Megaclite
A small, light-red irregular moon of Jupiter.
Megaclite (Jupiter XIX, formerly S/2000 J 8) is a small, irregular moon of Jupiter. It travels around the planet in a retrograde direction—meaning opposite to Jupiter's spin—at an average distance of about 23.5 million kilometers. Its orbit is highly inclined and eccentric, and it shares these orbital traits with the larger irregular moon Pasiphae, placing Megaclite in the Pasiphae group. The moons in this group are thought to be pieces of an asteroid or trans-Neptunian object that Jupiter captured and that later broke apart in a collision billions of years ago. However, Megaclite’s mean inclination and distinct color suggest it might have been captured independently, not linked to that ancient smash-up.
Discovered on 23 November 2000 by Scott S. Sheppard and his team from the University of Hawaiʻi, it was one of eleven Jovian moons found that month and was given the temporary designation S/2000 J 8. It received its permanent name in October 2002, after Megaclite, the mother of Thebe and Locrus by Zeus (Jupiter) in Greek mythology. The name was initially misspelled as Magaclite, a mistake corrected in November 2002, though some earlier studies still use the wrong form.
The moon orbits Jupiter at a mean distance of 23,640,100 kilometers, completing one lap every 734.6 days. Its orbital inclination is 148° relative to the ecliptic, and its eccentricity is a high 0.440. This orbit is constantly shifting due to gravitational pulls from the Sun and other planets.
As a member of the Pasiphae group, Megaclite belongs to a set of retrograde irregular moons with semimajor axes between about 22 and 25 million kilometers, inclinations from 141° to 158°, and eccentricities from 0.22 to 0.44. Yet because of its average inclination and different color, it is sometimes placed in its own category, separate from the other Pasiphae moons. Its spectral features also differ from Pasiphae’s, hinting at a different origin.
Megaclite is very faint from Earth, with an apparent visual magnitude around 21.7, so only large, sensitive telescopes can spot it. Assuming a low geometric albedo of 0.04—typical for irregular moons—its diameter is estimated at about 6 kilometers. Its shape is unknown, but given its small size, it is likely irregular, like many other small irregular moons.
Quick Facts
- Pronounced
- m · ɛ · ɡ · ə · ˈ · k · l · aɪ · t · iː
- Adjective
- Megaclitean ˌ · m · ɛ · ɡ · ə · k · l · ᵻ · ˈ · t · iː · ə · n
- Named After
- Μεγακλειτή Megaclītē
- Mpc Name
- Jupiter XIX
- Discoverer
- Scott S. Sheppard / David C. Jewitt / Yanga R. Fernandez / Eugene A. Magnier
- Discovery Site
- Mauna Kea Observatory
- Discovered
- 25 November 2000
- Satellite Of
- Jupiter
- Group
- Pasiphae group
- Epoch
- 2026-01-01
- Observation Arc
- 2000 · 2025 / 2025-12-21 (last obs)
- Periapsis
- 13.1 million km
Facts from the source article.
Lore & Background
Megaclite was discovered on 23 November 2000 by Scott S. Sheppard and a team from the University of Hawaiʻi, along with ten other Jovian moons, and given the temporary designation S/2000 J 8. It was named in October 2002 after Megaclite, mother by Zeus (Jupiter) of Thebe and Locrus in Greek mythology. The name was initially erroneously given as Magaclite, corrected in November 2002, though some earlier research still uses the incorrect form.
Megaclite orbits Jupiter in the retrograde direction at an average distance of 23.5 million km, completing one orbit in 734.6 days. Its orbit has a high inclination of 148° and an eccentricity of 0.440, and is subject to continuous changes due to gravitational perturbations from the Sun and other planets. It belongs to the Pasiphae group, a set of irregular retrograde moons believed to be fragments of an asteroid or trans-Neptunian object captured and destroyed by collision billions of years ago. However, Megaclite's mean inclination and different light-red color (B−V=0.94, V−R=0.41) compared to the grey Pasiphae (B−V=0.74, V−R=0.38) suggest it could be an independent object captured separately.
Most of Megaclite's physical properties are unknown. It is estimated to be about 6 km in diameter, assuming a low geometric albedo of 0.04 like other irregular moons. Its surface is dark and light red, and its shape is likely irregular due to its small size. It has not been imaged up close by a space probe; the European Space Agency's Jupiter Icy Moons Explorer (Juice) mission plans to observe it distantly to measure its rotation period and shape by watching brightness changes over time.
Reader's Guide
Megaclite is significant as one of Jupiter's many irregular moons, providing insight into the dynamics and history of the Jovian system. Its discovery in November 2000 by Scott S. Sheppard's team added to the growing catalog of small outer moons. As a member of the Pasiphae group, it shares orbital characteristics with other retrograde moons, but its distinct light-red color and mean inclination raise the possibility that it was captured independently, not from the same collision event that formed the group. This uncertainty highlights the complexity of the moon's origin and the challenges in understanding the capture and fragmentation processes of irregular satellites. Its small size (estimated 6 km diameter) and faint apparent magnitude of 21.7 mean it can only be observed by very large telescopes. The planned observations by the Juice mission may reveal its rotation period and shape, offering further clues about its nature. Megaclite's naming history—including the initial error as Magaclite—adds a minor footnote to its record. Overall, it represents a typical but potentially unique irregular moon whose study contributes to broader knowledge of Jupiter's satellite system and the history of captured objects.
Did You Know?
- It was initially erroneously named Magaclite, corrected in November 2002.
- Megaclite has a light-red surface color (B−V=0.94, V−R=0.41), unlike the grey color of Pasiphae.
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