Grooves Around Vesta’s Equator Likely Caused By Impact At Asteroid’s South Pole

Chuck Bednar for redOrbit.com – Your Universe Online
The deep belt-like grooves that encircle Vesta’s equator were likely caused by a massive impact on the south pole of the asteroid, according to research currently available online and scheduled for publication in the February 2015 edition of the journal Icarus.
As part of the study, senior author Peter Schultz, a professor of earth, environmental, and planetary sciences at Brown University, and his colleagues used computer simulations and an ultra-high-speed cannon at NASA’s Ames Research Center in California to discovered the processes through which those deep surface grooves formed.
“Vesta got hammered. The whole interior was reverberating, and what we see on the surface is the manifestation of what happened in the interior,” Schultz, who was joined on the research project by former Brown graduate student and current Johns Hopkins University researcher Angela Stickle and D.A Crawford of Sandia National Laboratories in Albuquerque, New Mexico, said in a statement Monday.
The study authors suggest that the Rheasilvia basin on the asteroid’s south pole was created by the impact of an object that collided with it at an angle instead of straight on. While they said the collision would have been a glancing blow, it still would have done enough damage to cause rocks deep within Vesta’s interior to crack and crumble seconds after impact, with major faults forming the canyons near its equator just minutes later.
“As soon as Pete and I saw the images coming down from the Dawn mission at Vesta, we were really excited,” explained Stickle. “The large fractures looked just like things we saw in our experiments. So we decided to look into them in more detail, and run the models, and we found really interesting relationships.”

During the study, the research team used the Ames Vertical Gun Range, a cannon with a 14-foot barrel that is used to simulate collisions on celestial bodies. They explained that the NASA instrument uses a combination of gunpowder and compressed hydrogen gas to launch projectiles at blinding speed, up to 16,000 miles per hour.
Using the Vertical Gun Range, Schultz and his team launched small projectiles at softball-sized spheres built from an acrylic material known as PMMA, which is usually clear but turns opaque at high stress points upon impact. By analyzing the impacts using special high-speed cameras capable of capturing one million shots per second, the study authors were able to witness how collision-related stress propagated through the material.
Their experiments revealed that the damage starts from the impact point, but quickly causes failure patterns to form inside the sphere, opposite the region where the actual collision took place. Those failures, the researchers said, grow inwards toward the center of the sphere, then spread outwards toward the edges.
“The researchers showed that the outward-blooming ‘rosette’ of damage extending to the surface is responsible for the troughs that form a belt around Vesta’s equator,” Brown’s Kevin Stacey explained. “The results answer some questions about Vesta’s belt that had long been puzzling. Chief among them is the orientation of the belt with respect to the crater. The belt’s angle isn’t exactly what would be expected if it were caused by the Rheasilvia impact.”
“These new experiments suggest that the crooked belt is the result of the angle of impact,” Stacey added. “An oblique impact causes the damage plane to be tilted with respect the crater. The orientation of Vesta’s belt sheds light on the nature of the impact. The researchers conclude that the object that created Rheasilvia came in at an angle less than 40 degrees, traveling at about 11,000 miles per hour.”
Vesta, the second largest asteroid in the solar system, recently played a key role in research which revealed water has existed on Earth longer than previously believed. In that study, scientists compared meteorite samples from the asteroid to ancient, unaltered meteorites known as carbonaceous chondrites, and found that they had matching hydrogen isotope ratios, and thus matched the chemical fingerprints of Earth’s hydrogen.
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