Heavy Planet Part 30

"And with all this, you say we're ahead?" cut in Guzmeen.

"Sure. Remember, the whole aim of the Esket act was to persuade the human beings to let us use s.p.a.ce ships. The self-support business was incidental, though useful. We expected to work the local-life myth up to a major menace before we could persuade Aucoin to let us fly, and spend months building up to it. We're far ahead on time, and haven't lost very much, the base at the Esket site, of course, and the Elsh and its crew, and just possibly Kabremm and his."

"But even Kabremm and Karfrengin aren't exactly expendable. There aren't very many of us. If Dondragmer and his crew don't keep alive until the Kalliff reaches them, we'll have taken a really serious loss; at least our dirigible crews weren't our scientists and engineers."

"Don's in no real danger. They can always be picked up by Beetchermarlf in the human s.p.a.ce ship-I mean our s.p.a.ce ship."

"And if anything goes wrong with that operation we're out not only our only s.p.a.ce ship but our only s.p.a.ce pilots."

"Which suggests to me," Barlennan said thoughtfully, "that we should try to regain some lost ground. As soon as the Kwembly is ready she should start hunting a suitable place and start replacing the Esket settlement. Don's scientists should have little trouble finding a good location; Dhrawn seems to be rich in metal ores. Maybe we should have him search closer to here so that communication will be quicker, though.

"We'll have to build more dirigibles; the one we have left isn't nearly enough for the work. Maybe we ought to design bigger ones."

"I've been wondering about that," a technician who had been listening silently up to this point spoke up. "Do you suppose that it would be smart to find out more, tactfully, of course, from the humans about dirigibles? We've never discussed the subject with them; they taught you about balloons years ago, and some of our own people got the idea of using the human power sources with them. We don't know if they ever used them at all. Maybe it isn't just bad luck that we've lost two out of our three in such a short time. Maybe there's something fundamentally wrong with the whole idea."

The commander gave a gesture of impatience.

"That's silly. I didn't try to pick up a complete scientific education from the aliens, since it was obviously going to take too long; but one thing I did gather was that the underlying rules are essentially simple. Once the humans started concentrating on basic rules, they went from sailing ships to s.p.a.ce ships in a couple of hundred years. Balloons, powered or not, are simple devices; I understand them perfectly myself. Putting an engine aboard doesn't change that; the same rules have to be working."

The technician eyed his commander thoughtfully, and thought briefly of electron tubes and television circuits before replying.

"I suppose," he said thoughtfully, "that a piece of a tent being blown away by the gale, and a ship being tacked into the wind, are also examples of the same rules at work."

Barlennan didn't want to give an affirmative answer, but he could find nothing better.

He was still trying to shrug off the technician's remark, but only succeeding in growing more and more doubtful of his situation, some twenty hours later when a messenger called him to the communication room. As soon as he entered, Guzmeen spoke briefly into a microphone; a minute later, a human face which neither of them recognized appeared on the screen.

"I am Ib Hoffman, Easy's husband and Benj's father," the stranger began without preamble. "I'm speaking to you two, Barlennan and Dondragmer, alone. The rest of the observing crew here are concentrating on a new emergency involving one of the cruisers. I'm using your language as best I can, with my wife standing by; she knows what I want to say, and will correct me if I slip too badly. I have decided that it is time to clear up some misunderstandings, but I don't plan to tell everyone here about them; you'll see why before I finish, if you don't already. I'm bothered mostly because I hate to call anyone a liar in any language.

"First, Barlennan, my hearty congratulations. I am just about certain that when we turned the barge over to a Mesklinite pilot we fulfilled one of your chief plans, probably well before you meant or expected it to mature. That's fine. I wanted that to happen. Probably you want to make interstellar flights on your own later on, too; that's also fine with me. I'll help.

"You seem to feel that many or most human beings would try to thwart you in this, and I have to admit that some would, though I think we have the most effective one under control now. You can't be sure that I'm being sincere now, for that matter; you're tricky enough yourself to expect it of other people. Too bad. How much you believe of what I say is beyond my control; I still have to say it.

