Europe's Ocean—the Case Strengthens

摘要

When a conductor is placed in a time-varying magnetic field, electrical currents are induced. These currents in turn create magnetic fields that can be detected. It is these physical principles that underlie the operation of metal detectors at airports and that give the magnetometer on the Galileo spacecraft the ability to "see" electrical conductors inside the moons of Jupiter. On page 1340 of this issue, Kivelson et al. present overwhelming evidence for a con-ducting layer near the surface of one of these moons, Europa. The most likely explanation is that Europa has a salty, global water ocean beneath its ice shell.