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Stranger Than Fiction

Just what does it take to make a habitable world? Keith Cooper is editor of Astronomy Now, the British monthly whose first editor was the fabled Patrick Moore. An accomplished writer on astronautics and astronomy as well as a Centauri Dreams regular, Keith has recently become editor of Principium, the newsletter of the Institute for Interstellar Studies, whose third issue has just appeared. In this essay, Keith looks at our changing views of habitable zones in light of recent work, and takes us to two famous science fictional worlds where extreme climates challenge life but do not preclude it. How such worlds emerge and how life might cope on them are questions as timely as the latest exoplanet findings.

by Keith Cooper


Literally overnight, two habitable planets – tau Ceti f and HD 85512b – were rendered barren and lifeless. What was the cause of this cataclysm? A nearby supernova? Asteroid impacts? On the contrary, it was something far more mundane.

A dozen light years away, scientists at Penn State University were re-analysing the extent to which habitable zones penetrate the space around stars; in other words, at what distance liquid water could potentially exist on a planetary surface assuming an Earth-like atmosphere. The basics for habitable zone theory had been worked out in part by, among others, Penn State’s James Kasting in decades previous. Building on his work, Ravi Kumar Kopparapu and Ramses Ramirez discovered that habitable zones are found further from their stars than had been envisaged (see Habitable Zones: A Moving Target for more).

The result was bad news for our two exoplanets. Suddenly, as the habitable zone shifted imperceptibly around them, they found themselves on the wrong side of the inner habitable zone boundary, too close to their respective stars. Consequently the Planetary Habitability Laboratory at the University of Puerto Rico, Arecibo, declared them uninhabitable. Too bad for any life-forms living there.

Despite only knowing the scarcest of details about these worlds – mass, radius, density, the amount of heating from their stars – these two worlds have been cast into the obsolescence in a manner that seems shockingly final. We know so little about these planets, how can we possibly say whether they are habitable or not, especially when the only standard we are holding them to is habitability for human beings?

Key Factors for Habitability

Determination of habitability is based on worlds not necessarily having exactly the same atmosphere as Earth, but at least having water and carbon dioxide, which are abundant and vital for life, Dr Abel Mendez of the Planetary Habitability Laboratory at the University of Puerto Rico, Arecibo, tells me. “The problem of the inner edge is that once you evaporate more water you get into a runaway greenhouse effect that will make the planet lose all its water,” he says.

There are other factors that play a part though. Just because a planet is inside a habitable zone doesn’t mean it is automatically habitable. The presence of an atmosphere, water, a global magnetic field, plate tectonics and a not too heavy impact rate are all factors. For those worlds close to the edges of the habitable zone, the margins are even narrower.

For example, habitability of planets on the edge could be largely dependent upon cloud cover, says Mendez, which can increase a planet’s albedo, or reflectivity, preventing heat from reaching the surface, but if there’s no way to see clouds on a planet many light years away, how can we just write off worlds like tau Ceti f and HD 85512b? Mendez admits nothing is for certain. “The intention of the habitable zone is to determine the limits [at which habitable planets can exist from their stars], but I will not call them hard limits yet due to uncertainties such as the effects of clouds.”

A constrained, limited view of habitability that says only Earth-like conditions will do limits the number of worlds we think would look friendly. And there’s nothing wrong with this approach – we know that a planet like Earth is suitable for life, so that is what we look for, whereas we don’t know yet whether life could exist on worlds like Europa or Titan, for example. It’s not that planetary scientists are ignoring other kinds of worlds, either. “Many groups are considering the more exotic possibilities, such as tidal habitable zones, habitable planets around white dwarfs, etc,” says Mendez. “The problem is that the habitability of such conditions are harder to observe or interpret than known biosignatures, and observational astronomers need to measure things, but we will get there.”

Science Fiction at the Boundaries

Until we do, however, we’re left to speculate with our imaginations and where is that not done best but in science fiction? So let’s take a look at a few imaginary worlds that are different to Earth but which could exist on the boundaries of the habitable zone and see how they stack up in comparison. Could reality really be as strange as fiction?

One common science fiction trope is the planet with the same climatic conditions over its entire globe, for example the desert planet, the ice planet, the jungle planet. In reality things are more complex – you can have what seems like all four seasons in one day on parts of the Earth. We don’t expect the same climate at the equator as at the poles. Meanwhile the change of seasons see cycles of weather, not just on our planet but on Mars, Saturn and Titan to name but three. What then do we make of our first two science fiction choices, the desert world Arrakis from Frank Herbert’s Dune, and the ice planet Hoth from The Empire Strikes Back?

