Oxygen trickle puts theory in a pickle.

Oxygen atoms in the atmosphere can sometimes acquire enough energy from the sun's heat to escape the hungry grasp of the earth. This loss of oxygen is thought to be a rather rare event because the escape energy required depends on the mass of the atom, and oxygen is a fairly heavy element; lighter atoms like hydrogen are much more likely to zip off into space.

But now a group of space scientists has discovered that the trickle of escaping oxygen is much greater--1037 times greater--than the theoretical rate associated with thermal processes alone. Using a spectrometer aboard NASA's Dynamic Explorer (DE-1) satellite, Andrew You of the Canadian National Research Council in Ottawa, along with Edward Shelley and William Peterson of the Lockheed Palo Alto (Calif.) Research Laboratory, found that about 5 X 107 kilograms of oxygen are lost from the polar regions of the ionosphere each year. This new value for the oxygen trickle is still small; it accounts for only 5 percent of the total oxygen content of the atmosphere over the last billion years. Moreover, the researchers estimate that this loss is more than counterbalanced by the addition of oxygen to the atmosphere from the dissociation of water vapor and the subsequent escape of hydrogen atoms.

But what is giving the oxygen atoms the extra energy to escape? Yau's group notes that the greatest amount of oxygen is lost when the activities of the sun and the earth's magnetosphere are at their peaks. The researchers think the oxygen atoms in the polar caps and the adjacent auroral regions of the earth are given an extra boost by charged particles, originally from the solar wind, which are trapped by and travel down the earth's magnetic field lines toward the poles. According to Yau, it wasn't until after the launch of the DE-1 satellite, which was the first spacecraft with the correct orbit and onboard instruments to see the effect, that the researchers realized there was a large outflow of energized oxygen atoms. "It was a surprise," he says. "No one had previously made a connection between magnetosphere physics and atmospheric processes."