NASA Mars spacecraft reveals
a more dynamic Red Planet
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.
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 recently by Nature Geoscience. Five wellmonitored 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
16
16
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.
For more information about NASA Mars exploration missions, visit: www.nasa.gov/mars. For more
about HiRISE, visit: http://hirise.lpl.arizona.edu.
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