4217 Engelhardt

4217 Engelhardt, provisional designation 1988 BO₂, is a stony Phocean asteroid and a potentially binary system from the inner regions of the asteroid belt, approximately 9 kilometers in diameter. It was discovered on 24 January 1988, by American astronomer Carolyn Shoemaker at Palomar Observatory in California, and later named after German mineralogist Wolf von Engelhardt.^[12]

4217 Engelhardt

Discovery[1]
Discovered by	C. Shoemaker
Discovery site	Palomar Obs.
Discovery date	24 January 1988
Designations
MPC designation	(4217) Engelhardt
Named after	Wolf von Engelhardt (German mineralogist)[2]
Alternative designations	1988 BO2 · 1944 RL 1951 RY1 · 1970 AA
Minor planet category	main-belt · Phocaea[3][4]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	72.73 yr (26,563 days)
Aphelion	2.8045 AU
Perihelion	1.8246 AU
Semi-major axis	2.3145 AU
Eccentricity	0.2117
Orbital period (sidereal)	3.52 yr (1,286 days)
Mean anomaly	272.23°
Mean motion	0° 16m 47.64s / day
Inclination	23.129°
Longitude of ascending node	355.44°
Argument of perihelion	348.79°
Known satellites	1 (P: 36.03 h)[5][a]
Physical characteristics
Dimensions	7.34±1.36 km[6] 8.742±0.356 km[7][8] 9.16±1.0 km[9] 9.24 km (derived)[3]
Synodic rotation period	3.066±0.001 h[10] 3.0661±0.0002 h[5][a]
Geometric albedo	0.2108±0.052[9] 0.231±0.046[7][8] 0.2489 (derived)[3] 0.37±0.17[6]
Spectral type	S[3][11]
Absolute magnitude (H)	12.10±0.67[11] · 12.20[6] · 12.3[1][3] · 12.50[7][9]

Classification and orbit

Engelhardt is a stony S-type asteroid and a member of the Phocaea family (701).^[4] It orbits the Sun in the inner main-belt at a distance of 1.8–2.8 AU once every 3 years and 6 months (1,286 days). Its orbit has an eccentricity of 0.21 and an inclination of 23° with respect to the ecliptic.^[1]

It was first identified as 1944 RL at Turku Observatory in 1944, extending the body's observation arc by 44 years prior to its official discovery observation at Palomar.^[12] It will pass about 0.0017 AU (250,000 km) from Earth threatening asteroid (29075) 1950 DA in 2736.^[13]

Physical characteristics

Lightcurves

In November 2004, a rotational lightcurve of Engelhardt was obtained from photometric observations by American astronomer Brian Warner at this Palmer Divide Observatory in Colorado.^[a] Lightcurve analysis gave a well-defined rotation period of 3.066 hours with a brightness amplitude of 0.16 magnitude (U=3).^[10]

In December 2011, a follow-up observation by Warner gave a period of 3.0661 hours with 0.18 amplitude (U=3).^[5] Due to a couple of supposed occultation and eclipsing events, Warner also suspects that Engelhardt might by a binary system with a minor-planet moon orbiting it every 36.03 hours. The result, however, is far from conclusive.^[a]

Diameter and albedo

According to the surveys carried out by the Infrared Astronomical Satellite IRAS, the Japanese Akari satellite, and NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Engelhardt measures between 7.34 and 9.16 kilometers in diameter and its surface has an albedo between and 0.231 and 0.37.^[7] The Collaborative Asteroid Lightcurve Link derives an albedo of 0.2489 and a diameter of 9.24 kilometers with on an absolute magnitude of 12.3.^[3]

Naming

Baltic German geologist and mineralogist Wolf von Engelhardt (1910–2008), expert on impact craters and related mineral metamorphism. He was a professor at the University of Tübingen and a longtime director of its Institute of Mineralogy and Petrography.^[2] The approved naming citation was published by the Minor Planet Center on 27 June 1991 (M.P.C. 18456).^[14]

Notes

1. Lightcurve plot of (4217) Engelhardt, at the Palmer Divide Observatory, by B. D. Warner (2011). The first plot gives a rotation period of 3.0661 hours. The second plot has that period subtracted and gives a possible orbital period of 36.03 hours for the presumed satellite.