Iocaste.space

Irregular moon of Jupiter (retrograde) · Outer Jovian system · Ananke group

Iocaste

Jupiter XXIV · S/2000 J 3

A five-kilometre backwards moon named after the queen of Thebes — and a lesson in how Jupiter’s moons get their names.

Key factsSpace and mythology book finder
Iocaste at a glance
Object typeIrregular, retrograde moon of Jupiter[1]
GroupAnanke group[1]
DiscoveredNov. 23, 2000, Mauna Kea, Hawaii[2]
DiscoverersS. S. Sheppard, D. C. Jewitt, Y. R. Fernandez, E. Magnier[2]
NamedOctober 2002, after Jocasta (Iocaste) of Thebes[1]
Size≈ 5.2 km across (radius 2.6 km, assuming albedo 0.04)[2]
ColourGrey, like Harpalyke and Praxidike[2]
Mean distance≈ 21.1 million km from Jupiter[3]
Orbital period≈ 625 days[3]
Inclination≈ 149° (retrograde)[3]
Eccentricity≈ 0.22[3]

A name chosen by the rules

Iocaste was named in October 2002 after Jocasta, queen of Thebes, the mother and wife of Oedipus.[1][5] The ending “e” follows the IAU’s policy for outer moons with retrograde orbits.[1]

How Jupiter’s moons are named

Jupiter’s moons are named after lovers and favourites of Jupiter (Zeus) and, since 2004, also their descendants. Names ending in “a” or “o” go to prograde irregular moons; names ending in “e” to retrograde ones.[4]

Ananke group

Iocaste orbits like the larger moon Ananke and belongs to the Ananke group, thought to be fragments of a captured asteroid broken up by a collision.[1][2] It shares a grey colour with Harpalyke and Praxidike.[2]

How big?

NASA gives a mean radius of about 2.6 km, assuming an albedo of 0.04 — so about 5.2 km across.[2] Like the rest of the Ananke group, it is not massive enough to pull itself round and is probably irregularly shaped.[2]

Space and mythology book finder

From Greek myths behind moon names to guides for exploring Jupiter, there’s a book for every reader. Answer five quick questions and we’ll suggest book categories that fit — with links to browse current titles.

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Orbit

Iocaste moves backwards around Jupiter at about 16.4–25.8 million km, completing a lap in about 625 days.[3]

Jupiter Callisto (1.88 million km)Himalia (11.44 million km) farthest ≈ 25.8 million km closest ≈ 16.4 million km
Top-down orbit of Iocaste to scale, computed from JPL orbital elements (a ≈ 21.06 million km, e ≈ 0.223).[3] Callisto and Himalia orbits shown for comparison.[3] Mean orbital elements; the real orbit is tilted steeply and shifts over time, so this top-down view flattens it onto one plane.

Myths and moons on the bookshelf

Jupiter’s moon names are a tour of Greek myth. Our book finder suggests mythology, astronomy and space-exploration books by age and interest.

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How Jupiter’s moons get their names

From Roman numerals to Greek myth: the IAU rules that gave Iocaste its name and its final “e”.

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Jocasta, queen of Thebes

The tragic figure behind the moon’s name.

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How do we know how big Iocaste is?

Why many small-moon sizes come with the phrase “assuming an albedo of 0.04”.

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Sources

  1. Iocaste (moon) — Wikipedia
  2. Iocaste — NASA Science
  3. Planetary Satellite Mean Elements — NASA JPL Solar System Dynamics
  4. Moons of Jupiter — Wikipedia
  5. Jocasta — Wikipedia
  6. Kalyke — Wikipedia

Figures are rounded; where sources differ we note it. Spotted an error? Tell us.