By Ron Cowen
Imagine a shift in the position of Earth’s continents so extreme that Alaska would move to the equator. Astronomers have now found evidence that such a shift actually happened on Jupiter’s large icy moon Europa. The sliding of the moon’s icy surface provides further evidence that an ocean lies beneath the ice, upping the odds that Europa has a subterranean habitat that could support some kind of life.
Paul Schenk of the Lunar and Planetary Institute in Houston and his colleagues arrived at those conclusions after using data from three spacecraft — Voyager, Galileo and New Horizons — to map several arc-shaped depressions spread far apart on Europa. Each of the depressions is about 500 kilometers long, and two of them lie exactly on opposite sides of the planet. The depressions are shallow enough that “you would not notice them if you were walking on Europa,” Schenk says.
According to models analyzed by Schenk’s team, these surface scars have just the right shape, size and location to be the fractures generated if the moon’s icy shell had sometime in the past rotated by 80°— nearly a quarter-turn.