What magnetic fields can tell us about life on other planets

November 21, 2018

Kepler 62 750 An artist’s concept of a super-Earth in the habitable zone of a star smaller and cooler than the sun. Such large planets could have long-lasting magma oceans that generate magnetic fields capable of protecting incipient life. The graphic was created to model Kepler-62f, one of many exoplanets discovered by NASA’s now inoperable Kepler space telescope. (Image courtesy of NASA Ames/JPL-Caltech/Tim Pyle)

Every school kid knows that Earth has a magnetic field – it’s what makes compasses align north-south and lets us navigate the oceans. It also protects the atmosphere, and thus life, from the sun’s powerful wind.

But what about other Earth-like planets in the galaxy? Do they also have magnetic fields to protect emerging life?

A new analysis looks at one type of exoplanet – super-Earths up to five times the size of our own planet – and concludes that they probably do have a magnetic field, but one generated in a totally novel way: by the planets’ magma oceans.

The surprising discovery that slowly churning melted rock at or under the surface can generate a strong magnetic field also suggests that in Earth’s early years, when it was largely a lump of melted rock, it also had a magma-generated magnetic field. This was in addition to its present-day field, which is generated in the liquid-iron outer core.

“This is a new regime for the generation of planetary magnetic fields,” said Burkhard Militzer, a UC Berkeley professor of earth and planetary science. “Our magnetic field on Earth is generated in the liquid outer iron core. On Jupiter, it arises from the convection of liquid metallic hydrogen. On Uranus and Neptune, it is assumed to be generated in the ice layers. Now we have added molten rocks to this diverse list of field-generating materials.”

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