ITHACA, N.Y., May 7 (UPI) -- NASA's Mars exploration rover Spirit has discovered evidence of an ancient volcanic explosion on the Red Planet.
National Aeronautics and Space Administration scientists said the finding made at "Home Plate" -- a plateau of layered bedrock at Spirit's landing site -- is the first explosive volcanic deposit identified with a high degree of confidence by Spirit or its twin, Opportunity.
Steve Squyres of Cornell University, principal investigator for the rovers' science instruments, said there's strong evidence the six-foot high layers of bedrock are dominated by basaltic rocks.
"When basalt erupts, it often does so as very fluid lava, rather than erupting explosively," Squyres said. "One way for basaltic lava to cause an explosion is for it to come into contact with water -- it's the pressure from the steam that causes it to go boom."
One of the strongest pieces of evidence for an explosive origin at Home Plate is a "bomb sag" preserved in rocks on the lower slopes of the plateau. Bomb sags form when rocks ejected skyward by volcanic explosion fall into soft deposits, deforming them as they land.
The findings are reported in the May 4 issue of the journal Science.