Arrakis first. Dry as a bone, it has no surface water and no precipitation. What little atmospheric moisture there is is harvested by wind-traps and the water then ferried by canal to underground reservoirs in anticipation of using it as part of the terraforming of the planet. In the novels, however, the planet is mostly sand dunes, inhabited of course by the fearsome sandworms, except for at the pole where a large slab of bedrock ringed by mountains provides a more habitable zone.


Image: A sandworm rears up out of the desert of Arrakis on the March, 1965 cover of Analog. I can never resist the chance to display the artwork of the remarkable John Schoenherr. What memories…

So how did Arrakis end up like this? In Dune, Frank Herbert described the world as having salt flats, indicating that it once had lakes. The introduction of the non-indigenous sandworms, in their protoform as ‘sand trout’, saw them sequester all of the water. Arrakis, described as orbiting the star Canopus, changed from a fertile world to a desert planet.

We have our own desert planet in the Solar System in the form of Mars, skirting the outer edge of the habitable zone. While there are no sandworms on the red planet, liquid water dried up on the surface long ago and today only exists in frozen ice caps, sub-surface ice or possibly in aquifers deep underground. Indeed, what happened to Mars’ water, and the truth behind the climatic history of the planet, are still something of mystery, but we can hazard a best guess.

We know that Mars once had running water on its surface, in the form of rivers, lakes and even a northern sea. They existed billions of years ago. Today we see only their long-lasting consequences on the Martian terrain: river channels, floodplains, a surface chemistry forever altered by the presence of liquid water. The problem with Mars is that it is small, which results in a double whammy for the planet: its diminutive size means not only a smaller gravitational field but also a greater loss of heat from its core. As Mars’ interior began to cool, its molten core began to stiffen and the magnetic dynamo contained within began to stall. These two things conspired to allow the solar wind to strip Mars’ atmosphere, including its water vapour. (The European Space Agency’s Mars Express spacecraft has actually witnessed this stripping in action, watching Mars’ atmosphere lose oxygen at a rate ten times faster that Earth’s atmosphere; see Earth’s Magnetic Field Provides Vital Protection.

Move Mars closer in to the Sun and you could easily have a warmer Arrakis-type world. So desert worlds are feasible and you don’t require sandworms to create them either. But what about the other extreme, an ice planet like Hoth?

Life on the Outer Edge

Twice in Earth’s history – 2.5 billion years ago, and about 700 million years ago – our planet completely froze over [PG note: I must have had a typo here before; see the comments below re the 700 million year figure]. Even the oceans were covered with a thick layer of ice, right down to the equator. Dubbed ‘Snowball Earth’, what causes such events is uncertain, but a significant reduction in atmospheric carbon dioxide (possibly as a result of increased silicate weathering in the warm and wet tropics as continents gathered there) or methane (destroyed through oxidisation, as a result of an oxygen influx into the atmosphere from the first oxygen-exhaling life-forms) would do the trick. Both carbon dioxide and methane are potent greenhouse gases; without them the planet cooled and must have teetered close to the edge of an abyss from which it would never recover.

Of course, it did recover. The freezing of the planet brought the carbon-silicate cycle to a halt. Water vapour froze out of the atmosphere, which meant that precipitation ground to a halt. Ice covered the land so there could be no weathering and ice topped the oceans, preventing carbonates from reaching the sea floor. The way out of this predicament for the planet was that there was still an input into the carbon-silicate system, namely carbon dioxide belched out by volcanoes. Gradually the atmosphere accumulated carbon dioxide, with no rain to wash it out. Temperatures rose and the Earth thawed, but the point is that ice planets can very easily happen, particularly if a world lacks plate tectonics to provide that carbon dioxide input that acts as part of a thermal blanket for the world. If there were a ‘slushy’ belt around the equator, which doesn’t quite freeze over, then some life may be able to survive, although it’s hard to imagine what ecology could flourish on a planet like Hoth to permit a food chain with the monstrous yeti-like wampas at the top. Ironically, if methane was the primary greenhouse force in early Earth’s atmosphere, and was destroyed by oxygen, then the discovery of another snowball planet around another star could potentially be a biosignature indicating the presence of oxygen-exhaling life on that world.

