120 Lachesis

120 Lachesis is a large main-belt asteroid. It was discovered by French astronomer Alphonse Borrelly on April 10, 1872, and independently by German-American astronomer Christian Heinrich Friedrich Peters on April 11, 1872, then named after Lachesis, one of the Moirai, or Fates, in Greek mythology.^[5] A Lachesean occultation of a star occurred in 1999 and was confirmed visually by five observers and once photoelectrically, with the chords yielding an estimated elliptical cross-section of 184 × 144 km.^[6]

120 Lachesis

3D convex shape model of 120 Lachesis
Discovery
Discovered by	Alphonse Borrelly
Discovery date	10 April 1872
Designations
MPC designation	(120) Lachesis
Pronunciation	/ˈlækɪsɪs/ LAK-iss-iss[1]
Named after	Lachesis
Alternative designations	A872 GB; 1910 CF; 1918 UB
Minor planet category	Main belt
Adjectives	Lachesian (/læˈkiːʃ(i)ən, ləˈkiːʒən/ la-KEE-sh(ee-)ən, lə-KEE-zhən)
Orbital characteristics[2]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc	143.70 yr (52485 d)
Aphelion	3.2814 AU (490.89 Gm)
Perihelion	2.95390 AU (441.897 Gm)
Semi-major axis	3.11767 AU (466.397 Gm)
Eccentricity	0.052528
Orbital period (sidereal)	5.50 yr (2010.7 d)
Average orbital speed	16.86 km/s
Mean anomaly	56.2095°
Mean motion	0° 10m 44.558s / day
Inclination	6.9643°
Longitude of ascending node	341.193°
Argument of perihelion	232.822°
Earth MOID	1.95464 AU (292.410 Gm)
Jupiter MOID	1.72275 AU (257.720 Gm)
TJupiter	3.204
Physical characteristics
Dimensions	155.132±1.133 km (IRAS)[2]
Mass	5.5×1018 kg
Equatorial surface gravity	0.0487 m/s2
Equatorial escape velocity	0.0920 km/s
Synodic rotation period	46.551 h (1.9396 d)[2][3]
Geometric albedo	0.0463±0.002[2]
Temperature	~158 K
Spectral type	C[4]
Absolute magnitude (H)	7.75[2]

This body is orbiting the Sun with a period of 5.50 years and an eccentricity (ovalness) of 0.05. The orbital plane is inclined by 7° to the plane of the ecliptic. Photometric observations of this asteroid were made in early 2009 at the Organ Mesa Observatory in Las Cruces, New Mexico. The resulting light curve shows a synodic rotation period of 46.551 ± 0.002 hours with a brightness variation of 0.14 ± 0.02 in magnitude.^[3] It is a very slow rotator^[7] with the longest rotation period of an asteroid more than 150 km in diameter.^[8] As a primitive C-type asteroid^[4] it is probably composed of carbonaceous material.