Weather Report

A Study of the Solar System

Article No. 12 by John W. Campbell, Jr. (pages 57-61 of May 1937's Astounding Stories)

THE British Nautical Almanac of 1850 lists the information that the Georgian Planet is 32,000 miles in diameter, 15 times as massive as the Earth and some 1,780 millions of miles from the Sun. This major planet was discovered, the tables show, by William Herschel (who became Sir William in honor of that accomplishment).

Peculiarly, Herschel, though universally credited with the discovery of the Georgian Planet, was not the first to see and record it, did not recognize it as a planet, and didn't know what kind of orbit it had. Finally, he didn't give it the modern name. In March of 1781 he first noticed that a certain, sixth-magnitude star displayed a fuzzy, indistinct image in his telescope.

That blurred image made him suspicious, and he watched it carefully for several nights, in order to apply the crucial test. If it were a body in the solar system, as he suspected, the Earth's motion in its orbit round the Sun would produce an apparent motion of the "star." The "star" moved; Herschel was convinced that he had discovered a new member of the solar system and joyously announced to the Royal Society that he had discovered a new -- comet. His data was published, and every one was interested. A number of observers watched and calculated on it. But it was not Herschel who pointed out that it could not possibly be a comet, that the elements of its orbit were such as to prove it to be a true planet.

At that time, when the first newly discovered planet of history was to be named, the custom of giving all planets names derived from Greek and Roman mythology had not been firmly fixed. Herschel immediately proposed the name Georgius Sidus, in honor of His Gracious Majesty, King George III, whose graciousness had not been appreciated, it had recently appeared, by certain of the transatlantic colonials.

England, being pleased, adopted the name, and England, being conservative, stuck with it from then to the year 1850, when the Nautical Almanac finally gave it up. In the meantime, a French astronomer had proposed the name Herschel, in honor of the discoverer. That did not succeed. Uranus was finally adopted. Bode, the great astronomer who was responsible for the purely empirical relationship called Bode's law, made that proposal. An appropriate name, Uranus, the planet of Urania, the muse of astronomy.

Curiously, Uranus is a sixth-magnitude object; that is, it is just bright enough to be seen by a trained, unaided eye, if the observer knows what he is looking for and looks in the right place. It is easily visible in a small telescope. But so tremendously distant is it -- 1,783,000,000 miles -- that it appears small despite its 32,000-mile diameter.

It displayed no disk recognizable as a planet. Its motion in the sky was extremely slow, due to the immense distance. These two factors alone had kept men from recognizing it as a planet. In fact, Lemonnier had previously observed and recorded it on twelve nights and barely missed recognizing it as a member of the solar system. It had been observed and recorded as a star many times in earlier years, and these earlier, unknowing observations helped to establish its orbit.

However, only within the last few years have we gained accurate knowledge of the axis and rotation of Uranus. The ease with which a planet can be observed depends on three main things: its position in the sky with respect to the Sun; the amount of light the planet receives from the Sun; and the distance of the planet from us. This last is important not because distance makes things look smaller -- though that is not negligible -- but because light intensity falls off as the square of the distance increases.

A beautiful example of that is our knowledge of the satellite system of Jupiter as compared to our knowledge of Uranus' moons. Light that reaches us from Jupiter's moons has traveled about 500,000,000 miles from the Sun to the Moon, and then another 400,000,000 miles back to Earth -- a total of 900,000,000 miles. The smallest discovered satellite of Jupiter is only some 15 miles in diameter. But light that reaches us from Uranus' smallest moon, Umbriel, has traveled 1,783,000,000 miles out, and nearly 1,700,000,000 miles back -- 3,483,000,000 miles. By that time it is not surprising that it is slightly diluted. Since it has gone nearly 3 times as far it is almost 9 times as hard to observe as Jupiter. Umbriel is 430 miles in diameter.

WE KNOW only 4 satellites: Ariel, 560 miles; Umbriel and Titania, 1000; and Oberon, 900 miles in diameter. Oberon, farthest from Uranus, is only 364,000 miles out. It seems almost a certainty that Uranus has at least one or two more, but they are not going to be found very readily. To see those known to-day requires the most powerful telescopes in existence. (The 200-inch telescope may make some change, but not much.)

There is another difficulty. All those satellites are within about one third of a million miles of 32,000-mile Uranus. Uranus is cold, apparently a surface of snow. It is intensely brilliant, compared to the satellites, and the angular distance between two bodies separated only one third of a million miles, more than one and three quarter billion miles distant is almost nonexistent. By the time you get enough light-gathering power in action to bring out small moons, Uranus has become so brilliant he fogs the plates.

The satellites are interesting because of their peculiar orbits. But Uranus is even more interesting, because of the wonderful and unholy seasons the planet has. From the accompanying sketches, you can see the relationship between its axis and the light of the Sun.

Uranus has the systemic prize for seasons. The arctic circle misses the antarctic circle by a scant 16 degrees. The "tropics," consequently, extend for 8 degrees, and during the extreme seasons (winter and summer), you will notice that the tropic zone, or equatorial region, is the only part of the planet which has day and night.

The one pole is facing almost directly toward the Sun, and simply spinning in useless circles, bathing in Sunlight. The other pole is freezing in the cold of outer space.

To finish the picture, remember that each of Uranus' seasons is measured in decades, not months. A year equals 84 of our years. For 42 consecutive years the Sun never sets at the north pole; while for all those 42 years the south pole never sees it. A man could be born, raise a family and have grandchildren before he saw the Sun for the first time!

