Curiosity really has made an impact on Mars. A sharp-eyed orbiter has spotted craters at the site where castoffs from the NASA rover's landing gear fell to the surface in August. Examining the damage can help reveal what it takes to scar the Red Planet.
Just after entering the Martian atmosphere, Curiosity's descent capsule dropped two laptop-sized blocks of tungsten, each weighing about 75?kilograms, which helped the craft tilt and glide towards its landing site in Gale crater.
The HiRISE camera on NASA's Mars Reconnaissance Orbiter has now snapped detailed photos of the surrounding area, showing that the blocks made craters 3?metres to 5?metres wide. The scars are about 80?kilometres to the west of Gale crater ? too far for the rover to investigate, because it can travel only about 100?metres per day.
But studying the impact zone from orbit can give planetary scientists cleaner data on Mars's surface and atmospheric properties than they could get from the hundreds of natural impact craters that they have already photographed.
"We think we kind of understand crater formation in terms of an object of a certain mass, at a certain velocity, should go ahead and create a crater of a certain size and depth," says Nadine Barlow of Northern Arizona University in Flagstaff. "But most of what we know is based on theory. This gives us some actual ground truth."
Scattershot asteroids
This isn't the first time we've studied artificial craters, says Jay Melosh of Purdue University in West Lafayette, Indiana. Discarded landing gear from other craft sent to the moon and Mars have been studied in detail, especially since the Mars Reconnaissance Orbiter arrived in Martian orbit in 2006. But the tungsten blocks, with their simple shapes, are closer to a theoretician's heart, he says.
"They made craters much closer to the kind of craters that natural asteroid impacts make."
The HiRISE camera also caught other impact scars flanking the ballast craters, which probably came from Curiosity's cruise module, the doughnut-shaped section that provided electricity and propulsion on the journey from Earth.
Mars is much closer than Earth to our solar system's main asteroid belt, and its much thinner atmosphere provides less protection from incoming space rocks. Melosh and colleagues have been trying to figure out the numbers and strengths of asteroids that regularly break up in the Martian atmosphere, based on the patterns that their pieces leave on the ground.
Seeing the scars from broken bits of the cruise stage, the durability of which is already known, will help test his theories. "For that reason, the debris from the ring is even more interesting," he says.
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