5120 Bitias
5120 Bitias (provisional designation 1988 TZ1) is a Jupiter Trojan asteroid roughly 48 kilometers in diameter that librates in the trailing Trojan camp at Jupiter's L5 Lagrange point, 60 degrees behind the planet in its orbit.
| Key fact | Detail |
|---|---|
| Orbit | Semi-major axis 5.264 AU, eccentricity 0.112, inclination 25.01°, orbital period 4,410 days (12.07 years)1 |
| Rotation | Rotation period of 15.21 hours1 |
| Observations | 2,359 Minor Planet Center observations; orbit determined from data beginning 14 September 1988 and last officially observed 3 July 20231 |
| Earth hazard | JPL CNEOS simulations show no close approaches to Earth, and the asteroid is not a viable human-exploration target under the NHATS study1 |
Orbit and classification
Bitias is a dark Jovian asteroid in a 1:1 mean-motion resonance with Jupiter, located in the trailing Trojan camp at the L5 Lagrange point.
It orbits the Sun at distances of 4.67 AU at perihelion and 5.85 AU at aphelion, completing one revolution every 12.07 years, with an average orbital speed of 12.99 km/s.1 Its inclination of about 25 degrees to the ecliptic is high for a Trojan; the Trojan population as a whole has an excited inclination distribution, with some objects reaching 35 degrees, a feature that any model of how the Trojans were captured must explain.2
Physical characteristics
Trojans overall are dominated by D- and P-type spectra, so an assumed C-type classification places Bitias among the less-red members of the population.3
A published value of 47.987 km with an albedo of 0.122 and a magnitude of 10.46 appears in JPL-derived physical parameter listings.1 The difference between the two diameter estimates comes from the assumed albedo: at a given brightness, a higher albedo implies a smaller body. For comparison, the largest Trojan, (624) Hektor, is about 250 km across, so Bitias is a mid-sized member of the swarm.3
Its rotation period is 15.21 hours.1
Discovery and naming
The discovery observation was made on 13 October 1988 by C. Shoemaker at Palomar Observatory, and the body's observation arc begins with a first observation at Palomar on 14 September 1988, one month before the official discovery.1 The Minor Planet Center records 2,359 observations used to determine its orbit, and the asteroid was last officially observed on 3 July 2023.1
Occultation predictions
Because Bitias passes in front of background stars as seen from Earth, its shadow path is predictable and useful for measuring its size directly. Stellar occultation predictions list Bitias events in 2024 and 2025, including an event on 21 November 2025 against the star TYC 2804−01516−1 with a shadow-chord duration of 3.4 seconds and a magnitude drop of 6.2.4 A RECON network observing guide for a 22 October 2025 event lists a cross-track diameter of 48.0 km used for deployment planning, with diameter estimates ranging from 50.8 km assuming a 5 percent albedo to 20.8 km assuming a 30 percent albedo, illustrating how strongly the size estimate depends on the assumed reflectivity.5
Context among the Trojans
Jupiter Trojans are small bodies trapped in the 1:1 resonance with Jupiter, librating around the stable L4 and L5 Lagrange points 60 degrees ahead of and behind the planet, whose orbit lies at about 5.2 AU from the Sun.3 The combined L4 and L5 populations are considerably smaller than the main asteroid belt, and their size-frequency distributions differ in shape from the main belt's. Current models argue that the Trojans were once denizens of the primordial Kuiper belt, trapped during the giant-planet instability early in solar system history, rather than captured planetesimals from the giant-planet zone.3 Objects like Bitias, with its high inclination and dark surface, are part of the population that NASA's Lucy mission, launched in October 2021, is exploring to test these origin models; Lucy is the first mission to visit the Trojan swarms, with flybys planned from 2027 through 2033.6
References
- Asteroid 5120 Bitias (1988 TZ1), Space Reference
- Bottke, W. F., Marschall, R., Nesvorný, D., and Vokrouhlický, D. (2023). Origin and Evolution of Jupiter's Trojan Asteroids. arXiv:2312.02864
- Bottke, W. F., and colleagues (2023). Origin and Evolution of Jupiter's Trojan Asteroids. Space Science Reviews 219, 83
- Occultations by major and minor planets, 2025, Region 7, VVS
- RECON event prediction for 5120_Bitias_20251022025544, Southwest Research Institute
- Lucy Mission Overview, NASA Science
Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Jupiter Trojans and other dynamical groups › Trojan-camp Jupiter Trojans
Initially written Oct 21, 2026 · Edited: Oct 25, 2026
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