And as on Earth, dawn at the south pole means sunset at the north pole, and spring or fall for the rest of the planet. During that transitional season, and only then, the rest of the planet has day-and-night alternations. Then, for a while, the tropic zone does become the warmest part of the planet, directly under the Sun. This (Earth) year it is spring on Uranus -- about March 10th, so to speak. What day the equator does get during the rest of the year simply means that for a brief period each day the Sun barely edges its way up over the horizon, hangs there a bit, then sinks down again. It does not rise more than 8° above the horizon during the winter.

What sort of temperature does the pole that is baking in the warm rays of the Sun attain? The weak Sunlight can raise the temperature to only about -185°C. The opposite pole, meanwhile, cools off during the 42-year cold snap. We can't measure it, because we are so near the Sun that we are practically in line with it; therefore, the Sun is always at our back, and we never see the night side of Uranus. It probably gets somewhere in the region of -220°C.

It would get colder than that but for one other feature characteristic of the giant planets: every one of them, from Jupiter to Neptune, can legitimately call the 200-mile-an-hour wind, which constitutes Earth's record, a gentle zephyr. On Uranus we can't ever see clouds, but it is a pretty safe bet that the winds that shriek over that planet would tear up a mountain.

WOULD that planet ever be useful to men? Certainly there is not, and never has been, any life on that ultra-frozen world of intolerable, crazy seasons. Suppose, somehow, a space expedition were to make its way to Uranus, land, and establish a space dome with the necessary heating and aërating devices. What sort of record of meteorological conditions would they bring back?

They would land on the pole facing the Sun. The atmosphere must be deep, enormously deep, with a tremendous pressure. But -- it may not be so high that space domes could not be built to withstand it here, for the temperature is low, horribly low. Ammonia, methane, hydrogen, helium, neon, the rare gases must make up the atmosphere.

The spectroscope shows us, powerful, broad bands of methane, and weak ammonia lines. There is reason enough for the latter. Ammonia freezes to a solid at about -77°C. Even solids give off some vapor (very noticeable with such things as camphor or iodine. Cheese is noted for its vapors, particularly Limburger) so there is a little ammonia present. The atmosphere must be wonderfully clear, utterly cloudless, for the ammonia is almost entirely frozen out. The methane, even, is nearly frozen out; the strength of the methane bands is probably due to the fact that we can see light that has passed through hundreds on hundreds of miles of diffuse vapor.

Our explorers look up to a jet-black sky, probably with dim, violently twinkling stars. The Sun is a tremendously brilliant star, shaking and wavering in the vast air currents sweeping high over-head. There is light enough here, light that seems utterly heatless, merely serving to bring out more vividly the vast, endless infinity of bleakness. Drift snow -- that stirs and moves restlessly on the calmest days, white, granular stuff -- solid methane.

As the days pass, the sun wabbles back and forth in a sky from which it never sets, year on year, of Earth time. But slowly, invisibly, the whole, vast landscape is sinking, sinking downward. The solid methane snow and packed, glacial ice beneath begin to appear.

As summer extends on and on, the "warmth" of the distant Sun, still as bright as 3,000 full Moons, warms the region enough to cause a slow sublimation of the solid methane. It does not melt, but vanishes like dry ice on Earth, passing directly to vapor. The drift snow ends, as the evaporating landscape settles down to the deep, heard-packed layers beneath. Test drills of the explorers bite down -- down -- down into the stuff, mile on mile. They know it is useless to hope. They get only corings of solid methane. For hundreds on hundreds of miles that layer of solid methane, ammonia and ice must extend. There is no rock, no mineral substance to be detected.

Slowly, the Sun moves toward the horizon as the end of the long summer approaches. They are not exactly at the poles, and for a brief time day and night alternate. The temperature is falling; winds are beginning to howl nearer them now. The high winds stop their steady, endless sweep and become troubled, circling and backing irregularly. Occasional howling gales sweep across the land at hundreds of miles per hour, scouring the endless, white plains. Four dim, lightless moons swing across the sky, day and night.

Then the Sun sets for the last time. Winter sets in. The gales become steady. They shriek and scream across the land, and snow -- solid methane -- begins to reappear. The opposite pole is warming, and the methane that fell there during the past season is subliming, joining the immense gales sweeping around the planet, and depositing here.

A new generation of investigators has taken over the station. They will not see the Sun until relief ships carry them away. Were they marooned here, they might die, after a full life, without seeing the Sun. The only heat that reaches this frozen waste is the heat given up by the methane that is falling as snow. It is changing from vapor to solid, releasing the heat that is absorbed at the opposite pole, in changing from solid to vapor.

It is death to step beyond the passages of the dome. They have their protective suits, but ten steps from the doorways they would be hopelessly lost in the solid wall of driving, drifting snow, were it even possible to stand motionless in the 500-mile-an-hour gale. Uranus is absolutely featureless as seen from Earth; the age-long drift and shift of countless billions of tons of methane has seen to that.

But a new danger menaces the domes. The methane is redepositing. Already within a few months, they are completely buried by the drift, which is still getting deeper and deeper. It is impossible to get out now; there is 500 feet of solid methane above the domes. Lifting arrangements force them upward to the surface. Again and again, as the winter continues, they must rise. Before the Sun shines here again, they may have lifted this dome miles upward, to keep atop the infinitude of solid methane that the endless, whistling gales are bringing.

But they leave. There is no need to stay longer, no need ever to come again. For two billion years these winters have alternated with the 42-year summers, each like the last. For billions more they will -- unchanged. There is no life, no value in the planet. Any minerals it might have are buried beneath thousands on thousands of miles of solid methane, ammonia and ice. A featureless, useless world trailed by useless, frozen corpses of satellites. Whatever treasures of mineral or other wealth the rocky core may hold, no man will ever reach.

No man will ever care. The very meteorological conditions would never be investigated: the insane weather of a useless planet.

So much more
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