On July 4th, NASA scientists aim to punch a hole in the belly of a comet. If they’re lucky, secrets of the solar system locked away for billions of years will spill out. The unprecedented mission, named Deep Impact akin to a dissection: Investigators hope that by blasting Tempel 1, an oblong comet roughly nine miles long, they’ll expose its basic anatomy.

Comets are whizzing relics. Mysterious amalgams of rock, ice, and dust, born with the solar system four point five billion years ago. They may have helped shape our cosmic neighbourhood. Many scientists think that comets brought to Earth a lot of the water and the organics that were needed to create life. The size, shape and depth of the impact crater, along with material ejected from it, will reveal the comet’s structure. Comets are key to understanding the whole planetary system.

Engineers designed two vehicles for the mission, and SUV-size flyby spacecraft, equipped with telescopes, cameras, a spectrometer, and an eight hundred and twenty pound impact craft that’s about the size of a washing machine. Launched in January, the flyby craft has carried the impactor to Tempel 1, eight-three million miles from Earth. AT about five hundred thousand miles from Tempel 1, it will release the impactor, and retreat to record the collision. The impactor will steer itself into the comet’s path, transmitting images until the comet slams into it with the force of nearly five tonnes of dynamite.

We expect a crater about the size of a football field. What exactly Deep Impact will reveal is all part of the excitement – and anxiety of long-distance science.