"I don't know how much of the basic situation you set up, but I can guess. I'm nearly sure the Esket disappearance was not genuine. I'm uncertain of the real status of the Kwembly. You probably know more of Dhrawn than you've reported. I won't say I don't care, because I do; we're here to learn as much as possible about Dhrawn, and what you don't tell us is a loss to the project. I can't threaten you with penalties for breach of contract, since I'm not completely certain you've broken it and am in no position to carry out threats. And in any case have less than no desire to even make threats. I do want to persuade you, though, that it will be better for both of us if we do without secrets. We're at a point where anything less than complete frankness is likely to cost us a lot and cost you everything. To make that point, I'm going to tell you a story.

"You know that human beings breathe oxygen much as you do hydrogen, though being so much larger we need a more complicated pumping system to get it through our bodies. Because of the details of that system, we suffocate if deprived of gaseous, free oxygen within a certain rather narrow range of pressures.

"About three quarters of Earth is covered by water. We cannot breathe under water without artificial equipment, but the use of such equipment is a common human sport. It consists essentially of a tank of compressed air and a valve system which releases the air to our breathing system as needed; simple and obvious.

"Six of our years ago, when Benj was eleven years old, he made such a device, designing it himself with my a.s.sistance. He made the pressure tank and regulator, using ordinary fabricating equipment such as may be found in most home workshops, just as he had made more complex things such as small gas turbines. He tested the parts with my help; they worked perfectly. He calculated how long the air in the tank would last him, and then tested the whole a.s.sembly under water. I went along as a matter of common-sense safety, using a commercial diving device.

"I am sure you know the principles of hydrostatics and the gas laws; at least, Easy has given me words for them in your language. You can see that at a certain depth, a lungful of air would have only half its volume at the surface. Benj knew this too, but reasoned that it would still be a lungful as far as oxygen content was concerned, so that a one-hour tank would be a one-hour tank regardless of depth, as long as tank pressure was above that of the water.

"To make a long story short, it didn't. He ran out of air in less than a third of the calculated time, and I had to make an emergency rescue. Because of the quick pressure change and some human peculiarities which you don't seem to share, he was very nearly killed. The trouble turned out to be that the human breathing rate is controlled, not by the oxygen in our blood, but by the carbon dioxide, one of the waste products. To maintain a normal equilibrium of that, we have to run normal volumes of air through our lungs, regardless of oxygen content or total pressure; hence, an hour's air supply at normal pressure is only half an hour thirty-three feet under water, a third of an hour at sixtysix, and so on.

"I don't want to insult anyone's intelligence by asking if he understands my point, but I'd like some comment from both of you on that story."

The answers were interesting, both in nature and arrival time. Barlennan's popped from the speaker with very little more than light-travel delay; Dondragmer's came much, much later, and did not overlap with his commander's.

"It is obvious that incomplete knowledge can lead to mistakes," said Barlennan, "but I don't see why that is especially applicable to the present case. We know that our knowledge can't be complete, and that our work here is dangerous for that reason. We have always known it. Why emphasize the point now? I'd much rather hear your report on the cruiser you say is in trouble. You make me suspect that you are leading up gently to the information that I have lost another cruiser because of something its designing engineers didn't know. Don't worry, I won't blame you for that. None of us could foresee everything."

Ib smiled sourly at the revelation of yet another human characteristic.

"That's not just what I had in mind, Commander, though there are valid aspects to what you have just said. I'd like to wait for Dondragmer's answer before I say any more, though."

It was another full minute, a slightly strained one, before the voice of the Kwembly's captain arrived.

"Your account is plain enough and you would probably have been briefer had you not meant to imply more. I suspect that your key point is not so much that your son got into trouble through ignorance, but that he did so even under your experienced adult supervision. I would take the implication to be that even though you aliens do not claim omniscience or omnipotence, we are in a certain amount of danger here no matter how closely you supervise and a.s.sist us, and we are adding unnecessarily to our danger any time we act on our own, like the student chemist who experiments on his own." Dondragmer had spent much more time at the College than had his commander.

"Right. Just what I meant," said Ib. "I can't ..."

"Just a moment," interrupted Easy. "Hadn't you better relay Don's remark to Barlennan first?"

"Right." Her husband gave a one-sentence summary of the captain's speech, and went on, "I can't force any policy on you, and would prefer not to even if I could. I don't expect you to make a complete revelation of everything that's gone on on Dhrawn since you first built the Settlement. In fact, I'd advise strongly against it; I have enough complications up here with the administration as it is. However, if Easy just happened to get an occasional talk with her old friends Destigmet and Kabremm, just as an example, I would have a better idea of what has gone on and be in a better position to keep things running smoothly at this end. I don't expect a spot decision on any matter of major policy change, Commander, but please think it over."

