Useful Comets

Natural Spaceships

OUR civilisation is at last beginning to pay serious attention to comets. Space probes like Nasa's Deep Space 1 are starting to give them the same attention that we have hitherto given to planets and their moons. This is a momentous development in view of the staggering number of comets that fill and surround our solar system. Surely there must be future uses for them. After all, an estimated 10 trillion (1 followed by 13 noughts) comets make up the spherical Oort Cloud that extends out to more than a light year from the Sun. Back in 1929 the physicist J.D. Bernal, one of the fathers of futuristic speculation, made a brilliant suggestion about how they could one day be used. In his book The World, the Flesh and the Devil he proposed that they could one day be turned into starships. Astronauts, instead of having to build and accelerate their own vehicles to cruise the great gulfs between the stars, would burrow into comets and convert them into speeding vessels.

What was so clever about this idea was his proposed use of the fiery tails of comets. For whether a comet is approaching the Sun or receding from it, its tail (as matter is vaporised and blown off the comet by the Sun's heat) is always pointed away from the Sun. Thus, as the inhabited comet reached ever higher speeds, the tails would repel oncoming debris that might otherwise dangerously collide with the ship. As Bernal saw the culmination of these tactics: ``Once acclimatised to space living, it is unlikely that man will stop until he has roamed over and colonised the universe, or that even this will be the end. Man will not ultimately be content to be parasitic on the stars but will invade them and organise them for his own purposes.'' This proposal is not entirely practical, since the tail would disappear when the comet left the Sun's neighbourhood and where the tail would be most needed. But the use of comets, for local travel, for interplanetary shipping, may certainly be worth considering. Another thinker who has boldly contemplated the use of comets is Freeman J. Dyson, who has suggested that trees could be grown on their surfaces. Not trees as we know them, but artificial trees that would be part plant and part machine, a mixed creation of DNA and the product of computer software. Rising from the weak gravity of comets at the edge of the solar system, they would be many miles high. They could sustain communities of thousands of people, and by constantly repairing themselves, they could last for millions of years. If these ideas seem wild, they are a great improvement on how people saw comets a few centuries ago, as devices for political forecasting. They were regarded as portents, as in Shakespeare's Julius Caesar: When beggars die there are no comets seen: The heavens themselves blaze forth the death of princes. It is likely that other Sun-like stars will prove to be surrounded by their own Oort Clouds of trillions of comets. As transport vehicles and dwellings they may prove one of the most important resources in the galaxy.