Wandering poles left scars on Europa

May 14, 2008
Wandering Poles Left Scars on Europa
Arc-shaped troughs (black and white arrows) extend 100s of kilometers on the surface of Jupiter's moon Europa. These enigmatic features are likely fractures resulting from a shift in Europa's spin axis. Vertical scale bar (right) is 100 km. Credit: P. Schenk/NASA/LPI

Curved features on Jupiter’s moon Europa may indicate that its poles have wandered by almost 90°, report scientists from the Carnegie Institution, Lunar and Planetary Institute, and University of California, Santa Cruz in the 15 May issue of Nature. Such an extreme shift suggests the existence of an internal liquid ocean beneath the icy crust, which could help build the case for Europa as possible habitat for extraterrestrial life.

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. With a radius of about 1500 kilometers, Europa is slightly smaller than the Earth’s moon.

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°. The previous axis of rotation is now located about 10° 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,” says 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.”

Such a change is called “true polar wander” as opposed to apparent polar wander caused by plate tectonics. There is evidence for true polar wander on Earth, and also on Mars and on Saturn’s moon Enceladus. “Our study adds Europa to this list,” says Matsuyama. “It suggests that planetary bodies might be more prone to reorientation than we thought.”

The study also 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,” says Matsuyama. “Therefore, our study provides an independent test for the presence of an interior liquid layer.”

Source: Carnegie Institution

Explore further: Saturn's moon Dione

Related Stories

Saturn's moon Dione

November 2, 2015

Thanks to the Cassini mission, a great deal has been learned about Saturn's system of moons (aka. the Cronian system) in the past decade. Thanks to the presence of an orbiter in the system, astronomers and space exploration ...

Jupiter's moon Ganymede

October 16, 2015

In 1610, Galileo Galilei looked up at the night sky through a telescope of his own design. Spotting Jupiter, he noted the presence of several "luminous objects" surrounding it, which he initially took for stars. In time, ...

Saturn's moon Titan

October 5, 2015

In ancient Greek lore, the Titans were giant deities of incredible strength who ruled during the legendary Golden Age and gave birth to the Olympian gods we all know and love. Saturn's largest moon, known as Titan, is therefore ...

Saturn's icy moon Enceladus

October 20, 2015

n the ongoing drive to unlock the secrets of Saturn and its system of moons, some truly fascinating and awe-inspiring things have been discovered. In addition to things like methane lakes and propane-rich atmospheres (Titan) ...

Long-stressed Europa likely off-kilter at one time

September 18, 2013

(Phys.org) —By analyzing the distinctive cracks lining the icy face of Europa, NASA scientists found evidence that this moon of Jupiter likely spun around a tilted axis at some point.

Is Phobos doomed?

November 25, 2014

"All these worlds are yours except Europa, attempt no landing there."

Recommended for you

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet May 14, 2008
This seems like a calculated piece of information to cover up the whole picture here. I remember a very distinct video on this site http://www.nealad...nmu.html (Clip #2) which is very interesting in regards to this "wandering poles leaving scars" hoopla. Now I know Neal Adams is not a scientist but sometimes logic wins out in the end instead of academics blowing steam up your @#$%^

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.