Phaethon
Key facts
- What it is
- Near-Earth asteroid (Apollo group), parent of the Geminids
- Size
- About 5–6 km across
- Discovered
- 1983, by the IRAS satellite
- Spacecraft
- DESTINY+ fly-by planned
- Orbit group
- Apollo
- Average distance from the Sun
- 1.27 au (about 190 million km)
- Time to go round the Sun
- 524 days
- Closest and farthest from the Sun
- 0.14 to 2.4 au
- Tilt of its orbit
- 22.3°
- Closest its orbit comes to Earth's
- 2,800,000 km (7.3 times the Moon's distance)
- Spins once every
- 3.6 hours
An au (astronomical unit) is Earth's average distance from the Sun, about 150 million km. Orbit figures are from open tracking data, figures last updated 1 Nov 2026.
Phaethon is the asteroid behind the Geminids, one of the richest meteor showers of the year. Every December, Earth passes through a stream of dust that follows Phaethon's orbit, and the grains burn up in our atmosphere as shooting stars. Most meteor showers come from comets, so a shower from an asteroid is a puzzle.
Phaethon was the first asteroid discovered from space. Simon Green and John Davies found it in October 1983 in data from the Infrared Astronomical Satellite. It is about 5 to 6 kilometres across and has an extraordinary orbit, coming within about 21 million kilometres of the Sun, closer than Mercury. At that distance its surface reaches several hundred degrees Celsius, hot enough to crack rock.
Spacecraft watching the Sun have seen Phaethon brighten briefly near its closest approach, and for a while this was thought to be dust being thrown off. More recent work suggests the brightening comes mostly from sodium released from the hot surface, glowing in sunlight. The heating and cracking may still shed small amounts of material, but not nearly enough to make the Geminids today. Many scientists now think the stream was produced by a more dramatic event, perhaps a break-up, a few thousand years ago.
Phaethon passed about 10 million kilometres from Earth in December 2017, a safe distance, giving radar a good view. A Japanese mission called DESTINY+ is planned to fly past it.
Phaethon is named after the son of the Sun god in Greek legend, who lost control of his father's chariot and flew too close to the Sun.
Coming close to Earth
Its next passes within about 30 million km of Earth, worked out from its orbit. Each one is a safe miss.
| Date | Distance | In Moon distances |
|---|---|---|
| 11 Dec 2050 | 12,000,000 km | 32 |
| 18 Dec 2060 | 17,000,000 km | 43 |
| 14 Dec 2093 | 3,000,000 km | 7.7 |
| 22 Dec 2103 | 26,000,000 km | 67 |
| 13 Dec 2136 | 8,200,000 km | 21 |
| 19 Dec 2146 | 14,000,000 km | 35 |
Related pages
Phaethon is the parent of the Geminids. Compare it with the comets behind other meteor showers, such as 2003 EH1, another body that looks like an asteroid but feeds a shower.