4138 Kalchas
4138 Kalchas is a large Jupiter trojan from the Greek camp, approximately in diameter. It was discovered on 19 September 1973 by Dutch astronomers Ingrid and Cornelis van Houten at Leiden on photographic plates taken by Tom Gehrels at the Palomar Observatory in California. The assumed C-type asteroid is the principal body of the proposed Kalchas family and has a rotation period of 29.2 hours. It was named after the seer Calchas from Greek mythology.
Orbit and classification
Kalchas is a dark Jovian asteroid in a 1:1 orbital resonance with Jupiter. It is located in the leading Greek camp at the Gas Giant's Lagrangian point, 60° ahead of its orbit. It orbits the Sun at a distance of 4.9–5.4 AU once every 11 years and 9 months. Its orbit has an eccentricity of 0.04 and an inclination of 2° concerning the ecliptic. The body's observation arc begins with a precovery taken at Palomar in May 1956, more than 17 years before its official discovery observation.Palomar–Leiden Trojan survey
While the discovery date aligns with the second Palomar–Leiden Trojan survey, Kalchas did not receive a prefixed survey designation, which was assigned for the discoveries made by the fruitful collaboration between the Palomar and Leiden observatories in the 1960s and 1970s. Gehrels used Palomar's Samuel Oschin telescope and shipped the photographic plates to Ingrid and Cornelis van Houten at Leiden Observatory, where astrometry was carried out. The trio are credited with the discovery of several thousand asteroids.Kalchas family
and Ricardo Gil-Hutton identified Kalchas as the principal body of a small Jovian asteroid family, using the hierarchical clustering method, which looks for groupings of neighboring asteroids based on the smallest distances between them in the proper orbital element space. According to the astronomers, the Kalchas family belongs to the larger Menelaus clan, an aggregation of Jupiter trojans, composed of several families, similar to the Flora family in the inner asteroid belt.However, this family is not included in David Nesvorný HCM-analysis from 2014. Instead, Kalchas is listed as a non-family asteroid of the Jovian background population on the Asteroids Dynamic Site, which is based on another analysis by Milani and Knežević.