for National Geographic News
Unlike, say, Mars's or Venus's, Earth's atmosphere was thought to be untouchable inside our protective magnetic field. But a new study says the sun is slowly "stealing" our atmosphere—and at a greater rate than on Mars or Venus.
Perhaps even more surprising, our planet's main solar defense may be a double agent, aiding and abetting the thievery.
(Related: "Stars Can Strip Gas Giants Naked.")
Mars, for example, probably started out with a thick atmosphere similar to Earth's. But without a magnetic field to protect the Martian atmosphere, the solar wind—actually a stream of charged particles from the sun—has been eroding it away.
Venus also lacks a magnetosphere and is being stripped of its atmospheric covering. Currently its rate of loss has outpaced that on Mars.
Typically hailed as a protective buffer from the sun's brute power, Earth's magnetosphere is actually helping the sun's energized particles strip away a tiny fraction of Earth's atmosphere, the new study says.
"We're, in fact, losing more oxygen and more hydrogen than even Venus is today," said Chris Russell, a professor of space physics at the University of California, Los Angeles.
"We often tell our colleagues and ourselves that we are fortunate living on this planet, because we have this magnetic shield that protects us," Russell said.
"It certainly does help, but we've come to the realization that, when it comes to the atmosphere, that's not true."
An international team of researchers has been tracking planetary atmospheres using the European Space Agency's Mars Express mission for Venus and Mars and NASA's Small Explorer Mission (SMEX) for Earth.
SMEX also harbors an instrument for measuring magnetic activity on Earth.
"On Earth the magnetosphere acts like an energy collector that interacts with the material that's coming from the sun and can draw energy out of the solar wind," Russell said.
But then Earth's magnetic field funnels and guides that energy to the upper atmosphere, heating the atmosphere and allowing bits of it to escape along the very same funnels that guided the energy in.
The precise physics have yet to be worked out, but there's no cause for alarm, Russell said.
At the current rate, our present atmospheric inventory can last at least until the sun—midway through its life now—turns into a red giant and engulfs Earth, Russell said.
"At that point," he said, "the loss of atmosphere becomes moot."
Findings presented this week at a meeting of the American Geophysical Union in Toronto, Canada.
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