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These images from the High Resolution Imaging
Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter show
how the appearance of dark markings on Martian slope changes with the seasons.
Image Credit: NASA/JPL-Caltech/Univ. of Arizona
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These images from the High Resolution Imaging
Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter show
how the appearance of dark markings on Martian slope changes with the seasons.
Image Credit: NASA/JPL-Caltech/Univ. of Arizona
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This image taken on May 19, 2010, shows an impact
crater that had not existed when the same location on Mars was previously
observed in March 2008.
Image Credit: NASA/JPL-Caltech/Univ. of Arizona
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NASA's Mars
Reconnaissance Orbiter has revealed to scientists slender dark markings --
possibly due to salty water – that advance seasonally down slopes surprisingly
close to the Martian equator.
"The equatorial surface region of Mars has been regarded as dry, free of
liquid or frozen water, but we may need to rethink that," said Alfred McEwen of
the University of Arizona in Tucson, principal investigator for the Mars
Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE)
camera.
Tracking how these features recur each year is one example of how the
longevity of NASA orbiters observing Mars is providing insight about changes on
many time scales. Researchers at the American Geophysical Union meeting Tuesday
in San Francisco discussed a range of current Martian activity, from fresh
craters offering glimpses of subsurface ice to multi-year patterns in the
occurrence of large, regional dust storms.
The seasonally changing surface flows were first reported two years ago on
mid-latitude southern slopes. They are finger-like features typically less than
16 feet (5 meters) wide that appear and extend down steep, rocky slopes during
spring through summer, then fade in winter and return the next spring. Recently
observed slopes stretch as long as 4,000 feet (1,200 meters).
McEwen and co-authors reported the equatorial flows at the conference and in
a paper published online Tuesday by Nature Geoscience. Five well-monitored sites
with these markings are in Valles Marineris, the largest canyon system in the
solar system. At each of these sites, the features appear on both north- and
south-facing walls. On the north-facing slopes, they are active during the part
of the year when those slopes get the most sunshine. The counterparts on
south-facing slopes start flowing when the season shifts and more sunshine hits
their side.
"The explanation that fits best is salty water is flowing down the slopes
when the temperature rises," McEwen said. "We still don't have any definite
identification of water at these sites, but there's nothing that rules it out,
either."
Dissolved salts can keep water melted at temperatures when purer water
freezes, and they can slow the evaporation rate so brine can flow farther. This
analysis used data from the Compact Reconnaissance Imaging Spectrometer for Mars
and the Context Camera on the MRO as well as the Thermal Emission Imaging System
experiment on NASA's Mars Odyssey orbiter.
Water ice has been identified in another dynamic process researchers are
monitoring with MRO. Impacts of small asteroids or bits of comets dig many fresh
craters on Mars every year. Twenty fresh craters have exposed bright ice
previously hidden beneath the surface. Five were reported in 2009. The 15 newly
reported ones are distributed over a wider range of latitudes and
longitudes.
"The more we find, the more we can fill in a global map of where ice is
buried," said Colin Dundas of the U.S. Geological Survey in Flagstaff, Ariz.
"We've now seen icy craters down to 39 degrees north, more than halfway from the
pole to the equator. They tell us that either the average climate over several
thousand years is wetter than present or that water vapor in the current
atmosphere is concentrated near the surface. Ice could have formed under wetter
conditions, with remnants from that time persisting today, but slowly
disappearing."
Mars' modern climate becomes better known each year because of a growing set
of data from a series of orbiters that have been studying Mars continually since
1997. That has been almost nine Martian years because a year on Mars is almost
two years long on Earth. Earlier missions and surface landers have added insight
about the dynamics of Mars' atmosphere and its interaction with the ground.
"The dust cycle is the main driver of the climate system," said Robert
Haberle of NASA's Ames Research Center in Moffett Field, Calif.
One key question researchers want to answer is why dust storms encircle Mars
in some years and not in others. These storms affect annual patterns of water
vapor and carbon dioxide in the atmosphere, freezing into polar ice caps in
winter and replenishing the atmosphere in spring. Identifying significant
variations in annual patterns requires many Martian years of observations.
The data emerging from long-term studies will help future human explorers of
Mars know where to find resources such as water, how to prepare for hazards such
as dust storms, and where to be extra careful about contamination with Earth
microbes.
Launched in 2005, Mars Reconnaissance Orbiter and its six instruments have
provided more high-resolution data about the Red Planet than all other Mars
orbiters combined. Data are made available for scientists worldwide to research,
analyze and report their findings.
NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the MRO and
Mars Odyssey missions for NASA's Science Mission Directorate in Washington.
Lockheed Martin Space Systems in Denver built both orbiters. The University of
Arizona Lunar and Planetary Laboratory operates the HiRISE camera, which was
built by Ball Aerospace & Technologies Corp. of Boulder, Colo.
For more information about NASA Mars exploration missions,
visit:
For more about HiRISE, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
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