Hoth was a world covered in ice. What about planets covered in water, such as Solaris in Stanislaw Lem’s novel of the same name (ignoring the fact that this fictional planet’s global ocean was actually a living entity)? According to the United States Geological Survey seventy percent of Earth’s surface is covered in water and simulations depicting planet formation suggest that planets could easily acquire much more water than Earth did; indeed, Earth is actually quite dry. Perhaps water is delivered to planets by comets and asteroids, or perhaps these water-worlds are born further out, beyond the ‘snow line’ where water-ice is prevalent, before migrating inwards to hotter climes where their ice melts. There’s even observational evidence for water-worlds – in February 2012 Hubble Space Telescope observations of the 6.5 Earth-mass world GJ 1214b, some forty light years distant, show that starlight passing through its atmosphere is being absorbed at the characteristic wavelength of water vapour, enough to contribute a large fraction of the planet’s mass.

All of these worlds – desert, ice and ocean planets – could potentially be habitable to a point; even in Earth’s own snowball periods, life persevered. However their occurrence was before the arrival of complex life and it is doubtful such life would have survived the onset of such a catastrophic change in climate. More to the point, Mars was once wet and warm with a thicker atmosphere, even if it was only for a short while, while still existing outside of the habitable zone. Now it is a barren. On the other hand Earth was once a frozen wilderness despite being in the habitable zone, but is now resplendent with life.

While habitable zones are a starting point, it is clear they are not necessarily the final word on habitability and locating planets within their limits does not guarantee that they are going to be Earth-like, nor does it automatically correspond that planets outside of the habitable zone will be inhospitable. Furthermore, astronomers also suspect that life could exist in such exotic locales as planets in ten hour-orbits around white dwarfs, on tidally locked worlds around red dwarfs, on exomoons orbiting gas giants and even on rogue planets that wander interstellar space, kept warm by their own innate radioactivity. Surely if any of these types of planet are discovered to be habitable it will prove that reality can be far stranger than fiction.


Comments on this entry are closed.

  • A. A. Jackson March 8, 2013, 10:28

    Side note on John Schoenherr.
    By memory, according to the SF/Fantasy film journal CineFantastique , David Lynch and the art department approached Schoenherr about working on the film version of Dune , but never directly did, tho the De Laurentiis-es paid him for the use of imagery, and he was a consultant on design, but is not listed in the credits for the film, not even ‘uncredited’. But the designs are noticeable.
    Poor Lynch, I still don’t know his familiarity with SF , he did try to treat the material with respect. But even he has said the material defeated him. He wanted two movies, made a 6 hour version , I don’t think that was ever edited into existence (tho the extended versions have show up), but the De Laurentiis-es would never commit to a longer version.
    Still Schoenherr’s concepts for John Campbell captured Herbert’s ecological concepts better than anybody, from then on Schoenherr became the canonical Dune illustrator.

  • Paul Gilster March 8, 2013, 11:21

    Interesting stuff — I hadn’t realized this about Schoenherr’s involvement with the film. My thoughts on the latter more or less mirror yours! Schoenherr’s cover art for Analog was so moody and evocative that just seeing some of the old covers brings back snatches of plot and character from stories I read fifty years ago.

  • Abelard Lindsey March 8, 2013, 12:03

    I first saw the David Lynch film when it came out in 1984. I did not like it at all, as was the opinion of most other Dune fans. However, the film has grown on me over the years and I now consider it not bad at all. The key is to treat it as an independent work of art, similar to but separate from the Herbert novel.

    There was an SF channel mini-series made about 10 years ago, which I saw when it first came out. I’ve seen it only once, and thought it was rather good.

  • Bynaus March 8, 2013, 12:30

    The second “Snowball Earth” episode was actually 700 million years ago, not 700’000. If there had been a SE episode in the Phanerozoic, I don’t think we would still be here!

  • casino implosion March 8, 2013, 13:33

    I had that edition of Dune. Always sort of wondered why beasts on a barren planet would need carnivourous mouths capable of eating a prey the size of an aircraft carrier.

  • RonSmith March 8, 2013, 14:44

    Snowball Earth 700,000 years ago? I believe you mean 700,000,000 years ago?

  • Mike NYC March 8, 2013, 15:07

    I think the later snowball earth date must be a misprint: about 650 million years ago, not 700, 000 years ago. e.g. here’s wikipedia


    The Snowball Earth hypothesis posits that the Earth’s surface became entirely or nearly entirely frozen at least once, some time earlier than 650 Ma (million years ago)….Another, much earlier and longer, snowball episode, the Huronian glaciation, which occurred 2400 to 2100 Ma may have been triggered by the oxygen catastrophe.

