Overview

2101 Adonis is a near-Earth object belonging to the Apollo group: asteroids whose orbits cross Earth's path and have semimajor axes greater than Earth's. It was one of the first such bodies to be identified, originally detected in 1936. Estimates place its diameter at roughly 1 kilometre, making it a relatively small but significant object in studies of near-Earth populations and impact hazards.

Discovery and observational history

Adonis was first reported by Belgian astronomer Eugène Delporte in 1936. At that time only a few observations could be made during its brief apparition, so its orbit could not be reliably determined and the object became lost to observers. It remained untracked until 1977, when American astronomer Charles T. Kowal recovered it and linked the observations to the earlier discovery. That recovery allowed astronomers to compute a stable orbit and include Adonis in catalogs of near-Earth asteroids.

Orbit, classification and physical nature

As an Apollo asteroid, Adonis follows an Earth-crossing path that brings it into the inner Solar System. Its size and surface properties have led some researchers to suggest it might be an extinct or dormant comet nucleus rather than a typical rocky asteroid—that is, a body that once exhibited cometary activity but has lost much of its volatile material. Such a history could explain spectral and dynamical characteristics and is consistent with other near-Earth objects that blur the line between comet and asteroid.

Close approaches and interactions with Earth

Adonis makes multiple relatively close approaches to Earth. In the 21st century it comes within about 30 million kilometres (30 Gm) on six occasions. The closest of these in this century is predicted to be about 5.3 Gm in 2036. While these distances are large compared with Earth's radius, they are close enough for precise radar and optical tracking during favourable apparitions and for studying how gravitational encounters alter the asteroid's orbit over time.

Importance and notable facts

Beyond its historical place as one of the earliest discovered near-Earth asteroids—second among Apollo discoveries after 1862 Apollo—Adonis is of interest for several reasons: its uncertain comet-like origin, its potential (but not certain) link to meteor showers, and its role as an example of an object that was lost and later recovered, illustrating challenges in tracking small Solar System bodies. For general background on similar objects see near-Earth asteroid resources. The name derives from the figure Adonis of classical myth and is associated with the goddess Venus (Aphrodite), reflecting a long tradition of naming small bodies after mythological characters. For discussion of comet-asteroid transition objects see material on extinct or dormant comets.

  • First discovery: Eugène Delporte, 1936
  • Rediscovery: Charles T. Kowal, 1977
  • Group: Apollo (Earth-crossing)
  • Estimated size: about 1 km in diameter
  • Notable approach: ~5.3 Gm from Earth in 2036