3361 Orpheus

3361 Orpheus (1982 HR) is an Apollo asteroid that was discovered on 24 April 1982 by Carlos Torres at Cerro El Roble Astronomical Station. Its eccentric orbit crosses that of Mars and Earth, and approaches Venus as well. From 1900 to 2100 it passes closer than 30 Gm (0.20 AU; 78 LD; 30 million km; 19 million mi) to Venus, 11; Earth, 33; and Mars, 14 times. It passed by Earth at a distance of about 0.03 AU (12 LD; 4.5 Gm; 4.5 million km; 2.8 million mi) in 1937, 1978, 1982, and 2021, and will do so again in 2025.^[1]

3361 Orpheus

Discovery
Discovered by	Carlos Torres
Discovery site	Cerro El Roble
Discovery date	24 April 1982
Designations
MPC designation	(3361) Orpheus
Pronunciation	/ˈɔːrfiːəs, ˈɔːrfjuːs/
Named after	Orpheus, a legendary Greek bard and prophet
Alternative designations	1982 HR
Minor planet category	PHA[1]
Adjectives	Orphean (Orphæan) /ɔːrˈfiːən/[2]
Orbital characteristics[1]
Epoch 13 June 2008 (JD 2454630.5)
Uncertainty parameter 0
Observation arc	11752 days (32.18 yr)
Aphelion	1.5999 AU (239.34 Gm)
Perihelion	0.81893 AU (122.510 Gm)
Semi-major axis	1.2094 AU (180.92 Gm)
Eccentricity	0.32288
Orbital period (sidereal)	1.33 yr (485.82 d)
Mean anomaly	283.408°
Mean motion	0° 44m 27.636s / day
Inclination	2.6849°
Longitude of ascending node	189.602°
Argument of perihelion	301.651°
Earth MOID	0.0139175 AU (2.08203 Gm)
Physical characteristics
Dimensions	0.3 km[1]
Mean radius	0.15 km
Synodic rotation period	3.532 h (0.1472 d)[1]
Absolute magnitude (H)	19.03[1]

3361 Orpheus is a potentially hazardous asteroid (PHA) because its minimum orbit intersection distance (MOID) is less than 0.05 AU (19 LD; 7.5 Gm; 7.5 million km; 4.6 million mi) and its diameter is greater than 140 metres (460 ft). The Earth-MOID is 0.0139 AU (5.4 LD; 2.08 Gm; 2.08 million km; 1.29 million mi).^[1] With an observation arc of 36 years, the orbit is well-determined for the next several hundred years.

The orbital solution includes non-gravitational forces.^[1]

Close approach^[1]

Date	JPL SBDB nominal geocentric distance	uncertainty region (3-sigma)
2021-11-21	5768611 km	± 18 km
2198-04-16	3908508 km	± 129 km[3]

Missions

Animation of DART's trajectory
  DART ·   65803 Didymos ·   Earth ·   Sun ·   2001 CB21 ·   3361 Orpheus

3361 Orpheus had been one of the originally proposed targets for the Near Earth Asteroid Rendezvous (NEAR) mission.

The proposed AIDA mission's spacecraft, Double Asteroid Redirection Test was a fly-by observation of 3361 Orpheus during its trajectory to asteroid 65803 Didymos but later cancelled.^{[4][clarification needed]}