Comet Wirtanen
Rosetta's first-choice target, which passed close to Earth in December 2018 and is a candidate for future missions.
Key facts
- Designation
- 46P/Wirtanen
- Type
- Jupiter-family comet
- Orbital period
- about 5.4 years
- Closest to the Sun
- about 1.06 AU (about 158 million km)
- Farthest from the Sun
- about 5.1 AU
- Tilt of orbit
- about 12°
- Nucleus
- about 1.2 km across
- Discovered
- by Carl Wirtanen at Lick Observatory, California, on 17 January 1948
- Returns
- at perihelion in 2024; next in 2029
Orbit
Wirtanen goes round the Sun every five and a half years, between Earth's orbit and Jupiter's. On 16 December 2018 it passed about 11.6 million km from Earth, one of the closest approaches of any comet in modern times, and could be seen in binoculars.
Size and nature
The nucleus is small, about 1.2 km across, yet it produces much water for its size. Like Hartley 2, it is one of the so-called hyperactive comets, where icy grains thrown into the coma add to the gas.
History
Carl Wirtanen found it on photographs at Lick Observatory in 1948. Close passes of Jupiter in 1972 and 1984 shrank its orbit, bringing it nearer the Sun.
Missions
Wirtanen was the original target of the European Rosetta mission. The launch was set for January 2003, but after an Ariane 5 rocket failed in December 2002 the launch was postponed and Wirtanen could no longer be reached in time. Rosetta was sent to 67P/Churyumov–Gerasimenko instead. Wirtanen remains a target studied for possible future missions.
Space missions
- Rosetta and Philae The first spacecraft to orbit a comet and to land on one.
Key dates
| Date | What happened |
|---|---|
| 17 January 1948 | Carl Wirtanen discovered Comet Wirtanen. |
| 16 December 2018 | Comet Wirtanen passed about 11.6 million km from Earth. |
Did you know?
During its close pass in December 2018 it appeared next to the Pleiades star cluster.
It is a typical small Jupiter-family comet, which made it a good choice for Rosetta.
Carl Wirtanen found several comets and asteroids at Lick Observatory.