[meteorite-list] Mars Rovers Finds That Water Persisted

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Jul 19 18:22:21 2004
Message-ID: <200407192216.PAA16192_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/news/news.jsp?id=ns99996178

Mars rover finds that water persisted
David L Chandler
New Scientist
July 19, 2004

Surface water on Mars existed across a significant span of time, not
just for years but eons, suggest new findings made by NASA's Mars rover
Opportunity.

Within a few weeks of its landing on Mars in January 2004, Opportunity
revealed what was uppermost on the twin rovers' agenda: that bodies of
liquid water once existed on the surface of Mars. But the evidence
proved what could have been only a solitary event - a single wet episode.

The new discovery, reported by NASA's Jet Propulsion Laboratory on
Friday, pushes the boundaries significantly further back, into
geological timescales.

After motoring down several metres into a the large Endurance crater,
Opportunity has found what science team member Jack Farmer of Arizona
State University calls "razorback," a ridge of thin, jagged vertical
plates sticking up at the edge of a flat expanse of bedrock.

The team suspects that the ridge is a layer of rock that formed when
earlier layers of rock cracked, and mineral-laden water percolated
through the cracks leaving deposits behind, forming veins, or "fracture
fill". Those deposits formed rock harder than the surrounding material,
so as the rock eroded away it left this harder ridge behind. The
fractures, Farmer says, may have been caused by the impact that produced
the crater.


Salt crystals

The surrounding rock is the very bedrock that Opportunity has been
studying ever since its arrival on Mars, first in a tiny crater called
Eagle, and for the last month in the much larger Endurance crater.

In both places, the layered bedrock has provided multiple lines of
evidence - unusual minerals, voids left by dissolved salt crystals, and
hematite spheres - showing that liquid water once flowed there. And at
the Endurance site, this evidence for water extends through five
successive geological layers, or units, extending back in time from the
original layer.

But the new "razorback" find dramatically extends this record. Formation
of such crack filling material requires liquid water, but at a time so
much later that these different layers of marine sediment had time to be
compacted into stone, hard enough to form sharp cracks rather than
crumbling.

The actual time span has not been estimated, but it reveals enough time
to strengthen the possibilities that life could have evolved on Mars.
The team is expects to spend most of this week analysing the razorback
with the rover's various spectrographs.

Dwindling sunlight

Meanwhile, there was great excitement on the other side of Mars. The
rover Spirit, skirting the edge of a hill called West Spur on the edge
of Columbia Hills and preparing to drive up it, has now driven over an
outcrop of bedrock - something that had never been seen before at
Spirit's site in Gusev crater.

"Eureka! We have found it!" exclaimed Matt Golombek of NASA-JPL, a
science team member. "Spirit has an outcrop under the rover wheels. And
an outcrop is the currency for geologists." Studying it should help
reveal the geological history of the Gusev site.

Both rovers are in the most scientifically interesting and technically
challenging terrain yet, though both are also somewhat limited by the
dwindling sunlight and plummeting temperatures as midwinter approaches
in September. And both remain healthy, despite one balky wheel on
Spirit, having more than doubled their 90-day design lifetimes.
   
Received on Mon 19 Jul 2004 06:16:06 PM PDT