23958 Theronice
23958 Theronice is a Jupiter trojan from the Greek camp, approximately in diameter. It was discovered on 10 November 1998, by astronomers with the LINEAR survey at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States. The dark Jovian asteroid belongs to the [|110 largest Jupiter trojans] and shows an exceptionally slow rotation of 562 hours.
Orbit and classification
Theronice is a dark Jupiter trojan in a 1:1 orbital resonance with Jupiter. It is located in the leading Greek camp at the Gas Giant's Lagrangian point, 60° ahead of its orbit. It is also a non-family asteroid in the Jovian background population. It orbits the Sun at a distance of 4.7–5.7 AU once every 12 years. Its orbit has an eccentricity of 0.10 and an inclination of 25° with respect to the ecliptic. The body's observation arc begins with its first observation as at the Kiso Observatory in November 1986, or 12 years prior to its official discovery observation at Socorro.Numbering and naming
This minor planet was numbered by the Minor Planet Center on 8 April 2001. It was named in April 2025 after Theronice, a princess of Olenus, daughter of King Dexamenus and mother of Amphimachus.Physical characteristics
Theronice is an assumed carbonaceous C-type asteroid. Most Jupiter trojans are D-types, with the remainder being mostly C and P-type asteroids. It has a typical V–I color index of 0.99 and a BR-color of 1.15.Rotation period
With a rotation period of 562 hours, this slow rotator belongs to the Top 100 slowest rotators known to exist. It is also the third-slowest rotator among the larger Jupiter trojans after 4902 Thessandrus and 7352 Hypsenor.In August 2015, a rotational lightcurve of Theronice was obtained from photometric observations by the Kepler space observatory during its K2 mission. Lightcurve analysis gave an exceptionally long period of hours with a brightness amplitude of 0.45 magnitude, somewhat indicative of a non-spherical shape. A second, lower-rated lightcurve from Kepler gave an alternative, even longer period of hours.
These results supersede a poor period determination made at the Sierra Nevada Observatory in 2007, which gave a period 12.080 hours.