Washington, May 15 : Scientists have determined that poles on Jupiter's moon Europa may have wandered by almost 90 degrees, an extreme shift that suggests the existence of an internal liquid ocean beneath the icy crust, which may host life.
The team of scientists, which came forward with the finding, is from the Carnegie Institution, Lunar and Planetary Institute, and University of California, Santa Cruz.
The research team, which included Isamu Matsuyama of the Carnegie Institution's Department of Terrestrial Magnetism, used images from the Voyager, Galileo, and New Horizons spacecraft to map several large arc-shaped depressions that extend more than 500 kilometers across Europa's surface.
By comparing the pattern of the depressions with fractures that would result from stresses caused by a shift in Europa's rotational axis, the researchers determined that the axis had shifted by approximately 80 degrees. The previous axis of rotation is now located about 10 degrees from the present equator.
The drastic shift in Europa's rotational axis was likely a result of the build-up of thick ice at the poles.
"A spinning body is most stable with its mass farthest from its spin axis," said Matsuyama. "On Europa, variations in the thickness of its outer shell caused a mass imbalance, so the rotation axis reoriented to a new stable state," he added.
Such a change is called "true polar wander" as opposed to apparent polar wander caused by plate tectonics.
The study has implications for liquid water inside Europa.
Scientists have hypothesized that Europa has an extensive subsurface ocean based on spacecraft photos that revealed its fractured, icy surface. The ocean beneath the crust would be kept liquid by heat generated by tidal forces from Jupiter's gravity.
The presence of heat and water may make life possible, even though the subsurface ocean is cut off from solar energy.
"The large reorientation on Europa required to explain the circular depressions implies that its outer ice shell is decoupled from the core by a liquid layer," said Matsuyama. "Therefore, our study provides an independent test for the presence of an interior liquid layer," he added.