Andrew Yee[_1_]
May 14th 08, 09:04 PM
Carnegie Institution of Washington
Washington, DC
Contact:
Isamu Matsuyama, 202-478-8863
Wednesday, May 14, 2008
Wandering Poles Left Scars on Europa
Washington, D.C. -- Curved features on Jupiter's moon Europa may indicate
that its poles have wandered by almost 90 deg, 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 and colleagues Paul Schenk
and Francis Nimmo, 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 deg. The previous
axis of rotation is now located about 10 deg 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."
Washington, DC
Contact:
Isamu Matsuyama, 202-478-8863
Wednesday, May 14, 2008
Wandering Poles Left Scars on Europa
Washington, D.C. -- Curved features on Jupiter's moon Europa may indicate
that its poles have wandered by almost 90 deg, 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 and colleagues Paul Schenk
and Francis Nimmo, 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 deg. The previous
axis of rotation is now located about 10 deg 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."