Researchers were stunned to discover recently that Earth is losing more of its atmosphere than Venus and Mars, which have negligible magnetic fields.
This may mean our planet's magnetic shield may not be as solid a protective screen as once believed when it comes to guarding the atmosphere from an assault from the sun.
"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," said Christopher Russell, a professor of geophysics and space physics at the University of California, Los Angeles.
"It certainly does help in some of those areas but ... in the case of the atmosphere, this may not be true," he said.
Russell and others came to this realization 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 told Discovery News. "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 said. "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 funneled into the planet's atmosphere along its magnetic field lines.
"The wind has to flow around this large magnetic obstacle in its path," Russell said. "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," said Scott Bailey, with the Center for Space Science and Engineering 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," Russell said.
Russell presented his research at the American Geophysical Union conference in Toronto last week. He and his colleagues are working on paper that details the comparative atmospheric losses of Earth, Venus and Mars.