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 1865.9 days and an eccentricity (ovalness) of 0.23. The orbital plane is tilted at an angle of 6.17° to the plane of the ecliptic. Photometric data collected during 2009 were used for light curve analysis of this asteroid, yielding a rotation period of 18.48 hours with a brightness variation of 0.45 in magnitude. The result is close to the 18.347 hours period from a study performed in 2003. The asteroid is roughly 42 km in diameter.