Here's a strange scenario: You move farther away from a
fire, getting cooler and cooler, until suddenly you are burning up.
That's essentially what happens in the sun: Its outer layer,
the corona, is inexplicably hot. A new study may complicate things further by
poking holes in a leading theory that aims to account for the puzzling
phenomenon.
Last year, astrophysicist Steve Tomczyk of the National Center for Atmospheric Research in Boulder, Colo., and his colleagues asserted
that corkscrew-shaped Alfven waves were converting the motion energy of the
sun's roiling material into heat.
But the authors of the new study argue that the waves Tomczyk's
team saw were not Alfven waves but kink waves.
"Kink waves look like kinks in hair or rope," said
University of Warwick astrophysicist Tom Van
Doorsselaere, one of the researchers behind the new study. "Kink
waves can't explain why the
corona is so hot. They carry less energy with them."
Van Doorsselaere said he and his
colleagues used a more complex model than Tomczyk and found that the wave observations are not consistent
with Alfven waves, and must be kink waves.
"At the moment I can't see
any other explanation that could explain the observations," Van
Doorsselaere told SPACE.com. "I would have wished the other
authors were right because it would have been good news to finally solve the
problem."
The new study was published March
6, 2008, in the Astrophysical Journal Letters.
Van Doorsselaere said Tomczyk
and his colleagues still think Alfven waves
could be behind the corona's heat.
"They're not convinced that we are right, but they are
convinced that our opinion should be published and discussed," he said.
"Probably at upcoming conferences, there will be some lively discussion of
this."
The sun is not alone in having an inexplicably scorching
outer layer.
"We think our sun is pretty typical for corona
behavior," Van Doorsselaere said. "There are other stars with even
bigger and more active coronas."
Our sun, being so close to us, provides the best opportunity
to study this phenomenon. Scientists still hold out hope we can get to the
bottom of the mystery soon.
"To test this we need better observations," Van
Doorsselaere said. "We're getting better telescopes and satellites to look
at the sun. There are several missions coming up to hopefully resolve the
problem."
He said NASA's upcoming Solar Dynamics Observatory, to be
launched sometime at the end of 2008 or beginning of 2009, or ESA's Solar
Orbiter, set to launch in 2015, could be the keys to success.
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