9799 Thronium,provisional designation:1996 RJ, is a largeJupiter trojan from theGreek camp and the parent body of a small, unnamedasteroid family(006), approximately 68 kilometers (42 miles) in diameter. It was discovered on 8 September 1996, by American astronomerTimothy Spahr at theCatalina Station of theSteward Observatory near Tucson, Arizona, in the United States.^[1] The assumedC-type asteroid belongs to the50 largest Jupiter trojans and has a relatively longrotation period of 21.52 hours.^[4] It was named for the ancient Greek city ofThronium mentioned in theIliad.^[2]

Thronium is a dark Jovianasteroid orbiting in the leadingGreek camp at Jupiter'sL₄Lagrangian point, 60° ahead of the Gas Giant's orbit in a1:1 resonance(seeTrojans in astronomy). It orbits the Sun at a distance of 4.9–5.4 AU once every 11 years and 10 months (4,320 days;semi-major axis of 5.19 AU). Its orbit has aneccentricity of 0.05 and aninclination of 31° with respect to theecliptic.^[3] The body'sobservation arc begins in December 1986, with its first observation as1986 XP₅ at the Observatory of the University of St Andrews (482), Scotland, almost 10 years prior to its official discovery observation at Catalina Station.^[1]

Thronium is also theparent body of a small, unnamedasteroid family with thefamily identification number006.^[6][7] The family seems to be young, compact and consist of only 7 known members.^[14]: 23 Only a few families have been identified among the Jovian asteroids; four of them in the Greek camp. This potentially collisional family was first characterized by Jakub Rozehnal and Miroslav Brož in 2014.^[8]

The other members of this family include the unnamed Jovian asteroids(89938),(226027),(243316),(254691),(388876) and(392189).^[14]

Thisminor planet was numbered on 8 December 1998 after its orbit had been sufficiently secured (M.P.C. 33211).^[15] On 14 May 2021, the object was named by theWorking Group for Small Bodies Nomenclature (WGSBN), after the ancient Greek city ofThronium. In Greek mythology and mentioned in theIliad (Catalogue of Ships), it was one of the places from which theLocrians joined theAchaeans.^[2]

1996 RJ is an assumed, carbonaceousC-type asteroid.^[4] Nesvorný does not give an overallspectral type for this unnamed family, but derives an albedo of 0.06(see below), which is also typical for carbonaceous C-types.^[14]: 23

In October 2009, a rotationallightcurve of1996 RJ was obtained fromphotometric observations byStefano Mottola using a 1.2-meter telescope at theCalar Alto Observatory in Spain. Lightcurve analysis gave a longer-than averagerotation period of 21.52 hours with a brightness amplitude of 0.16magnitude (U=2+).^[4][12]

According to the surveys carried out by the Infrared Astronomical SatelliteIRAS, the JapaneseAkari satellite and theNEOWISE mission of NASA'sWide-field Infrared Survey Explorer,1996 RJ measures between 64.87 and 72.42 kilometers in diameter and its surface has analbedo between 0.037 and 0.060.^[9][10][11]

TheCollaborative Asteroid Lightcurve Link derives an albedo of 0.0603 and a diameter of 65.06 kilometers based on anabsolute magnitude of 9.6.^[4]

• Long-term evolution of asteroid families among Jovian Trojans, Jakub Rozehnal and Miroslav Brož (2014)
• Asteroid Lightcurve Database (LCDB), query form (infoArchived 16 December 2017 at theWayback Machine)
• Discovery Circumstances: Numbered Minor Planets (5001)-(10000) – Minor Planet Center
• 9799 Thronium atAstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 9799 Thronium 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 Timothy B. Spahr
• Named minor planets
• Astronomical objects discovered in 1996

• 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