12929 Periboea

12929 Periboea (provisional designation 1999 TZ₁) is a Jupiter trojan from the Trojan camp at the L₅ Lagrangian point, discovered by American astronomer Charles W. Juels on 2 October 1999 at the Fountain Hills Observatory in Arizona.¹⁰ Its orbit has a semi-major axis of 5.2546 au, an eccentricity of 0.0418, an unusually high inclination of 43.41°, and a period of 12.05 years.¹ The asteroid measures roughly 54 km across according to survey catalogs, or 62 km per the Johnston archive.¹

Discovery and naming

The asteroid was found on 2 October 1999 at the Fountain Hills Observatory in Arizona and received the provisional designation 1999 TZ₁; it also carries the earlier alternate designation 1992 CF₆, indicating a precovery identification.¹⁰

On 14 May 2021 the IAU's Working Group for Small Body Nomenclature named it Periboea, after a mortal woman in Greek mythology, the eldest daughter of Assaracamenos. The name follows the IAU convention under which Trojan asteroids, those librating in 1:1 resonance with Jupiter, are named for heroes of the Trojan War, with objects at L₅ (the trailing camp) taking Trojan-side names.³ The naming citation appeared in the WGSBN Bulletin.⁴

Orbit and classification

Periboea orbits the Sun in a 1:1 mean-motion resonance with Jupiter as a member of the Trojan camp at the L₅ Lagrangian point. Its orbit has a semi-major axis of 5.2546 au, an eccentricity of 0.0418, and an unusually high inclination of 43.41°, with an orbital period of 12.05 years.¹

Reclassification from centaur. The Minor Planet Center initially classified Periboea as a centaur, a population of objects that cross or approach the giant planets. JPL's CNEOS orbital simulations show no close approaches to Earth, and the object is not classified as potentially hazardous.⁵

The orbit is well determined. Observations used in orbit solutions reach back to 16 September 1953, giving an observation arc of more than 64 years; the Lucky Star ephemeris solution based on 3,812 observations has an RMS residual of 0.122 arcseconds, and a later solution uses 4,569 observations through July 2025.^{1 • 6} The Minor Planet Center records 2,929 observations used to determine its orbit.⁵

Physical characteristics

Periboea is a dark, low-albedo body, consistent with the C-type spectral type assumed for it. Its absolute magnitude is listed between 9.3 and 10.1 depending on the source.¹Stellar occultation data from the Dark Energy Survey give a g-band geometric albedo of 0.0395 ± 0.0020, lower than the thermal-infrared survey values, and absolute magnitudes of 10.717 ± 0.021 in the g band and 9.845 ± 0.020 in the z band.² A stellar occultation campaign is planned for October 2026 to refine its shape.⁷

Context among the Trojans

Jupiter trojans are bodies trapped in 1:1 resonance with Jupiter at the L₄ and L₅ Lagrange points, 60° ahead of and behind the planet; the leading L₄ swarm is called the Greek camp and the trailing L₅ swarm the Trojan camp.⁸ Periboea's high orbital inclination of about 43° places it among the more strongly inclined members of the L₅ swarm, and objects with similar orbits include 1208 Troilus, 1870 Glaukos, and 2223 Sarpedon.⁵ The trojan population is thought to have been captured by Jupiter early in the Solar System's history, likely from the trans-Neptunian region, and NASA's Lucy mission is surveying members of both swarms.⁹

References

1. (12929) Periboea, Lucky Star, Observatoire de Paris LESIA
2. Peixoto, V. F. (2022). The Small Bodies of the Solar System, UFRJ thesis
3. Naming of Astronomical Objects, IAU
4. WGSBN Bulletin 1, #1 (2021)
5. Asteroid Periboea, Space Reference
6. (12929) Periboea, NIMAv7 orbit solution, Lucky Star
7. RECON event prediction for 12929 Periboea, 14 October 2026
8. Consequences of planetary migration on the minor bodies of the early solar system, A&A
9. How Were the Trojan Asteroids Discovered and Named?, NASA
10. IAU Minor Planet Center, minorplanetcenter.net

Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Jupiter Trojans and other dynamical groups › Trojan-camp Jupiter Trojans

Initially written Oct 21, 2026 · Edited: Oct 25, 2026

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