  • Keith Cooper March 8, 2013, 15:36

    Oops, yes I did indeed mean 700 million years, right before the Cambrian explosion, not 700,000 years! Thanks for pointing out the mistake!


  • Paul Gilster March 8, 2013, 15:38

    Yes, I just changed the text from an earlier typo. Thanks for pointing it out!

  • Rob Henry March 8, 2013, 17:08

    Too me this article was strong on suggestion but short on commitment. It would have helped to speculate about how much closer a planet of certain atmospheric composition could have approached its sun, and still retained traditional HZ conditions at its poles if it original water inventory was sufficiently low.

    One inference that I find too dogmatic though is that of complex life being adversely effected by extreme conditions. While I agree that non-cyclic rapid changes in conditions are deleterious to higher life, from both an evolutionary perspective, and from the evidence of our own biosphere, it actually requires a certain degree of difficulty for its complex strategies to give it an advantage over simple ones. I often call on the counterexample of a stream, and ask you to think of pouring the perfect nutrient mix and continuous sunlight of the perfect wavelengths for optimal growth of its complex organisms. That river will, of cause, explode with life, but all the higher forms will die in the face of competition.

    And that, casino implosion, is why finding giant sandworms on the surface of dune, is as unlikely as finding the largest carnivore on Earth’s surface atop the frozen desert of the artic tundra. (hint: sandworms obviously filter feed through some subsurface ecosphere, and use their ability to surface as a comparative advantage over lower forms)

  • Adam March 8, 2013, 18:27

    A point Keith Cooper might find interesting is the suggestion that Arrakis like planets, with low amounts of water, actually have wider habitable zones than water-planets, like Caladan. According to work by Yutaka Abe & Kevin Zahnle, Arrakis-like planets are able to retain liquid water – in the form of lakes near the poles – to much higher insolation levels than planets covered by water. Here’s their paper: Habitable Zone Limits for Dry Planets. Venus might have gone through a Dry Planet phase as recently as 1 Gya, before the greehouse runaway finally took hold.

    Another exotic possibility that Keith didn’t mention is the Hydrogen Greenhouse planet, which Raymond Pierrehumbert and Eric Gaidos have studied. In their 2011 paper, “Hydrogen Greenhouse Planets Beyond the Habitable Zone”, they make the case for photosynthetic life being viable out to 10 AU or so thanks to a H/He rich atmosphere keeping the planet warm. With such broad habitable zones (from 2 AU to 10 AU in the case of the Sun) then such planets might prove more abundant than traditional “Earth-like” planets.

  • torque_xtr March 8, 2013, 18:30

    One liter of oceanwater contains about 5 ml (standard conditions) of oxygen, and the solubility increases linearly with the partial pressure of O2. So, it’s entirely possible that on some right-mass ocean-superearth orbiting an active star, water photodissociates and hydrogen escapes, but oxygen remains and accumulates. If the pressure is around 100 bars, the concentration of oxygen dissolved in water exceeds that in our atmospheric air, and humans could swim in that ocean and live underwater without scubas, given 0,9%-salinity and abscence of toxic/predatorious lifeforms of course. Such colonies may be something utterly weird – only natural tools and materials, like fish bones, no fires except some risky craft at the surface, involving ores brought from the bottom (if accessible) and dead biomass as a fuel, no fast transport, no convenient way to remove all kind of waste (whew!), but some bilions of cubic kilometers of warm water to feel the freedom and another existence.

    Reality could be stranger than fiction. Now there are two whole new classes of worlds – oceanworld superearths/light neptunes and tidally locked furnace-day-freezer-night hot earths – that have arrived at the imagination playground only after the latest discoveries and have been quite outside the scope of imagination before…

  • James Jason Wentworth March 8, 2013, 21:48

    It is prudent to take all pronouncements about the extent of habitable zones with a salt lick, as even those who make such pronouncements freely admit that they are just “best estimates, made using current data.” For example:

    Consider a real planet, our Mercury, for a moment. Despite its proximity to the Sun, it has ice in permanently-shadowed craters at its poles. There could be micro-climates favorable for microbial life deep in and/or under the ice where even *liquid* water may exist, warmed by subsurface heat. Such heat could come from decaying radioactive elements in the rocks (Mercury apparently has a lot of such heavy elements), magma, or its large, molten iron core. Even if Mercury has no “home-grown” life, meteorite-hitch-hiking terrestrial microbes could have been sent there via Earth impacts, perhaps with a little Mariner 10-type gravitational assistance from Venus.

