20947 Polyneikes

20947 Polyneikes (provisional designation 2638 T-2) is a Jupiter Trojan asteroid, a body locked in the 1:1 mean-motion resonance with Jupiter at the leading L4 Lagrange point (orbit position where gravity balances, letting objects stay fixed relative to a planet), discovered on 29 September 1973 at Palomar Observatory by the astronomers C. J. van Houten, I. van Houten-Groeneveld, and Tom Gehrels.⁴ It is named after Polyneikes (Polynices), the Theban prince of Greek mythology whose story is told in the Theban cycle.¹

Discovery

Polyneikes was found on 29 September 1973 at Palomar Observatory during the Palomar–Leiden survey, a collaboration in which plates taken with the Palomar Schmidt telescope were scanned and measured at Leiden.

Orbit and dynamical class

Jupiter Trojans are trapped at the stable L4 and L5 Jovian Lagrange points, and their 1:1 mean-motion resonance with Jupiter keeps their current orbits stable over the lifetime of the Solar System.²

Physical properties

The estimated diameter of Polyneikes is about 23 km, a size typical of the many mid-sized members of the Trojan swarms, whose largest members reach roughly 250 km across.³ Trojans are thought to be more primitive than main-belt asteroids, and the most likely formation scenario for the Trojan clouds involves inward scattering of planetesimals from the trans-Neptunian region followed by capture into the 1:1 resonance with Jupiter.²

Naming

The minor planet is named for Polyneikes, a figure of the Greek mythological tradition, in keeping with the convention that Jupiter Trojans are named after heroes of the Trojan War and related legend.^{1 • 3}

References

1. Lutz D. Schmadel, Dictionary of Minor Planet Names, 5th edition
2. Mottola, S. et al. (2024). Shapes, Rotations, Photometric and Internal Properties of Jupiter Trojans. Space Science Reviews 220, 17.
3. Lucy Mission: Frequently Asked Questions, NASA Science
4. (20947) Polyneikes, IAU Minor Planet Center
5. (20947) Polyneikes – asteroid discovered 1973 | AsteroidName

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

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

© 2026 EdgeChat AI, a subsidiary of Biostate AI. Free to use with credit under the Edgepedia Community License. Developers: read Edgepedia by API or MCP. Embed a reference card.