Comet Schwassmann–Wachmann 1
A 60-kilometre icy body on a nearly circular orbit beyond Jupiter, which erupts several times a year.
Key facts
- Designation
- 29P/Schwassmann–Wachmann
- Type
- Centaur (an icy body between Jupiter and Neptune)
- Orbital period
- about 14.9 years
- Closest to the Sun
- 5.8 AU (about 860 million km)
- Farthest from the Sun
- 6.3 AU
- Tilt of orbit
- about 9.4°
- Nucleus
- about 60 km across
- Discovered
- by Arnold Schwassmann and Arno Wachmann at Hamburg on 15 November 1927
- Returns
- always active: its distance from the Sun barely changes
Orbit
Unlike most comets, Schwassmann–Wachmann 1 follows an almost circular orbit just outside Jupiter's. It never comes close to the Sun or to Earth. It is a centaur, one of the icy bodies that have drifted inward from the Kuiper belt beyond Neptune and now wander among the giant planets. Jupiter's pull will eventually push it inward or outward.
Size and nature
The nucleus is about 60 km across, far larger than most comets near the Sun. Even at its distance, where water stays frozen, it is always active, driven by carbon monoxide ice turning to gas. Several times a year it has outbursts, brightening dozens or hundreds of times in hours. Amateur observers around the world monitor it, so outbursts are seen within hours.
History
Arnold Schwassmann and Arno Wachmann found it at Hamburg in 1927, during an outburst. Older photographs from 1902 were later found to show it too. The James Webb Space Telescope has studied its gas in detail.
Why it matters
Centaurs like this are thought to be the supply of future Jupiter-family comets. Studies suggest it lies near a 'gateway' through which bodies pass from the outer Solar System to the inner, so it is a preview of the comets that may one day shed meteor showers near Earth.
Key dates
| Date | What happened |
|---|---|
| 15 November 1927 | Arnold Schwassmann and Arno Wachmann discovered the outbursting comet 29P. |
Did you know?
About ten outbursts a year have been recorded in recent years.
It is one of the largest comet nuclei known.
It is always far enough out to stay cold, yet it is always active.