Earth's Leaky Atmosphere

Summary (Sep 02, 2008): Using satellite observations, scientists have discovered why the Earth is constantly leaking oxygen into space. The finding provides insight into the mechanisms behind oxygen loss on our planet.

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Earth's Leaky Atmosphere

Based on an ESA news release

Cluster watches Earth's leaky atmosphere

A new study is helping scientists understand how oxygen is expelled from the Earth's atmosphere.
Credit: Rensselaer Polytechnic Institute

Oxygen is constantly leaking out of Earth's atmosphere and into space. Now, ESA's formation-flying quartet of satellites, Cluster, has discovered the physical mechanism that is driving the escape. It turns out that the Earth's own magnetic field is accelerating the oxygen away.

The new work uses data collected by Cluster from 2001 to 2003. During this time, 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 Earth'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. "It is a bit like a sling-shot effect," says Nilsson.

Auroras on Earth are formed when energetic particles from the sun collide with the Earth's atmosphere.
Credit: Michigan Tech

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. "Cluster allowed us to measure the gradient of the magnetic field and see how it was changing direction with time," says Nilsson.

Before the space age, scientists believed that Earth'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 Earth's atmosphere from direct interaction with the solar wind.

"We are beginning to realize just how many interactions can take place between the solar wind and the atmosphere," 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 aurora. 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 Earth's magnetic environment.

Artistic illustration of Earth's magnetic field. Earth's magnetic field protects the planet from harmful solar and cosmic radiation, but also has profound affects on our atmosphere.
Credit: NASA

The Cluster data were captured over the poles with the satellites flying at an altitude of anywhere between 30,000 and 64,000 kilometers. Measurements taken by earlier satellites during the 1980s and 1990s showed that the escaping ions were traveling faster the higher they were observed. This implied that some sort of acceleration mechanism was involved and several possibilities were proposed. Thanks to this new Cluster study, the mechanism accounting for most of the acceleration has now been identified.

At present, the escape of oxygen is nothing to worry about. Compared to the Earth'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. "We can only predict these future changes if we understand the mechanisms involved," says Nilsson.

Artist impression of the four Cluster spacecraft. From orbit, the Cluster mission is collecting the most detailed information to date about how the solar wind affects our planet. Cluster began its mission in February of 2001 and has been extended until December of 2009.
Credit: ESA

For now, Cluster will continue collecting data and providing new insights into the complex magnetic environment surrounding our planet.

Related Web Sites

Astrobiology Roadmap Goal 6: Life's Future on Earth and Beyond
Cluster Maps Convection
A Breathable Earth
Breathing Oxygen Earlier
Argon Provides Atmospheric Clues
Adding Up Atmospheres

Note: Terrestrial Climate History

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Tuesday, September 02, 2008