To some it was just another boring space mission, but hitting a comet with a probe is no easy thing, writes Shane Hegarty
For a billion years, give or take an aeon, Comet Tempel 1 quietly went about its business. On its regular laps of the solar system, it thwacked the odd meteorite and was occasionally delayed by the gravitational pull of Jupiter. But it had certainly never hit anything like it did on Monday, when a spacecraft the size of a Volkswagen Beetle journeyed 134 million kilometres (83 million miles) just to get run over by it.
We can be blasé when we read of another probe launched into space just so it can get clobbered by a passing rock, but Deep Impact was the latest in a series of missions that not only stretch our imagination and widen our knowledge but that also deserve our admiration. The age of the explorer may be largely behind us, and there is more romance in the image of a frost-bitten adventurer than a boffin in front of a computer, but machines such as Deep Impact - and the scientists behind them - are pulling off some staggering feats as trailblazers in a new age of exploration.
This week's collision was such an achievement that even Nasa scientists were at first sceptical of their chances of hitting the target. It was an impressive needle to thread, given that Deep Impact took six months to travel several million miles to hit a target only 14km (8.7 miles) long and 4km (2.5 miles) wide. The craft actually consisted of two portions: the doomed Impactor, and the Flyby, which acted as an eyewitness. In order to see what the comet is made of, designers had to ensure the Impactor created a decent crater before it was vaporised. It hit the comet at a relative speed of 37,000kph (22,990mph). That's 10km (six miles) a second, which is enough to take it from Dublin to New York in nine minutes. And it did it while sending back pictures as it smashed into the surface, which you could then watch at home within minutes of the collision.
Space exploration goes wrong often enough that we should marvel when it goes right. The smallest of problems can be catastrophic. When the Genesis spacecraft, having scooped dust from the sun, returned to Earth last year it crashed in the desert when its parachute failed to open. Someone had put the chute switches on backwards.
Yet, we've been pretty successful for a species that only got a machine a few feet off the ground as recently as 100 years ago. We have now landed a probe on an asteroid. Next year, a probe will return to Earth with samples collected from a comet's tail. And as Deep Impact crashed into its comet, another probe - Rosetta - turned to take a few snaps on its way to becoming the first spacecraft to land on a comet. The European Space Agency spacecraft will not reach its destination until 2014, after a four billion mile journey.
It's been a particularly busy year. Just after Christmas, the Huygens probe landed on one of Saturn's moons, Titan, and sent back pictures of a place that looked remarkably familiar. There were canyons and rocks and a river delta. It was recognisable enough that you could forget the probe was sitting in a freezing, poisonous land of methane lakes and orange clouds 800 million miles from home. To give you an idea of how far away that is, if the Earth was scaled all the way down to the size of a grain of sand, Saturn would still be about 350ft away.
To get there, it piggybacked on the Cassini probe, which had travelled the long way around by being flung around the sun, Venus, then Earth and Venus twice again and finally Jupiter before it had the speed to get to Saturn.
That's 3.5 billion kilometres (2.2 billion miles) in all. And once it reached Saturn it had to thread its way through the planet's famous rings, zip around a few moons and avoid ones it didn't know were even there - all the while, sending back pictures and a stream of data on each encounter before parachuting into an alien planet and surviving long enough to show us what it's like.
We do not know yet if there is life elsewhere in the solar system, but mankind continues to reach into its cosmic nooks and crannies. Scattered about the asteroids, moons, planets and comets are various probes that have made epic journeys from Earth.
The two Voyager spacecraft launched within a fortnight of each other in 1977 continue their long trudge out of the galaxy, so far away now that it takes almost a full day to send a signal and receive a reply. Voyager 1 is still dutifully filing back reports from twice the distance it is from here to Pluto, with less computer power than is in your microwave oven. It covers an astonishing one million miles a day. It sends back an electronic signal which, when it reaches us, is about 20 billion times weaker than that of a digital wristwatch.
These are mind-boggling statistics, which is perhaps why we don't always pause to realise just how remarkable these space missions are. Not that everyone is impressed. A Russian astrologer is suing Nasa for the Deep Impact collision on the grounds that the probe "ruins the natural balance of forces in the universe", and "deforms her horoscope". On Earth, then, not all life is intelligent.