Rendezvous With Rama

chapter 2. Intruder
By the year 2130, the Mars-based radars were discovering new asteroids at the rate of a dozen a day. The SPACEGUARD computers automatically calculated their orbits, and stored away the information in their enormous memories, so that every few months any interested astronomer could have a look at the accumulated statistics. These were now quite impressive.

It had taken more than a hundred and twenty years to collect the first thousand asteroids, since the discovery of Ceres, largest of these tiny worlds, on the very first day of the nineteenth century. Hundreds had been found and lost and found again; they existed in such swarms that one exasperated astronomer had christened them "vermin of the skies". He would have been appalled to know that SPACEGUARD was now keeping track of half a million. Only the five giants - Ceres, Pallas, Juno, Eunomia and Vesta - were more than two hundred kilometres in diameter; the vast majority were merely oversized boulders that would fit into a small park. Almost all moved in orbits that lay beyond Mars; only the few that came far enough sunwards to be a possible danger to Earth were the concern of SPACEGUARD. And not one in a thousand of these, during the entire future history of the solar system, would pass within a million kilometres of Earth. The object first catalogued as 31/439, according to the year and the order of its discovery, was detected while still outside the orbit of Jupiter. There was nothing unusual about its location; many asteroids went beyond Saturn before turning once more towards their distant master, the sun. And Thule II, most far-ranging of all, travelled so close to Uranus that it might well have been a lost moon of that planet. But a first radar contact at such a distance was unprecedented; clearly, 31/439 must be of exceptional size. From the strength of the echo, the computers deduced a diameter of at least forty kilometres; such a giant had not been discovered for a hundred years. That it had been overlooked for so long seemed incredible.

Then the orbit was calculated, and the mystery was resolved - to be replaced by a greater one. 31/439 was not travelling on a normal asteroidal path, along an ellipse which it retraced with clockwork precision every few years. It was a lonely wanderer between the stars, making its first and last visit to the solar system - for it was moving so swiftly that the gravitational field of the sun could never capture it. It would flash inwards past the orbits of Jupiter, Mars, Earth, Venus and Mercury, gaining speed as it did so, until it rounded the sun and headed out once again into the unknown.

It was at this point that the computers started flashing their "Hi there! We have something interesting" sign, and for the first time 31/439 came to the attention of human beings. There was a brief flurry of excitement at SPACEGUARD Headquarters, and the interstellar vagabond was quickly dignified by a name instead of a mere number. Long ago, the astronomers had exhausted Greek and Roman mythology; now they were working through the Hindu pantheon. And so 31/439 was christened Rama.

For a few days, the news media made a fuss of the visitor, but they were badly handicapped by the sparsity of information. Only two facts were known about Rama - its unusual orbit, and its approximate size. Even this was merely an educated guess, based upon the strength of the radar echo. Through the telescope, Rama still appeared as a faint, fifteenth magnitude star - much too small to show a visible disc. But as it plunged in towards the heart of the solar system, it would grow brighter and larger, month by month; before it vanished for ever, the orbiting observatories would be able to gather more precise information about its shape and size. There was plenty of time, and perhaps during the next few years some spaceship on its ordinary business might be routed close enough to get good photographs. An actual rendezvous was most unlikely; the energy cost would be far too great to permit physical contact with an object cutting across the orbits of the planets at more than a hundred thousand kilometres an hour.

So the world soon forgot about Rama; but the astronomers did not. Their excitement grew with the passing months, as the new asteroid presented them with more and more puzzles.

First of all, there was the problem of Rama's light curve. It didn't have one.

All known asteroids, without exception, showed a slow variation in their brilliance, waxing and waning within a period of a few hours. It had been recognized for more than two centuries that this was an inevitable result of their spin, and their irregular shape. As they toppled end over end along their orbits the reflecting surfaces they presented to the sun were continually changing, and their brightness varied accordingly.

Rama showed no such changes. Either it was not spinning at all or it was perfectly symmetrical. Both explanations seemed equally unlikely.

There the matter rested for several months, because none of the big orbiting telescopes could be spared from their regular job of peering into the remote depths of the universe. Space astronomy was an expensive hobby, and time on a large instrument could easily cost a thousand dollars a minute. Dr. William Stenton would never have been able to grab the Farside two-hundred-metre reflector for a full quarter of an hour, if a more important programme had not been temporarily derailed by the failure of a fifty cent capacitor. One astronomer's bad luck was his good fortune.

Bill Stenton did not know what he had caught until the next day, when he was able to get computer time to process his results. Even when they were finally flashed on his display screen, it took him several minutes to understand what they meant.

The sunlight reflected from Rama was not, after all, absolutely constant in its intensity. There was a very small variation - hard to detect, but quite unmistakable, and extremely regular. Like all the other asteroids, Rama was indeed spinning. But whereas the normal "day" for an asteroid was several hours, Rama's was only four minutes.

Dr. Stenton did some quick calculations, and found it hard to believe the results. At its equator, this tiny world must be spinning at more than a thousand kilometres an hour; it would be rather unhealthy to attempt a landing anywhere except at the poles. The centrifugal force at Rama's equator must be powerful enough to flick any loose objects away from it at an acceleration of almost one gravity. Rama was a rolling stone that could never have gathered any cosmic moss; it was surprising that such a body had managed to hold itself together, and had not long ago shattered into a million fragments.

An object forty kilometres across, with a rotation period of only four minutes - where did that fit into the astronomical scheme of things? Dr. Stenton was a somewhat imaginative man, a little too prone to jump to conclusions. He now jumped to one which gave him a very uncomfortable few minutes indeed.

The only specimen of the celestial zoo that fitted this description was a collapsed star. Perhaps Rama was a dead sun - a madly spinning sphere of neutronium, every cubic centimetre weighing billions of tons... At this point, there flashed briefly through Dr. Stenton's horrified mind the memory of that timeless classic, H. G. Wells's The Star. He had first read it as a very small boy, and it had helped to spark his interest in astronomy. Across more than two centuries of time, it had lost none of its magic and terror. He would never forget the images of hurricanes and tidal waves, of cities sliding into the sea, as that other visitor from the stars smashed into Jupiter and then fell sunwards past the Earth. True, the star that old Wells described was not cold, but incandescent, and wrought much of its destruction by heat. That scarcely mattered; even if Rama was a cold body, reflecting only the light of the sun, it could kill by gravity as easily as by fire.

Any stellar mass intruding into the solar system would completely distort the orbits of the planets. The Earth had only to move a few million kilometres sunwards - or starwards - for the delicate balance of climate to be destroyed. The Antarctic icecap could melt and flood all low-lying land; or the oceans could freeze and the whole world be locked in an eternal winter. Just a nudge in either direction would be enough.

Then Dr. Stenton relaxed and breathed a sigh of relief. This was all nonsense; he should be ashamed of himself.

Rama could not possibly be made of condensed matter. No star-sized mass could penetrate so deeply into the solar system without producing disturbances which would have betrayed it long ago. The orbits of all the planets would have been affected; that, after all, was how Neptune, Pluto and Persephone had been discovered. No, it was utterly impossible for an object as massive as a dead sun to sneak up unobserved.

In a way, it was a pity. An encounter with a dark star would have been quite exciting.

While it lasted...