Deep Impact
The mission that fired a copper projectile into a comet to see what lay beneath its crust.
Key facts
- Agency
- NASA (United States)
- Type of mission
- Comet impactor and flybys
- Target
- Comet 9P/Tempel 1, then comet 103P/Hartley 2
- Launched
- 12 January 2005
- Status
- Ended 2013
The surface of a comet is dark and crusty, hiding the ice and dust inside. Deep Impact was built to dig beneath it in the most direct way possible.
The impact
On 4 July 2005 the spacecraft released an impactor, a 370-kilogram block made largely of copper, into the path of comet 9P/Tempel 1. It struck at about 10 kilometres per second, releasing as much energy as several tonnes of explosive. The flyby spacecraft, watching from a safe distance, recorded a brilliant flash and a huge, slowly spreading cloud of material.
The ejected material was extremely fine, like talcum powder, showing that the comet's surface is a loose, fluffy dust. Instruments detected water ice, carbon dioxide, clays and carbonates in the cloud. Clays and carbonates usually need liquid water to form, which surprised scientists, as comets were thought always to have been frozen. The nucleus, about 7.6 kilometres long, also had small patches of water ice on its surface.
The dust hid the crater, but Stardust photographed it in 2011: a subdued crater about 150 metres wide.
Hartley 2
Renamed EPOXI, the spacecraft flew past comet 103P/Hartley 2 on 4 November 2010. This small, peanut-shaped comet, about 2 kilometres long, was blasting out jets of carbon dioxide gas that carried chunks of ice into space.
Why it matters to meteorites
The mixture found at Tempel 1, including minerals altered by water, narrowed the gap between comets and water-rich carbonaceous chondrites.
Key dates
| Date | What happened |
|---|---|
| 12 January 2005 | Deep Impact launched on a Delta II rocket. |
| 4 July 2005 | The impactor struck comet 9P/Tempel 1. |
| 4 November 2010 | Flew past comet 103P/Hartley 2 as the EPOXI mission. |
| August 2013 | Contact with the spacecraft was lost. |
See where this mission fits among all the others in the mission timeline.
Did you know?
The impactor was made of copper because copper would not be confused with the comet's own chemistry in the measurements.
The impact barely changed the comet's orbit, by a tiny fraction of a millimetre per second.
Related pages
Comets connected with this mission: Comet Tempel 1, Comet Hartley 2. See all comets.