23958 Theronice (provisional designation1998 VD₃₀) is aJupiter trojan from theGreek camp, approximately 47 kilometers (29 miles) in diameter. It was discovered on 10 November 1998, by astronomers with theLINEAR survey at theLincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States.^[1] The dark Jovianasteroid belongs to the110 largest Jupiter trojans and shows an exceptionallyslow rotation of 562 hours.^[8]

Theronice is a darkJupiter trojan in a 1:1orbital resonance withJupiter. It is located in the leadingGreek camp at the Gas Giant'sL₄Lagrangian point, 60° ahead of its orbit(seeTrojans in astronomy). It is also a non-family asteroid in theJovian background population.^[4] It orbits the Sun at a distance of 4.7–5.7 AU once every 12 years (4,370 days;semi-major axis of 5.23 AU). Its orbit has aneccentricity of 0.10 and aninclination of 25° with respect to theecliptic.^[2] The body'sobservation arc begins with its first observation as1986 WG₉ at theKiso Observatory in November 1986, or 12 years prior to its official discovery observation at Socorro.^[1]

Thisminor planet wasnumbered by theMinor Planet Center on 8 April 2001 (M.P.C. 42554).^[9] It wasnamed in April 2025 afterTheronice, a princess ofOlenus, daughter of KingDexamenus and mother ofAmphimachus.^[10]

Theronice is an assumed carbonaceousC-type asteroid.^[8] Most Jupiter trojans areD-types, with the remainder being mostly C andP-type asteroids. It has a typicalV–I color index of 0.99 and aBR-color of 1.15.^[8]

With arotation period of 562 hours, thisslow rotator belongs to theTop 100 slowest rotators known to exist. It is also the third-slowest rotator among the larger Jupiter trojans after4902 Thessandrus (738 hours) and7352 Hypsenor (648 hours).

In August 2015, a rotationallightcurve of Theronice was obtained fromphotometric observations by theKepler space observatory during itsK2 mission. Lightcurve analysis gave an exceptionally long period of562±4 hours with a brightness amplitude of 0.45magnitude, somewhat indicative of a non-spherical shape (U=2).^[7] A second, lower-rated lightcurve fromKepler gave an alternative, even longer period of1143±155 hours (U=2).^[8][11]

These results supersede a poor period determination made at theSierra Nevada Observatory in 2007, which gave a period 12.080 hours (U=1).^[8][12]

According to the survey carried out by theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer and the JapaneseAkari satellite, Theronice measures 46.00 and 47.91 kilometers in diameter and its surface has analbedo between 0.076 and 0.084, respectively.^[5][6] TheCollaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a larger diameter of 50.77 kilometers based on anabsolute magnitude of 10.2.^[8]

• Asteroid Lightcurve Database (LCDB), query form (infoArchived 16 December 2017 at theWayback Machine)
• Discovery Circumstances: Numbered Minor Planets (20001)-(25000) – Minor Planet Center
• Asteroid (23958) 1998 VD30 at the Small Bodies Data Ferret
• 23958 Theronice atAstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 23958 Theronice at theJPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters

• Minor planet object articles (numbered)
• Jupiter trojans (Greek camp)
• Discoveries by LINEAR
• Slow rotating minor planets
• Astronomical objects discovered in 1998
• Named minor planets

• Articles with short description
• Short description matches Wikidata
• Use dmy dates from June 2018
• Webarchive template wayback links
• JPL Small-Body Database ID different from Wikidata