NASA's Mars Rover Finds Evidence of Ancient Volcanic Explosion

NASA’s Mars Rover Finds Evidence of Ancient Volcanic Explosion
Jet Propulsion Laboratory
May 03, 2007

NASA’s Mars Exploration Rover Spirit has discovered evidence of an
ancient volcanic explosion at “Home Plate,” a plateau of layered
approximately 2 meters (6 feet) high within the “Inner Basin” of
Columbia Hills, at the rover’s landing site in Gusev Crater. This is
first explosive volcanic deposit identified with a high degree of
confidence by Spirit or its twin, Opportunity.

There is strong evidence that those layers are from a volcanic
explosion, said Steve Squyres of Cornell University, Ithaca, N.Y.
Squyres is principal investigator for the rovers’ science instruments.
The findings about volcanic activity are reported in a paper published
in the May 4 issue of the journal Science.

Evidence shows the area near Home Plate is dominated by basaltic
“When basalt erupts, it often does so as very fluid lava, rather than
erupting explosively,” Squyres said. “One way for basaltic lava to
an explosion is for it to come into contact with water - it’s the
pressure from the steam that causes it to go boom.”

Scientists suspect that the explosion that formed Home Plate may have
been caused by an interaction of basaltic lava and water. “When you
at composition of the rocks in detail, there are hints that water may
have been involved,” Squyres said. One example is the high chlorine
content of the rocks, which might indicate that basalt had come into
contact with a brine.

One of the strongest pieces of evidence for an explosive origin for
Plate is a “bomb sag” preserved in layered rocks on the lower slopes
the plateau. Bomb sags form in volcanic explosions on Earth when rocks
ejected skyward by the explosion fall into soft deposits, deforming
as they land.

Spirit arrived at Home Plate in February 2006 and spent several months
exploring it in detail before driving to “Low Ridge” to pass the
winter. Spirit has now returned to Home Plate to continue exploration
there. “We decided to go back to Home Plate, once the Martian winter
ended, because it is one of the most interesting places that we’ve
on Gusev Crater,” Squyres said. “Last year we primarily explored the
northern and eastern sides of it. This time we’re hoping to get to the
southern and western sides.” Spirit’s continued exploration of Home
Plate will focus largely on testing the idea that water was involved
its formation process.

Spirit and Opportunity are in their fourth year of exploring Mars.
successfully completed their three-month prime missions in April 2004,
and the missions have been extended four times. As of April 26, Spirit
had spent 1,177 sols, or Martian days, on the surface of Mars and had
driven 7,095 meters (4.4 miles), and Opportunity had spent 1,157 sols
and driven 10,509 meters (6.5 miles).

“Considering their age, both rovers are in good health. All science
instruments are functioning and continuing to return superb science
data,” said John Callas, project manager of the Mars Exploration Rover
mission at NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

JPL manages the Mars Exploration Rover project for NASA’s Science
Mission Directorate. JPL is a division of the California Institute of
Technology in Pasadena.

For images and information about the rovers and their discoveries on
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Media contacts: Guy Webster/Natalie Godwin 818-354-6278/0850
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown 202-358-1726
NASA Headquarters, Washington