Kalyke: the reddest moon in its family

How two telescopes in 2002 showed one Carme-group moon didn’t match the rest.

Published 2026-10-23

The Carme group’s moons look like siblings: similar orbits, similar light-red colours. Kalyke breaks the pattern.^[4][2]

The 2002 observations

• 14 January 2002, Nordic Optical Telescope, La Palma: V−R = 0.72, V−I = 0.96.^[1]
• 13 March 2002, MMT Observatory, Mount Hopkins, Arizona: B−V = 0.94, V−R = 0.70, V−I = 0.88.^[1]

For comparison, typical Carme-group colours are B−V 0.76 and V−R 0.47.^[4]

A debated detail

The V−R value points to a very red object, while V−I is more moderate. The observers suspected the V−I value might be an artifact of CCD fringing. A later paper argued it was real, because it repeated between observations, and could reflect an absorption feature of mafic silicate.^[1]

Why it matters

If that absorption feature were found near 1 μm, Kalyke would be just as likely to have come from the main asteroid belt as from the outer Solar System.^[1]

Numbered citations link to the sources list on the Kalyke overview page.