Washington, Dec 17 : Dust avalanches around impact craters on Mars may be the result of the shock wave preceding the actual impact, a new study has claimed.
According to a study led by Kaylan Burleigh at the University of Arizona, when a meteorite careens toward the dusty surface of the Red Planet, it kicks up dust and can cause avalanching even before the rock from outer space hits the ground.
“We expected that some of the streaks of dust that we see on slopes are caused by seismic shaking during impact,” Burleigh said.
“We were surprised to find that it rather looks like shockwaves in the air trigger the avalanches even before the impact,” he said.
Since the atmosphere of Mars is thin, which is 100 times less dense than that of the Earth, even small rocks that would burn up or break up before they could hit the ground here on Earth crash into the Martian surface relatively unimpeded.
Each year, about 20 fresh craters between 1 and 50 meters (3 to 165 feet) show up in images taken by the HiRISE camera on board NASA''''s Mars Reconnaissance Orbiter.
For this study, the team zoomed in on a cluster of five large craters, which all formed in one impact event close to Mars’ equator, about 825 kilometres (512 miles) south of the boundary scarp of Olympus Mons, the tallest mountain in the solar system.
Previous observations by the Mars Global Surveyor orbiter, which imaged Mars for nine years until 2006, showed that this cluster was blasted into the dusty surface between May 2004 and February 2006.
The authors interpret the thousands of downhill-trending dark streaks on the flanks of ridges covering the area as dust avalanches caused by the impact. The largest crater in the cluster measures 22 meters, or 72 feet across and occupies roughly the area of a basketball court.
Most likely, the cluster of craters formed as the meteorite broke up in the atmosphere, and the fragments hit the ground like a shotgun blast.
Narrow, relatively dark streaks varying from a few meters to about 50 meters in length scour the slopes around the impact site.
“The dark streaks represent the material exposed by the avalanches, as induced by the airblast from the impact,” Burleigh said.
“I counted more than 100,000 avalanches and, after repeated counts and deleting duplicates, arrived at 64,948,” he said.
When Burleigh looked at the distribution of avalanches around the impact site, he realized that their number decreased with distance in every direction, consistent with the idea that they were related to the impact event.
However, it wasn’t until he noticed a pair of peculiar surface features resembling a curved dagger, described as scimitars, extending from the central impact crater, that the way in which the impact caused the avalanches became evident.
“Those scimitars tipped us off that something other than seismic shaking must be causing the dust avalanches,” Burleigh said.
As a meteor screams through the atmosphere at several times the speed of sound, it creates shockwaves in the air. Simulating the shockwaves generated by impacts on Martian soil with computer models, the team observed the exact pattern of scimitars they saw on their impact site.
“We think the interference among different pressure waves lifts up the dust and sets avalanches in motion. These interference regions, and the avalanches, occur in a reproducible pattern,” Burleigh said.
“We checked other impact sites and realized that when we see avalanches, we usually see two scimitars, not just one, and they both tend to be at a certain angle to each other. This pattern would be difficult to explain by seismic shaking,” he said.
In the absence of plate tectonic processes and water-caused erosion, the researchers concluded that small impacts might be more important in shaping the Martian surface than previously thought.
“This is one part of a larger story about current surface activity on Mars, which we are realizing is very different than previously believed,” Alfred McEwen, one of the co-authors of the study, said.
“We must understand how Mars works today before we can correctly interpret what may have happened when the climate was different, and before we can draw comparisons to Earth,” he added.
The study has been published in published in the planetary science journal Icarus. (ANI)
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