| Minorplanet: | yes |
| 30942 Helicaon | |
| Background: |
|
| Discovery Ref: |   |
| Discovered: | 8 February 1994 |
| Mpc Name: | (30942) Helicaon |
| Pronounced: | [1] |
| Named After: | Helicaon  |
| Mp Category: | Jupiter trojan  |
| Orbit Ref: |   |
| Epoch: | 23 March 2018 (JD 2458200.5) |
| Uncertainty: | 0 |
| Observation Arc: | 24.20 yr (8,840 d) |
| Perihelion: | 4.8375 AU |
| Semimajor: | 5.1860 AU |
| Eccentricity: | 0.0672 |
| Period: | 11.81 yr (4,314 d) |
| Mean Motion: | / day |
| Inclination: | 22.871° |
| Asc Node: | 143.60° |
| Arg Peri: | 272.38° |
| Jupiter Moid: | 0.1294 AU |
| Tisserand: | 2.8390 |
| Mean Diameter: | |
| Albedo: | |
| Abs Magnitude: | 11.30 |
30942 Helicaon is a Jupiter trojan from the Trojan camp, approximately 33km (21miles) in diameter. It was discovered on 8 February 1994, by Belgian astronomer Eric Elst at ESO's La Silla Observatory in northern Chile. The dark Jovian asteroid has a long rotation period of 44.8 hours. It was named after the Trojan warrior Helicaon from Greek mythology.
As all Jupiter trojan, Helicaon is in a 1:1 orbital resonance with Jupiter. It is located in the trailering Trojan camp at the Gas Giant's Lagrangian point, 60° behind its orbit . It is also a non-family asteroid of the Jovian background population. It orbits the Sun at a distance of 4.8–5.5 AU once every 11 years and 10 months (4,314 days; semi-major axis of 5.19 AU). Its orbit has an eccentricity of 0.07 and an inclination of 23° with respect to the ecliptic.
The body's observation arc begins with its official discovery observation at La Silla in February 1994.
This minor planet was named from Greek mythology after the Trojan warrior Helicaon, son of Antenor and King Priam's daughter, Laodice. The official naming citation was published by the Minor Planet Center on 26 July 2010 .
Helicaon is an assumed C-type asteroid, while most larger Jupiter trojans are D-types.
In February 2015, a rotational lightcurve of Helicaon was obtained from photometric observations over at total of 12 nights of photometric observations by Robert Stephens at the Center for Solar System Studies in Landers, California. Lightcurve analysis gave a rotation period of hours with a brightness amplitude of 0.18 magnitude . While not being a slow rotator, Helicaon has a significantly longer period than most larger Jupiter trojans (see table below).
According to the survey carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, Helicaon measures 32.54 kilometers in diameter and its surface has an albedo of 0.050, while the Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a diameter of 30.59 kilometers based on an absolute magnitude of 11.3.