4946 Askalaphus
4946 Askalaphus (provisional designation 1988 BW1) is a large Jupiter Trojan asteroid, a minor planet that shares Jupiter's orbit while librating (oscillating around a stable orbital point rather than circling freely) around the leading L4 Lagrange point, about 48 kilometers in diameter and roughly the size of the U.S. state of Rhode Island1. It was discovered on 21 January 1988 by the husband-and-wife team of Carolyn S. Shoemaker and Eugene M. Shoemaker at Palomar Observatory2.
| Key fact | Detail |
|---|---|
| Designation | (4946) Askalaphus; provisional designation 1988 BW12 |
| Discovery | 21 January 1988, Palomar Observatory, by C. S. Shoemaker and E. M. Shoemaker2 |
| Orbit | Semi-major axis 5.321 AU, eccentricity 0.0487, inclination 21.86°, period 4,480 days (12.27 years)1 |
| Hazard status | Not a Near Earth Object and not potentially hazardous; its orbit stays 4.06 AU from Earth's orbit at the closest point1 |
| Absolute magnitude | H = 10.18 to 10.23, depending on the orbit solution used1 • 2 |
Discovery and naming
The asteroid was found on 21 January 1988 at Palomar Observatory and received the provisional designation 1988 BW1 before being permanently numbered 49462. Under the International Astronomical Union's naming rules, Trojan asteroids librating in 1:1 resonance with Jupiter are named for heroes of the Trojan War, with Greeks at L4 and Trojans at L53.
Orbit and classification
Askalaphus is a Jupiter Trojan, one of the small bodies trapped in a 1:1 mean motion resonance with Jupiter that librate around the stable L4 and L5 Lagrange points, 60 degrees ahead of and behind the planet4. Its orbit carries it around the Sun every 4,480 days, or 12.27 years, at distances between 5.06 AU at perihelion and 5.58 AU at aphelion1. The orbit is moderately inclined, at 21.86° to the ecliptic, and the average orbital speed is 12.92 km/s1. The Czech asteroid database at the University of West Bohemia lists a Tisserand parameter relative to Jupiter of 2.9, a value characteristic of Trojan orbits2.
No threat to Earth. Because the asteroid never leaves the outer solar system, NASA JPL has not classified it as potentially hazardous1. Its orbit remains 4.06 AU from Earth's orbit even at the closest point of the two ellipses, and orbital simulations by NASA JPL's Center for Near Earth Object Studies show no close approaches to Earth1. The Czech database gives the largest future Earth approach in its computed ephemeris as 4.04 AU on 3 June 20292. The asteroid is also not considered a viable target for human exploration by the NHATS study, which screens near-Earth objects for accessible trajectories1.
Physical properties
The JPL-based diameter is 48.21 km, which places Askalaphus among the larger known asteroids; Space Reference describes it as larger than 99% of asteroids1.
The rotation has been observed photometrically: the asteroid completes one turn on its axis every 22.73 hours, measured as 22.731 ± 0.018 hours1.
Observation record
The orbit is well determined from a long observational arc. Space Reference, drawing on Minor Planet Center data, states that observations used for the orbit date back to 11 December 1950, with 2,725 recorded observations and a last official observation on 1 April 20231. The Czech database, at a later epoch, lists 4,683 observations across 31 oppositions spanning 1950 to 20262. The two counts differ because they reflect different database snapshots and observation sets, but both show a data arc of more than seven decades, which is what pins the orbit with high precision.
Space Reference lists 1868 Thersites, 1872 Helenos, and 3801 Thrasymedes as objects with orbits sharing similar characteristics1.
Context among the Jupiter Trojans
The Jupiter Trojans are remnants of the early solar system, a population considerably smaller than the main asteroid belt, and models of planetary migration indicate they were captured onto resonant orbits from a wide range of initial eccentricities and inclinations4 • 5. No Trojan has yet been visited by a planetary mission, so knowledge of these bodies comes from ground-based and infrared-satellite measurements6.
References
- Asteroid Askalaphus (4946), Space Reference
- Planetka (4946) Askalaphus, Planety, University of West Bohemia
- Naming of Astronomical Objects, International Astronomical Union
- Origin and Evolution of Jupiter's Trojan Asteroids, arXiv
- The Capture of Trojan Asteroids by the Giant Planets During Planetary Migration, arXiv
- Design of an in-situ science mission to a Jupiter Trojan, Advances in Space Research (ScienceDirect)
Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Jupiter Trojans and other dynamical groups › Greek-camp Jupiter Trojans › Lesser Achaean warriors
Initially written Oct 21, 2026 · Edited: Oct 25, 2026
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