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99 percent pure water ice found on Mars | NASA's Mars Reconnaissance Orbiter (MRO) has revealed sub-surface water ice that may be 99 percent pure, halfway between the North Pole and the equator on the Red Planet. "We knew there was ice below the surface at high latitudes
of Mars, but we find that it extends far closer to the equator than you would
think, based on Mars' climate today," said Shane Byrne of the University of Arizona,
a member of the High Resolution Imaging Science Experiment, or HiRISE, which runs
the high-resolution camera on NASA's Mars Reconnaissance Orbiter. "The other surprising
discovery is that ice exposed at the bottom of these meteorite impact craters
is so pure," Byrne said. "The thinking before was that ice accumulates below the
surface between soil grains, so there would be a 50-50 mix of dirt and ice. We
were able to figure out, given how long it took that ice to fade from view, that
the mixture is about one percent dirt and 99 percent ice," he added. Scientists
used several instruments on the Mars Reconnaissance Orbiter, or MRO, in quick
succession in detecting and confirming highly pure, bright ice exposed in new
craters, ranging from 1.5 feet to 8 feet deep, at five different Martian sites.
In August 2008, the orbiter's Context camera team examined their images for any
dark spots or other changes that weren't visible in earlier images of the same
area. Meteorites usually leave dark marks when they crash into dust-covered Mars
terrain. The HiRISE team, which bases its operations at the UA Lunar and Planetary
Laboratory, followed up in September 2008 by taking high-resolution images of
the dark spots. "We saw something very unusual when we followed up on the first
of these impact craters, and that was this bright blue material poking up from
the bottom of the crater. It looked a lot like water ice. And sure enough, when
we started monitoring this material, it faded away like you'd expect water ice
to fade, because water ice is unstable on Mars' surface and turns directly into
water vapor in the atmosphere," Byrne said. A few days later that September, the
orbiter's "CRISM" team used their Compact Reconnaissance Imaging Spectrometer
for Mars and got the spectral signature of water ice exposed in one of the impact
craters, further clinching the discovery. How far water ice extends toward the
equator depends largely on how much water has been available in the Martian atmosphere
in the recent past. "The ice is a relic of a more humid climate not very long
ago, perhaps just several thousand years ago," Byrne said. |
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