Amalthea (moon)

**Amalthea** is the third closest moon to Jupiter. It was found on September 9, 1892, by Edward Emerson Barnard and named after Amalthea, a nymph in Greek mythology. It is also known as ****.

On Amalthea, Jupiter would be an amazing sight in its sky, looking 92 times bigger than the Full Moon. Amalthea is the biggest of the closer moons of Jupiter. Non-spherical and reddish in colour, it is thought to have of water ice with unknown amounts of other materials. Its surface has big craters and high mountains.

Pictures of Amalthea were taken in 1979 and 1980 by the _Voyager 1 and 2_ spacecraft, and later, in more detail, by the _Galileo_ orbiter in the 1990s.

## Discovery and naming

Amalthea was found on September 9, 1892 by Edward Emerson Barnard using the 36 inch (91 cm) telescope at Lick Observatory. It was the first new moon of Jupiter since Galileo Galilei's  discovery of the Galilean moons in 1610.

The moon is named after the nymph Amalthea from Greek mythology who nursed the infant Zeus (the Greek equivalent of Jupiter) with goat's milk. Its Roman numeral designation is . The name "Amalthea" was not adopted by the IAU until 1975, although it had been in use for many decades. The name was suggested by Camille Flammarion. Before 1975, Amalthea was most commonly known simply as . The adjectival form of the name is _Amalthean_.

## Orbit

Amalthea circles Jupiter at a distance of 181,000 km (2.54 Jupiter radii). The orbit of Amalthea has an eccentricity of 0.003 and an inclination of 0.37° relative to the equator of Jupiter.

## Physical characteristics

The surface of Amalthea is very red  The reddish color may be due to sulfur coming from Io or some other non ice material. Bright patches of green appear on the major slopes of Amalthea, but the nature of this color is currently unknown. The surface of Amalthea is a bit brighter than surfaces of other closer moons of Jupiter.

## How Amalthea looks from Jupiter

From Jupiter's surface —or rather, from just above its cloudtops— Amalthea would appear very bright, shining with a magnitude of −4.7, similar to that of Venus from Earth.

## How Jupiter looks from Amalthea

From the surface of Amalthea, Jupiter would look enormous: it would look 92 times bigger than the Full Moon.

## Exploration

In 1979-1980, the _Voyager 1 and 2_ spacecraft made the first images of Amalthea, which resolved its surface. They also measured the moon's surface temperature.  Later, the _Galileo_ orbiter completed taking pictures of Amalthea's surface and a close flyby enabled it to constrain the moon's internal structure and composition.

## Other websites

- Amalthea Profile  by NASA's Solar System Exploration
- Another find for Galileo – Galileo Millennium Mission status report (2003-04-09)
- Jupiter's Amalthea Surprisingly Jumbled – JPL press release (2002-12-09)
- _Jupiter From Amalthea_ , a painting by Frank Hettick, 2002.

## Infobox (planet)

- **name**: Amalthea
- **image**: Amalthea PIA02532.png
- **caption**: Galileo probe, Galileo images of Amalthea
- **bgcolour**: #a0ffa0
- **discoverer**: Edward Emerson Barnard, E. E. Barnard
- **discovered**: September 9, 1892
- **mean orbit radius**: 181365.84 ± 0.02 kilometer, km (2.54 R<sub>J</sub>)
- **eccentricity**: 0.00319 ± 0.00004
- **periapsis**: 181,150 kilometer, km
- **apoapsis**: 182,840 kilometer, km
- **period**: 0.49817943 ± 0.00000007 d (11 h 57 min 23 s)
- **avg speed**: 26.57 km/s
- **inclination**: 0.374 ± 0.002° (to Jupiter's equator)
- **satellite of**: Jupiter (planet), Jupiter
- **dimensions**: 250×146×128 km³
- **mean radius**: 83.5 ± 2.0 km
- **volume**: (2.43 ± 0.22)×10<sup>6</sup> cubic kilometer, km³
- **mass**: 2.08 ± 0.15 kilogram, kg
- **density**: 0.857 ± 0.099 g/cm³
- **surface grav**: ~0.020 Acceleration, m/s² (~0.002 g)
- **escape velocity**: ~0.058 km/s
- **rotation**: synchronous rotation, synchronous
- **axial tilt**: zero
- **albedo**: 0.090 ± 0.005
- **magnitude**: 14.1
- **max temp 1**: 165 K
- **mean temp 1**: 120 K