# 15977 Pyraechmes

**15977 Pyraechmes** (provisional designation 1998 MA<sub>11</sub>) is a Jupiter Trojan asteroid, a roughly 44-kilometer body that shares Jupiter's orbit in a 1:1 mean-motion resonance from the L5 Lagrangian point, 60 degrees behind the planet. It was discovered on 19 June 1998 by astronomers of the Lincoln Near-Earth Asteroid Research (LINEAR) program at the ETS site of Lincoln Laboratory near Socorro, New Mexico, in the United States.<sup>[5](https://www.minorplanetcenter.net/db_search/show_object?object_id=15977)</sup>

| Key fact | Detail |
|---|---|
| Designations | 15977 Pyraechmes = 1998 MA<sub>11</sub>; alternate 1999 NG<sub>2</sub><sup>[5](https://www.minorplanetcenter.net/db_search/show_object?object_id=15977)</sup> |
| Discovery | 19 June 1998, LINEAR, ETS of Lincoln Laboratory, near Socorro, New Mexico<sup>[5](https://www.minorplanetcenter.net/db_search/show_object?object_id=15977)</sup> |
| Orbit | Semimajor axis 5.18 AU; period 4,309 days (11 years 10 months); eccentricity 0.05; inclination 17°<sup>[5](https://www.minorplanetcenter.net/db_search/show_object?object_id=15977)</sup> |
| Naming | After Pyraechmes, Paeonian leader slain by Patroclus; name approved April 2025<sup>[1](https://www.wgsbn-iau.org/files/Bulletins/V005/WGSBNBull_V005_005.pdf)</sup> |

## Orbit and classification

It circles the Sun at a distance of 4.9 to 5.4 AU once every 11 years and 10 months (4,309 days; semimajor axis 5.18 AU). Its orbit has an eccentricity of 0.05 and an inclination of 17 degrees with respect to the ecliptic.<sup>[6](https://asteroidname.com/asteroid/pyraechmes)</sup>

Because the orbit never approaches Earth's, the asteroid is not classified as potentially hazardous; its closest possible distance to [Earth's orbit](https://www.edgepedia.org/earths-orbit) is 3.96 AU.<sup>[2](https://www.spacereference.org/asteroid/15977-1998-ma11)</sup>

## Discovery and precovery

The official discovery observation was made on 19 June 1998 by the LINEAR survey at Socorro.<sup>[6](https://asteroidname.com/asteroid/pyraechmes)</sup>

## Numbering and naming

The name Pyraechmes was approved by the IAU Working Group Small Bodies Nomenclature and announced in its bulletin of 7 April 2025. The naming citation reads that Pyraechmes "was a leader of the Paeonian horsemen from Amydon. He was the first to be killed by Patroclus who fought while wearing Achilles armor," an episode from the Iliad.<sup>[1](https://www.wgsbn-iau.org/files/Bulletins/V005/WGSBNBull_V005_005.pdf)</sup>

## Physical characteristics

**Slow rotation.** [Robert Stephens](https://www.edgepedia.org/robert-stephens) of the Center for Solar System Studies observed Pyraechmes on three nights in 2013 but could not derive a meaningful rotational lightcurve, because the amplitude never changed appreciably.

## Context among Jupiter's Trojans

The Trojans of Jupiter are asteroids sharing nearly the planet's own orbit, staying either ahead of or behind it in a co-orbital configuration at an angular separation of roughly 60 degrees.<sup>[3](https://www.nature.com/articles/nature03540)</sup> Their inclinations cover a fairly uniform range from 0° to 35° in both the L4 and L5 regions, with a median inclination of 10°, and their eccentricities tend to be below 0.15, values required to remain within the stable zones around the Lagrangian points.<sup>[4](https://springerlink.fh-diploma.de/article/10.1007/s11214-023-01031-4)</sup> Pyraechmes fits this population: its 17° inclination is above the population median, and its eccentricity of 0.05 is well within the stable range.<sup>[4](https://springerlink.fh-diploma.de/article/10.1007/s11214-023-01031-4)</sup>

Dynamical studies indicate that most Trojans many tens of kilometers in diameter or larger are on stable orbits and can be treated as survivors of whatever processes created the [Trojan](https://www.edgepedia.org/trojan-celestial-body) population.<sup>[4](https://springerlink.fh-diploma.de/article/10.1007/s11214-023-01031-4)</sup> The leading explanation for the Trojans' broad inclination distribution is that they formed in more distant regions and were captured into co-orbital motion with Jupiter during the migration of the giant planets, in a short period of chaos just after Jupiter and Saturn crossed their mutual 1:2 resonance.<sup>[3](https://www.nature.com/articles/nature03540)</sup>

## References

1. [WGSBN Bulletin, Volume 5, #5, 2025 April 7, Working Group Small Bodies Nomenclature, IAU](https://www.wgsbn-iau.org/files/Bulletins/V005/WGSBNBull_V005_005.pdf)
2. [Asteroid 15977 (1998 MA11), Space Reference](https://www.spacereference.org/asteroid/15977-1998-ma11)
3. [Morbidelli, A., Levison, H. F., Tsiganis, K., & Gomes, R. (2005). Chaotic capture of Jupiter's Trojan asteroids in the early Solar System. Nature 435, 462–465.](https://www.nature.com/articles/nature03540)
4. [Origin and Evolution of Jupiter's Trojan Asteroids, Space Science Reviews (2023)](https://springerlink.fh-diploma.de/article/10.1007/s11214-023-01031-4)
5. [(15977) Pyraechmes, IAU Minor Planet Center](https://www.minorplanetcenter.net/db_search/show_object?object_id=15977)
6. [(15977) Pyraechmes – asteroid discovered 1998 | AsteroidName](https://asteroidname.com/asteroid/pyraechmes)

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*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*

*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*

License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license