4138 Kalchas (// KAL-kəs), provisional designation 1973 SM, is a large Jupiter trojan from the Greek camp, approximately 53 kilometers (33 miles) 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.
|Discovered by||C. J. van Houten|
I. van Houten-G.
|Discovery site||Palomar Obs.|
|Discovery date||19 September 1973|
|MPC designation||(4138) Kalchas|
|Pronunciation||// · KAL-kəs|
|1973 SM · 1986 VU6|
|Jupiter trojan |
Greek  · background 
|Orbital characteristics |
|Epoch 23 March 2018 (JD 2458200.5)|
|Uncertainty parameter 0|
|Observation arc||61.48 yr (22,454 d)|
|11.73 yr (4,286 d)|
|0° 5m 2.4s / day|
|Jupiter MOID||0.019 AU|
V–I = 0.810±0.038
Orbit and classificationEdit
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 L4 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 (4,286 days; semi-major axis of 5.16 AU). Its orbit has an eccentricity of 0.04 and an inclination of 2° with respect to the ecliptic. The body's observation arc begins with a precovery taken at Palomar in May 1956, more than 17 years prior to its official discovery observation.
Palomar–Leiden Trojan surveyEdit
While the discovery date aligns with the second Palomar–Leiden Trojan survey, Kalchas did not receive a "T-2" 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 (also known as the 48-inch Schmidt 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.
Fernando Roig and Ricardo Gil-Hutton identified Kalchas as the principal body of a small Jovian asteroid family, using the hierarchical clustering method (HCM), 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 which is composed of several families, similar to the Flora family in the inner asteroid belt.:9,10
However this family is not included in David Nesvorný's HCM-analysis from 2014. Instead, Kalchas is listed as a non-family asteroid of the Jovian background population on the Asteroids Dynamic Site (AstDyS) which based on another analysis by Milani and Knežević.
This minor planet was named from Greek mythology after Calchas, a Greek prophet during the Trojan War. The official naming citation was published by the Minor Planet Center on 11 March 1990 (M.P.C. 16043).
In December 2011, a rotational lightcurve of Kalchas was obtained by Robert Stephens at GMARS (G79) in California. Lightcurve analysis gave a well-defined rotation period of 29.2±0.1 hours with a brightness variation of 0.40 magnitude (U=3). In July and August 2015, photometric observations by the Kepler space observatory determined two concurring periods of 29.13 and 29.411 hours (U=2+/2+).
Diameter and albedoEdit
According to the surveys carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer and the Japanese Akari satellite, Kalchas measures 46.46 and 61.04 kilometers in diameter and its surface has an albedo of 0.082 and 0.057, respectively. The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a diameter of 53.16 kilometers based on an absolute magnitude of 10.1.
- "4138 Kalchas (1973 SM)". Minor Planet Center. Retrieved 23 June 2018.
- "JPL Small-Body Database Browser: 4138 Kalchas (1973 SM)" (2017-10-29 last obs.). Jet Propulsion Laboratory. Retrieved 23 June 2018.
- "List of Jupiter Trojans". Minor Planet Center. 1 June 2018. Retrieved 23 June 2018.
- "Asteroid (4138) Kalchas – Proper Elements". AstDyS-2, Asteroids – Dynamic Site. Retrieved 23 June 2018.
- Grav, T.; Mainzer, A. K.; Bauer, J. M.; Masiero, J. R.; Nugent, C. R. (November 2012). "WISE/NEOWISE Observations of the Jovian Trojan Population: Taxonomy". The Astrophysical Journal. 759 (1): 10. arXiv:1209.1549. Bibcode:2012ApJ...759...49G. doi:10.1088/0004-637X/759/1/49. Retrieved 23 June 2018. (online catalog)
- Usui, Fumihiko; Kuroda, Daisuke; Müller, Thomas G.; Hasegawa, Sunao; Ishiguro, Masateru; Ootsubo, Takafumi; et al. (October 2011). "Asteroid Catalog Using Akari: AKARI/IRC Mid-Infrared Asteroid Survey". Publications of the Astronomical Society of Japan. 63 (5): 1117–1138. Bibcode:2011PASJ...63.1117U. doi:10.1093/pasj/63.5.1117. Retrieved 23 June 2018. (online, AcuA catalog p. 153)
- French, Linda M.; Stephens, Robert D.; Coley, Daniel R.; Megna, Ralph; Wasserman, Lawrence H. (July 2012). "Photometry of 17 Jovian Trojan Asteroids". The Minor Planet Bulletin. 39 (3): 183–187. Bibcode:2012MPBu...39..183F. ISSN 1052-8091. Retrieved 23 June 2018.
- "LCDB Data for (4138) Kalchas". Asteroid Lightcurve Database (LCDB). Retrieved 23 June 2018.
- "Minor Planet Discoverers". Minor Planet Center. 31 May 2018. Retrieved 23 June 2018.
- Roig, F.; Ribeiro, A. O.; Gil-Hutton, R. (June 2008). "Taxonomy of asteroid families among the Jupiter Trojans: comparison between spectroscopic data and the Sloan Digital Sky Survey colors" (PDF). Astronomy and Astrophysics. 483 (3): 911–931. arXiv:0712.0046. Bibcode:2008A&A...483..911R. doi:10.1051/0004-6361:20079177. Retrieved 29 June 2018.
- Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families" (PDF). Asteroids IV: 297–321. arXiv:1502.01628. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. Retrieved 29 June 2017.
- "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 23 June 2018.
- Ryan, Erin Lee; Sharkey, Benjamin N. L.; Woodward, Charles E. (March 2017). "Trojan Asteroids in the Kepler Campaign 6 Field". The Astronomical Journal. 153 (3): 12. Bibcode:2017AJ....153..116R. doi:10.3847/1538-3881/153/3/116. Retrieved 23 June 2018.
- Szabó, Gy. M.; Pál, A.; Kiss, Cs.; Kiss, L. L.; Molnár, L.; Hanyecz, O.; et al. (March 2017). "The heart of the swarm: K2 photometry and rotational characteristics of 56 Jovian Trojan asteroids" (PDF). Astronomy and Astrophysics. 599: 13. arXiv:1609.02760. Bibcode:2017A&A...599A..44S. doi:10.1051/0004-6361/201629401. Retrieved 23 June 2018.
- Asteroid Lightcurve Database (LCDB), query form (info)
- Dictionary of Minor Planet Names, Google books
- Discovery Circumstances: Numbered Minor Planets (1)-(5000) – Minor Planet Center
- Asteroid 4138 Kalchas at the Small Bodies Data Ferret
- 4138 Kalchas at AstDyS-2, Asteroids—Dynamic Site
- 4138 Kalchas at the JPL Small-Body Database