Irene Klotz
Discovery
News
Our planet's magnetic shield may not be as solid a
protective screen from the sun as once believed, according to new
research.
Christopher Russell, a professor of geophysics and space physics
at the University of
California, Los Angeles says Earth is losing more of its
atmosphere than Venus and Mars, which have negligible magnetic
fields.
Russell presented his research at a recent American Geophysical Union
conference in Toronto.
"We often tell ourselves that we are very fortunate living on
this planet because we have this strong magnetic shield that
protects us from all sorts of things that the cosmos throws at us -
cosmic rays, solar flares and the pesky solar wind," says
Russell.
"It certainly does help in some of those areas but ... in the
case of the atmosphere, this may not be true."
Russell and others came to this realisation while meeting at a
comparative planetology conference last month.
"Three of us who work on Earth, Venus and Mars got together and
compared notes," Russell says. "We said, 'Oh my goodness - what
we've been telling people about the magnetic shield is not
correct.'"
The perpetrators are streams of charged particles blasting off
the sun in what is known as the solar wind.
"The interaction of solar wind with Venus and Mars is pretty
simple," Russell says.
"The wind comes in, carries a magnetic field, which wraps around
the ionosphere of the planet. The ionosphere is basically dragged
away."
Earth's magnetic field interacts with the solar wind, drawing
out energy that gets funnelled into the planet's atmosphere along
its magnetic field lines.
"The wind has to flow around this large magnetic obstacle in its
path," Russell says. "The two are not friction-free."
In addition to triggering aurorae, the process causes Earth's
atmosphere to heat up to the point where atmospheric gases can
escape along the field lines, where they are then picked up by the
solar wind.
"The visible manifestation of geomagnetic activity is the aurora
- the sun interacts with magnetosphere and causes it to glow - but
there are other things that go on when the particles interact with
the atmosphere," says Scott Bailey, with the Center for Space Science and
Engineering Research at Virginia Polytechnic Institute.
Despite the rather mind-boggling rate at which Earth is losing
atmosphere - 5×1025 molecules per second - scientists
say there is no cause for alarm.
If the loss rate stays the same, the planet's atmosphere will
last for several more billion years.
"Ultimately we're trying to understand why Venus, Mars and Earth
atmospheres behave so different when initially the planets were
pretty much the same," says Russell.
Russell and colleagues are working on a paper that details the
comparative atmospheric losses of Earth, Venus and Mars.
