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NASA's Curiosity rover found evidence for an
ancient, flowing stream on
Mars at a few sites, including the rock Image credit:
NASA/JPL-Caltech/MSSS
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Washington: NASA's Curiosity rover
mission has found evidence a stream once ran vigorously across the area on Mars
where the rover is driving. There is earlier evidence for the presence of water
on Mars, but this evidence -- images of rocks containing ancient streambed
gravels -- is the first of its kind.
Scientists are
studying the images of stones cemented into a layer of conglomerate rock. The
sizes and shapes of stones offer clues to the speed and distance of a long-ago
stream's flow.
"From the size of
gravels it carried, we can interpret the water was moving about 3 feet per
second, with a depth somewhere between ankle and hip deep," said Curiosity
science co-investigator William Dietrich of the University of California,
Berkeley. "Plenty of papers have been written about channels on Mars with
many different hypotheses about the flows in them. This is the first time we're
actually seeing water-transported gravel on Mars. This is a transition from
speculation about the size of streambed material to direct observation of
it."
The finding site lies
between the north rim of Gale Crater and the base of Mount Sharp, a mountain
inside the crater. Earlier imaging of the region from Mars orbit allows for
additional interpretation of the gravel-bearing conglomerate. The imagery shows
an alluvial fan of material washed down from the rim, streaked by many apparent
channels, sitting uphill of the new finds.
The rounded shape of
some stones in the conglomerate indicates long-distance transport from above
the rim, where a channel named Peace Vallis feeds into the alluvial fan. The
abundance of channels in the fan between the rim and conglomerate suggests
flows continued or repeated over a long time, not just once or for a few years.
The discovery comes
from examining two outcrops, called "Hottah" and "Link,"
with the telephoto capability of Curiosity's mast camera during the first 40
days after landing. Those observations followed up on earlier hints from
another outcrop, which was exposed by thruster exhaust as Curiosity, the Mars Science
Laboratory Project's rover, touched down.
"Hottah looks
like someone jack-hammered up a slab of city sidewalk, but it's really a tilted
block of an ancient streambed," said Mars Science Laboratory Project
Scientist John Grotzinger of the California Institute of Technology in
Pasadena.
The gravels in
conglomerates at both outcrops range in size from a grain of sand to a golf
ball. Some are angular, but many are rounded.
"The shapes tell
you they were transported and the sizes tell you they couldn't be transported
by wind. They were transported by water flow," said Curiosity science
co-investigator Rebecca Williams of the Planetary Science Institute in Tucson,
Ariz.
The science team may
use Curiosity to learn the elemental composition of the material, which holds
the conglomerate together, revealing more characteristics of the wet
environment that formed these deposits. The stones in the conglomerate provide
a sampling from above the crater rim, so the team may also examine several of
them to learn about broader regional geology.
The slope of Mount
Sharp in Gale Crater remains the rover's main destination. Clay and sulfate
minerals detected there from orbit can be good preservers of carbon-based
organic chemicals that are potential ingredients for life.
"A long-flowing
stream can be a habitable environment," said Grotzinger. "It is not
our top choice as an environment for preservation of organics, though. We're
still going to Mount Sharp, but this is insurance that we have already found
our first potentially habitable environment."
During the two-year
prime mission of the Mars Science Laboratory, researchers will use Curiosity's
10 instruments to investigate whether areas in Gale Crater have ever offered
environmental conditions favorable for microbial life.
NASA's Jet Propulsion
Laboratory, a division of Caltech, built Curiosity and manages the Mars Science
Laboratory Project for NASA's Science Mission Directorate, Washington.