Space · Moons

Callirrhoe

A moon of Jupiter — First identified as an asteroid; later realized to be a captured retrograde Jovian moon.

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Quick facts

Parent planet

Jupiter

Diameter (mean)

9 km

Mass

8.7 × 10¹⁴ kg
1.2e-08 Moon masses

Mean orbital radius

24,102,000 km

Orbital period

758.8 Earth days

Discovery year

1999

Discoverer

James Scotti et al.

Naming origin

Greek nymph, daughter of Achelous

Surface conditions

Callirrhoe was initially designated as the asteroid 1999 UX18 before its orbital characteristics betrayed it as a Jovian outer irregular. It is a 9-km retrograde body in the Pasiphae group, similar in size to many small captured Kuiper Belt fragments.

Missions and observations

Every Jupiter-system mission has had an opportunity to image or characterize Callirrhoe. The list below is the Jupiter-system mission catalog; specific Callirrhoe encounters are documented in mission archives.

Mission	Year at Jupiter	Status
Pioneer 10 NASA	1973	Completed
Pioneer 11 NASA	1974	Completed
Voyager 1 NASA	1979	Completed
Voyager 2 NASA	1979	Completed
Ulysses NASA/ESA	1992	Completed
Galileo NASA	1995	Completed
Cassini-Huygens NASA/ESA/ASI	2000	Completed
New Horizons NASA	2007	Completed
Juno NASA	2016	Active
Europa Clipper NASA	2030	On the way
JUICE ESA	2031	On the way

Naming etymology

Callirrhoe was a daughter of the river god Achelous and a lover of Zeus. The IAU adopted the name in 2002.

Methodology & sources

Diameter, mass, and orbital parameters from JPL Solar System Dynamics — Physical Parameters. Discovery year and discoverer from the JPL Satellite Discovery Circumstances. Naming etymology from the IAU Working Group for Planetary System Nomenclature. Stylized SVG hero composed from NASA / JPL imagery as visual reference; no photographs are reproduced.