NASA's
Spirit rover has stumbled upon evidence of an ancient volcanic explosion at
"Home Plate," a plateau of layered bedrock near the rover's landing
site in Gusev Crater.
The finding
lends more evidence to the idea that Mars had a watery past, and marks the
first explosive volcanic deposit seen by Spirit or its rover twin, Opportunity. However, scientists have long known ancient Mars was
volcanic. The evidence is plain: Olympus Mons, the tallest known volcano
and mountain in our solar system.
Steve Squyres of Cornell University, said the rock's
layers are probably from a volcanic explosion. The findings are detailed in
the May 4 issue of the journal Science.
Evidence
shows the area near Home Plate is mostly basaltic rock--indicating water may
have mixed with magma beneath the Martian ground. When basalt erupts, Squyres said, it's normally smooth-flowing lava and not
blown outward. "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."
The explosive
basalt isn't the only red flag for water. Another example is the high chlorine
content of the rocks, which might indicate that basalt had come into contact
with brine, or saltwater.
But one of
the strongest pieces of evidence is a "bomb
sag" on the lower slopes of the plateau. On Earth, bomb sags
form when rocks eject skyward by a volcanic explosion and fall into soft
deposits which deform as they land.
Spirit and Opportunity are in their fourth year of exploring
Mars. As of April 26, Spirit had spent 1,177 sols, or Martian days, on the
surface of Mars and had driven 4.4 miles, and Opportunity
had spent 1,157 sols and driven 6.5 miles.
"Considering
their age, both rovers are in good health," said John Callas, project manager
of the Mars Exploration Rover mission at NASA's Jet Propulsion Laboratory, Pasadena, California.
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