# 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 Island](https://www.edgepedia.org/rhode-island)[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1). It was discovered on 21 January 1988 by the husband-and-wife team of Carolyn S. Shoemaker and Eugene M. Shoemaker at [Palomar Observatory](https://www.edgepedia.org/palomar-observatory)[2](https://astronomia.zcu.cz/planety/planetka-4946).
| Key fact | Detail |
|---|---|
| Designation | (4946) Askalaphus; provisional designation 1988 BW1[2](https://astronomia.zcu.cz/planety/planetka-4946) |
| Discovery | 21 January 1988, Palomar Observatory, by C. S. Shoemaker and E. M. Shoemaker[2](https://astronomia.zcu.cz/planety/planetka-4946) |
| Orbit | Semi-major axis 5.321 AU, eccentricity 0.0487, inclination 21.86°, period 4,480 days (12.27 years)[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1) |
| Hazard status | Not a Near Earth Object and not potentially hazardous; its orbit stays 4.06 AU from Earth's orbit at the closest point[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1) |
| Absolute magnitude | H = 10.18 to 10.23, depending on the orbit solution used[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1) • [2](https://astronomia.zcu.cz/planety/planetka-4946) |
## 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 4946[2](https://astronomia.zcu.cz/planety/planetka-4946). Under the International Astronomical Union's naming rules, [Trojan](https://www.edgepedia.org/trojan-celestial-body) asteroids librating in 1:1 resonance with Jupiter are named for heroes of the [Trojan War](https://www.edgepedia.org/trojan-war), with Greeks at L4 and Trojans at L5[3](https://iauarchive.eso.org/public/themes/naming/).
## 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 planet[4](https://arxiv.org/abs/2312.02864). 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 aphelion[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1). The orbit is moderately inclined, at 21.86° to the ecliptic, and the average orbital speed is 12.92 km/s[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1). The Czech asteroid database at the University of West Bohemia lists a [Tisserand parameter](https://www.edgepedia.org/tisserand-parameter) relative to Jupiter of 2.9, a value characteristic of Trojan orbits[2](https://astronomia.zcu.cz/planety/planetka-4946).
**No threat to Earth.** Because the asteroid never leaves the outer solar system, NASA JPL has not classified it as potentially hazardous[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1). Its orbit remains 4.06 AU from [Earth's orbit](https://www.edgepedia.org/earths-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 Earth[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1). The Czech database gives the largest future Earth approach in its computed ephemeris as 4.04 AU on 3 June 2029[2](https://astronomia.zcu.cz/planety/planetka-4946). The asteroid is also not considered a viable target for human exploration by the NHATS study, which screens near-Earth objects for accessible trajectories[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1).
## Physical properties
The JPL-based diameter is 48.21 km, which places Askalaphus among the larger known asteroids; Space [Reference](https://www.edgepedia.org/reference) describes it as larger than 99% of asteroids[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1).
The rotation has been observed photometrically: the asteroid completes one turn on its axis every 22.73 hours, measured as 22.731 ± 0.018 hours[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1).
## Observation record
The orbit is well determined from a long observational arc. Space Reference, drawing on [Minor Planet Center](https://www.edgepedia.org/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 2023[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1). The Czech database, at a later epoch, lists 4,683 observations across 31 oppositions spanning 1950 to 2026[2](https://astronomia.zcu.cz/planety/planetka-4946). 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](https://www.edgepedia.org/1868-thersites), [1872 Helenos](https://www.edgepedia.org/1872-helenos), and [3801 Thrasymedes](https://www.edgepedia.org/3801-thrasymedes) as objects with orbits sharing similar characteristics[1](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1).
## Context among the Jupiter Trojans
The [Jupiter Trojans](https://www.edgepedia.org/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 inclinations[4](https://arxiv.org/abs/2312.02864) • [5](https://arxiv.org/abs/1003.2137). No Trojan has yet been visited by a planetary mission, so knowledge of these bodies comes from ground-based and infrared-satellite measurements[6](https://www.sciencedirect.com/science/article/abs/pii/S0032063322001969).
## References
1. [Asteroid Askalaphus (4946), Space Reference](https://www.spacereference.org/asteroid/4946-askalaphus-1988-bw1)
2. [Planetka (4946) Askalaphus, Planety, University of West Bohemia](https://astronomia.zcu.cz/planety/planetka-4946)
3. [Naming of Astronomical Objects, International Astronomical Union](https://iauarchive.eso.org/public/themes/naming/)
4. [Origin and Evolution of Jupiter's Trojan Asteroids, arXiv](https://arxiv.org/abs/2312.02864)
5. [The Capture of Trojan Asteroids by the Giant Planets During Planetary Migration, arXiv](https://arxiv.org/abs/1003.2137)
6. [Design of an in-situ science mission to a Jupiter Trojan, Advances in Space Research (ScienceDirect)](https://www.sciencedirect.com/science/article/abs/pii/S0032063322001969)
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*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*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license