Barlennan, being a sea captain by training and trade, was accustomed to the need for quick decisions. Furthermore, circ.u.mstances had already compelled thoughts on similar lines to circulate in his tiny head. Finally, his only really basic policy was to ensure his own survival and that of his crew. He answered Ib promptly.

"Easy may get her talk with Destigmet, but not right away; the Esket is a long distance from here. I will also have to wait to tell you all that I'd like to, because I must first hear from you the details of the trouble you mentioned when you first called. You said that another of my cruisers was in trouble.

"Please tell me just what has happened, so I can plan what help to request from you."

Ib and Easy Hoffman looked at each other and grinned in mingled relief and triumph.

But it was Benj who made the key remark. This was later on, in the aerology lab, when they were recounting to him and McDevitt all that had been said. The boy looked up at the huge globes of Dhrawn, and the tiny area where the lights indicated partial knowledge.

"I suppose you think he's a lot safer now, down there."

It was a sobering thought.

WHIRLIGIG WORLD1.

Writing a science fiction story is fun, not work. If it were work I wouldn't be writing this article, which would then const.i.tute a chapter for a textbook. I don't plan to write such a text, since if the subject is teachable I'd be creating compet.i.tion and if it isn't I'd be wasting time.

The fun, and the material for this article, lies in treating the whole thing as a game. I've been playing the game since I was a child, so the rules must be quite simple. They are; for the reader of a science-fiction story, they consist of finding as many as possible of the author's statements or implications which conflict with the facts as science currently understands them. For the author, the rule is to make as few such slips as he possibly can.

Certain exceptions are made by both sides, of course. For example, it is commonly considered fair to ignore certain of Dr. Einstein's theories, if the story background requires interstellar travel. Sometimes a pa.s.sing reference is made to travel through a "hypers.p.a.ce" in which light can travel faster or distances are shorter, but in essence we ignore the speed-of-light rule since we can-so far-see no way around it. The author a.s.sumes that problem, or perhaps others equally beyond our present ability to solve, to be answered, and goes ahead from there. In such a case, of course, fair play demands that all such matters be mentioned as early as possible in the story, so that the reader has a chance to let his imagination grow into the new background.

I always feel cheated when the problem which has been developed in a story is solved by the discovery in the last chapter of antigravity, time travel, or a method of reviving the dead; such things must be at least near full development and known to the reader long enough in advance to give him a chance to foresee the ending. I have always a.s.sumed, perhaps wrongly, that others felt as I do; I try to write accordingly.

In Mission of Gravity I've been playing this game as fairly as I could.

The author has one disadvantage, of course; all his moves must be completed first. Once the story is in print, the other side can take all the time in the world to search out the mistakes; they can check with reference libraries or write letters to universities, if they play the game that seriously. Sooner or later the mistakes will come out; there is no further chance to correct them. If Mission of Gravity contains such errors, they're out of my hands now. I did my best to avoid them, but you still have a good chance to win. As I said, my moves were fun, not work.

The basic idea for the story came nearly ten years ago. In 1943 Dr. K. Aa. Strand published the results of some incredibly-to anyone but an astronomer-painstaking work on the orbit of the binary star 61 Cygni, a star otherwise moderately famous for being the first to have its parallax, and hence its distance, measured. In solving such a problem, the data normally consist of long series of measurements of the apparent direction and distance of one star from the other; if the stars are actually moving around each other, and the observations cover a sufficient fraction of a revolution, it is ordinarily possible if not easy to compute the actual relative orbit of the system-that is, the path of one a.s.suming that the other is stationary. Dr. Strand's work differed from the more usual exercises of this type in that his measures were made from photographs. This eliminated some of the difficulties usually encountered in visual observation, and supplied a number of others; but there was a net gain in overall accuracy, to the extent that he was not only able to publish a more accurate set of orbital elements than had previously been available, but to show that the orbital motion was not regular.

The fainter star, it seemed, did not move around the brighter in a smooth ellipse at a rate predictable by the straightforward application of Kepler's laws. It did, however, move in a Keplerian path about an invisible point which was in turn traveling in normal fashion about the other sun.

