Underground nuclear testing results could explain strange Mars craters

Lessons learned from underground nuclear tests and volcanoes could explain how a category of unusual impact craters formed on Mars, a U.S. astronomer says. The distinctive martian craters feature a thin-layered outer deposit that extends well beyond the typical range of ejected material thrown out by impacts, Northern Arizona University astronomer and physicist Nadine Barlow said. She has dubbed the craters seen in high-resolution images of the martian surface Low-Aspect-Ratio Layered Ejecta Craters. She was studying the images for inclusion in a catalog of martian craters. "I had to ask, 'What is going on here?'" Barlow said. A review of "explosion literature" revealed a phenomenon known as base surge, she said, where after a large explosion fine-grain material forms a cloud and moves out along the surface, eroding the surface and picking up more material, creating an extensive outer deposit. Adjusting equations from volcano research for martian conditions could accurately explain the "thin, sinuous, almost flame-like deposits" seen on Mars, she said. "So we think we're on to something," she said. The craters are found primarily at higher latitudes where thick, fine-grained sedimentary deposits are rich with subsurface ice. "The combination helps vaporize the materials and create a base flow surge," Barlow said. She presented the findings this week at the American Astronomical Society Division for Planetary Sciences in Denver.