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Kallichore is ∼4 kilometers in size and thus one of the small known Irregular moons of Jupiter. It has been discovered with the Canada-France-Hawai’i Telescope on Mauna Kea in February 2003 by a group of astronomers led by S. Sheppard; the discovery announcement followed in March 2003 joint with 20 other Irregular Jovian moons.
The orbit of Kallichore around Jupiter is very much perturbed by the Sun. Averaged over thousands of years, the mean distance to Jupiter is ∼23.0 million kilometers, with one revolution around the planet (as seen from Jupiter) on a retrograde orbit requiring 1 year, 8 months and 2 weeks from “full-moon” to “full-moon”, or almost exactly two sidereal years. Kallichore is a member of the Carme group, made up of Irregular moons orbiting Jupiter retrogradely at mean distances of ~22.7 to ~23.6 million km and mean inclinations to the ecliptic of 164.4° to 164.9°. Not averaged, but current (early 21st century), Kallichore’s distance to Jupiter varies between ~17.7 and ~30.4 million km during one orbit around Jupiter (periapsis and apoapsis distance, respectively).
In early October 2031, the 🛰️Juice spacecraft of the European Space Agency (ESA) will come closer than 0.6 million kilometers to Kallichore. This will be the closest approach of Juice to any Irregular Jovian moon. (Second closest will be a Themisto at 1.1 million km.) An alternate path of the first orbit might bring Juice as close as 153,000 km to this little moon, and even a really close targeted flyby appears possible at low fuel cost. This is currently under investigation (700 and 2200 km are possible flyby altitudes), a decision is expected for late 2026.
On 30 Nov and 05 Dec 2025, Kallichore has been observed with the WFC3 camera of the Hubble Space Telescope (GO/DD 18215) at a spatial resolution of 125 kilometers per pixel and a Solar-phase angle of ~8°. Goal of the observations was to improve astrometry to narrow down the uncertainty of the path of a stellar occultation on 15 Dec 2025 over Türkiye, Europe and the US. This occultation of an ~13th magnitude star in constellation Gemini was successfully recorded from three telescopes of the OAVdA observatory at Aosta Valley in Italy.
The combined observations (HST, the stellar occultation, plus a follow-up observation by the 10.4-meters Gran Telescopio de Canarias (GTC) on 21 Jan 2026) reduced the positional uncertainty (1−σ) of Kallichore on 05 Oct 2031 (the potential Juice flyby epoch) by ~80%, from 1544 to 265 kilometers. Furthermore, Kallichore was found to have an elongated shape with a size ratio (long to short axis) of 1.5 at least, and a black surface with an albedo of only ~4%.
• Wikipedia article of Kallichore
• Paper by Rizos et al. (2026) in Nature Astronomy on HST and GTC observations, and a stellar occultation of Kallichore. Press release →here.
• Animated gif of the 16 HST Kallichore images
• Conference paper by Boutonnet and Rocci (2026) at the AIAA SciTech 2026 Forum about the ESA study on the Juice Kallichore flyby
Last update: 02 Aug 2026 — page content is best displayed on a screen at least 1024 pixels wide
© Tilmann Denk (2026)