7641 Cteatus, provisional designation: 1986 TT₆, is a large Jupiter trojan from the Greek camp, approximately 70 kilometers (43 miles) in diameter. It was discovered on 5 October 1986, by Slovak astronomer Milan Antal at the Toruń Centre for Astronomy in Piwnice, Poland.^[1] The dark D-type asteroid is notably inclined and has longer-than-average rotation period of 27.8 hours.^[4] It belongs to the 50 largest Jupiter trojans. It was named from Greek mythology for Cteatus, the conjoined twin and father of Amphimachus.^[2]

Orbit and classification

Cteatus is a dark Jovian asteroid orbiting in the leading Greek camp at Jupiter's L₄ Lagrangian point, 60° ahead of its orbit in a 1:1 resonance (see Trojans in astronomy). It is also a non-family asteroid in the Jovian background population.^[6][13]

It orbits the Sun at a distance of 4.9–5.5 AU once every 11 years and 11 months (4,350 days; semi-major axis of 5.21 AU). Its orbit has an eccentricity of 0.05 and a notably high inclination of 35° with respect to the ecliptic.^[3] The asteroid was first observed as 1975 VT₅ at Crimea–Nauchnij in November 1975. The body's observation arc begins with its official discovery observation at the Toruń Centre.^[1]

Numbering and naming

This minor planet was numbered by the Minor Planet Center on 22 May 1997 (M.P.C. 29897).^[14] On 14 May 2021, the object was named by the Working Group for Small Bodies Nomenclature (WGSBN), after Cteatus from Greek mythology, who had a conjoined twin. His son Amphimachus was one of the leaders of the Elean contingent in the Trojan War.^[2]

Physical Characteristics

In the SDSS-based taxonomy, Cteatus is a dark D-type asteroid.^[12] It has also been characterized as a D-type by Pan-STARRS' survey.^[4][11] Its V–I color index of 0.98 agrees with that of most Jovian D-type asteroids.^[4]

Rotation period

In October 2009, a rotational lightcurve of Cteatus was obtained from photometric observations by Italian astronomer Stefano Mottola at the Calar Alto Observatory in Spain. Lightcurve analysis gave a well-defined rotation period of 27.770 hours with a brightness amplitude of 0.40 magnitude (U=3).^[4][10] While not being a slow rotator, its period is significantly longer than that of most larger Jupiter trojans, which have a spin rate of typically 10 hours. The body's relatively high brightness variation of 0.40 magnitude is also indicative of a non-spherical shape.

Diameter and albedo

According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, this asteroid measures between 68.97 and 75.28 kilometers in diameter and its surface has an albedo between 0.062 and 0.071.^[7][8][9] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.0647 and a diameter of 68.89 kilometers based on an absolute magnitude of 9.4.^[4]