  • Adam March 8, 2013, 22:55

    Hi torque_xtr
    Interesting idea though I have heard that breathing water is very tiring. We’ll need something better than lungs to adapt to such a world.

  • GaryChurch March 8, 2013, 23:46

    Mars might actually be a place to build an artificial world of tunnels filled with water deep below the surface of the planet. It is machines to dig tunnels like those depicted in the Matrix series of movies that are missing.
    The alternative is an H-bomb powerful enough to create a sports arena sized cavern. Wait a year or two for the really contaminated material to cool off a little and then shovel out the bad stuff, add water and electricity (from a Moon manufactured thorium reactor?) and move in.

    But after the Moon I think Ceres and the icy moons of the outer solar system are better places to establish colonies. Mars might appeal to a specialized mining concern also seeking to create a new underwater-underground world but those tunneling machines are massive affairs and getting components for them from a factory on the Moon to Mars might be a problem.
    It might require a lunar solar powered beam propulsion system beaming tremendous energies into a super-heavy lift vehicle to send such mechanical excavators to Mars and other bodies. It may prove to be fairly easy to mix water and artificial light to grow more than enough food to live on- or it may prove extremely difficult due to unforeseen effects on organisms in a low gravity closed cycle environment.
    I could see Mars using H-bombs to excavate caverns in anticipation of such a solar system beam propulsion highway.

  • Eniac March 9, 2013, 15:44


    It is machines to dig tunnels like those depicted in the Matrix series of movies that are missing.

    If by “missing” you mean they do not exist, think again. Don’t underestimate the Swiss, who have written the book on tunnel boring. c.f. here: http://en.wikipedia.org/wiki/Tunnel_boring_machine

  • Rob Henry March 9, 2013, 16:45

    Adam and toque, Concentration isn’t everything, activity is at least, or more important. Human’s can’t cope with more than 200,000 Pa of oxygen activity even in the short term, go very much higher than that (you go to 10,000,000Pa)and all our tissue would spontaneously oxidise. Fixing that is probably beyond genetic engineering, since every biomolecule in our body would be effected.

    Lesser problems, but still significant, are those such as O2’s narcotic effect, and modifying our lungs to take isotonic water such that alveoli sill have the right surface tension (if indeed they are off any use at all in this different diffusion environment), and the leaching of rare but biologically important ion’s through the lungs

    Better news is that our breathing is not driven by need for O2 intake, but CO2 disposal, so we don’t need nearly as much O2 as you think.

  • tom March 10, 2013, 3:18

    Philosophically & scientifically, the search for life is of paramount importances. Since the microscope, discovery of photosynthesis & evolutionary theory; the story of living systems on Earth are clearing the pathway of ‘How Life occurs in Nature.’
    Though life sciences are far from conclusively establishing a Life principle, Life does exist and we are cognitive of this experience.
    But we should not be blinded by optimistic biases or impatient desires to leap for ‘any answer than no answer’.
    Just processing the size & age of the Universe, it is a false sense of cold confidence that Earth being the only life bearing planet to date, only because we haven’t ‘turned over’ enough teaspoons of sand on the great cosmic shoreline?

  • GaryChurch March 10, 2013, 14:40

    “If by “missing” you mean they do not exist, think again.”

    If by “they do not exist”, do you mean I am unaware of what I am talking about?


    I was thinking about buying this but it might be awhile before we have anthing that can put the several hundred tons of components where they need to go. And then there is the nuclear power plant you would need to run it on what ever moon or dwarf body you were excavating.

  • torque_xtr March 10, 2013, 17:46

    Haven’t found anything about oter than perfluorocarbons liquid breathing, but I guess there is a range of conditions that allow even water breathing, in the range of tens of bars of O2 and close-to-physiological salinity. The activity problem is something unknown, but the activity of dissolved oxygen in water is somewhat lower and could allow some breathing, combined with greater CO2 solubility. Maybe some hours/days/weeks for unmodified humans and indefinitely long at some very favorable conditions of after some genetic engineering. More, I think the bottleneck is the salinity, the hyperpressure abiogenic O2 atmospheres may be common among middle-mass waterworlds, but the needed concentration of Na+, Cl-, K+, Mg+ and whole other bunch of ions simultaneously is a big strain. But the galaxy is big…

  • Adam March 11, 2013, 4:28

    Hi Rob
    You misunderstand. I am well aware of O2 toxicity – Dole discusses the physiological aspects of breathing in some detail. A breathable H2/He/O2 mix is predominantly H2/He, with ~5% O2 or less. At 10 bars that means ~0.5 bar O2 – preferably lower. People have lived in pressure chambers to ~72 bar, for deep diving conditioning experiments, breathing hydro-heli-ox mixtures. Hydrogen can cause narcosis and some means of counteracting that would be required for long-term living at high-pressures.

