1867 Deiphobus

1867 Deiphobus (provisional designation 1971 EA) is a large Jupiter Trojan asteroid that shares Jupiter's orbit, librating about the L5 Lagrangian point 60 degrees behind the planet; its orbit was determined from observations dating back to March 3, 1971.¹ It ranks among the next ten largest known Jupiter Trojans, after the six largest.² Thermal radiometry and occultation measurements give consistent sizes near 120 km, and it is among the more highly inclined large Trojans, with an inclination of 26.914 degrees.^{2 • 3} Deiphobus is the namesake of one of the four statistically robust collisional families identified at L5, and no spacecraft has ever visited it.^{8 • 2}

Orbit and classification

Deiphobus shares Jupiter's orbit around the Sun, librating about the L5 Lagrangian point 60 degrees behind the planet. Its orbit has a semi-major axis of 5.1276 AU, an eccentricity of 0.0436, and an inclination of 26.914 degrees, which places it among the more highly inclined large Trojans; the orbital planes of the ten largest Trojan targets in one mission study ranged from 3.1 to 26.9 degrees, with Deiphobus at the upper end.²

The Minor Planet Center records 3,488 observations used in the orbit determination, and the observation arc spans 46.15 years (16,858 days) as of a 2017 epoch, giving an uncertainty parameter of 0.¹ Orbital simulations by NASA JPL's CNEOS show no close approaches to Earth; the asteroid's orbit stays at least 3.88 AU from Earth's orbit at its closest point.¹

Physical properties

Thermal radiometry and occultation measurements give consistent sizes near 120 km. A RECON occultation deployment plan for a December 2025 event used a cross-track diameter of 118.2 km, with a 130.0 km estimate assuming a 5 percent albedo.³

A radiometric survey of large Trojans found an effective radius of 57.9±1.8 km with albedo 0.063±0.006 under one beaming-parameter assumption, and 69.0±2.2 km with albedo 0.045±0.005 under another, illustrating how the assumed thermal model shifts the derived size and albedo.⁴

Rotation

The first photometric observations of Deiphobus were made by Linda French at Cerro Tololo Inter-American Observatory in 1987 as part of a CCD study of four L5 Trojans; the partial lightcurve suggested a rotation period longer than 24 hours.⁵

Spin modeling places Deiphobus among Trojans with large variations of pole latitude; in the Cassini state 2 configuration its pole obliquity would exhibit large oscillations.⁶

Dynamical context and family membership

Deiphobus belongs to the L5 swarm, whose members are named for Trojan characters of the Homeric epics, while the leading L4 swarm carries Greek names.⁷ A 2024 analysis of Catalina Sky Survey data found that the previously known Ennomos collisional family actually consists of two overlapping families, named Deiphobus and Ennomos, making Deiphobus the namesake of one of the four statistically robust families identified at L5.⁸

Long-term numerical integrations of Trojan stability show that the reference particle of (1867) Deiphobus, together with those of (3451) Mentor and (884) Priamus in the L5 swarm, escapes the Trojan population over the integration, meaning the asteroid's orbit is dynamically less secure than those of the most stable Trojans.⁹

Exploration and observation

No spacecraft has visited Deiphobus or any Jupiter Trojan other than the targets of NASA's Lucy mission; scientific knowledge of the large Trojans comes from ground-based measurements.² A design study for an in-situ Trojan mission selected Deiphobus among the next ten largest known Trojans as a sample target, using a Jupiter gravity assist followed by 7 to 9 years of flight, for a total transfer of 13 to 15 years.² Stellar occultation campaigns, such as the RECON network event of December 5, 2025, provide the ground-based size constraints used to refine its diameter.³

References

1. Asteroid 1867 Deiphobus (1971 EA), Space Reference
2. Design of an in-situ science mission to a Jupiter Trojan, Planetary and Space Science (ScienceDirect)
3. RECON observing guide for 1867_Deiphobus_20251205060634, Southwest Research Institute
4. The Albedo Distribution of Jovian Trojan Asteroids, Fernandez et al.
5. Rotation properties of four L5 Trojan asteroids from CCD photometry, Icarus 72, 325–341 (1987)
6. Shape models and spin states of Jupiter Trojans: Testing the streaming instability formation scenario (ResearchGate)
7. Jupiter Trojans, Rocks in Space
8. Orbital and absolute magnitude distribution of Jupiter Trojans, Vokrouhlický et al. (arXiv:2401.15537)
9. Stability of Jovian Trojans and their collisional families, Monthly Notices of the Royal Astronomical Society 495, 4085 (2020)

Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Main-belt asteroids and numbered minor planets

Initially written Oct 20, 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.