Encyclopedia Entry #10 – Amalthea

Amalthea is a moderate sized moon of Jupiter. Although it is relatively small, it’s the fifth largest natural satellite of Jupiter. It’s also the largest of the inner satellites of Jupiter. It was discovered in 1892, and is also known as Jupiter V. It’s tidally locked with Jupiter, as most moons are, especially those that are close to the planet.

Amalthea

Data

  • Dimensions: 250 × 146 × 128 km
  • Mass: (2.08±0.15)×1018 kg
  • Density: 0.857±0.099 g/cm³
  • Surface gravity: ≈ 0.020 m/s² (≈ 0.002 g)
  • Albedo: 0.090±0.005
  • Temperature: 120 K (-153°C)
  • Mean orbital radius: 181,365.84±0.02 km
  • Orbital period: 0.498 d (11 h, 57 min, 23 s)
  • Inclination: 0.374°±0.002° (to Jupiter’s equator)
  • Eccentricity: 0.00319±0.00004

Name Origin

Amalthea is named after the nymph from Greek mythology who nursed the infant Zeus. She is sometimes represented as a goat who suckled Zeus in a cave on Crete, or as a goat-tending nymph who fed him the milk of her goat.

5 Interesting Facts

1. Amalthea was discovered by Edward Emerson Barnard on September 9, 1892, at Lick Observatory.

2. The colour of Amalthea is red, which is thought to either come from Io or some other non-ice material.

3. The largest crater, Pan, is 100 km across, covering a huge portion of one side of the moon.

4. Due to the size of Amalthea, its gravity should have pulled it into a more spheroid shape. However, it’s thought that the moon is made of a more rigid material, allowing it to retain its highly irregular shape.

5. If you were to view Jupiter from the surface of Amalthea, it would be 46 degrees across, or about one quarter of the sky from horizon to horizon.

Due to the closeness of the satellite to Jupiter, and the high amount of radiation in that region, a clear image of Amalthea has never been taken. The image provided is from the Galileo probe, and is the clearest available.

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