Magnetic death leaves Earth-like exoplanets dried out

Seemingly habitable exoplanets may be missing their magnetic shielding, leaving them exposed to damaging radiation.

To support life as we know it, planets need thick, water-rich atmospheres and liquid surface water. These conditions have so far only been hinted at, based mostly on a planet's distance from its star.

But water can get blasted away by stellar winds unless the planet has a strong magnetic field, point out Jorge Zuluaga at the University of Antioquia in Colombia and colleagues. Mars and Venus do not have magnetic fields, and it is thought that stellar winds stripped away the bulk of Mars's atmosphere, while Venus's was left with mostly carbon dioxide, making it toxic.

A magnetic field would also protect a planet's surface inhabitants from dangerous stellar radiation.

Cooling period

A churning molten core helps to generate a magnetic field, so the team calculated how long it would take a rocky planet to cool so much that this magnetic dynamo stopped working.

They then checked three well-known exoplanets thought to be potentially habitable: Gliese 581d, HD 40307g and GJ 667Cc. The first two might have magnetic fields just barely strong enough, they found, but the third is doomed.

Zuluaga therefore stresses the importance of considering magnetic fields when thinking about whether a planet would be a good place to live. "If we want to evaluate as well as possible the habitability of a planet, we need that information, not only the distance to the star."

Journal reference: arxiv.org/abs/1304.2909

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