The sad magnetic state of the solar system’s rocky worlds


PLANETARY PROTECTION  Earth’s magnetic field deflects charged solar particles toward the planet’s poles, generating auroras. This photo was taken from (and shows parts of) the International Space Station.

Above: NASA; Below, from top: NASA, JHUAPL, Carnegie Inst. for Science; JPL-Caltech/NASA; NASA; JPL-Caltech/NASA

A powerful global magnetic field envelops Earth in a cozy blanket of protection against bursts of solar particles (see “The magnetic mystery at the center of the Earth“). But the solar system’s other rocky worlds aren’t so lucky.

MercuryMercury: Paltry

The most petite planet has an appropriately puny magnetic field, just 1.1 percent as strong as Earth’s (SN Online: 5/7/15).

VenusVenus: Zilch

Earth’s nearest neighbor doesn’t generate a planet-wide magnetic field, so the solar wind penetrates and is gradually stripping away the atmosphere.

moonThe moon: Lost

Magnetized lunar rocks hauled back by Apollo astronauts show that, at some point, the ancient moon had a hefty magnetic field. It has since died out (SN Online: 12/4/14).

MarsMars: Collapsed

The Red Planet lacks a global magnetic field today, but magnetized regions of Martian crust point to an ancient magnetic field that eventually fizzled.

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