  • Ronald March 11, 2013, 8:56

    Interesting thoughts here on the resilience and adaptability of life and the extent of the HZ.
    Well, the definition of HZ as per Kasting et al. does not claim much more than delimiting the zone within which liquid surface water can exist. So, this is not necessarily an absolute boundary for all life, but still seems a reasonable delimitation for complex (‘higher’) life, i.e. multi-celled life with specialized organs.
    Remarkable is the fact that the new Kasting, Ramirez et al. study, plus other studies in this field, do not differ much with regard to the inner edge of the HZ, usually from about 0.93 to 0.99 AU in the case of our own solar system. There really seems to be little extra room there before a runaway greenhouse effect takes place.
    Also telling is the fact that this inner boundary of the (long-term) HZ was shifted outward by the new Kasting et al. study, from 0.95 to 0.97 – 0.99 AU. This could mean that the time Earth has left for complex life is effectively reduced from 0.5 – 0.6 gy (about the time since the Cambrian explosion) to only 0.1 – 0.3 gy, half or less of what it has had so far!

  • Dmitri March 11, 2013, 13:57

    John Schoenherr and his SF art work is just astounding! Going through his paintings the most impression on me had his take on Ben Bova’s Kinsman – http://2.bp.blogspot.com/-Ok8L-Y10hTo/THFzJ1IOPbI/AAAAAAAAFNs/C-QCFDJ4xjI/s1600/07+JOHN+SCHOENHERR+-+KINSMAN.jpg
    The picture has so much life in it. Same goes for his version of Chewbacca! They have so much life and soul depicted – http://johnschoenherr.blogspot.com/2010/09/george-lucas-stole-chewbacca-but.html

    Is there more similar artists I should look for?

    All this istantly recalls René Laloux animations in the ’80s. His 1982 Les Maîtres du temps (Time masters) got me at that time in so many ways it burned vivid memories into memory. Later I re-discovered the animation again and despite decades away I was still the same way into it. The white faceless angels on Gamma 10 is still my the most scary ETI.

    All his other animations La Planète sauvage (Fantastic Planet) 1973, Les Années lumière (Gandahar ) 1988 are in the same league of timeless SciFi animations.

  • Rob Henry March 11, 2013, 17:00

    Torque, you could be correct that a dry powder is more sensitive to a given partial pressure of O2 than a wet slurry, but, other that our external surfaces, the aqueous phase is how most of our body experiences O2 tension. In that regards it is notable that our lungs maintain wet surfaces at all times – this is why each exhaled breath contains water vapour saturated at the 37C level. The resulting insensible loss is why high altitude mountain climbers dehydrate so easily.

    Adam, that ultimate diving mix of yours still retains 5% O2 only for the following reason. Breathing gas can never contain more than 200,000Pa O2 partial pressure so the other gasses in the mix are upped to allow deeper and deeper diving. Unfortunately, all gasses have a narcotic effect, but this is lowest in He and H2. I believe that ultimate mix you give is just that at which even these gases boarder on having a dangerous narcotic effect (or some other effect), when partial O2 pressure reaches 200,000Pa. I can’t see how your 72 bar figure is possible for gas breathing for anything other than minutes, and would greatly appreciate a reference there.

    And chemical potentials also alter with pressure as of itself, though judging from biochemical stress from organisms brought up from different levels in the ocean, my guess would be that 10 million Pa could be coped with little genetic modification, and several-many times this with lots of GE.

    And torque, hyperbaric conditions are occasionally used in medicine to force O2 into someone’s plasma. Here they can use pure O2, and are also limited to 200,000Pa. That is why the fluid those rats are breathing is not water.

    I now realise that your 100 bar figure was for a Earth composition atmosphere, not O2 partial pressure, so that the gap is actually “just” an order of magnitude. As I posited earlier, you could bridge at least half this gap by GE humans to take higher blood bicarbonate levels, since ordinary healthy non-diving humans never breath to obtain oxygen, their ventilation being entirely set by a need to eliminate CO2.

