[meteorite-list] Rover Spirit Finds Evidence of Early Martian Volcanic Activity - And Further Hints of a Watery Past

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 9 May 2007 17:34:25 -0700 (PDT)
Message-ID: <200705100034.RAA06794_at_zagami.jpl.nasa.gov>

Chronicle Online e-News

Rover Spirit finds evidence of early Martian volcanic activity at
Home Plate plateau -- and further hints of a watery past

http://www.news.cornell.edu/stories/May07/squyres.pyroclastic.html

May 8, 2007

By Lauren Gold
Cornell University
LG34 at cornell.edu

A plateau on Mars known as Home Plate shows evidence of long-past
explosive volcanic activity, say scientists on NASA's Mars
Exploration Rover mission. And data collected during the rover
Spirit's initial pass across the 90-meter (295 feet) wide plateau
also supports earlier findings indicating that water once existed at
or beneath the planet's surface.

The research appeared in the May 4 issue of the journal Science.

Home Plate's finely layered appearance made it one of the most
tantalizing targets within Spirit's reach in Gusev Crater, said Steve
Squyres, the mission's principal investigator and the Goldwin Smith
Professor of Astronomy at Cornell. The rover captured its first
panoramic image of Home Plate in August 2005 from the summit of
Husband Hill and reached the plateau in the Columbia Hills' inner
basin in February 2006.

It quickly sent back an image Squyres called "one of the neatest
pictures we've taken with the rovers." The image shows a small (4
centimeter) rock fragment nestled within a downward deflection in
otherwise ruler-straight lines of layering -- a feature likely to be
what geologists call a bomb sag. These usually form when a rock
fragment (the bomb) is thrown upward in an explosion; then lands in
deformable material, causing the material to sag beneath it.

Chemical analysis shows the rock is made of the same material
(basalt) as volcanic rocks around it, indicating the explosion was
not the result of an impact by an exotic source (such as a
meteorite). The rock also shows tiny spherical particles that look
like accretionary lapilli -- coagulated bits of ash that typically
rain down after a volcanic explosion.

Any volcanic activity at Home Plate probably happened billions of
years ago -- but part of what makes it intriguing, said Squyres, is
its similarity to regions on other parts of the planet.

"There are lots and lots of places on Mars where, from orbit, you see
layered deposits locally that kind of look like this," said Squyres,
"and so it really raises the possibility that a lot of these things
all over the planet could be explosive volcanic deposits."

That the rocks at Home Plate are basalt -- not a material normally
associated with explosions -- also hints that water was involved.
"When basalt erupts, it often does so as very fluid lava, rather than
erupting explosively," Squyres said. But a notable exception comes
when hot basalt meets water to cause a steam-driven explosion.

The bomb sag -- now dry, but shaped as if the rock sitting in it
landed with a splat instead of a thud -- is a second hint that the
surface was once wet. A third is the material's high chlorine
content, which may point to past exposure to a briny fluid.

Home Plate may be the site of an early impact crater that was later
filled in by volcanic debris, according to stereo images that show
the layered rocks around its edge all sloping in toward the plateau's
center. Billions of years of erosion could have stripped away the
surrounding material but left the debris protected by the crater's
rim -- resulting in the current plateau.

The Science paper is based on data collected during a frenetic few
months in 2006, as Spirit was chugging down the Columbia Hills toward
a safe place to ride out the Martian winter.

The route to safety included a path across Home Plate -- leaving
Spirit's drivers on Earth with a dilemma.

"There was all this fabulous science around us," Squyres said. But
with winter approaching, the team had the harrying task of getting
Spirit to its destination in time, while gathering as much data as
possible along the way. "We got an amazing amount of science done,
all things considered," he said. "But there's more work to be done
here." Spirit is now back at Home Plate, continuing exploration there.

Another sol, another discovery ... (and no one's yawning)

A year after Spirit first reached Home Plate plateau, the rover and
its twin Opportunity are still healthy and plugging away.

Spirit, having made it through the winter, is back for a second pass
at Home Plate (now driving ably on five wheels after its right front
wheel died last year). And the baseball theme for names at Home Plate
continues: Last year, rocks in the area were named to honor players
from the Negro Leagues of the early 20th century; discoveries this
year celebrate women from the All-American Girls Professional
Baseball League of the 1940s and '50s.

Meanwhile, Opportunity, on Meridiani Planum on the opposite side of
the planet, has been exploring the rim of Victoria Crater and is now
heading back to an alcove called Duck Bay. From there, it will look
for a place to start the tricky descent into the crater.

Both rovers are well past sol 1,100 of their 90-sol warranty (a sol
is a Martian day). Mission members in Ithaca and at NASA's Jet
Propulsion Lab in Pasadena have settled into a routine Squyres calls
"a sort of Earth time-Mars time hybrid." And there's always more to
do.

"We now have an operations concept that is sustainable in the long
run," said Squyres. "We can keep doing this as long as we need to."

-- 

Received on Wed 09 May 2007 08:34:25 PM PDT