Heavy Planet (62 page)
Authors: Hal Clement
“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.
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 assistance. 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 assembly 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.
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.”
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.
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 assist 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, circumstances 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.
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.
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.
Writing a science fiction story is fun, not work. If it were work I wouldn’t be writing this article, which would then constitute a chapter for a textbook. I don’t plan to write such a text, since if the subject is teachable I’d be creating competition 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 passing reference is made to travel through a “hyperspace” 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 assumes 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 assumed, perhaps wrongly, that others felt as I do; I try to write accordingly.
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 assumed, 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.
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.
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 assuming 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.
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
assuming
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.
assuming
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 assume 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 principal eclipse is a sun larger, hotter, and brighter than our own; we can tell its size, mass, 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 assume 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 mass of the visible stars, indicated that the dark body has a mass only about sixteen thousandths that of the sun—many times smaller than any star previously known. It was still about sixteen times the mass of Jupiter, the largest planet we knew. Which was it—star or planet? Before deciding on the classification 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 VV
2
Cephei or Epsilon
2
Aurigae class 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.
2
Cephei or Epsilon
2
Aurigae class 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 mass 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.
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 assume 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.
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 massive 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 mass 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 shells 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 mass 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 mass—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 Uranus or Neptune, and a surface gravity over three hundred times what we’re used to.
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 mass 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 shells 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 mass 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 mass—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 Uranus 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.
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 mass, 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 mass; that is, whether it was of homogeneous 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.
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 mass; that is, whether it was of homogeneous 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 mass, 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 promise
2
—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.
2
—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.
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