Scientists will tomorrow attempt to blast a hole in a distant comet using a 39-inch wide projectile fired from a space craft.
If it succeeds, the Deep Impact mission will be a technological triumph for mission controllers at NASA.
The aim is to smash out a chunk of the icy surface of comet Tempel 1, 133 million miles from Earth, to see what lies beneath.
By analysing the comet’s interior and the cloud of dust and ice thrown out by the explosion, scientists hope to answer fundamental questions about the formation of the Solar System.
But hitting a target less than 3.7 miles wide from a distance of 537,000 miles is no easy feat.
Controllers will steer both space craft and impactor to the comet from their mission base at Nasa’s Jet Propulsion Laboratory in Pasadena, California.
At precisely the right time, they will release the 820-pound copper and aluminium projectile into the path of the comet, which is hurtling through space at 23,000mph.
The projectile and Tempel 1 will come together in spectacular fashion at about 6.52am on Monday, London time.