inner moon · moon of Jupiter
Amalthea
A small, reddish, potato-shaped inner moon of Jupiter – the last moon discovered by eye at the telescope.
- Distance from Earth today
- 815.7 million km5.452 AU · light: 45 min 21 s
- Distance from the Sun today
- 795.2 million km5.316 AU
- As of
- 4 November 2026position from NASA/JPL orbital elements
Where it is today
Top view of the plane of Earth’s orbit, compressed distance scale. Open on the big map with the time slider →
Facts
- Diameter
- 167 km
- Mass
- 2.47 × 10¹⁸ kg
- Density
- 1,011 kg/m³
- Mean distance from the planet
- 181,400 km
- Orbital period
- 12.0 h
- Orbital eccentricity
- 0.0030
- Orbital inclination
- 0.4°
Source of the figures: JPL SSD – Planetary Satellites (public domain).
Discovery: 1892 – Edward Emerson Barnard
Description
Amalthea is the largest of Jupiter's small inner moons, orbiting well inside the path of Io. Edward Emerson Barnard found it in 1892 at Lick Observatory, and it was the last moon in the Solar System discovered by direct visual observation rather than photography or spacecraft. It is irregular, elongated and one of the reddest objects known. When the Galileo spacecraft flew close by in 2002, its gravity measurements showed that Amalthea is surprisingly light for its size, suggesting a porous pile of icy rubble. Dust knocked off its surface by impacts feeds one of Jupiter's faint gossamer rings.