This artist’s impression shows how the solar wind shapes the magnetospheres of Venus (top), Earth (middle) and Mars (bottom). Earth has an internal magnetic field which makes its magnetosphere bigger (unlike Venus and Mars). The lines coming out of the Sun symbolise the outward propagation of the solar wind (planet’s distances are not shown to scale). Credits: ESA
This animation shows how a particular stream of the solar wind sweeps through space, interacting with both Earth and Mars. Credits: ESA
This artist’s impression shows 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. Credits: ESA
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. This allowed a direct evaluation of the effectiveness of Earth’s magnetic field in protecting our atmosphere.
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.
“The shielding effect of the magnetic field is easy to understand and to prove in computer simulations, thus it has become the default explanation,” says Yong Wei from the Max-Planck-Institut für Sonnensystemforschung, Germany, who led the study.