4057 Demophon

4057 Demophon (provisional designation 1985 TQ) is a large Jupiter Trojan asteroid from the Greek camp, approximately 46 kilometers (29 miles) in diameter. It shares Jupiter's orbit around the Sun¹ and is named after Demophon, the prince of Athens who took part in the Trojan War.

Orbit and classification

Demophon is a member of the Greek camp of Jupiter Trojans, the population of asteroids that orbits the Sun at Jupiter's L4 Lagrange point, 60 degrees ahead of the planet². Its orbit has a semi-major axis of 5.22 astronomical units, an eccentricity of 0.118, and an inclination of 2.88 degrees to the ecliptic². The same source lists it among L4 Trojans selected as bodies of potential scientific interest for spacecraft mission design².

Resonant dynamics

Demophon is notable among Trojans for its proximity to a secular resonance, a slow gravitational interaction involving the precession rates of its orbit. In the resonant-structure study of Jupiter's Trojans by Philippe Robutel and Florence Gabern, Demophon appears in the family of actual Trojans lying within 0.1 arcsec per year of resonances of the form 4g + ν2,5 + p5g5 + p6g6 + q5s5 + q6s6 = 0, where g and s are the frequencies of perihelion and node precession and ν2,5 is a combination of planetary frequencies⁴. For Demophon the computed distance to the exact resonance is 0.002 arcsec per year⁴.

Very close to the resonance. The same study notes that some actual asteroids, with Demophon as the first named example, are really very close to one of these resonances, at a distance below 2 × 10⁻³ arcsec per year, and that in some cases it can be numerically shown that such particles are captured by the resonance, with the critical angle inside the resonance librating over a period of about several million years⁴. The companion paper on long-term stability and diffusion tracks the evolution of Demophon's critical angle over tens of millions of years of numerical integration, illustrating this slow libration⁵.

Physical properties

The Kepler space telescope's Campaign 6, which observed a field containing Trojan asteroids, produced a well-constrained lightcurve for Demophon. The fitted rotation period is 29.824 ± 0.240 hours, with a lightcurve amplitude of 0.209 ± 0.026 magnitudes, an absolute magnitude of 10.10, and an effective diameter of 45.683 ± 6.581 km³. An independent K2 photometry analysis by Gy. M. Szabó and colleagues reports a period of 29.925 hours with the same amplitude of 0.209 magnitudes⁶.

Naming

The asteroid is named after Demophon, the prince of Athens in Greek mythology, son of King Theseus and Phaedra.

References

1. Asteroid Demophon, Space Reference
2. Design of End-to-End Trojan Asteroid Reconnaissance (Stuhow, Wilson et al., AAS 2014)
3. Trojan Asteroids in the Kepler Campaign 6 Field, The Astronomical Journal 153, 116 (2017)
4. The observed Trojans and the global dynamics around the L4 point (Robutel & Gabern)
5. The resonant structure of Jupiter's Trojan asteroids – I. Long-term stability and diffusion, MNRAS 372, 1463 (2006)
6. Gy. M. Szabó et al., K2 photometry of Jupiter Trojan asteroids

Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Jupiter Trojans and other dynamical groups › Greek-camp Jupiter Trojans › Argonauts and pre-war heroes

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

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