Shifting sand dunes spotted on Mars

Images captured by NASA spacecraft showed that wind-blown sand dunes moving across the Martian surface.

Washington: For the first time, scientists
have discovered shifting sand dunes and ripples all over Mars,
a finding which suggests strong winds keep the sandy surface
of the Red planet much more active than ever imagined.

Images captured by NASA spacecraft Mars Reconnaissance
Orbiter showed that wind-blown sand dunes moving across the
Martian surface, sometimes up to several yards at a time, the
scientists said.

"Mars either has more gusts of wind than we knew about
before, or the winds are capable of transporting more sand,"
lead researcher Nathan Bridges, a planetary scientist at the
Applied Physics Laboratory of Johns Hopkins University in the
US, said.

"We used to think of the sand on Mars as relatively
immobile, so these new observations are changing our whole
perspective," Bridges was quoted as saying by

Scientists have long known that the red dust on Mars can
swirl and blow about in many ways, ranging from vast dust
storms to small whirlwinds, called dust devils. But less than
10 years ago, astronomers still thought the Martian dunes and
sand ripples were either immobile or moved too minutely to
ever see.

According to the scientists, who detailed their findings
in the journal Geology, the dark sand grains of Mars are
harder to move than those of Earth`s deserts and beaches
because they are larger, and because the Martian atmosphere is
thinner than Earth`s.

Wind tunnel tests have shown that 130 kmph gusts are
required on Mars to move a single a patch of sand, while on
Earth, the winds about 16 kmph can achieve the same feat.

But such high wind speeds on Mars are relatively rare,
according to observations from NASA`s Viking landers collected
in the 1970s and 1980s.

The first clues of the Red Planet`s moving sand dunes
came from NASA`s Mars Global Surveyor. More evidence was found
by NASA`s Mars Exploration Rovers which detected shifting sand
when they touched down on the surface of Mars in 2004.

"Sand moves by hopping from place to place," said Matthew
Golombek, co-author of the study and a member of the Mars
Exploration Rover and Mars Reconnaissance Orbiter teams at
NASA`s Jet Propulsion Laboratory in Pasadena. "Before rovers
landed on Mars, we had no clear evidence of sand moving."

But the researchers also saw several areas where the sand
dunes did not move, which indicates that not all of the sand
on Mars blows in the wind.

"The sand dunes where we didn`t see movement today could
have larger grains, or perhaps their surface layers are
cemented together," said Bridges. "These studies show the
benefit of long-term monitoring at high resolution."

It could be that the areas that seem stationary just take
longer to move, which could be triggered by climate cycles on
Mars that last thousands of years, the researchers said.

According to them, Mars may once have been warm enough
for the carbon dioxide that is now frozen in the polar ice
caps to freely form a thicker atmosphere, and the resulting
stronger winds could have been responsible for transporting


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