  • Rob Henry March 11, 2013, 17:05

    Also note torque, you would still have a gap though. Perhaps the water would have to be cooled to obtain sufficient O2, and our body temperatures reset around that new temperature.

  • Dmitri March 12, 2013, 6:10

    @GaryChurch March 8, 2013 at 23:46
    [Mars might actually be a place to build an artificial world of tunnels filled with water deep below the surface of the planet. It is machines to dig tunnels like those depicted in the Matrix series of movies that are missing.
    The alternative is an H-bomb powerful enough to create a sports arena sized cavern. Wait a year or two for the really contaminated material to cool off a little and then shovel out the bad stuff, add water and electricity (from a Moon manufactured thorium reactor?) and move in.]

    There is no need for earth digging machines. Mars has natural caverns beneath the ground deep enough for archeogeology, astrobiology, habitation, microclimat control and etc. Last week released papers on this:
    * summary – http://www.nasa.gov/mission_pages/MRO/news/mro20130307.html
    * paper in Science – http://www.sciencemag.org/content/early/2013/03/06/science.1234787

    Terraforming with nuclear, “an H-bomb powerful enough to create a sports arena sized cavern” is chapter humanity has already passed. Russians first cocked up w/ Aral Sea water supply redirecting it into Uzbekistan’s cotton fields – crop so water demanding on arid land. Later came idea to fix the damage by reversing the Siberian rivers to Aral Sea w/ channels carved by nuclear bombs. It all was under the aegis of use of atomic power for peacful applications. First stage of the plan was redirecting the water into Volga. Later extending the channels to Aral Sea. 1971 was made first test explosion. The whole construction to Volga river would have taken 268 detonations. Luckily they abondoned the idea soon after – mainly due to fallout.

    Lake Chagan in Kazakhstan is nuclearly terraformed – that notorious “a sports arena sized” body of water.

    Project Taiga footage – http://www.youtube.com/watch?v=0ZSFhSCnIB0
    Project Chagan footage – http://www.youtube.com/watch?v=yCblDxKmgHw

    In these experiments yield 15 kiloton was used. A dream of using H-bomb is an echo from General Douglas MacArthur Korean War period. He demanded nuclear weapons to send commies back to North where they came. Would have been it in his way we would not have had the 38th parallel treaty and Nort and South Korea. We would have in history books how the nuclear weapons were used in war, probably dwarfing Hiroshina and Nakasaki.

    During design of Tzar Bomba Andrei Sakharov once made a joke why not build an 100 Mt bomb, why do a meager 50Mt one, as there is no limits to scale up the H-bomb’s yield. The calculations made them backed down in fright of ecological and atmospheric impact. The 57Mt Tzar Bomba went to 60 km high and the mushroom cloud was 90 km in diameter. There is no way that kind of energy would just stay under Marsian ground plus the impact the non-existen Mars atmosphere will have .

    I must give credit as actually this rises a question how big scale terraforming / excavations on other planets should be done and what is the exact goal. I do hope politically charged trigger-happy approach on this subject is in far past of history. AFAIK Peaceful Use Of Space Treaty prohibits open and underground nuclear explosions in space, other celestial bodies included.

  • GaryChurch March 16, 2013, 13:06


    3 kilotons makes a pretty big cavern; 3 megatons will make a bigger one and 30 megatons an even bigger one. If you want big spaces to grow food and conduct industrial operations on another body in space then this is the way to go. Difficult to transport 100 ton tunneling machines to the Moon. Not difficult to transport a drilling rig and a bomb. Bruce Willis would agree.

  • Dmitri March 17, 2013, 14:31

    Then it makes 3 projects which were conservated after test trials. That’s not even question why, just need is to make wise conclusion to carry on on the feasible path.

    Rather than nuke Mars under the aegis of peaceful application of nuclear power Mars itself play into the hands for digging machines. As the planet is thermally dead and assuming shifts and moves in frozen tectonic is nonexistent one could dig rather easily into Mars’ soil as deep as want and at whatever angel necessary. On Earth the deepest borehole is 12km. The deepest mine is at 4500 km and yet man can’t be there w/o proper ventilation and cooling. High humidity and 45-60C is not environment where you can exist. On Mars to reach these kind of parameters probably have to dig tens of kilometers. The caves discovered under 3km the crust is facinating – natural cavern with 180m ceiling it’s 3 Statue of Liberty with spare room (or 4 minus the torch).

