18 Melpomene

18 Melpomene is a large, bright main-belt asteroid that was discovered by J. R. Hind on 24 June 1852,^[11] and named after Melpomenē, the Muse of tragedy in Greek mythology. Its historical symbol was a dagger over a star; as of 2023 it was in the pipeline for Unicode 17.0 as U+1CECB 𜻋 ().^[12][13]

18 Melpomene

Discovery
Discovered by	John Russell Hind
Discovery date	24 June 1852
Designations
MPC designation	(18) Melpomene
Pronunciation	/mɛlˈpɒmɪniː/[1]
Named after	Melpomenē
Minor planet category	Main belt
Adjectives	Melpomenean /mɛlpɒmɪˈniːən/[2]
Symbol	(historical)
Orbital characteristics[3]
Epoch 17.0 October 2024 (JD 2460600.5)
Aphelion	2.796 AU (418.3 million km)
Perihelion	1.794 AU (268.4 million km)
Semi-major axis	2.295 AU (343.3 million km)
Eccentricity	0.21827
Orbital period (sidereal)	1,269.91 d (3.48 yr)
Mean anomaly	113.8711°
Inclination	10.132°
Longitude of ascending node	150.34°
Time of perihelion	2023-Sep-11
Argument of perihelion	228.05°
Earth MOID	0.81 AU (121 million km)
Jupiter MOID	2.70 AU (404 million km)
TJupiter	3.543
Physical characteristics
Dimensions	170 × 155 × 129 km[4] (150 × 125 km)[5] (150 × 170 km)[6]
Mean diameter	141±2 km[7] 139.594±2.452 km[3]
Flattening	0.19[a]
Mass	(4.5±0.9)×1018 kg[7] 3.0×1018 kg[4]
Mean density	3.06±0.62 g/cm3[7] 1.69±0.66 g/cm3[4]
Synodic rotation period	11.57 h (0.48 d)[3] 11.570306±0.000005 h[7] 11.573 h (0.48 d)[8]
Axial tilt	64°[7]
Pole ecliptic latitude	19°±2°[7]
Pole ecliptic longitude	12°±2°[7]
Geometric albedo	0.221 (calculated)[7] 0.223[9] 0.181 ± 0.033[3]
Spectral type	S[3][7]
Apparent magnitude	7.5[10] to 12.0
Absolute magnitude (H)	6.35[3] 6.51[7]
Angular diameter	0.23" to 0.059"

Melpomene is classified as an S-type asteroid and is composed of silicates and metals. This asteroid is orbiting the Sun at a distance of 2.296 AU with a period of 3.48 years and an eccentricity (ovalness) of 0.22. The orbital plane is tilted at an angle of 10.1° to the plane of the ecliptic.^[3]

Melpomene occulted the star SAO 114159 on 11 December 1978. A possible Melpomenean satellite with a diameter of at least 37 km was detected. The satellite candidate received a provisional designation S/1978 (18) 1.^[14] In 1988 a search for satellites or dust orbiting this asteroid was performed using the UH88 telescope at the Mauna Kea Observatories, but the effort came up empty.^[15] Melpomene was observed with the Hubble Space Telescope in 1993. It was able to resolve the asteroid's slightly elongated shape, but no satellites were detected.^[5]

Melpomene has been studied by radar.^[16] Photometric observations during 2012 provided a rotation period of 11.571±0.001 h with a brightness variation of 0.34±0.02 in magnitude, which is consistent with previous studies.^[17] It has a mean diameter of 141±2 km.^[7][3]

Melpomene can reach an apparent magnitude of +7.9 at a favorable opposition near perihelion, such as occurred in September 2002 when it was 0.814 AU (121.8 million km; 317 LD) from Earth.^[18]

Notes

1. Flattening derived from the maximum aspect ratio (c/a): ${\displaystyle f=1-{\frac {c}{a}}}$, where (c/a) = 0.81±0.06.^[7]