Oxygen is constantly leaking out of Earthâ€™s atmosphere and into space. Measurements taken by satellites during the 1980s and 1990s showed the escaping ions were traveling faster the higher they were observed. This implied that some sort of acceleration mechanism was involved. Now, new work on data collected by a group of formation-flying satellites called Cluster shows that Earthâ€™s own magnetic field is accelerating the oxygen away. But don’t worry, compared to the Earthâ€™s stock of the life-supporting gas, the amount escaping is negligible. However, in the far future when the Sun begins to heat up in old age, the balance might change and the oxygen escape may become significant.
From data collected from 2001 to 2003, Cluster amassed information about beams of electrically charged oxygen atoms, known as ions, flowing outwards from the polar regions into space. Cluster also measured the strength and direction of the Earthâ€™s magnetic field whenever the beams were present.
Hans Nilsson, Swedish Institute of Space Physics, headed a team of space scientists who analyzed the data. They discovered that the oxygen ions were being accelerated by changes in the direction of the magnetic field. â€œIt is a bit like a sling-shot effect,â€ says Nilsson.
Having all four Cluster spacecraft was essential to the analysis because it gave astronomers a way to measure the strength and direction of the magnetic field over a wide area. â€œCluster allowed us to measure the gradient of the magnetic field and see how it was changing direction with time,â€ says Nilsson.
Before the space age, scientists believed that Earthâ€™s magnetic field was filled only with particles from the solar wind, the constant sleet of particles that escapes from the Sun. They thought this formed a large cushion that protected the Earthâ€™s atmosphere from direct interaction with the solar wind.
â€œWe are beginning to realize just how many interactions can take place between the solar wind and the atmosphere,â€ says Nilsson. Energetic particles from the solar wind can be channeled along the magnetic field lines and, when these impact the atmosphere of the Earth, they can produce aurorae. This occurs over the poles of Earth. The same interactions provide the oxygen ions with enough energy to accelerate out of the atmosphere and reach the Earthâ€™s magnetic environment.
The Cluster data were captured over the poles with the satellites flying at an altitude of anywhere between 30,000 and 64,000 kilometers. The data is helping scientists to understand what might happen in the future. â€œWe can only predict these future changes if we understand the mechanisms involved,â€ says Nilsson.