[meteorite-list] Sandtrapped Rover Makes a Big Discovery

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 3 Dec 2009 16:54:38 -0800 (PST)
Message-ID: <200912040054.nB40scJC020889_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2009/02dec_troy.htm

Sandtrapped Rover Makes a Big Discovery
NASA Science News
12.02.2009

*December 2, 2009:* Homer's Iliad tells the story of Troy, a city
besieged by the Greeks in the Trojan War. Today, a lone robot sits
besieged in the sands of Troy while engineers and scientists plot its
escape.

Welcome to "Troy" - Mars style. NASA's robotic rover Spirit is bogged
down on the Red Planet in a place the rover team named after the ancient
city.

So why aren't scientists lamenting?

"The rover's spinning wheels have broken through a crust, and
we've found something supremely interesting in the disturbed soil," says
Ray Arvidson of the Washington University in St. Louis.

Spirit, like its twin rover Opportunity, has roamed the Red Planet for
nearly 6 years. During that time, the rover has had some close calls and
come out fighting from each. In fact, it's been driving backwards since
one of its wheels jammed in 2006.

>From the beginning, the rovers' motto has been "follow the water." Both
rovers have been searching Mars for minerals formed in the presence of
H_2 O. Mars appears dry today, but minerals can provide clues that water
was once there.

"It's been easy for Opportunity to find such minerals," explains
Arvidson. "Opportunity landed in an ancient lake bed. Spirit has had to
work much harder. Spirit landed in basaltic plains formed by lava flows
chewed up by repeated meteoroid impacts. There's been little evidence of
anything that was ever very wet."

But when Spirit reached an area of Mars called the "Columbia Hills," the
whole complexion of the mission changed. "Spirit came across iron
hydroxide, a mineral that forms in the presence of water. That alerted
us to the change. We started coming across more and more rocks formed in
the presence of water."

Then Spirit got stuck in a patch of loose soil on the edge of a small
crater. Heavy sigh. Stuck again.

But wait!

"Spirit had to get stuck to make its next discovery," says Arvidson.

As the rover tried to break free, its wheels began to churn up the soil,
uncovering sulfates underneath.

"Sulfates are minerals just beneath the surface that shout to us that
they were formed in steam vents, since steam has sulfur in it. Steam is
associated with hydrothermal activity ??? evidence of water-charged
explosive volcanism. Such areas could have once supported life."

"And most amazingly, the boundary between the sulfate-rich soil and the
soil with just the generic concentration of sulfates runs right down the
middle of the stranded rover. Spirit is lodged on the edge of a crater
-- sitting astride the boundary!"

"Also, the robot found that the top of the sulfate material is crusty.
Ancient sulfates probably formed this crust as they were processed by
variations in climate associated with changes in Mars' orbit over
millions of years."

Here's what the scientists think: When a Martian pole faces the sun in
Martian summer, it gets warmer at that pole and the water ice shifts to
the equator. It even snows there! Warm dark soil under the snow causes
the bottom layer of snow to melt. The water trickles into the sulfates,
dissolving the water-soluble iron sulfates and forming a crust with the
calcium sulfates remaining.

"By being stuck at Troy, Spirit has been able to teach us about the
modern water cycle on Mars." Indeed, Spirit's saga at Troy has given
scientists material evidence of past water on Mars on two time scales:
ancient volcanic times, and cycles ongoing to the present day.

"We've sat here for more than 6 months. That's a long time to take
measurements. We've learned a lot. Troy is a good place to be under
siege, but we're ready to leave."

Will Spirit break free to continue its incredible journey? Tune in to
Science at NASA to find out if the escape plan works.

Author: Dauna Coulter <dauna.d.coulter at nasa.gov> |
Editor: Dr. Tony Phillips <james.a.phillips at earthlink.net> |
Credit: Science at NASA <http://science.nasa.gov>
Received on Thu 03 Dec 2009 07:54:38 PM PST