winds in the atmosphere of Mars. A plume hitting a raised feature on the surface would disturb the flow, resulting in great tornado-like vortices to reach the surface—this phenomenon would, eventually, scour narrow streaks on the surface.

“Where these vortices encounter the surface, they sweep away the small particles that sit loose on the surface, exposing the bigger blocky material underneath, and that’s what gives us these streaks,” says Schultz.

“We know these formed at the same time as these large craters, and we can date the age of the craters. So now we have a template for looking at erosion.”

Furthermore, these findings are hoped to provide invaluable information about the surface of Mars back when it was hit by some external object. According to the experiments, it is thought that volatile substances, such as layers of water ice on Mars, influence the amount of vapour generated from an impact. Therefore, streaks might help researchers determine whether ice was present on Mars back then.

“The next step is to really dig into the conditions that cause the streaks,” says Schultz. “They may have a lot to tell us, so stay tuned.”

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