Solar Fantasies
February 3rd, 2006 by threesixtyAs of this writing, the exploration of the farther reaches of the Solar System, by spacecraft, lander, and telescope, continues apace. Cassini continues its swings around Saturn, with each pass discovering new facts and new questions about the planet and its moons. The MER rovers on Mars roll into new landscapes every day (well, Spirit does; Opportunity’s been stuck in one place for a while, though it should start moving again soon). The New Horizons spacecraft was launched a few days ago and is en route for Pluto; while recent measurements of thermal emissions from the trans-Neptunian object 2003 UB313 show it to be about 30% bigger than Pluto, making it a candidate for a tenth planet.
But there was a time — not so long ago, a little over forty years, well within living memory (and even those of us who are not quite old enough to remember the era directly may have had a little contact with it by being exposed to out-of-date astronomy books) — when we didn’t have to explore the Solar System with satellites — we’d already explored it in our imaginations for sixty-odd years, and we knew what it was like, what we would find when (not if) we ventured off Earth in our rocket ships. And although pretty much everything we knew was wrong — and though the Solar System turns out to be, in some ways, weirder than we ever imagined — nothing quite recaptures the sheer romance of that vision of our planetary neighborhood. Founded, originally, on the science of the day, it ended up taking on a life of its own in pulp magazines, comic books and science fiction novels — only, in the end, to be brutally despatched by the same science that had first breathed life into it.
Let’s take a look at some of the longer-lived fantasies about our solar system, how they were born, and how they died:
Vulcan (1859-1916)
First, one of the shorter-lived fantasies, which was only occasionally echoed in the literature. There was, in 1859, an erroneous report of a telescopic observation of a small planet moving across the Sun, inside the orbit of Mercury. The astronomer Urbain Le Verrier (who contributed to Galle’s discovery of Neptune) called this imaginary planet “Vulcan”. Repeated telescopic searches failed to turn anything up (were the Vulcanians blocking the astronomers using telepathic thought-screens?). But some physicists thought it might account for the precession of Mercury’s highly elliptical orbit. In 1916, however, Einstein’s theory of General Relativity accounted for Mercury’s orbit without reference to Vulcan. Nonetheless, Vulcan occasionally popped up in science fiction stories over the next decades, and perhaps helped inspire the name of the Star Trek planet. The imaginary Vulcan never was very popular, however; being as close to the Sun as it was supposed to be, it would hardly be much more than an orbiting lump of charcoal, and so very uncomfortable.
Mercury (1889-1962)
The planet Mercury has always been rather difficult to observe, because it is so close to the Sun; good observations can only be made when it is at its greatest elongation — the farthest distance from the Sun, as viewed from Earth. For a long time nobody was able to make out anything on its surface. Then, in 1889, the Italian astronomer Giovanni Schiaparelli (who will show up again) claimed to show by observation that Mercury was tidally locked in its orbit — that is, like most of the larger planetary moons, its rotation (day) was the same as its revolution (year) and so it always had one face turned toward the object it revolved around, in this case the Sun. Mercury’s year was well known to be just under 88 days.
Mercury is so close to the Sun that it could be assumed that it would be extremely hot, assuming it exposed all of its sides to the Sun equally. However, if it was tidally locked, then one of its faces would always be turned away from the Sun, and would be not hot but freezing cold, as no sunlight would ever reach it. But if Mercury rocked back and forth in its orbit a little bit, as the Moon does, then there would be a narrow belt of twilight where the Sun would rise and set, just above and below the horizon. Temperatures in that zone might be fairly mild; and if Mercury had an atmosphere, the “twilight belt” could be habitable.
This was actually the scientific consensus for over sixty years, not merely science fiction. It had a grain of truth to it: Mercury’s rotation and revolution are synchronized, only instead of the ratio being 1:1, it is 3:2 (3 rotations for every 2 Mercurian years). As, by chance, the viewing geometry for observing Mercury from Earth is most favorable at just about every 2nd Mercurian year, which meant that the same face of Mercury would be visible in a sequence of such observations. The dream of the “twilight belt” died in 1962, when thermal measurements of Mercury’s “darkside” turned out to be far warmer than would be expected for a surface that never saw the Sun! In 1965, radio astronomy allowed for a precise determination of Mercury’s rotation period — 58.6 days.
There remains one smidgen of hope for those who miss the romance of the “twilight belt”; even though all of Mercury is exposed to the Sun, there are two places where the Sun is always on the horizon, and where certain craters might always be in darkness, namely, Mercury’s north and south poles. Astronomers guess that such permanently dark craters might hide caches of frozen water ice.
Venus (1918-1962)
The planet Venus was a complete mystery until comparatively recently. This is because it is shrouded in a layer of opaque haze which prevents visible light from returning from its surface. Even its rotation period could only be guessed at by attempting to observe cloud movements; but since, in visible light, Venus’ clouds barely show any differentiation at all, there was no consensus, with suggestions varying from a 24-hour day (like Earth’s) to a day synchronized with Venus’ 224.7-day year.
Venus was therefore open for all kinds of guesswork, almost all of it wrong. A correct generalization was that, since Venus was closer to the Sun than Earth, it must be warmer. This is true; however, nobody correctly guessed how much warmer it would be. A further line of reasoning came from the supposition that the outer planets had formed earliest, and the inner planets later. Venus therefore must be younger than Earth, and should look like Earth in the past. As for the clouds, the first assumption was that they were clouds of water vapor, like those on Earth. But for Venus to be permanently clouded over, it must have enormous amounts of water and water vapor: it must be a soaked, soggy, swampy planet where it rained all the time.
Add these suppositions together, and you start looking into Earth’s past for a warmer, wetter, more primitive period. The Swedish chemist Svante Arrhenius, a believer in panspermia (the idea that all the planets had been ’seeded’ with life by spores from an outside source), declared in 1918 that “A very great part of the surface of Venus is no doubt covered with swamps, corresponding to those on the Earth in which the coal deposits are formed, except that they are about 30°C warmer”. His evocative description (much longer than the part quoted) of a humid Venus, covered in luxuriant vegetation, more humid than the Congo, and reminiscent of the tropical swamps of the Carboniferous period in Earth’s history (which Arrhenius may not have realized actually formed during a climatological cold snap) was so memorable that it persisted even after spectroscopic studies in the ’20s failed to detect any trace of water in Venus’ atmosphere at all. The concept of a desert Venus never caught on, and as late as the 1950s various proposals were made for a global ocean on Venus — including one made entirely of carbonated water! Fictional portrayals of Venus tended to alternate between a rainforest Venus and an oceanic Venus, and occasionally combined elements of both.
In the late 1950s, microwave studies seemed to show that Venus had a temperature of over 300°C; but nothing was conclusively proven until the Mariner 2 probe flew past Venus in 1962, showing that Venus temperature actually went up to about 500°C (over 900°F) — hot enough to melt lead (admittedly, a metal with a low melting point). It was devoid of water, though there was plenty of carbon dioxide — the high temperatures were driven by a greenhouse effect. The clouds were not water vapor, but droplets of sulfur dioxide and sulfuric acid. Venus’ rotation turned out actually to be slowly retrograde, with a period of 243 days.
Venus was also briefly thought to have a moon, called “Neith”. This spurious moon was observed near Venus at various points from 1672 on; detailed investigation showed that most of the claimed observations were actually stars that happened to be visible near Venus at the time of observation. Other instances may have been optical effects from imperfect telescopes. By the end of the 19th century, Venus was known to be moonless. Nonetheless, Leigh Brackett, in her story “The Moon that Vanished”, described a former Venusian moon which had impacted the planet, thus recapitulating the true story of the vanishing of the imaginary “Neith” as a fiction about the disappearance of a real moon of Venus.
Mars (1877-1895-1965)
The fantastic Mars is probably the best remembered of all the planets; most astronomers, anyway, recall that for a long time Mars was imagined to have impossibly straight lines criss-crossing its surface, called “canals”, and that some people insisted on attributing them to a Martian civilization (never mind that any structure big enough to be visible from another planet is well beyond the capability of any technology we know of).
The Martian canals were born in 1877, when Giovanni Schiaparelli discerned faint lines connecting the dark patches on Mars that had already been observed for centuries. After long periods of observation, he drew up a map — the best that had been made to that date — of Mars, showing it criss-crossed with over sixty such lines, some thicker, some thinner. In all cases they connected the darker areas; in some places, they came together and crossed in darker nodes.
In Schiaparelli’s scheme, these lines, which he called canali — Italian for grooves, channels, or canals (the term canale had already been used for a Martian feature by Father Secchi, though in a different sense) — spanned the Martian continents and drained into vast seas, which was how the dark patches on Mars appeared to him. The whole thing looked like some kind of planet-wide drainage system — could these canals have been deliberately built in order to dispose of excess water on a soggy Mars?
Schiaparelli’s discovery excited an amateur astronomer with a great deal of excess cash, one Percival Lowell, of a rich Massachusetts family. Retreating to Flagstaff, Arizona, he began observations of Mars from what was then a place with excellent viewing conditions — and he confirmed the existence of Schiaparelli’s canals (in his book Mars, published 1895). Not only that, but he saw more of them — in fact, he was seeing lines all over the place. (He also saw canals on Venus, but this was never made much of.) Of course he believed that they had to be made by intelligent Martians; no lines that straight, no system that vast, could be produced by nature. More importantly for the image people would have of Mars, Lowell saw lines running through what Schiaparelli had assumed were oceans; that meant that they could not be oceans at all, but had to be dry land. In fact, given that there were lines everywhere on Mars, all of Mars had to be dry as a bone, except for the polar caps (which Lowell assumed were made of water ice - which they in fact are, though overlaid with layers of frozen carbon dioxide). The dark patches — some observers perceived them as green — might be some sort of surface vegetation, seeing that they changed with the seasons.
Lowell’s conclusions on the dryness of Mars were correct, though for the wrong reasons. For of course, the lines did not exist. They were, at worst, entirely imaginary, and at best an attempt by the eye to connect minute features too small to be resolved individually. The dark patches (only green when perceived against the reddish background of the rest of Mars) were neither oceans nor vegetation, but simply a darker soil, whose borders shifted with each sandstorm - which on Mars can sometimes be planetwide in scale.
Many astronomers could not see the canals and disputed their existence. Cartographers of Mars sometimes drew canals, sometimes not, more often sketchily hinted at them. Lowell however believed firmly in their existence to his dying day; in his mind, they were the vast architectural project of a dying race on a waterless planet, doomed to maintain their existence by pumping water from the polar caps.
This is the vision of Mars that was taken up by science fiction writers, first of all by Edgar Rice Burroughs in his A Princess of Mars (first serialized in 1912). Burroughs was not, then or later, a good writer, but his choice of topic was new to most, and his picture of a decadent civilization on a dying planet overrun by savage, inhuman hordes left a deep impression. Burroughs introduced many details incompatible with Lowell’s vision — for instance, Lowell had to believe that, in order for his canal system to function, the surface of Mars had to be flat as a marble, something decidedly uninteresting for a fiction writer. Burroughs’ Mars had once had seas, but they had vanished; thus, once again, the history of beliefs about a planet was recapitulated in the fictitious history of the planet.
Later writers composed much better stories of Mars than Burroughs ever wrote, and many details of the fantasy Mars changed; but the general concepts of an arid Mars dotted with ancient decaying civilizations remained in stories of Mars written as late as the 1960s. The canals were usually marginal to the stories, but they were usually there. Then, in 1965, the Mariner 4 probe flew past Mars and took pictures which revealed a cratered, moonlike terrain — but no canals. Later probes showed more interesting features, including real “channels” — but these were natural features, carved during gigantic floods at a very ancient epoch in Mars’ past. The fantasy Mars of seventy years had ceased to exist.
Beyond Mars
Beyond Mars there were no such fixed conventions as dominated the mental images of Mercury, Venus, and Mars. The asteroid belt was viewed then as now, as collection of small, airless, mostly uninteresting rocks. There was however a theory that it had once been a single planet, which had then violently disintegrated — recapitulating, perhaps, the brief period in the early 19th century when the asteroid Ceres had indeed been accepted as a “fifth planet”. It is now generally thought that the asteroids never formed a single cohesive mass, though doubtless there has been a good deal of mutual impact and shattering of the original bodies of the belt. Some asteroids are little more than piles of rubble, only loosely held together by a very weak gravity. However, the “fifth planet” concept, suggesting some occult power that could have destroyed an entire world, figures in a number of science fiction stories, and may have suggested the idea of the exploding world of Krypton in the Superman mythos.
Jupiter and Saturn were sometimes regarded as habitable worlds; it was understood that their cloud layers obscured whatever surface lay beneath, but it was not until the late ’30s or ’40s that it entered the fictional consciousness that there was nothing underneath except more clouds. That left the moons of Jupiter and Saturn; consideration of their distance from the Sun might prompt the reflection that they were too cold for life; however, many writers simply ignored this (even putting jungles on the moons of Jupiter), or gave some excuse for warmer temperatures like the moons’ internal heat.
As a matter of fact, Jupiter’s innermost large moon, Io, is volcanic, and in spots can be remarkably hot; but the overall temperature is still bitterly cold. Jupiter’s other moons are no better, though there is believable speculation that the icy outer shell of Europa hides a sub-surface ocean of water. Saturn’s moons are even colder; on Titan, ice is as hard as rock and methane flows like water.
Uranus, Neptune, and Pluto had even fewer fans than Jupiter and Saturn, being generally correctly judged to be too cold and dim to support life, and too far away to be terribly interesting even as colonies.
The consensus view of the solar system, accepted as science in the early 1920s and propagated, even after it had become doubtful, by science fiction writers long after, lasted in its entirety less than 50 years — though some of its elements were far older. Nonetheless it was curiously powerful and produced a vast literature, which though of very variable quality, is at its best both inspiring and thought-provoking. As the memory of that period fades, it is worth preserving a record of what was believed to be true, or at least possible, about our neighboring worlds at that time.