MessageToEagle.com – A new study sheds light on strange grooves crisscrossing the surface of the Martian moon Phobos.
A new study suggests that grooves were made by rolling boulders blasted free from an ancient asteroid impact. Researchers simulated the movement of debris from Stickney crater, a huge gash on one end of Phobos’ oblong body. The models show that boulders rolling across the surface in the aftermath of the Stickney impact could have created the puzzling patterns of grooves seen on Phobos today.
“These grooves are a distinctive feature of Phobos, and how they formed has been debated by planetary scientists for 40 years,” said Ken Ramsley, a planetary science researcher at Brown University who led the work. “We think this study is another step toward zeroing in on an explanation.”
Many different explanations have been put forward to explain the origin of the grooves, first observed by NASA’s Mariner and Viking missions in tlhe 1970s. It has been suggested the grooves are signs of structural failure, groove-carving debris comes from large impacts on Mars,
For a moon the size of the diminutive Phobos (27 kilometers across at its widest point), Stickney is a huge crater at 9 kilometers across. The impact that formed it would have blown free tons of giant rocks, making the rolling boulder idea entirely plausible, Ramsley says. But there are also some problems with the idea and there are several questions that lack answers.
How could there be grooves created at two different times from one single event? What’s more, a few grooves run through Stickney itself, suggesting that the crater must already have been there when the grooves formed. There’s also a conspicuous dead spot on Phobos where there are no grooves at all.
Why would all those rolling boulders just skip one particular area?
To explore those questions, Ramsley designed computer models to see if there was any chance that the “rolling boulder model” could recreate these confounding patterns. The models simulate the paths of the boulders ejected from Stickney, taking into account Phobos’ shape and topography, as well as its gravitational environment, rotation and orbit around Mars.
Ramsley said he had no expectations for what the models might show. He wound up being surprised at how well the model recreated the groove patterns seen on Phobos.
“The model is really just an experiment we run on a laptop,” Ramsley said. “We put all the basic ingredients in, then we press the button and we see what happens.”
The models showed that the boulders tended to align themselves in sets of parallel paths, which jibes with the sets of parallel grooves seen on Phobos.
The simulations show that because of Phobos’ small size and relatively weak gravity, Stickney stones just keep on rolling, rather than stopping after a kilometer or so like they might on a larger body. In fact, some boulders would have rolled and bounded their way all the way around the tiny moon. That circumnavigation could explain why some grooves aren’t radially aligned to the crater. Boulders that start out rolling across the eastern hemisphere of Phobos produce grooves that appear to be misaligned from the crater when they reach the western hemisphere.
That round-the-globe rolling also explains how some grooves are superposed on top of others. The models show that grooves laid down right after the impact were crossed minutes to hours later by boulders completing their global journeys. In some cases, those globetrotting boulders rolled all the back to where they started — Stickney crater. That explains why Stickney itself has grooves.
MessageToEagle.com