There was nothing intrinsically surprising about this discovery; the implication was plain. One of the two stars-it was not possible to tell which, since measures had been made a.s.suming the brighter to be stationary-was actually accompanied by another, invisible object; the invisible point which obeys the normal planetary and stellar laws was the center of gravity of the star-unknown object system. Such cases are by no means unusual.

To learn which of the two suns is actually attended by this dark body, we would have to have more observations of the system, made in relation to one or more stars not actually part thereof. Some stars exist near enough to the line of sight for such observations to be made, but if they have been reduced and published the fact has not come to my attention. I chose to a.s.sume that the object actually circles the brighter star. That may cost me a point in the game when the facts come out, but I won't be too disheartened if it does.

There was still the question of just what this object was. In other such cases where an invisible object betrayed its presence by gravity or eclipse, as in the system of Algol, we had little difficulty in showing that the companion was a star of some more or less normal type-in the case of Algol, for example, the "dark" body causing the princ.i.p.al eclipse is a sun larger, hotter, and brighter than our own; we can tell its size, ma.s.s, luminosity, and temperature with very considerable precision and reliability.

ORBIT of MESKLIN The positions of the isotherms and time of isotherm crossing are approximate and a.s.sume that the sun is 61 Cygni A In the case of the 61 Cygni system, the normal methods were put to work; and they came up immediately with a disconcerting fact. The period and size of the orbit, coupled with the fairly well-known ma.s.s of the visible stars, indicated that the dark body has a ma.s.s only about sixteen thousandths that of the sun-many times smaller than any star previously known. It was still about sixteen times the ma.s.s of Jupiter, the largest planet we knew. Which was it-star or planet? Before deciding on the cla.s.sification of an object plainly very close to the borderline, we must obviously decide just where the borderline lies.

For general purposes, our old grade-school distinction will serve: a star shines by its own light, while a planet is not hot enough for that and can be seen only by reflected light from some other source. If we restrict the word "light" to mean radiation we can see, there should be little argument, at least about definitions. (If anyone brings up nontypical stars of the VV2 Cephei or Epsilon2 Aurigae cla.s.s I shall be annoyed.) The trouble still remaining is that we may have some trouble deciding whether this Cygnus object shines by intrinsic or reflected light, when we can't see it shine at all. Some educated guessing seems in order.

There is an empirical relation between the ma.s.s of a star, at least a mainsequence star, and its actual brightness. Whether we would be justified in extending this relation to cover an object like 61 Cygni C-that is, third brightest body in the 61 Cygni system-is more than doubtful, but may be at least suggestive. If we do, we find that its magnitude as a star should be about twenty or a little brighter. That is within the range of modern equipment, provided that the object is not too close to the glare of another, brighter star and provided it is sought photographically with a long enough exposure. Unfortunately, 61 C will never be more than about one and a half seconds of arc away from its primary, and an exposure sufficient to reveal the twentieth magnitude would burn the image of 61 A or B over considerably more than one and a half seconds' worth of photographic plate. A rotating sector or similar device to cut down selectively on the light of the brighter star might do the trick, but a job of extraordinary delicacy would be demanded. If anyone has attempted such a task, I have not seen his published results.

If we a.s.sume the thing to be a planet, we find that a disk of the same reflecting power as Jupiter and three times his diameter would have an apparent magnitude of twenty-five or twenty-six in 61 C's location; there would be no point looking for it with present equipment. It seems, then, that there is no way to be sure whether it is a star or a planet; and I can call it whichever I like without too much fear of losing points in the game.

I am supposing it to be a planet, not only for story convenience but because I seriously doubt that an object so small could maintain at its center the temperatures and pressures necessary for sustained nuclear reactions; and without such reactions no object could maintain a significant radiation rate for more than a few million years. Even as a planet, though, our object has characteristics which will call for thought on any author's part.

