3200 Phaethon is a small near‑Earth object best known as the parent body of the Geminid meteor shower. Discovered in 1983 by observations from a spacecraft, Phaethon has characteristics of both asteroids and comets: it looks like a rocky asteroid at most times but sheds dust when it passes very close to the Sun, earning descriptions such as a "rock comet" or an asteroid with cometary activity. At roughly 5 kilometers across, it is one of the larger near‑Earth objects with a highly eccentric, Sun‑skimming orbit.

Physical characteristics

Phaethon appears relatively dark and unremarkable in visible light but shows occasional dust release near perihelion. Its diameter is commonly cited near 5 km, and photometric studies indicate a relatively rapid rotation. Thermal stresses and surface cracking from extreme heating during close solar passages are believed to produce the dust that replenishes the Geminid stream. Because it lacks a sustained coma or large volatile supply like typical comets, Phaethon is often classified as an extinct or dormant cometary nucleus, or alternatively as an active asteroid.

Orbit and activity

Phaethon is an Apollo‑class object: its orbit crosses those of Mercury, Venus, Earth and Mars. Its perihelion distance is extremely small—about 0.14 astronomical units—so it gets far closer to the Sun than Mercury does. At those near‑Sun distances the surface can reach temperatures high enough to drive fracturing and episodic dust release rather than the sublimation of ices that powers traditional comets. This behavior explains how Phaethon supplies the Geminid meteoroid stream even though it looks like an asteroid most of the time.

History, discovery and name

Phaethon was announced in October 1983 after detection by a spaceborne infrared telescope, making it notable as the first asteroid found by a spacecraft. Its name derives from the Greek myth of Phaëton, the son of the sun god who lost control of his father’s chariot, a fitting reference to the object’s extreme closeness to the Sun. Subsequent ground‑based observations refined its orbit and confirmed its connection with the Geminids through orbital analyses and meteoroid dynamics.

Exploration, significance and future encounters

Because Phaethon links an asteroid‑like object with an active meteor stream, it is of strong interest to planetary scientists studying the continuum between asteroids and comets, near‑Earth object hazards, and the processes that produce meteoroid streams. Space mission planners have proposed or developed flyby missions to study Phaethon up close to sample its surface properties and dust environment. Periodic close approaches to Earth make it accessible for observation, and long‑term orbit calculations identify several future encounters of interest to observers and mission designers.