A week ago, Nasa's Deep Space 1 satellite zipped past an asteroid, missing it by a cosmic hair's breadth (10 miles was the planned approach distance), travelling at 50 times the velocity of a jetliner, seven times that of a bullet, and twice even that of the space shuttle.
But this is not the end of the story. It's barely the first line. In recent weeks many have looked back 30 years to the Apollo 11 landing, and recalled Neil Armstrong's words as he set foot on the Moon. Trouble is, Nasa and others took them too literally. For decades space programmes have been dominated by giant leaps, to Mars, Jupiter, Saturn and beyond. Splendid endeavours, but each cost billions, and all could be lost by single hiccups (as with Mars Observer).
In reality there is a host of other worlds closer at hand ripe for our exploration, and accessible with smaller, faster and cheaper probes.
For the cost of one mission to the outer planets taking 20 years to complete, one can send 10 probes to nearby targets, like the asteroids and comets that we must understand if we are to survive. Either we take care of them, or they'll take care of us, as they did the dinosaurs.
Deep Space 1 (DS1) is a technology tester. It uses various new capabilities developed in the "Star Wars" (Strategic Defense Initiative) programme. But it has already returned invaluable data. Its initial target is 1992 KD, an Earth-approaching asteroid, which just a week before was formally named by the International Astronomical Union as "Braille", in honour of the man who developed the printing system by which books and text are encoded for the blind.
The name is appropriate: we are feeling our way into space. That spacecraft is just the first in a series. DS2, DS3 and DS4 are missions to quite different astronomical targets, with several asteroids and comets among the list of likely destinations. DS1 itself, if all goes well, will be sent on to comet Borelly in 2001, and then to a hybrid object called 4015 Wilson-Harrington.
This was discovered in the late 1940s by two astronomers named Wilson and Harrington. It was clearly a comet (sporting a tail of gas and dust). By the time it was accidentally re-discovered in 1979 it seems to have died, being simply an inert rock.
Even before DS1, Nasa had two spacecraft on their way to near-Earth objects. One mission Near (Near-Earth Asteroid Rendezvous) was launched three years back. This satellite was intended to rendezvous with an asteroid called 433 Eros in February, but a command failure caused the necessary rocket burn to be missed. All is not lost, though. Near gets another chance to meet Eros early next year, demonstrating another advantage of such projects: miss one encounter and another opportunity can be arranged.
It is thought that comets supplied the primordial material which made the evolution of life on earth feasible, so we'd like to have samples to study. This is the aim of Nasa's Stardust mission, launched in February, to encounter comet Wild 2 in 2004 and return some dust grains in 2006. Astrochemists are already drooling over the thought of what the samples may reveal. As with most missions, there is a suite of instruments on board, and the camera carried by Stardust has a resolution much better than that which ESA's Giotto probe turned on comet Halley.
Stardust will visit just one comet, whereas the Contour (Comet Nucleus Tour) programme plans excursions to at least three. After launch in 2002, Contour will approach comet Encke the following year. In terms of the numbers of orbits observed, this is the best-known comet. Since it was discovered in 1786 comet Encke has winged by more than 60 times, because it takes just 3.3 years to circuit the Sun. On the other hand, comet Halley takes 76 years, and has been witnessed by humankind 29 times since our earliest definite record of an appearance in 240 BC.
After Encke, in 2006 Contour will visit comet Schwassmann-Wachmann 3, a body which has recently broken apart and behaved erratically. All being well, comet d'Arrest will be met two years thereafter, providing a different perspective: this is about the most predictable comet known, in terms of its brightness sticking to calculations based on prior data.
After that it is hoped that some target of opportunity will appear, perhaps a new comet like Hale-Bopp or Hyakutake, the vivid apparitions of the past few years. Estimates suggest a 98% chance that a suitable new target comet will be discovered in time for Contour to meet it some time around 2010, adding another species to the cometary zoo. The metaphor is apt: comets are diverse in their sizes and behaviour. It makes no more sense to think that you understand feline behaviour just because you've spent five years studying your pet cat: there are also lions and tigers (and bears, as Dorothy told us in The Wizard of Oz).
Perhaps the most ambitious cometary mission is ESA's Rosetta probe, due for launch in 2003. This will orbit comet Wirtanen in 2011, putting a sophisticated lander down to study the nucleus in detail. The satellite's name indicates its aims: just as the Rosetta Stone (now in the British Museum) allowed the French linguist Champollion and British physicist Thomas Young to decipher the secrets of Egyptian hieroglyphics in the early 19th century, so this space mission is expected to provide the key to comets.
Rosetta, though, can sample only the uppermost part of the cometary nucleus.
Reasoning that the pristine material lies deep below the surface, where solar heating has not penetrated, Nasa scientists aim to blast away the crust of a comet in 2005 using a probe called Deep Impact. A half-ton copper projectile will slam into comet Tempel 1, excavating a huge crater and exposing its primordial composition. The Japanese space agency is also active in the asteroid/comet sphere. In 2002 its Muses-C satellite will be sent to an asteroid called Nereus; it got that name because it is indeed "near us."
On board will be a tiny rover vehicle the size of a shoebox, being developed with Nasa assistance. The planned way it will roam the asteroidal surface is staggering. With such low masses asteroids have minute escape speeds: one could almost jump off of them, never to return. The rover will traverse Nereus by springing upwards, taking hours to drop again to the surface, by which time the asteroid will have turned beneath it. This is "stop the world I want to get off" in reverse.
Clearly the next decade will be a golden age of comet and asteroid exploration. However, this will be only the beginning. The above space missions are financed by the respective nations' taxpayers, but the commercialisation of space is well under way. A Californian concern called SpaceDev is also planning a privately-funded mission. When the Japanese Muses-C probe gets to Nereus, it can expect company, a probe called Near-Earth Asteroid Prospector - and prospecting for minerals is what it will be doing.
• Duncan Steel's book Eclipse was recently published by Headline (London, £12.99).
