Amalthea Fact Sheet
What Is Known About Amalthea SO FAR
Galileo Images of Amalthea (February - June 1997)
Table of Contents
Amalthea Summary
Amalthea was discovered by the exceptionally keen eyesight of American
astronomer Edward Barnard in 1892 using the 36 inch (91 cm) refractor telescope
at Lick Observatory. This was the first discovery of a Jovian moon since
Galileo's discovery in 1610. Barnard's
discovery of Amalthea was also the last moon of any planet to be discovered
by direct visual observation.
Voyager 1 Image (March 1979)
Amalthea is the largest of Jupiter's smaller moons. It is one of Jupiter's
four inner moons that orbits inside the orbit of Io. With its irregular shape,
measuring 270x170x150 km, Amalthea has a striking resemblence to the potato-shaped
Phobos, the well-known moon orbiting Mars, but it is ten times larger. Like
most satellites of Jupiter, Amalthea is in a synchronous rotation, with the
same blunt end always pointing towards Jupiter.
Shaded Relief Map of Amalthea Courtesy of Phil Stooke
Amalthea is heavily cratered, with two large craters. The larger crater, Pan,
is 90 km long and lies in the "northern hemisphere", and the other large
crater, Gaea, is 75 km long and straddles the south pole of the moon. Pan
is at least 8 km deep and Gaea is probably twice as deep. The local relief
on Amalthea reaches 20 km, and two mountains are known, Mons Ida and Mons
Lyctos.
Voyager 1 Image (March 1979)
Amalthea is a dark object and reddish in color. In fact, Amalthea is the
reddest object in the solar system. The red color is probably caused by
sulfur from Io's volcanoes spiraling down to Jupiter and impacting on Amalthea.
Bright patches observed on the major slopes of Amalthea are green in color.
The nature of the green color is unknown, but observations from the Galileo
spacecraft may shed some light on the composition of the bright spots.
Voyager 1 Image (March 1979)
Amalthea's orbit is only 181,300 km from Jupiter, or only 2.5 Jupiter radii.
Being this close to Jupiter, Amalthea is exposed to the intense radiation field
of Jupiter, and is exposed to high dosages of energetic ions, protons and
electons in the Jovian magnetosphere. Additionally, Amalthea is bombarded
with high-velocity micrometeorites, as well as heavy ions - mostly sulfur,
oxygen and sodium diffusing away from Io.
37K
Voyager 1 Image of Amalthea (March 1979)
Amalthea Quick-Look Statistics
Discovery: Sep 9, 1892 by Edward Barnard
Diameter (km): 270x170x150
Mass (kg): 7.17e+18
Mass (Earth = 1): 1.1988e-06
Surface Gravity (Earth = 1): 0.0055 - 0.0085
Mean Distance from Jupiter (km): 181,300
Mean Distance From Jupiter (Rj): 2.539
Mean Distance from Sun (AU): 5.203
Orbital period (days): 0.498179
Rotational period (days): 0.498179
Density (gm/cm?3) 1.8
Orbit Eccentricity: 0.003
Orbit Inclination (degrees): 0.40
Orbit Speed (km/sec): 26.47
Escape velocity (km/sec): 0.0842
Visual Albedo: 0.06
Surface Composition: Rock/Sulfur?
Amalthea Images
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