5025 Mecisteus

5025 Mecisteus (provisional designation 1986 TS₆) is a large Jupiter trojan asteroid from the Greek camp, approximately 50 kilometers (31 miles) in diameter, named after the Greek hero Mecisteus who fought in the Trojan War. Slovak astronomer Milan Antal detected the asteroid on 5 October 1986 at the Toruń Centre for Astronomy in Piwnice, Poland, and it received its name in 2021.¹

|---|---|

| Discovery | 5 October 1986, by Milan Antal at Toruń–Piwnice, Poland (observatory code 092)¹ |

Discovery and naming

The body's observation arc begins with its official discovery observation at Piwnice in October 1986.⁵ The Working Group for Small Body Nomenclature records the discovery as 1986-10-05, discoverer M. Antal, site Piwnice, observatory code 092.¹

In 2021 the asteroid was named after Mecisteus of Greek mythology. According to the official naming citation, Mecisteus was killed alongside his father Echius while defending the Achaean ships, and earlier in the battle he helped recover the wounded Teucer and Hypsenor.¹ The name follows the convention for Jupiter trojans, which are named after characters from Greek mythology, with heroes of the Greek side populating the L4 camp.²

Orbit

A Czech orbital database, using a later epoch of 21 November 2025 and 4,329 observations over 30 oppositions, gives a period of 11.827 years and lists upcoming perihelion passages on 31 October 2022, 28 August 2034, and 26 June 2046.³

Because it stays near Jupiter's distance from the Sun, Mecisteus never comes close to Earth. The closest listed approach is 4 December 2034 at 3.84 AU, and it is faintest from Earth on 29 September 2028 at magnitude 18.7; its brightest listed apparition is 19 September 2032 at magnitude 17.0.³

Physical properties

Infrared surveys give two size estimates that differ by more than the quoted uncertainties. The discrepancy is typical for dark, distant asteroids, where diameter and albedo trade off against each other in the thermal models fitted to infrared flux.

Context among the trojans

Jupiter's trojans are asteroids that follow essentially the same orbit as Jupiter, leading or trailing the planet by about 60 degrees in stable co-orbital motion.⁴ No spacecraft has visited it; NASA's Lucy mission, launched in October 2021 on a 12-year tour, is the first spacecraft to visit any of the trojans, flying by several of the larger members of the two swarms.²

References

1. Working Group for Small Body Nomenclature Bulletin, Volume 1, No. 12 (naming citation for (5025) Mecisteus), IAU
2. NASA's Lucy Mission: A Journey to the Young Solar System, NASA Science
3. Planetka Mecisteus (5025), Planety, University of West Bohemia
4. Chaotic capture of Jupiter's Trojan asteroids in the early Solar System, Nature
5. IAU Minor Planet Center, minorplanetcenter.net

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

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