    There is no need to transport heavy machinery to Mars if we could figure out how to produce tools and machinery by now rapidly evolving 3D printing technology from resources Mars provides. It has plenty of them the question is energy supply.

    Still nukes are something from Dr. Strangelove, though I love the movie.

  • Dmitri March 17, 2013, 18:35

    No, I was wrong. Not 3 projects.

    Right now in the States is a boom of domestic gas and oil production mainly due to fracturing crust – shale oil, shale gas. The business is so big that even Hollywood made the entry into the sector – Promised Land w/ Matt Damon.

    Russians have discovered it long time ago. In the 50’s and 60’s they explored the possibilities by fracturing the crust by kiloton explonsions. They succeeded. It gave results but still fallout was an issue.

    What they also did was successfully close uncontrolled wells. When Deepwater Horizon accident happened it was luckily contained in 90 days. Just 90 days. Russians struggeled to close a runaway gas well which raged three years. YEARS, not months, YEARS. Can’t say what yield they used but it turned out to be successfull. The same approach was used for later times when these totally out of hand wells happened. In total they abondened both approaches. Well, nowadays noone would consider nuke one’s soil just for economic benefits.

    Now if the Deepwater Horizon well would have been still runaway for 3 years? That would have meant it would been leaking up until this very moment. Would US have used use a kiloton nuke to close the well for good?

    Entry from wikipedia – http://en.wikipedia.org/wiki/Deepwater_Horizon_oil_spill#Considerations_of_using_explosives
    “Considerations of using explosives

    In mid-May, United States Secretary of Energy Steven Chu assembled a team of nuclear physicists, including hydrogen bomb designer Richard Garwin and Sandia National Laboratories director Tom Hunter.[71] Oil expert Matthew Simmons maintained that a nuclear explosion was the only way BP could permanently seal the well and cited successful Soviet attempts to seal off runaway gas wells with nuclear blasts. A spokesperson for the US Energy Department said that “neither Energy Secretary Steven Chu nor anyone else” ever considered this option.[72][73] On 24 May BP ruled out conventional explosives, claiming that if blasts failed to clog the well, “we would have denied ourselves all other options.”[74]”

    At that time Russians on their news channels openly discussed usage of nukes after all failed attempts. Yeah, noone have tried to detonate a kiloton device at 910 m (3000 feet) or deeper, but there is always a first.

    This is a clear case of terraforming using nukes. These are good examples of extreme measures when the usage is justified. Would US consider to do underwater kilton nuke explosion on it’s soil for these kind of desperate measure?

    Regardles of the answer the question is will we perform earthmoving attempts on the Mars the same way IF we already know the outcomes from the history on Earth. The same moral and political issues will arise like with the theoretical Deepwater Horizon closing.

    Power is nothing without control.

  • Eniac March 18, 2013, 0:06

    Not difficult to transport a drilling rig and a bomb. Bruce Willis would agree.

    Yes, but did Bruce Willis consider that drilling rigs generally weigh between 100 and 500 tons, no less than tunneling machines? You do get a bigger bang with the bomb, but I am afraid mass to transport does not favor one or the other method, much.

  • GaryChurch March 18, 2013, 11:02

    “-drilling rigs generally weigh between 100 and 500 tons, no less than tunneling machines?”

    Lightweight rigs that drill a hole a couple feet in diameter straight down weigh no less than a giant tunneling machine? Puh-leez.

    I do not believe that is anywhere close to the truth.

  • Eniac March 18, 2013, 23:33

    Lightweight rigs that drill a hole a couple feet in diameter straight down weigh no less than a giant tunneling machine? Puh-leez.

    How deep do you want to make your hole? The drill string alone may easily go over your weight limit, not even counting all the machinery at the top end. Here is a table of drill string specifications: http://www.drill-pipes.com/drill-pipe-specifications.php.

    The largest on there is 6 5/8 inches in diameter and weighs 25 lb/ft, or roughly 40 tons per km. For a diameter of a “couple of feet”, it would be presumably much, much heavier still. Then, you need casing, cement, drill fluid, etc…. I think you get the idea. Certainly more than 100 tons. “Puh-leez” indeed.

  • GaryChurch March 19, 2013, 13:46

    Let us not start another endless debate.
    It would most likely be possible to use a penetrator accelerated in space to the speed necessary to penetrate to the desired depth. Space is good for getting things to go fast.
    So no tunneling machine, no drilling rig, just a bomb designed to go really deep and explode- leaving the entry channel for access.