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

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.

Mercury: 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).

Venus: 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.

The 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).

Mars: 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.