Amalthea

Jupiter V

Amalthea [am-al-THEE-uh] is one of Jupiter's smaller moons. It was named after the nymph who nursed the infant Jupiter with goats milk. It was discovered in 1892 by the American astronomer Edward Emerson Barnard while making observations from the Lick Observatory with a 36 inch (91 centimeter) refractory telescope. Amalthea was the last moon in the solar system to be discovered through direct visual observation. It was also the first moon of Jupiter to be discovered since Galileo's discovery of the four Galilean Moons in 1610.

Amalthea is extremely irregular, having dimensions of about 270x165x150 kilometers in diameter. It is heavily scarred by craters, some of which are extremely large relative to the size of the moon. Pan, the largest crater, measures 100 kilometers across and is at least 8 kilometers deep. Another crater, Gaea, measures 80 kilometers across and is probably twice as deep as Pan. Amalthea has two known mountains, Mons Lyctas and Mons Ida with local relief reaching up to 20 kilometers. The surface is dark and reddish in color apparently caused by a dusting of sulfur originating from Io's volcanoes. Bright patches of green appear on the major slopes of Amalthea. The nature of this color is currently unknown.

Amalthea rotates synchronously with its long, blunt axis pointed towards Jupiter. Because of Amalthea's close proximity to Jupiter, it is exposed to the intense Jovian radiation field. It continuously receives high doses of energetic ions, protons, and electrons produced by the Jovian magnetosphere. In addition it is bombarded with micrometeorites, and heavy sulfur, oxygen, and sodium ions that have been striped away from Io.

Amalthea Statistics

Discovered by ........................ Edward Emerson Barnard
Date of discovery ...................................... 1892

Mass (kg) .......................................... 7.17e+18
Mass (Earth = 1) ................................. 1.1998e-06
Radius (km) ....................................... 135x84x75
Radius (Earth = 1) ............................... 2.1167e-02
Mean density (gm/cm^3) .................................. 1.8

Mean distance from Jupiter (km) ..................... 181,300
Rotational period (days) ........................... 0.498179
Orbital period (days) .............................. 0.498179
Mean orbital velocity (km/sec) ........................ 26.47

Orbital eccentricity .................................. 0.003
Orbital inclination .................................... 0.40°

Escape Velocity (km/sec) ............................. 0.0842

Visual geometric albedo ................................ 0.05
Magnitude (Vo) ......................................... 14.1

Views of Amalthea

Amalthea (GIF, 13K)
This image of Amalthea was acquired by the Voyager 1 spacecraft on March 5, 1979. (Credit: Calvin J. Hamilton)

Shaded Relief Map of Amalthea (GIF, caption)
This is a shaded relief map of Amalthea, a small satellite of Jupiter. As with all maps, it is the cartographer's interpretation; not all features are necessarily certain given the limited data available. This interpretation stretches the data as far as possible. (Courtesy Phil Stooke)

Jupiter Adrastea Thebe

Author: Calvin J. Hamilton.