Mars Rovers Break Driving Records, Examine Salty Soil
On three consecutive days, NASA's Mars Exploration Rover
Opportunity accomplished unprecedented feats of martian
motion, covering more total ground in that period than either
Opportunity or its twin, Spirit, did in their first 70 days
Image right: Opportunity used its navigation camera to take the images combined into this view of the rover's surroundings on Opportunity's 387th martian day, or sol (Feb. 24, 2005). In the full image, the eastern edge of a small crater dubbed "Naturaliste," can seen in the right foreground. Image credit: NASA/JPL.
+ Full image.
Spirit, meanwhile, has uncovered soil that is more than half
salt, adding to the evidence for Mars' wet past. The golf-
cart-size robots successfully completed their three-month
primary missions in April 2004 and are continuing extended
Opportunity set a one-day distance record for martian
driving, 177.5 meters (582 feet), on Feb. 19. That was the
first day of a three-day plan transmitted to the rover as a
combined set of weekend instructions. During the preceding
week, engineers at NASA's Jet Propulsion Laboratory had sent
Opportunity and Spirit an upgrade of the rovers' software,
onboard intelligence the rovers use for carrying out day-to-
The new record exceeded a two-week old former best by 13
percent. As on all previous long drives by either rover, the
traverse began with "blind" driving, in which the rover
followed a route determined in advance by rover planners at
JPL using stereo images. That portion lasted an hour and
covered most of the day's distance. Then Opportunity switched
to "autonomous" driving for two and a half hours, pausing
every 2 meters (6.6 feet) to look ahead for obstacles as it
chose its own route ahead.
The next day, Opportunity used its new software to start
another drive navigating for itself. "This is the first time
either rover has picked up on a second day with continued
autonomous driving," said Dr. Mark Maimone, rover mobility
software engineer at JPL. "It's good to sit back and let the
rover do the driving for us."
Not only did Opportunity avoid obstacles for four hours of
driving, it covered more ground than a football field.
Opportunity has a favorable power situation, due to
relatively clean solar panels and increasing minutes of
daylight each day as spring approaches in Mars' southern
hemisphere. This allows several hours of operations daily.
On the third day of the three-day plan, the robotic geologist
continued navigating itself and drove even farther, 109
meters (357 feet), pushing the three-day total to 390 meters
(nearly a quarter mile). In one long weekend, Opportunity
covered a distance equivalent to more than half of the 600
meters that had been part of each rover's original mission-
success criteria during their first three months on Mars.
Opportunity has now driven 3,014 meters (1.87 miles) since
landing; Spirit even farther, 4,157 meters (2.58 miles).
Opportunity is heading south toward a rugged landscape called
"etched terrain," where it might find exposures of deeper
layers of bedrock than it has seen so far. Spirit is
climbing "Husband Hill," with a pause on a ridge overlooking
a valley north of the summit to see whether any potential
targets below warrant a side trip.
As Spirit struggled up the slope approaching the ridgeline,
the rover's wheels churned up soil that grabbed scientists'
attention. "This was an absolutely serendipitous discovery,"
said Dr. Steve Squyres of Cornell University, Ithaca, N.Y.,
principal investigator for the rovers' science instruments.
"We said, 'My gosh, that soil looks very bright. Before we go
away, we should at least take a taste."
The bright patch of disturbed soil, dubbed "Paso Robles," has
the highest salt concentration of any rock or soil ever
examined on Mars. Combined information gained from inspecting
it with Spirit's three spectrometers and panoramic camera
suggests its main ingredient is an iron sulfate salt with
water molecules bound into the mineral. The soil patch is
also rich in phosphorus, but not otherwise like a high-
phosphorus rock, called "Wishstone," that Spirit examined in
December. "We're still trying to work out what this means,
but clearly, with this much salt around, water had a hand
here," Squyres said.
Meanwhile, scientists are re-calibrating data from both
rovers' alpha particle X-ray spectrometers. These instruments
are used to assess targets' elemental composition. The sensor
heads for the two instruments were switched before launch.
Therefore, data that Opportunity's spectrometer has collected
have been analyzed using calibration files for Spirit's, and
vice-versa. Fortunately, because the sensor heads are nearly
identical, the effect on the elemental abundances determined
by the instruments was very small. The scientists have taken
this opportunity to go back and review the results for the
mission so far and re-compute using correct calibration
files. "The effect in all cases was less than the
uncertainties in results, so none of our science conclusions
are affected," Squyres said.
JPL, a division of the California Institute of Technology in
Pasadena, has managed NASA's Mars Exploration Rover project
since it began in 2000. Images and additional information
about the rovers and their discoveries are available on the
Guy Webster (818) 354-6278
NASA's Jet Propulsion Laboratory
Dolores Beasley (202) 358-1753
NASA Headquarters, Washington