Asteroid 2101, the second of the Apollo group to be discovered, by the Belgian astronomer Eugène Joseph Delporte (1882–1955) in 1936, when it passed within 0.015 au (2.2 million km) of the Earth. It was not seen again until 1977. Adonis is about 1 km in diameter. Its orbit has a semimajor axis of 1.87 au, period 2.57 years, perihelion 0.44 au, aphelion 3.31 au, and inclination 1°.3.