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Magnetic waves
turn up solar heat
By Camille M. Carlisle
Scientists are getting warmer in their
hunt for a reason why the sun’s outer
atmosphere is so hot. The key may be
magnetic waves long sought but only
recently spotted, an international team
reports in the July 28 Nature.
Combined with observations reported
earlier this year of high-speed gas jets
shooting up into the sun’s outer atmosphere, or corona, the magnetic waves
may explain why the thin halo of super-hot gas blazes at temperatures as high as
a couple million kelvins. The waves may
also account for the solar wind particles
that stream off the corona at hundreds of
kilometers per second.
“These are results that
have been awaited for 50
years,” says Peter Cargill of
Imperial College London
and the University of St.
Andrews in Scotland.
Solar physicists have
struggled all that time to
understand how the corona
can be so hot when the layer
below it, the chromosphere,
is much cooler. One theory is
that waves traveling through
the sun’s magnetic field
transport energy up from
the seething solar surface.
These oscillations move
along magnetic field lines like vibrations
on a plucked guitar string. In 2007 a team
including Scott McIntosh of the National
Center for Atmospheric Research in
Boulder, Colo., finally detected these
waves in the chromosphere. Now, using a
sensitive instrument aboard
NASA’s Solar Dynamics
Observatory, McIntosh and
colleagues have discovered
magnetic waves throughout
the corona and the transi-
tion zone between it and the
chromosphere.
Gas jets (green
in this false-color
image) and magnetic
waves may superheat
the sun’s corona.
Fresh hints of salt water on Mars
Seasonal patterns consistent with presence of briny seeps
By Camille M. Carlisle
Salt water oozing from rocky outcrops
may account for seasonal dark streaks on
some Martian slopes, researchers suggest in the Aug. 5 Science.
The American and Swiss scientists
haven’t actually detected any water,
frozen or liquid. Nor can they explain
how the water would be replenished in
the dry, harsh Martian environment.
But given how the lines grow and fade
each year with the seasons, the team’s
conclusion is “entirely justified,” says
Michael Hecht of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who
was not involved with the research. If
the idea pans out, the stripes will add to
previous evidence suggesting that salty
water continues to be widespread on
the Red Planet. So far, no one has found
The dark streaks in this enhanced-
color, 3-D image of Newton Crater’s
inner rim appear every Martian spring.
undisputed evidence of liquid water
currently active on the planet’s surface.
Looking at images from the Mars
Reconnaissance Orbiter, the research
team discovered lines that appear in late
spring and grow throughout the summer, fading as the weather cools. Some
look to be near small channels, and all
are on steep bedrock, such as crater rims.
Hundreds to thousands of the skinny
streaks appear at seven sites that cluster in the middle southern latitudes, a
location akin to the subtropics on Earth.
The researchers spotted other candidate
sites elsewhere, including to either side
of the planet’s equator.
Briny water melting and freezing
just underground could explain these
seasonal landscape patterns, the team
argues. On Mars, liquid water would
boil on the surface and freeze just
below it, says study coauthor Alfred
McEwen, a planetary geologist at the
University of Arizona in Tucson. Brine
would evaporate, too, but not as fast.
And brine freezes at a lower temperature than pure water does, so it could
stick around long enough as a liquid to
leave a mark.
FROM TOP: AIA/SDO/NASA; NASA, JPL-CALTECH, UNIV. OF ARIZONA
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