4946 Askalaphus

4946 Askalaphus ( ə-SKAL-ə-fəs; prov. designation: 1988 BW₁) is a Jupiter trojan from the Greek camp, approximately 52 kilometers (32 miles) in diameter. It was discovered on 21 January 1988 by American astronomer couple Carolyn and Eugene Shoemaker at the Palomar Observatory in California.^[1] The dark D-type asteroid belongs to the 100 largest Jupiter trojans and has a rotation period of 22.7 hours.^[10] It was named after Ascalaphus from Greek mythology.^[1]

Askalaphus 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 on its orbit (see Trojans in astronomy).^[4] It is also a non-family asteroid of the Jovian background population.^[5] It orbits the Sun at a distance of 5.0–5.6 AU once every 12 years and 3 months (4,479 days; semi-major axis of 5.32 AU). Its orbit has an eccentricity of 0.05 and an inclination of 22° with respect to the ecliptic.^[3] The body's observation arc begins with a precovery taken at Palomar in December 1950, more than 37 years prior to its official discovery observation.^[1]

This minor planet was named from Greek mythology after Ascalaphus (Askalaphus), son of Ares and Astyoche, and twin brother of Ialmenos. The two brothers belonged to the Argonauts. Leader of the Orchomenian contingent in the Trojan War, he was killed in battle by Deiphobus's spear.^[1] The official naming citation was published by the Minor Planet Center on 12 July 1995 (M.P.C. 25443).^[13]

In the SDSS-based taxonomy, Askalaphus is a D-type asteroid.^[7][12] It has also been characterized as a D-type by Pan-STARRS' survey.^[10][11] Its V–I color index of 0.94, is typical for most larger Jupiter trojans (see table below).^[10]

In May 1992, a rotational lightcurve of Askalaphus was obtained from photometric observations by Italian astronomer Stefano Mottola using the ESO 1-metre telescope at La Silla Observatory in northern Chile. Lightcurve analysis gave a rotation period of 22.731±0.018 hours with a brightness amplitude of 0.40 magnitude (U=3). With a period close to that of the Earth, a complete observational coverage of the lightcurve was challenging and had to be carefully planned.^[9][10]

According to the surveys carried out by the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, The Infrared Astronomical Satellite IRAS, and the Japanese Akari satellite, Askalaphus measures between 48.21 and 66.10 kilometers in diameter and its surface has an albedo between 0.046 and 0.069.^[6][7][8] The Collaborative Asteroid Lightcurve Link assumes a standard albedo for a carbonaceous asteroid of 0.057 and calculates a diameter of 50.77 kilometers based on an absolute magnitude of 10.2.^[10]

• Asteroid Lightcurve Database (LCDB), query form (info Archived 16 December 2017 at the Wayback Machine)
• Dictionary of Minor Planet Names, Google books
• Discovery Circumstances: Numbered Minor Planets (1)-(5000) – Minor Planet Center
• 4946 Askalaphus at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• 4946 Askalaphus at the JPL Small-Body Database  
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters