Analog SFF, December 2006

by Dell Magazine Authors

  [Footnote 5: The lifting power of a balloon is proportional to the difference between the molecular weights of the gas inside versus that outside. Air has a molecular weight of about 29; that of Venus's atmosphere is about 43.2 (Table 1), for a difference of 14.2. Helium (He) has a molecular weight of 4, so the relative lifting power of He in air is 29-4, or 25. And 14.2/25—55%.]

  There are a couple of potential problems, though. First, 55 km off the ground is right in the middle of Venus's “zonal retrograde superrotation,” a layer of perennial winds that circle Venus completely in about 4 Earth days. They spin in the same direction as Venus rotates, but considerably faster. At the equator the windspeed is about 60 meters per second, or 134 mph—the speed of a Category 4 hurricane. Still, that's not the problem it seems. As long as the flow is reasonably smooth, you don't care what your airspeed is with respect to the surface. It won't be like bouncing around in a permanent Katrina! And it has an advantage: Landis points out that riding Venus's superrotation gives a day-night cycle that is considerably more convenient than the 4 monthsexperienced on the surface.

  There will be bumps occasionally, though. There is some wind shear in the vicinity, particularly around the 46—48 km level, and Pioneer Venus photos suggested that there are also local convection cells near the subsolar point. Perhaps the habs will try to stay in middle latitudes instead, to avoid passing directly under the Sun. This would also have the advantage that the temperature would be lower near the 1-bar level. Alternatively, maybe they just batten down the hatches every four days when they cross at high noon!

  Now for the second problem: the 55-km height is also rightin the middle of the main cloud deck, which extends from roughly 45 to 70 km above the surface.

  This probably isn't a showstopper either, though. There's a widespread misconception that the Venus clouds are very thick. They aren't: by terrestrial standards they're extremely thin, mere haze or smog rather than “clouds.” Even at their thickest the visibility is a few kilometers. They're opaque when seen from the outside only because they're dozens of kilometers deep.

  So, at least the hab wouldn't be floating through perpetual fog, although it certainly messes up stargazing out of the upper deck. Maybe airborne excursions up to the top of the cloud layer will be popular. During daylight it would probably look like a very smoggy sky in L.A., although the sky would be more yellowish than brown. That's another problem: The clouds are made of micron-sized droplets of sulfuric acid, so the hab will have to be made of corrosion-resistant material. Carbon composites, fabricated directly from the CO2, should work fine. Solar power should also be eminently practical, as the sky will be very bright.

  Elsewhere ("Diamond Ether, Nanotechnology, and Venus,” Nov ‘99) I've talked about Venus's long-term value as a source of carbon, the “ultimate material” of molecular nanotechnology. After all, its atmosphere is the biggest off-Earth carbon reservoir in the Inner System. I proposed nanobugs that would convert CO2 into a solid polymorph, “carba,” that could be gathered up more conveniently for offworld shipment[6]. Ultimately, too, after a few thousand years Venus would be terraformed as a by-product, as the bulk of her atmosphere was removed.

  [Footnote 6: Carba has since been synthesized, but alas, the current version is only stable under extreme pressure!]

  I think we now know where the carba miners are going to live.

  * * * *

  Other atmospheres?

  Many years ago, Poul Anderson wrote a story ("Brake,” Aug ‘57) about a derelict spaceship that took refuge in Jupiter's atmosphere. The ship had a sturdy enough hull that it could float deep within the atmosphere while waiting for rescue.

  So what, then, about floating habitats on the outer planets?

  Unfortunately, they don't look too promising. Jupiter, of course, is a bad bet for long-term habitation, without even looking at other problems, because of its 2.6-g surface gravity—barring major gengineering of the human organism. But even Saturn, Uranus, and Neptune have serious problems, despite their nearly Earthlike gravities (Table 1).

  First, the “room temperature” level corresponds to pressures well above one atmosphere—equivalent to over 2000 ft down in Earth's ocean, in the case of Uranus and Neptune. Now, this isn't completely a showstopper: The habs could be filled with a helium-oxygen mixture, instead of air, as is done with divers making extremely deep forays in Earth's oceans. It does complicate things, though.

  More important, the atmospheric compositions are roughly solar: hydrogen with some helium mixed in. Even a helium-oxygen mixture, although much less dense than ordinary air, will be denser than that! So these habs cannotsupport themselves just with the buoyancy of their contained air. They will need to be supported by separate buoyancy chambers, at a substantial cost in both complexity and safety.

  Even more important, the atmospheres of these planets are highly turbulent. Look at the seething zones and belts on Jupiter! At the very least a hab will be buffeted around unmercifully, and at worst it will be carried down into the hotter, higher-pressure zones below to be destroyed. It doesn't look good for Poul's story, either, even ignoring the turbulence. At the 100-bar level, where the spaceship was to have floated, the temperature in the real Jupiter has already risen to some 440ºC.

  The outer planets may be good sites for scientific stations—populated by AIs, perhaps!—but I don't see permanent settlements by biological humans.

  * * * *

  And elsewhere?

  The discovery (finally!) of planets around other stars broadens the potential playing field quite a bit, especially since it may well be that Earthlike planets are much rarer than we'd thought (see “Just How Average Is the Solar System?", Sept ‘97). However, the “hot Jupiters” that have been discovered—massive planets orbiting extremely close to their parent stars, closer than Mercury is to the Sun—look to be even worse bets for floathabs than our own giant planets. For one thing, unless a planet is a reasonable distance from its star, there isno temperate level. Temperatures go from merely very hot at the outer part of the atmosphere to extremely hot inside. Even Venus is cold out at the edge of its atmosphere—that's why there's a room-temperature level farther down. Second, if the planets’ atmospheres are largely hydrogen and helium, as seems to be the case, the buoyancy problem becomes even worse. Hot hydrogen and helium are even less dense than cold! Any gas, of course, becomes less dense if its pressure is held constant while its temperature is raised.

  However, I suspect that Venus-type worlds might be fairly common in the Universe. As opposed to Earths (i.e., planets supporting liquid water), which may well require a fairly stringent set of initial conditions, it seems easy to make a Venus. All you need is a planet, fairly close to its star, whose gravity is low enough that it can't keep hydrogen but high enough to keep heavier gases. Since it's hot, all the CO2 and H2O stay in the atmosphere, so the CO2 doesn't get safely precipitated out into limestone, as has happened on Earth[7]. Then the H2O is split up over geologic time by incoming ultraviolet (UV) light ("photodissociation"), with the hydrogen escaping to space. Voila! A Venus.

  [Footnote 7: Earth has just as much CO2 as Venus does; the difference is we're standing on it.]

  I have trouble coming up with any reasonable scenarios for other heavier-than-air atmospheres, though. Carbon and oxygen are both abundant heavy elements, so CO2 is common. It's pretty benign, too. Sulfur dioxide might well be a major atmospheric component somewhere (Io would have an SO2 atmosphere if it were bigger), but it's both reactive and toxic (see “Fire, Brimstone, and Maybe Life?", July ‘90). To dismiss another possibility, hydrocarbons are too vulnerable to photodissociation to be reasonable as major atmospheric constituents on close-in planets. They'd have some serious flammability issues for oxygen-containing habs, too! Finally, although other heavy gases exist, they're made up of rare elements and so seem unlikely as major atmospheric components. Sulfur hexafluoride, SF6, for example, is very heavy (molecular weight = 146!) and (surprisingly) nontoxic[8]. Fluorine,
however, is a very rare element, some ten thousand times less abundant than oxygen (see “Those Halogen Breathers,” Oct ‘84).

  [Footnote 8: Although UV photochemistry from the parent star might make small amounts of some seriously nasty compounds like S2F10

  Settling the Universe in Venus-style floathabs, and presumably slowly terraforming the host planet in the process, hasn't been an element in SF, so far as I know. But maybe it will make up one part of the interstellar diaspora.

  Copyright (c) 2006 Stephen L. Gillett, Ph. D.

  * * * *

  Acknowledgments

  I'm very grateful to Geoff Landis and Mitchell Burnside Clapp for sharing their thoughts and expertise on Venus with me.

  * * * *

  Selected References

  Hubbard, W. B., Planetary Interiors, Van Nostrand Reinhold, 1984.

  Hunten, D.M., L. Colin, T.M. Donahue, and V.I. Moroz, eds., Venus, University of Arizona Press, Space Science Series, 1983.

  Landis, Geoffrey A., “Colonization of Venus,” in AIP Conference Proceedings Vol. 653, pp. 1193-1198, 2003. (Conference on Human Space Exploration, Space Technology & Applications International Forum, Albuquerque NM, Feb. 2—6 2003)

  * * * *

  About the Author:

  Till recently Steve Gillett was a research professor at the Mackay School of Mines, University of Nevada, Reno, where he'd worked on Paleozoic paleomagnetism, lunar resources, and seismic risk at Yucca Mountain, Nevada, the proposed high-level nuclear waste repository. He also taught intro geology classes including one on planetary geology. He is now involved in several start-up ventures on applications of nanotechnology in environment and resources. He has a white paper on this topic online at the Foresight Institute (www.foresight.org). Gillett has a B.S. in geology from Caltech and a Ph.D. from SUNY Stony Brook.

  * * * *

  Table 1.

  Earthlike temperature levels in other Solar System atmospheres

  —

  Venus

  P (bars): 0.53

  T (degrees C): 29.2

  g: 0.91

  Atmosphere composition: CO2(95%), N2(5%)

  MW: 43.2

  Notes: 55 km above surface

  —

  Jupiter

  P (bars): 5.5

  T (degrees C): 26.9

  g: 2.65

  Atmosphere composition: H2(88%), He (12%)

  MW: 2.2

  Notes: Equiv. depth = 145'

  —

  Saturn

  P (bars): 8.6

  T (degrees C): 26.9

  g: 1.13

  Atmosphere composition: H2(88%), He (12%)

  MW: 2.2

  Notes: Equiv. depth = 245'

  —

  Uranus

  P (bars): 65

  T (degrees C): 26.9

  g: 0.92

  Atmosphere composition: H2(88%), He (12%)

  MW: 2.2

  Notes: Equiv. depth = 2060'

  —

  Neptune

  P (bars): 65

  T (degrees C): 26.9

  g: 1.16

  Atmosphere composition: H2(88%), He (12%)

  MW: 2.2

  Notes: Equiv. depth = 2060'

  —

  P is pressure: 1 bar = 10 newtons/cm2 = 0.986923 atmospheres = 100,000 pascals. “g” is surface gravity, Earth = 1. Only major components shown in atmosphere composition; outer planet composition assumed from solar. Percentages are by volume. “MW” is average molecular weight. Venus data from the Venus reference atmosphere (Advances in Space Research, 5, 1986); outer planet data from Hubbard (1984, p. 273). “Equiv. depth” is the depth corresponding to the pressure in Earth's oceans.

  [Back to Table of Contents]

  IN TIMES TO COME

  If you're reading this, you're probably familiar with “Clarke's Law,” stating that “Any sufficiently advanced technology is indistinguishable from magic.” In “Emerald River, Pearl Sky,” the lead novella for our January/February double issue (with a Bob Eggleton cover), Rajnar Vajra takes you to a future in which that takes on a new kind of truth. It's a colorful, flashy, weird place that might first make you think you're reading fantasy—but if you know Vajra, you'll know he has something up his sleeve. I won't tell you just what, but I will say it includes an exhilarating dose of solid entertaining, as well as a sobering thought for our time....

  We'll have two quite different fact articles: one on why the poles might be good places for lunar settlements and how they might be shielded against radiation, and one by Richard A. Lovett on how we might adapt to running out of oil—including one option you probably haven't heard much about. Lovett also has a special feature on writing about things you're not familiar with, plus a short story. That last is just one of an unusually diverse collection of fiction, also featuring stories by such writers as Kristine Kathryn Rusch, Carl Frederick, Grey Rollins, Jerry Oltion, and Stephen L. Burns. And, last but far from least, we'll have the conclusion of Robert J. Sawyer's novel, Rollback.

  [Back to Table of Contents]

  DOUBLE DEAD by Grey Rollins

  Copies of ourselves, of whatever sort, could have all kinds of uses....

  The door was open, of course. It usually is. It's cooler that way. Sometimes, if I'm lucky, the secretary from the lawyer's office down the hall stops to talk to me. She's a divorced mother of two, working for an ambulance chaser. She makes just enough to pay someone else to watch her children and buy food. It's a precarious existence, treading the fine line between getting by and going broke. I've loaned her small amounts of money from time to time, but never been repaid. She sometimes seems to be hinting that she'd like me to ask her out. I've never been able to decide whether she's interested in me or looking for a currency donor. It's not acceptable for a man to ask that question. Not out loud; not even in the silence of his own mind. Women can wonder whether a man is only interested in sex, but if a man dares question a woman's motives, lightning bolts smite the infidel who dared question her intentions. Never doubt that double standards still exist.

  Not having a client and not having the secretary to talk to at the moment, I was reading a novel. Granted, it's not the recommended thing. When a client comes in, you're supposed to be squinting at a hastily scrawled note written by a dying man, or cleaning your gun. Also acceptable is romancing a beautiful woman, but only if it's her husband who's about to come through the door. Otherwise the frisson of danger is lost and it doesn't play properly in the noir school of detective work.

  "Ahem,” came the delicate cough from my doorway.

  I looked up ... and froze in astonishment. The beautiful woman had arrived and was leaning casually against my doorframe. The fantasy developed quickly in my mind: the significant look, a little quick repartee, the first hesitant kiss ... I opened my mouth to utter the requisite witty—

  "Dinos in the Dark?” she inquired, her head canted slightly to read the title of my book. “Let me guess ... your favorite author is T. Rex Stout, right?"

  "Emily Brontesaurus, actually,” I said. This was not at all the way things were supposed to go. I gave her a mock scornful look. “You're late. I finished cleaning my gun an hour ago. That was the cue for your grand entrance."

  She nodded her head once, the hint of a smile on her lips. “Good save.” She stepped into my office. “I'm—"

  "Amanda McBey,” I finished for her, saving her the trouble of an entirely superfluous introduction. Her most recent picture had been a bit of a disappointment, but no one, no matter how jaded or cynical, was counting her career as over. She was just entering her twenty-ninth year and had every right to expect the next ten years of her life to handily eclipse the success of the last ten.

  "And you're Jack Sawyer,” she said, completing the symmetry of our introductions. “You come highly recommended. Your handling of the John Holland case made quite an impression in certain circles.” She slid into my visitor's chair with the unstudied grace of a panther.

  I slipped Dinos into a desk dra
wer ... discretely, I hoped. “So what can I do for you, Ms. McBey?"

  She gave me a sly smile. “I liked the honesty of having the book out on the desk. Now you're trying to clean up your first impression."

  "You've got an eye for detail. If you ever need another career, you'd be a natural as a detective.” This was empty banter on my part and we both knew it. Amanda McBey needed a job as a detective the way she needed termites in her forty-seven-room bungalow up in the hills. If all else failed, she could go back to being a model, that being how she got her start. Her looks were often likened to those of a sexually mature elf. It was those ungodly, slightly tilted, blue-gray eyes that did it. Mere mortal women aren't granted eyes such as those. Nor, short of selling their souls, are they granted bodies like the one perched in my visitor's chair.

  She was gracious enough to laugh, perhaps even in genuine amusement. “If it's any consolation, I read the book.” She leaned forward and whispered conspiratorially, “And liked it, too ... but if you ever tell anyone that, I'll call you a liar."

  "Your secret is safe with me.” I leaned back in my chair and steepled my fingers. “I could sit here and talk to you for the rest of the my life, but the ring on your finger tells me I would be ill-advised to ask you to dinner. Besides, I'm not wearing my tux, silly me, so I doubt they'd let me into The Orchard or Ernie's or wherever the elite eat these days."

  "Funny you should mention my ring—"

  "Ah, the plot thickens,” I said.

  She gave me a small smile. “You knew it had to, sooner or later. It's like this; my husband didn't come home Thursday night. His publicist has a cover story ready to go as soon as the media find out, but so far we've been lucky."

  "Let's see ... this is Tuesday, so—"

  "Before you start down that road, let me complicate matters a bit. They found his body late yesterday."

  My stomach dropped along with my jaw. “Oh, I'm so sorry. I shouldn't have—"