Comet Hartley 2
A small, hyperactive peanut-shaped comet that blew out snowballs, visited by the Deep Impact spacecraft in 2010.
Key facts
- Designation
- 103P/Hartley
- Type
- Jupiter-family comet
- Orbital period
- about 6.5 years
- Closest to the Sun
- about 1.06 AU (about 159 million km)
- Farthest from the Sun
- about 5.9 AU
- Tilt of orbit
- about 13.6°
- Nucleus
- about 2.2 km long, peanut-shaped
- Discovered
- by Malcolm Hartley at Siding Spring, Australia, on 15 March 1986
- Returns
- at perihelion in 2023; next in 2030
Orbit
Hartley 2 goes round the Sun every six and a half years, from just outside Earth's orbit to beyond Jupiter's. In October 2010 it passed about 18 million km from Earth.
Size and nature
The nucleus is a peanut about 2.2 km long, with rough ends and a smooth waist. For its size it is extraordinarily active. Jets of carbon dioxide gas burst from the rough ends and carry out chunks of water ice, some as big as golf balls or footballs, which then turn to vapour in sunlight around the comet. That is why such a small comet makes so much water.
History
Malcolm Hartley found it in 1986 on photographs taken with the UK Schmidt Telescope in Australia. In 2011 the Herschel space observatory measured the deuterium in its water and found a value close to that of Earth's oceans. That briefly revived the idea that comets brought Earth's water, though Rosetta's very different result from 67P later showed that comets vary.
Missions
After striking Tempel 1, the Deep Impact flyby spacecraft was given a new task, called EPOXI, and sent to Hartley 2. It passed about 700 km from the nucleus on 4 November 2010, revealing the jets and the cloud of ice chunks.
Space missions
- Deep Impact The mission that fired a copper projectile into a comet to see what lay beneath its crust.
Key dates
| Date | What happened |
|---|---|
| 15 March 1986 | Malcolm Hartley discovered Comet Hartley 2. |
| 4 November 2010 | The Deep Impact spacecraft flew past Comet Hartley 2. |
Did you know?
Hartley 2 is the smallest comet nucleus a spacecraft has photographed close up.
Its carbon dioxide jets are driven by ice that turns to gas at far lower temperatures than water ice.
It was the fifth comet nucleus ever photographed.