Astronomy Picture of the Day |
APOD: 2001 July 31 - Oceans Under Jupiters Callisto
Explanation:
Why does
Jupiter's moon
Callisto alter the
magnetic field of Jupiter in its vicinity?
Callisto itself does not have a strong magnetic field.
One possible answer is that
Callisto harbors sub-surface oceans of
electrically conducting salt-water.
This hypothesis was
bolstered recently by a new analysis of how
Callisto creates and dissipates heat.
Callisto is thought to create heat by the
radioactive decay of internal rock -- a process that keeps the
Earth's mantle molten.
Callisto may not be able to dissipate this heat very efficiently,
however, as it has thick layers of ice and rock on its surface.
Perhaps this heat is enough to keep sub-surface water from
freezing into ice.
With this hypothesis, Callisto joins two other of
Jupiter's moons,
Europa and
Ganymede,
in candidates for sub-surface oceans.
Callisto's oceans, however,
might prove too hostile to support
Earth-like life.
APOD: 2001 January 16 - Europa Rotating
Explanation:
Evidence has been mounting that beneath the
vast planes of ice that cover
Europa lies water --
liquid oceans that might be home to
alien life.
The smallest of
Jupiter's
Galilean Moons
(which include
Io,
Ganymede, and
Callisto), Europa's deep interior is composed of mostly of
silicate rock.
Upon close inspection, many
surface cracks
stop abruptly only to continue on somewhere else -- indicating
surface plates that might be sliding.
The
above time-lapse sequence is a composite of images
taken during the
Voyager spacecraft flyby of the moon twenty years ago.
Not all regions are resolved in high detail.
The movie shows
Europa during a complete rotation,
which corresponds to a complete revolution around
Jupiter since
Europa always keeps the same face toward the giant planet.
The cause of many of the surface colors on
Europa also remains a
topic of research.
APOD: 1999 March 4 - Ganymede Mosaic
Explanation:
Ganymede, one of
the four Galilean moons of Jupiter, is the largest moon
in the Solar System.
With a diameter of 5,260 kilometers it is even
larger than planets Mercury and Pluto
and just over three quarters the size of Mars.
Ganymede is locked in
synchronous rotation with Jupiter.
This detailed mosaic
of images from the Galileo spacecraft
shows the trailing hemisphere of this planet-sized moon.
Speckled with bright young craters, Ganymede's
surface shows a mixture of
old, dark, cratered
terrain and lighter regions laced with
grooves and ridges.
Ganymede's true colors tend toward subtle browns and grays, but
this mosaic's colors have been enhanced to increase surface contrasts.
The violet shades extending from the top and bottom are likely due
to frost particles in Ganymede's polar regions.
APOD: 2002 December 18 - Io Volcano Culann Patera
Explanation:
What causes the unusual colors surrounding Io's volcanoes?
Io,
the innermost
large moon of
Jupiter, is known to be the most
tumultuous body in the
Solar System.
Approximately the size of
Earth's Moon, Io undergoes nearly
continuous volcanic eruptions
from an interior heated by
gravitational tides from Jupiter and Jupiter's other large moons.
The robot spacecraft Galileo currently orbiting Jupiter
has been monitoring the active volcano Culann Patera over the past few years.
The above images indicate that the
volcano
has produced not only red and black colored
lava flows, but yellow
sulfur patches from explosive plumes.
Green colors may arise when these processes affect the same terrain.
White patches may be caused, in part, by
sulfur dioxide
snow.
As Galileo has fulfilled its
mission objectives and is running low on maneuvering fuel, NASA plans to
crash the spacecraft into Jupiter during 2003.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
NASA Web Site Statements, Warnings, and
Disclaimers
NASA Official: Jay Norris.
Specific rights apply.
A service of:
EUD at
NASA /
GSFC
& Michigan Tech. U.