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Amalthea (moon)

Amalthea
Amalthea PIA02532.png
Galileo images of Amalthea
Discovery
Discovered byE. E. Barnard
Discovery timeSeptember 9, 1892
Orbit
Shortest distance from what it orbits around181,150 km[1]
Longest distance from what it orbits around182,840 km[1]
Avgdistance from the center of its orbital path181365.84 ± 0.02 km (2.54 RJ)[2]
How egg-shaped its orbit is
("eccentricity")
0.00319 ± 0.00004[2]
How long it takes to complete an orbit0.49817943 ± 0.00000007 d (11 h 57 min 23 s)[2]
Average speed26.57 km/s[1]
Angle above the reference plane
("inclination")
0.374 ± 0.002° (to Jupiter's equator)[2]
What it orbitsJupiter
Size and Other Qualities
Measures250×146×128 km³[3]
Average distance from its center to its surface83.5 ± 2.0 km[3]
Volume inside it(2.43 ± 0.22)×106 km³[4]
Mass2.08 ± 0.15×1018 kg[4]
Average density0.857 ± 0.099 g/cm³[4]
Gravity at its surface~0.020 m/s² (~0.002 g)[1]
Slowest speed able to escape into space
("escape velocity")
~0.058 km/s[1]
How long it takes to turn around one timesynchronous[3]
Angle at which it turns
(in relation to its orbit)
zero[3]
How much light it reflects0.090 ± 0.005[5]
Surface temp. Min. Avg. Max.
[7] 120 K 165 K
Seeming brightness
("apparent magnitude")
14.1 [6]

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.[8] It is also known as Jupiter V.

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.[3]

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.[3]

Discovery and naming

Amalthea was found on September 9, 1892 by Edward Emerson Barnard using the 36 inch (91 cm) telescope at Lick Observatory.[8] 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.[8] Its Roman numeral designation is Jupiter V. The name "Amalthea" was not adopted by the IAU until 1975,[9] although it had been in use for many decades. The name was suggested by Camille Flammarion.[10] Before 1975, Amalthea was most commonly known simply as Jupiter V. 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.[2]

Physical characteristics

The surface of Amalthea is very red [3] The reddish color may be due to sulfur coming from Io or some other non ice material.[3] Bright patches of green appear on the major slopes of Amalthea, but the nature of this color is currently unknown.[3] The surface of Amalthea is a bit brighter than surfaces of other closer moons of Jupiter.[5]

Galileo images showing Amalthea's irregular shape

How Amalthea looks from Jupiter

Computer simulation of Amalthea and Jupiter. The 'camera' is 1,000km from Amalthea and the field of view is 26°.

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.[3] 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.

References

1. Calculated on the basis of other parameters
2. Cooper, N.J.; Murray, C.D.; Porco, C.C.; Spitale, J.N. (2006). "Cassini ISS astrometric observations of the inner jovian satellites, Amalthea and Thebe". ICARUS 181: 223–234. .
3. Thomas, P.C.; Burns, J.A.; Rossier, L.; et al. (1998). "The Small Inner Satellites of Jupiter". ICARUS 135: 360–371. . Archived from the original on 2011-02-12. Retrieved 2007-12-07.
4. Anderson, J.D.; Johnson, T.V.; Shubert, G.; et al. (2005). "Amalthea’s Density Is Less Than That of Water". Science 308: 1291–1293. . Archived from the original on 2007-06-28. Retrieved 2007-12-07.
5. Simonelli, D.P.; Rossiery, L.; Thomas, P.C.; et al. (2000). "Leading/Trailing Albedo Asymmetries of Thebe, Amalthea, and Metis". ICARUS 147: 353–365. . Archived from the original on 2007-06-28. Retrieved 2007-12-07.
6. "Classic Satellites of the Solar System". Observatorio ARVAL. Archived from the original on 2011-08-25. Retrieved 2007-09-28.
7. Simonelli, D.P. (1982). "Amalthea: Implications of the temperature observed by Voyager". ICARUS 54: 524-538. .
8. Barnard, E. E. (1892). "Discovery and Observation of a Fifth Satellite to Jupiter". Astronomical Journal 12: 81–85.
9. IAUC 2846: Satellites of Jupiter1975 October 7. Archived 2020-06-02 at the Wayback Machine
10. USGS Astrogeology Research Program, Gazetteer of Planetary Nomenclature. Archived 2007-07-26 at WebCite