[meteorite-list] Mars Rover Yielding New Clues While Lodged in Martian Soil

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.cfm?release=2009-102  

Mars Rover Yielding New Clues While Lodged in Martian Soil
Jet Propulion Laboratory
June 25, 2009

PASADENA, Calif. -- NASA's Mars rover Spirit, lodged in Martian soil
that is causing traction trouble, is taking advantage of the situation
by learning more about the Red Planet's environmental history.

In April, Spirit entered an area composed of three or more layers of
soil with differing pastel hues hiding beneath a darker sand blanket.
Scientists dubbed the site "Troy." Spirit's rotating wheels dug
themselves more than hub deep at the site. The rover team has spent
weeks studying Spirit's situation and preparing a simulation of this
Martian driving dilemma to test escape maneuvers using an engineering
test rover at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

A rock seen beneath Spirit in images from the camera on the end of the
rover's arm may be touching Spirit's belly. Scientists believe it
appears to be a loose rock not bearing the rover's weight. While Spirit
awaits extraction instructions, the rover is keeping busy examining
Troy, which is next to a low plateau called Home Plate, approximately
3.2 kilometers (2 miles) southeast of where Spirit landed in January 2004.

"By serendipity, Troy is one of the most interesting places Spirit has
been," said Ray Arvidson of Washington University in St. Louis. Arvidson
is deputy principal investigator for the science payloads on Spirit and
its twin rover, Opportunity. "We are able here to study each layer, each
different color of the interesting soils exposed by the wheels."

One of the rover's wheels tore into the site, exposing colored sandy
materials and a miniature cliff of cemented sands. Some disturbed
material cascaded down, evidence of the looseness that will be a
challenge for getting Spirit out. But at the edge of the disturbed
patch, the soil is cohesive enough to hold its shape as a steep
cross-section.

Spirit has been using tools on its robotic arm to examine tan, yellow,
white and dark-red sandy soil at Troy. Stretched-color images from the
panoramic camera show the tints best.

"The layers have basaltic sand, sulfate-rich sand and areas with the
addition of silica-rich materials, possibly sorted by wind and cemented
by the action of thin films of water. We're still at a stage of multiple
working hypotheses," said Arvidson. "This may be evidence of much more
recent processes than the formation of Home Plate...or is Home Plate
being slowly stripped back by wind, and we happened to stir up a deposit
from billions of years ago before the wind got to it?"

Team members from NASA's Johnson Space Center in Houston feel initial
readings suggest that iron is mostly present in an oxidized form as
ferric sulfate and that some of the differences in tints at Troy
observed by the panoramic camera may come from differences in the
hydration states of iron sulfates.

While extraction plans for the rover are developed and tested during the
coming weeks, the team plans to have Spirit further analyze the soil
from different depths. This research benefits from having time and
power. In April and May, winds blew away most of the dust that had
accumulated on Spirit's solar panels.

"The exceptional amount of power available from cleaning of Spirit's
solar arrays by the wind enables full use of all of the rover's science
instruments," said Richard Moddis of the Johnson team. "If your rover is
going to get bogged down, it's nice to have it be at a location so
scientifically interesting."

The rover team has developed a soil mix for testing purposes that has
physical properties similar to those of the soil under Spirit at Troy.
This soil recipe combines diatomaceous earth, powdered clay and play
sand. A crew is shaping a few tons of that mix this week into contours
matching Troy's. The test rover will be commanded through various
combinations of maneuvers during the next few weeks to validate the
safest way to proceed on Mars.

Spirit's right-front wheel has been immobile for more than three years,
magnifying the challenge. While acknowledging a possibility that Spirit
might not be able to leave Troy, the rover team remains optimistic.
Diagnostic tests on Spirit in early June provided encouragement that the
left-middle wheel remains useable despite an earlier stall.

"With the improved power situation, we have the time to explore all the
possibilities to get Spirit out," said JPL's John Callas, project
manager for Spirit and Opportunity. "We are optimistic. The last time
Spirit spun its wheels, it was still making progress. The ground testing
will help us avoid doing things that could make Spirit's situation worse."

Images and further information about Spirit and Opportunity are
available at: http://marsrovers.jpl.nasa.gov and
http://www.nasa.gov/rovers .

Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez at jpl.nasa.gov

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown at nasa.gov

2009-102