Comet Borrelly
A dark, bowling-pin-shaped comet, the second nucleus ever photographed up close.
Key facts
- Designation
- 19P/Borrelly
- Type
- Jupiter-family comet
- Orbital period
- about 6.8 years
- Closest to the Sun
- about 1.3 AU (about 195 million km)
- Farthest from the Sun
- about 5.9 AU
- Tilt of orbit
- about 30°
- Nucleus
- about 8 km long
- Discovered
- by Alphonse Borrelly at Marseille on 28 December 1904
- Returns
- at perihelion in 2022; next around 2029
Orbit
Borrelly goes round the Sun every seven years, from beyond Mars's orbit out to Jupiter's.
Size and nature
The nucleus is about 8 km long and shaped like a bowling pin. Its surface reflects only about 3 per cent of sunlight, making it one of the darkest objects in the Solar System. Only a small part of it is active, and jets of gas and dust come from a few spots. It showed no signs of water ice on the surface, which is hidden beneath a dark crust.
History
Alphonse Borrelly found it from Marseille at the end of 1904. It has been seen at most returns since.
Missions
Deep Space 1 was a test craft for new technology, including an ion engine that pushed with a gentle, steady thrust. After its main task, it was sent to Borrelly and flew about 2,200 km from the nucleus on 22 September 2001, even though its star tracker, which kept it pointing the right way, had failed and engineers had to improvise. The pictures were the sharpest of a comet nucleus at that time, and they showed rolling plains, ridges and dark spots. Deep Space 1 was switched off in December 2001.
Space missions
- Deep Space 1 The spacecraft that proved ion engines in deep space, then flew past a comet.
Key dates
| Date | What happened |
|---|---|
| 28 December 1904 | Alphonse Borrelly discovered Comet Borrelly. |
| 22 September 2001 | Deep Space 1 flew past Comet Borrelly. |
Did you know?
Deep Space 1 was the first spacecraft to rely on an ion engine for its main propulsion.
Borrelly's surface is darker than fresh asphalt.
Only Halley's nucleus had been photographed close up before Borrelly.