NASA’s Spirit has found hints of a water history in a rock at Mars’
Gusev Crater, but it is a very different type of rock than those in
which NASA’s Opportunity found clues to a wet past on the opposite
side of the planet.
A dark volcanic rock dubbed “Humphrey,” about 60 centimeters (2 feet)
tall, shows bright material in interior crevices and cracks that looks
like minerals crystallized out of water, Dr. Ray Arvidson of
Washington University, St. Louis, reported at a NASA news briefing
today at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. He is the
deputy principal investigator for the rovers’ science instruments.
“If we found this rock on Earth, we would say it is a volcanic rock
that had a little fluid moving through it,” Arvidson said. If this
interpretation is correct, the fluid — water with minerals dissolved
in it — may have been carried in the original magma that formed the
rock or may have interacted with the rock later, he said.
The clues appear in an interior exposure of “Humphrey” where Spirit’s
rock abrasion tool scraped away the rock’s surface to a depth of 2
millimeters (.08 inch). To gain more confidence that the bright
material seen in cracks and pores is not dust that has intruded from
the surface over the millenia, scientists intend to have Spirit grind
more deeply into another dark rock, not yet selected. The bright
material is not debris from the grinding process, said Stephen Gorevan
of Honeybee Robotics, New York, lead scientist for the abrasion tool.
The amount of water suggested by the possible crystals in “Humphrey”
is far less than what is indicated by the minerals and structures that
Opportunity has revealed in rocks at Meridiani. Rover scientists
announced the Opportunity findings earlier this week. “Mars is a
diverse planet,” Arvidson said today.
Spirit is headed toward a crater nicknamed “Bonneville,” about 150
meters (500 feet) in diameter, where scientists hope to see rocks from
beneath the region’s surface volcanic layer. Those rocks may tell yet
a different story from an earlier era of Gusev Crater’s past.
At Meridiani Planum, Opportunity has finished taking a set of 114
microscope images of a rock called “Last Chance” to examine details of
the rock’s layering structure. The sequence required more than 400
commands and more than 200 positions of Opportunity’s robotic arm,
said Opportunity Mission Manager Matt Wallace of JPL. “Our activities
are getting increasingly complex,” he noted.
Spirit completed its 60th martian day, or sol, at Gusev late Thursday.
Opportunity completed its 40th sol at Meridiani at 9:32 a.m. Friday,
PST. “Between the two rovers, we’ve had a terrific 100 days on Mars.
This last week has been particularly exciting,” Wallace said.
A new color view, combining several frames from Opportunity’s
panoramic camera, adds information about the rover’s likely
destination after finishing work in and around the small crater where
it landed. From partway up the inner slope of that 22-meter-diameter
(72-foot-diameter) crater, the rover has an improved view of a crater
nicknamed “Endurance,” about 10 times as big and about 700 meters
(2,300 feet) to the east. “We can see features in the rim, maybe
streaks, maybe layers,” said Dr. Jim Bell of Cornell University,
Ithaca, N.Y., lead scientist for both rovers’ panoramic cameras.
The same new view across the flat plain of Meridiani also shows
Opportunity’s jettisoned heat shield, a trail of marks left by the
airbag bounces and a solitary dark rock about 40 centimeters (16
inches) across. Bell said, “Not only did we get incredibly lucky to
get this hole-in-one in the crater, but on the way into the crater we
hit with the airbags the only rock around.”
Both rovers carry magnets supplied by Denmark for experiments to
analyze martian dust. Dust covers much of Mars’ surface and hangs in
the atmosphere, occasionally rising into giant dust storms. One of
the magnets is designed to exclude any magnetic dust particles from
landing in the center of a target area. During Spirit’s time on Mars,
dust has accumulated on other parts of the target while the center has
remained “probably the cleanest area anywhere on the surface of the
rover,” said Dr. Morten Madsen, science team member from the Center
for Planetary Science, Copenhagen, Denmark.
“Most, if not all of the dust particles in the martian atmosphere are
magnetic,” Madsen said. Another of the magnets is within reach of the
rover’s robotic arm. Examination of dust on the target by instruments
on the end of the arm will soon yield further information about the
composition of the dust, he said.
