Callirrhoe (/kəˈlɪroʊ.iː/; Greek: Καλλιρρόη), also known as Jupiter XVII, is one of Jupiter's outer natural satellites. It is an irregular moon that orbits in a retrograde direction. Callirrhoe was imaged by Spacewatch at Kitt Peak National Observatory from October 6 through November 4, 1999,^[8] and originally designated as asteroid 1999 UX₁₈.^[9][10] It was discovered to be in orbit around Jupiter by Tim Spahr on July 18, 2000, and then given the designation S/1999 J 1.^[1][11] It was the 17th confirmed moon of Jupiter.^[8]

It was named in October 2002 after Callirrhoe, daughter of the river god Achelous, one of Zeus' (Jupiter's) many conquests.^[12]

Callirrhoe has an apparent magnitude of 20.8,^[7] making it even fainter than dwarf planet Eris at magnitude 18.7.^[13] Jupiter is about 2.1 billion times brighter than Callirrhoe.^{[lower-alpha 2]}

Callirrhoe is about 9.6 kilometers in diameter,^[6] and orbits Jupiter at an average distance of 24.1 million kilometers in 747.09 days, at an inclination of 141° to the ecliptic (140° to Jupiter's equator) with an eccentricity of 0.28. This object was probably captured long ago from a heliocentric orbit and the Sun's gravitational influence makes this orbit highly erratic.^[8]

It belongs to the Pasiphae group, irregular retrograde moons orbiting Jupiter at distances ranging between 22.8 and 24.1 million kilometers, and with inclinations ranging between 144.5° and 158.3°. However, while Pasiphae is gray (B−V=0.74, V−R=0.38, V−I=0.74) in color, Callirrhoe is light red (B−V=0.72, V−R=0.50, V−I=1.02) and more similar to Megaclite.^[14]

As a navigation exercise, the New Horizons spacecraft imaged Callirrhoe on January 10, 2007.^[15]