Although sixteen times as ma.s.sive as Jupiter, it is not sixteen times as bulky. We know enough about the structure of matter now to be sure that Jupiter has about the largest volume of any possible "cold" body. When ma.s.s increases beyond this point, the central pressure becomes great enough to force some of the core matter into the extremely dense state which we first knew in white dwarf stars, where the outer electronic sh.e.l.ls of the atoms can no longer hold up and the nuclei crowd together far more closely than is possible under ordinary-to us, that is-conditions. From the Jupiter point on up, as ma.s.s increases the radius of a body decreases-and mean density rises enormously. Without this effect-that is, if it maintained Jupiter's density with its own ma.s.s-61 C would have a diameter of about two hundred fifteen thousand miles. Its surface gravity would be about seven times that of the Earth. However, the actual state of affairs seems to involve a diameter about equal to that of Ura.n.u.s or Neptune, and a surface gravity over three hundred times what we're used to.

Any science fiction author can get around that, of course. Simply invent a gravity screen. No one will mind little details like violation of the law of conservation of energy, or the difference of potential across the screen which will prevent the exchange of anything more concrete than visual signals; no one at all. No one but Astounding readers, that is; and there is my own conscience too. I might use gravity screens if a good story demanded them and I could see no legitimate way out; but in the present case there is a perfectly sound and correct means of reducing the effective gravity, at least for a part of a planet's surface. As Einstein says, gravitational effects cannot be distinguished from inertial ones. The so-called centrifugal force is an inertial effect, and for a rotating planet happens to be directed outward-in effect-in the equatorial plane. I can, therefore, set my planet spinning rapidly enough to make the characters feel as light as I please, at least at the equator.

If that is done, of course, my nice new world will flatten in a way that would put Saturn to shame; and there will undoubtedly be at least one astronomer reading the story who will give me the raised eyebrow if I have it squashed too little or too much. Surely there is some relation between ma.s.s, and rate of spin, and polar flattening- I was hung up on that problem for quite a while. Since I had other things to do, I didn't really concentrate on it; but whenever a friend whose math had not collapsed with the years crossed my path, I put it up to him. My own calculus dissolved in a cloud of rust long, long ago. I finally found the answer-or an answer-in my old freshman astronomy text, which is still in my possession. I was forcibly reminded that I must also take into account the internal distribution of the planet's ma.s.s; that is, whether it was of h.o.m.ogeneous density or, say, almost all packed into a central core. I chose the latter alternative, in view of the enormous density almost certainly possessed by the core of this world and the fact that the outer layers where the pressure is less are presumably of normal matter.

I decided to leave an effective gravity of three times our own at the equator, which fixed one value in the formula. I had the fairly well known value for the ma.s.s, and a rough estimate of the volume. That was enough. A little slide-rule work gave me a set of characteristics which will furnish story material for years to come. I probably won't use it again myself-though that's no promise2-and I hereby give official permission to anyone who so desires to lay scenes there. I ask only that he maintain reasonable scientific standards, and that's certainly an elastic requirement in the field of science fiction.

The world itself is rather surprising in several ways. Its equatorial diameter is forty-eight thousand miles. From pole to pole along the axis it measures nineteen thousand seven hundred and forty, carried to more significant figures than I have any right to. It rotates on its axis at a trifle better than twenty degrees a minute, making the day some seventeen and three quarter minutes long. At the equator I would weigh about four hundred eighty pounds, since I hand-picked the net gravity there; at the poles, I'd be carrying something like sixty tons. To be perfectly frank, I don't know the exact value of the polar gravity; the planet is so oblate that the usual rule for spheres, to the effect that one may consider all the ma.s.s concentrated at the center for purposes of computing surface gravity, would not even be a good approximation if this world were of uniform density. Having it so greatly concentrated helps a great deal, and I don't think the rough figure of a little under seven hundred Earth gravities that I used in the story is too far out; but anyone who objects is welcome if he can back it up. (Some formulae brought to my attention rather too late to be useful suggest that I'm too high by a factor of two; but whose formulae are the rougher approximations I couldn't guess-as I have said, my math has long since gone to a place where I can't use it for such things. In any case, I'd still stagger a bit under a mere thirty tons.) CROSS SECTION of MESKLIN.

Shaded portion represents Earth on the same scale. Dotted lines are arctic and antarctic circles. Listed values of gravity (effective), represented by numbers at appropriate lat.i.tudes, are very approximate.

