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.
The most petite planet has an appropriately puny magnetic field, just 1.1 percent as strong as Earth’s (SN Online: 5/7/15).
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).
The Red Planet lacks a global magnetic field today, but magnetized regions of Martian crust point to an ancient magnetic field that eventually fizzled.