161989 Cacus

161989 Cacus (prov. designation: 1978 CA) is a stony asteroid, classified as near-Earth object and a potentially hazardous asteroid of the Apollo group, approximately 1 kilometer in diameter. It was discovered on 8 February 1978, by German astronomer Hans-Emil Schuster at ESO's La Silla Observatory in northern Chile.^[2] Its orbit is confined between Venus and Mars.

161989 Cacus

Shape model of Cacus from its lightcurve
Discovery[1][2]
Discovered by	H.-E. Schuster
Discovery site	La Silla Obs.
Discovery date	8 February 1978
Designations
MPC designation	(161989) Cacus
Named after	Cacus (Roman mythology)[2]
Alternative designations	1978 CA
Minor planet category	Apollo · NEO · PHA[1]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	38.59 yr (14,096 days)
Aphelion	1.3634 AU
Perihelion	0.8828 AU
Semi-major axis	1.1231 AU
Eccentricity	0.2140
Orbital period (sidereal)	1.19 yr (435 days)
Mean anomaly	345.40°
Mean motion	0° 49m 41.16s / day
Inclination	26.060°
Longitude of ascending node	161.24°
Argument of perihelion	102.16°
Earth MOID	0.0152 AU · 5.9 LD
Physical characteristics
Mean diameter	0.64±0.02 km[3] 1.126±0.073 km[4] 1.86 km[5] 1.9 km[6]
Synodic rotation period	3.7538±0.0019 h[6] 3.756 h[7] 3.761 h[5] 3.77±0.11 h[8]
Geometric albedo	0.09[6] 0.119 (derived)[6] 0.199±0.052[4] 0.46±0.09[3]
Spectral type	Tholen = S[1][6] · Q[9] B–V = 0.910[1] U–B = 0.484[1]
Absolute magnitude (H)	16.58[6][7] · 17.1[4] · 17.2[1] · 17.32[5] · 17.43[3]

This minor planet was named from Roman mythology, after Cacus, a fire-breathing monster, which was killed by Hercules.^[2] The official naming citation was published by the Minor Planet Center on 24 November 2007 (M.P.C. 61270).^[10]

Close approaches^[1]

Date	JPL SBDB nominal geocentric distance	uncertainty region (3-sigma)
1941-09-02	2418754 km	± 6 km
2022-09-01	8607710 km	± 21 km[11]