I can even justify such a planet, after a fashion, by the current(?) theories of planetary system formation. Using these, I a.s.sume that the nucleus forming the original protoplanet had an orbit of cometary eccentricity, which was not completely rounded out by collisions during the process of sweeping up nearly all the raw material in the vicinity of its sun. During the stage when its "atmosphere" extended across perhaps several million miles of s.p.a.ce, the capture of material from orbits which were in general more circular than its own would tend to give a spin to the forming world, since objects from outside its position at any instant would have a lower velocity than those from farther in. The rotation thus produced, and increased by conservation of angular momentum as the ma.s.s shrank, would be in the opposite direction to the world's...o...b..tal motion. That does not bother me, though; I didn't even mention it in the story, as nearly as I can now recall.

The rate of spin might be expected to increase to the point where matter was actually shed from the equator, so I gave the planet a set of rings and a couple of fairly ma.s.sive moons. I checked the sizes of the rings against the satellite orbits, and found that the inner moon I had invented would produce two gaps in the ring similar to those in Saturn's decoration. The point never became important in the story, but it was valuable to me as atmosphere; I had to have the picture clearly in mind to make all possible events and conversations consistent. The inner moon was ninety thousand miles from the planet's center, giving it a period of two hours and a trifle under eight minutes. The quarterperiod and third-period ring gaps come about twelve and nineteen thousand miles respectively from the world's surface. The half-period gap would fall about thirty-three thousand miles out, which is roughly where Roche's Limit would put the edge of the ring anyway (I say roughly, because that limit depends on density distribution too.) SCALE DRAWING of MESKLIN and RING SYSTEM Inner ring reaches to less than 1,000 miles of planet's surface; gaps are of corresponding width.

On the whole, I have a rather weird-looking object. The model I have of it is six inches in diameter and not quite two and a half thick; if I added the ring, it would consist of a paper disk about fourteen inches in diameter cut to fit rather closely around the plastic wood spheroid. (The model was made to furnish something to draw a map on; I like to be consistent. The map was drawn at random before the story was written; then I bound myself to stick to the geographic limitations it showed.) I was tempted, after looking at it for a while, to call the book Pancake in the Sky, but Isaac Asimov threatened violence.3 Anyway, it looks rather more like a fried egg.

There are a lot of characteristics other than size, though, which must be settled before a story can be written. Since I want a native life form, I must figure out just what conditions that form must be able to stand. Some of these conditions, like the temperature and gravity, are forced on me; others, perhaps, I can juggle to suit myself. Let's see.

Temperature depends, almost entirely, on how much heat a planet receives and retains from its sun. 61 Cygni is a binary system, but the two stars are so far apart that I needn't consider the other one as an influence on this planet's temperature; and the one which it actually circles is quite easy to allow for. Several years ago I computed, partly for fun and partly for cases like this, a table containing some interesting information for all the stars within five pa.r.s.ecs for which I could secure data. The information consists of items such as the distance at which an Earth-type planet would have to revolve from the star in question to have the present temperatures of Earth, Venus, and Mars, and how long it would take a planet to circle the sun in question in each such orbit. For 61 Cygni A, the three distances are about twenty-eight, thirty-nine, and sixty-nine million miles, respectively. As we have seen, 61 C's...o...b..t is reasonably well known; and it is well outside any of those three distances. At its closest-and a.s.suming that the primary star is 61 A-it gets almost near enough to be warmed to be about fifty below zero, Centigrade.4 At the other end of its rather eccentric orbit, Earth at least would cool to about minus one hundred eighty, and it's rather unlikely that this world we are discussing gets too much more out of the incoming radiation. That is a rather wide temperature fluctuation.

The eccentricity of the orbit is slightly helpful, though. As Kepler's laws demand, the world spends relatively little time close to its sun; about four fifths of its year it is outside the minus one hundred fifty degree isotherm, and it is close enough to be heated above minus one hundred for only about one hundred thirty days of its eighteen-hundred-day year-Earth days, of course. Its year uses up around one hundred forty-five thousand of its own days, the way we've set it spinning. For practical purposes, then, the temperature will be around minus one hundred seventy Centigrade most of the time. We'll dispose of the rest of the year a little later.

Presumably any lifeform at all a.n.a.logous to our own will have to consist largely of some substance which will remain liquid in its home planet's temperature range. In all probability, the substance in question would be common enough on the planet to form its major liquid phase. If that is granted, what substance will meet our requirements?

