Starry-Eyed Scientists Enthusiastic With Findings
The Opportunity rover
has found evidene on Mars that's got scientists buzzing back on
Earth. On Tuesday, NASA held a press conference to announce the
out-of-this-world news: Mars had water. The Mars exploration
team claims they have found evidence suggesting Mars was once a
water-rich world, thanks to some data collected by the Opportunity
rover within a small crater at near an area called Meridiani
Planum. Evidence the rover found in a rock outcrop led scientists
to the conclusion. Clues from the rocks' composition, such as the
presence of sulfates, and the rocks' physical appearance, such as
niches where crystals grew, helped make the case for a watery
history.
"Liquid water once flowed through these rocks. It changed their
texture, and it changed their chemistry," said Dr. Steve Squyres of
Cornell University, Ithaca, N.Y., principal investigator for the
science instruments on Opportunity and its twin, Spirit. "We've
been able to read the tell-tale clues the water left behind, giving
us confidence in that conclusion." Dr. James Garvin, lead scientist
for Mars and lunar exploration at NASA Headquarters, Washington,
said, "NASA launched the Mars Exploration Rover mission
specifically to check whether at least one part of Mars ever had a
persistently wet environment that could possibly have been
hospitable to life. Today we have strong evidence for an exciting
answer: Yes."
Opportunity has more work ahead. It will try to determine
whether, besides being exposed to water after they formed, the
rocks may have originally been laid down by minerals precipitating
out of solution at the bottom of a salty lake or sea. The first
views Opportunity sent of its landing site in Mars' Meridiani
Planum region five weeks ago delighted researchers at NASA's Jet
Propulsion Laboratory, Pasadena (CA), because of the good fortune
to have the spacecraft arrive next to an exposed slice of bedrock
on the inner slope of a small crater.
The robotic field geologist has spent most of the past three
weeks surveying the whole outcrop, and then turning back for
close-up inspection of selected portions. The rover found a very
high concentration of sulfur in the outcrop with its alpha particle
X-ray spectrometer, which identifies chemical elements in a sample.
"The chemical form of this sulfur appears to be in magnesium, iron
or other sulfate salts," said Dr. Benton Clark of Lockheed Martin
Space Systems, Denver. "Elements that can form chloride or even
bromide salts have also been detected."
At the same location, the rover's Mossbauer spectrometer, which
identifies iron-bearing minerals, detected a hydrated iron sulfate
mineral called jarosite. Germany provided both the alpha particle
X-ray spectrometer and the Mossbauer spectrometer. Opportunity's
miniature thermal emission spectrometer has also provided evidence
for sulfates. On Earth, rocks with as much salt as this Mars rock
either have formed in water or, after formation, have been highly
altered by long exposures to water. Jarosite may point to the
rock's wet history having been in an acidic lake or an acidic hot
springs environment. The water evidence from the rocks' physical
appearance comes in at least three categories, said Dr. John
Grotzinger, sedimentary geologist from the Massachusetts Institute
of Technology, Cambridge: indentations called "vugs," spherules and
crossbedding.
Pictures from the rover's panoramic camera and microscopic
imager reveal the target rock, dubbed "El Capitan," is thoroughly
pocked with indentations about a centimeter (0.4 inch) long and
one-fourth or less that wide, with apparently random orientations.
This distinctive texture is familiar to geologists as the sites
where crystals of salt minerals form within rocks that sit in briny
water. When the crystals later disappear, either by erosion or by
dissolving in less-salty water, the voids left behind are called
vugs, and in this case they conform to the geometry of possible
former evaporite minerals.
Round particles the size of BBs are embedded in the outcrop.
From shape alone, these spherules might be formed from volcanic
eruptions, from lofting of molten droplets by a meteor impact, or
from accumulation of minerals coming out of solution inside a
porous, water-soaked rock. Opportunity's observations that the
spherules are not concentrated at particular layers in the outcrop
weigh against a volcanic or impact origin, but do not completely
rule out those origins. Layers in the rock that lie at an angle to
the main layers, a pattern called crossbedding, can result from the
action of wind or water. Preliminary views by Opportunity hint the
crossbedding bears hallmarks of water action, such as the small
scale of the crossbedding and possible concave patterns formed by
sinuous crestlines of underwater ridges.
The images obtained to date are not adequate for a definitive
answer. So scientists plan to maneuver Opportunity closer to the
features for a better look. "We have tantalizing clues, and we're
planning to evaluate this possibility in the near future,"
Grotzinger said.