Science: Earth’s Magnetic Field

Earth’s magnetic field provides vital protection

A chance alignment of planets during a passing gust of the solar wind has allowed scientists to compare the protective effects of Earth’s magnetic field with that of Mars’ naked atmosphere. The result is clear: Earth’s magnetic field is vital for keeping our atmosphere in place.


The alignment took place on 6 January 2008. Using ESA’s Cluster and Mars Express missions to provide data from Earth and Mars, respectively, scientists compared the loss of oxygen from the two planets’ atmospheres as the same stream of solar wind hit them.

They found that while the pressure of the solar wind increased at each planet by similar amounts, the increase in the rate of loss of martian oxygen was ten times that of Earth’s increase. Such a difference would have a dramatic impact over billions of years, leading to large losses of the martian atmosphere, perhaps explaining or at least contributing to its current tenuous state.

The result proves the efficacy of Earth’s magnetic field in deflecting the solar wind and protecting our atmosphere. They now hope to extend their work by incorporating data from ESA’s Venus Express spacecraft, which also carries a sensor that can measure the loss of its atmosphere.
Venus will provide an important new perspective on the issue because like Mars, it has no global magnetic field, yet it is similar in size to Earth and has a much thicker atmosphere. It will therefore provide unique data to help place the Earth and Mars results in context.

Images: (1) Propagation of a solar wind stream. (2) The magnetosphere of Mars: unlike Earth, which has an internal magnetic field, Mars lacks a planet-wide magnetic field so the martian magnetosphere is smaller than the terrestrial one. (3) How the solar wind shapes the magnetospheres of Venus (top), Earth (middle) and Mars (bottom).