Isaac Asimov and I spent a pleasant evening trying to find something that would qualify. We wanted it not only liquid within our temperature limits, but a good solvent and reasonably capable of causing ionic dissociation of polar molecules dissolved in it. Water, of course, was out; on this world it is strictly a mineral. Ammonia is almost as bad, melting only on the very hottest days. We played with ammonia's a.n.a.logues from further along the periodic table-phosphine, arsine, and stibine-with carbon disulfide and phosgene, with carbon suboxide and hydrogen fluoride, with saturated and unsaturated hydrocarbons both straight and with varying degrees of chlorine and fluorine subst.i.tution, and even with a silicone or two. A few of these met the requirements as to melting and boiling points; some may even have caused dissociation of their solutes, though we had no data on that point for most. However, we finally fell back on a very simple compound.

It boils, unfortunately, at an inconveniently low temperature, even though we a.s.sume a most unlikely atmospheric pressure. It cannot be expected to be fruitful in ions, though as a hydrocarbon it will probably dissolve a good many organic substances. It has one great advantage, though, from my viewpoint; it would almost certainly be present on the planet in vast quant.i.ties. The substance is methane-CH4.

Like Jupiter, this world must have started formation with practically the "cosmic" composition, involving from our viewpoint a vast excess of hydrogen. The oxygen present would have combined with it to form water; the nitrogen, to form ammonia; the carbon to form methane and perhaps higher hydrocarbons. There would be enough hydrogen for all, and plenty to spare-light as it is, even hydrogen would have a hard time escaping from a body having five thousand times the ma.s.s of Earth once it had cooled below red heat-at first, that is. Later, when the rotational velocity increased almost to the point of real instability, it would be a different story; but we'll consider that in a moment. However, we have what seems to be a good reason to expect oceans of methane on this world; and with such oceans, it would be reasonable to expect the appearance and evolution of life forms using that liquid in their tissues.

But just a moment. I admitted a little while ago that methane boils at a rather lower temperature than I wanted for this story. Is it too low? Can I raise it sufficiently by increasing the atmospheric pressure, perhaps? Let's see. The handbook lists methane's critical temperature as about minus eighty-two degrees Centigrade. Above that temperature it will always be a gas, regardless of pressure; and to bring its boiling point up nearly to that value, a pressure about forty-six times that of our own atmosphere at sea level will be needed. Well, we have a big planet, which should have held on to a lot of its original gases; it ought to have a pressure of hundreds or even thousands of atmospheres-whoops! we forgot something.

At the equator, effective gravity-gravity minus centrifugal effect-is three times Earth normal. That, plus our specification of temperature and composition of the atmosphere, lets us compute the rate at which atmospheric density will decrease with alt.i.tude. It turns out that with nearly pure hydrogen, three g's, and a temperature of minus one hundred fifty for convenience, there is still a significant amount of atmosphere at six-hundred-miles alt.i.tude if we start at forty-odd bars for surface pressure-and at six hundred miles above the equator of this planet the centrifugal force due to its rotation balances the gravity! If there had ever been a significant amount of atmosphere at that height, it would long since have been slung away into s.p.a.ce; evidently we cannot possibly have a surface pressure anywhere near forty-six atmospheres. Some rough slide-rule work suggests eight atmospheres as an upper limit-I used summer temperatures rather than the annual mean.

At that pressure methane boils at about minus one hundred forty-three degrees, and for some three hundred Earth days, or one-sixth of each year, the planet will be in a position where its sun could reasonably be expected to boil its oceans. What to do?

Well, Earth's mean temperature is above the melting point of water, but considerable areas of our planet are permanently frozen. There is no reason why I can't use the same effects for 61 C; it is an observed fact that the axis of rotation of a planet can be oriented so that the equatorial and orbital planes do not coincide. I chose for story purposes to incline them at an angle of twenty-eight degrees, in such a direction that the northern hemisphere's midsummer occurs when the world is closest to its sun. This means that a large part of the northern hemisphere will receive no sunlight for fully three quarters of the year, and should in consequence develop a very respectable cap of frozen methane at the expense of the oceans in the other hemisphere. As the world approaches its sun the livable southern hemisphere is protected by the bulk of the planet from its deadly heat output; the star's energy is expended in boiling off the north polar "ice" cap. Tremendous storms rage across the equator carrying air and methane vapor at a temperature little if any above the boiling point of the latter; and while the southern regions will warm up during their winter, they should not become unendurable for creatures with liquid methane in their tissues.

