Nasa scientists have been giving details of a space mission to crash a projectile into a comet, peeling away its outer skin in order to look inside.
Deep Impact will punch a crater in Comet Tempel 1
The audacious Deep Impact mission will launch on 12 January from Cape Canaveral, Florida, and will arrive at Comet Tempel 1 six months later.
A mothership will eject the 360kg projectile, called an "impactor", directly into the path of Tempel 1.
The projectile will hit the comet on 4 July, 24 hours after its release.
"Deep Impact will be the first mission to peel away the outer layer of a comet and peer inside its nucleus," said Tom Morgan, Deep Impact programme scientist.
Scientists hope the projectile will punch a crater in the comet, allowing them to analyse the interior. But this is not a given - some scientists think the impactor could just compress the outer surface when it hits.
From a distance of 500km, Deep Impact will analyse Temple 1's chemistry and structure by taking pictures and readings as comet debris is hurled out.
The impactor will also carry a camera to take pictures as it is hurled into Tempel 1.
"This camera will give us the closest images yet of a comet's surface. It will probably be sandblasted in the last minute before impact before being destroyed," said Deep Impact principal investigator Professor Mike A'Hearn.
Under optimal conditions, the camera could send back images of the comet's surface with a resolution of up to 20cm per pixel.
But if the camera gets sandblasted in the final minute before impacting, this could drop to 3m per pixel.
The collision with the impactor is not expected to divert the path of Tempel 1.
The mission was due to launch at the end of December. But during a review, mission scientists and engineers found a few errors, which included a heat ring that had to be replaced.
Deep Impact has a "window" in which it has to launch, which lasts until 28 January.