Kalyke

The odd one out

All Carme-group moons are light red — except Kalyke, which is considerably redder.^[2] Its spectrum has been compared to that of 5145 Pholus, another very reddish object.^[1]

Extremely dark

Infrared thermal measurements by the WISE spacecraft gave Kalyke an albedo of just 2.9%, corresponding to a diameter of 6.9 km. That makes it one of the least reflective bodies in the Solar System.^[1]

Measured twice in 2002

Astronomers observed Kalyke on 14 January 2002 with the Nordic Optical Telescope on La Palma (V−R 0.72, V−I 0.96) and on 13 March 2002 with the MMT Observatory in Arizona (B−V 0.94, V−R 0.70, V−I 0.88).^[1] They concluded it was very red, consistent with a centaur or trans-Neptunian object, though the classification was uncertain.^[1]

Where did it come from?

The rest of the Carme group probably came from a D-type asteroid, perhaps a Hilda or Jupiter trojan.^[4] Kalyke’s redness suggests it may be an interloper from the outer Solar System — or a remnant of the object that struck the Carme parent body, though settling into such a similar orbit would be unusual.^[4]

Orbit

Kalyke orbits backwards between roughly 17.2 and 29.4 million km from Jupiter, once every 727 days.^[3]

The name

Discovered as S/2000 J 2, it was named in October 2002 after Kalyke, or Calyce, of Greek mythology.^[1] NASA describes her as the mother of Endymion by Zeus, according to some authors.^[2]

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