Precession should be quite rapid, of course, because of the tremendous equatorial bulge, which will give the sun's gravity a respectable grip even though most of the world's ma.s.s is near its center. I have not attempted to compute the precessional period, but if anyone likes to a.s.sume that a switch in habitable hemispheres occurring every few thousand years has kept the natives from building a high civilization I won't argue. Of course, I will also refrain from disagreement with anyone who wants to credit the periodic climate change with responsibility for the development of intelligence on the planet, as our own ice ages have sometimes been given credit for the present mental stature of the human race. Take your pick. For story purposes, I'm satisfied with the fact that either possibility can be defended.

The conditions of the planet, basically, are pretty well defined. There is still a lot of detail work. I must design a life form able to stand those conditions-more accurately, to regard them as ideal-which is not too difficult since I don't have to describe the life processes in rigorous detail. Anyone who wants me to will have to wait until someone can do the same with our own life form. Vegetation using solar energy to build up higher, unsaturated hydrocarbons and animal life getting its energy by reducing those compounds back to the saturated form with atmospheric hydrogen seemed logical enough to me. In the story, I hinted indirectly at the existence of enzymes aiding the reduction, by mentioning that plant tissues would burn in the hydrogen atmosphere if a sc.r.a.p or two of meat were tossed onto the fuel.

The rest of the detail work consists of all my remaining moves in the game-finding things that are taken for granted on our own world and would not be true on this one. Such things as the impossibility of throwing, jumping, or flying, at least in the higher lat.i.tudes; the tremendously rapid decrease of air density with height in the same regions, producing a mirage effect that makes the horizon seem above an observer all around; the terrific Coriolis force that splits any developing storm into a series of relatively tiny cells-and would make artillery an interesting science if we could have any artillery; the fact that methane vapor is denser than hydrogen, removing a prime Terrestrial cause of thunderstorm and hurricane formation; the rate of pressure increase below the ocean surface, and what that does to the art of navigation; the fact that icebergs won't float, so that much of the ocean bottoms may be covered with frozen methane; the natural preference of methane for dissolving organic materials such as fats rather than mineral salts, and what that will do to ocean composition-maybe icebergs would float after all. You get the idea.

The trouble was, I couldn't possibly think of all these things in advance; time and again a section of the story had to be rewritten because I suddenly realized things couldn't happen that way. I must have missed details, of course; that's where your chance to win the game comes in. I had an advantage; the months during which, in my spare hours, my imagination roamed over Mesklin's vast areas in search of inconsistencies. Now the advantage is yours; I can make no more moves in the game, and you have all the time you want to look for the things I've said which reveal slips on the part of my imagination.

Well, good luck-and a good time, whether you beat me or not.

ADDENDUM TO "WHIRLIGIG WORLD".

When Mission of Gravity was finished in late 1952, I had a perfectly honest degree in astronomy. I nevertheless made a few mistakes, including one in basic physics; I said, somewhere in the story, that the Bree would sail faster with the wind behind her. Predictably, a sailor caught that one.

More seriously, I erroneously took for granted that the figure of rotation which was Mesklin would be an oblate spheroid, and did all the gravity calculation (on a slide rule) a.s.suming that most of its ma.s.s was degenerate matter very close to the center. John Campbell told me when he accepted the story that a mathematician had told him that Euler must be spinning in his grave, but I still don't know what theorem I violated.

More usefully, a few years after the story was published, members of the M.I.T. Science Fiction Society (MITSFS) managed to get enough computer time to figure out more nearly what the planet's shape would be. They were presumably right; all I could console myself with was the realization that I had written the story to give pleasure to people even if that wasn't quite the specific pleasure I'd had in mind.

I eventually did get a computer, wrote a relevant program in BASIC6, and came up with an object looking more like the discus used in field and track sports-an object fairly sharply curved at the poles, much flatter in the midlat.i.tudes, and coming almost to a real edge at the equator. With arbitrarily chosen three g's at the equator, the polar gravity came out to only about 275, as I recall.

I a.s.sume that readers with appropriate background knowledge and computer hardware will want to check this. Maybe someone will want to write a book on the things that minor differences in the basic a.s.sumptions will do to Mesklin's shape.

Personally, I wound up doing forty years of high school teaching instead of being an astronomer essentially because of my mathematical weaknesses.

BY HAL CLEMENT.