Adrastea (minor planet designation: 239 Adrastea) is a main belt asteroid. It was discovered by Johann Palisa on 18 August 1884 in Vienna, and was named after the Greek nymph Adrasteia. This asteroid is orbiting the Sun at a distance of 2.97 AU with a period of 5.11 years and an eccentricity (ovalness) of 0.23. The orbital plane is tilted at an angle of 6.17° to the plane of the ecliptic.^[1]

239 Adrastea

3D model based on lightcurve data
Discovery
Discovered by	Johann Palisa
Discovery date	18 August 1884
Designations
MPC designation	(239) Adrastea
Pronunciation	/ædrəˈstiːə/
Named after	Adrasteia
Alternative designations	A884 QA, 1915 TD 1955 MK1, 1956 UJ
Minor planet category	Main belt
Orbital characteristics[1]
Epoch 31 July 2016 (JD 2457600.5)
Uncertainty parameter 0
Observation arc	131.66 yr (48,087 d)
Aphelion	3.66279 AU (547.946 Gm)
Perihelion	2.2695 AU (339.51 Gm)
Semi-major axis	2.96616 AU (443.731 Gm)
Eccentricity	0.23486
Orbital period (sidereal)	5.11 yr (1,865.9 d)
Average orbital speed	17.25 km/s
Mean anomaly	233.617°
Mean motion	0° 11m 34.584s / day
Inclination	6.1746°
Longitude of ascending node	180.634°
Argument of perihelion	210.15°
Physical characteristics
Dimensions	41.52±1.4 km[1]
Synodic rotation period	18.4707 h (0.76961 d)[1]
Geometric albedo	0.0777±0.006[1]
Temperature	unknown
Spectral type	unknown
Absolute magnitude (H)	10.4[1]

Photometric data collected during 2009 were used for light curve analysis of this asteroid, yielding a rotation period of 18.48±0.03 h with a brightness variation of 0.45±0.05 in magnitude. The result is close to the 18.347±0.003 h period from a study performed in 2003.^[2] The asteroid is roughly 42 km in diameter.^[1]