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Risk Mitigation for Advanced Civilizations

Alastair Reynolds’ 2008 novel House of Suns contains what must be the most outrageous solution for an endangered civilization I’ve ever encountered. Set some 6 million years in the future, the story involves technologies at the Kardashev Type III level — in other words, civilizations that are capable of harnessing the energy of entire galaxies. At one point, a supermassive star whose pending death threatens a local civilization is enclosed in an enormous ‘stardam,’ made out of remnant ‘ringworlds’ from a long-lost culture that litter the galaxy.

I believe we’re normally considered to be at about Kardashev level 0.7, so a feat like this is utterly the stuff of science fiction, but in Reynolds’ hands it makes for a robust tale. Here’s how future humans discuss it in the novel:

To dam a star, to enclose it completely, would require the construction of a Dyson shell. Humans can shroud a star with a swarm of bodies, a Dyson cloud, but we cannot forge a sphere. Instead we approximate one by surrounding a star with thousands of ringworlds, all of similar size but with no two having exactly the same diameter. We make a discus and then start tilting, until each ringworld is encircling the star at a unique angle. The light of the star rams through the narrowing gaps as the ringworlds tighten into their final orientation. Shutters close on a fierce, deadly lantern.

And there you are — what would have been death by supernova becomes averted as the energies of the dying star bounce back and forth between these myriad reflecting surfaces until over aeons, they gradually leak out as infrared. If this seems surreal, the novel even trumps the stardam with a star (in the Andromeda galaxy) completely enclosed in a representation of the Platonic Solids. To learn how this came about, I send you to Reynolds, for whom I’ve developed great admiration in the last five or six years. This is an author whose concepts are big enough to call up Olaf Stapledon and Star Maker (1937).

The Threat from Exploding Stars

I was delighted to see that Milan Ćirković, whose work we’ve looked at frequently in these pages, mentions House of Suns in his new paper, slated to appear in Acta Astronautica. Ćirković (Astronomical Observatory, Belgrade) has been a key player in the definition and exploration of so-called Dysonian SETI, which involves moving beyond radio and optical wavelengths to consider the possible signature that a truly advanced civilization might leave through its activities, which do not necessarily involve communication.

We looked last summer at the possibility of ‘stellified’ objects, in a Ćirković paper that considered the manipulation of a gas giant or even a brown dwarf to extract energy, and the SETI observables this might create (see SETI: Detecting ‘Stellified’ Objects, or Rethinking SETI’s Targets). The new work, written with Branislav Vukotić (University of Oxford) looks at the response by an advanced civilization to threats from supernovae and gamma ray bursts (GRBs), with the nod toward the Reynolds novel coming in as an extreme response by what the paper refers to as humanity++, a civilization capable of interstellar flight and engineering at the interstellar level. This is a culture that may be biological or not, but it is one capable of changing its environment at large scales of space, time and energy.


Image: On January 21, 2014, astronomers witnessed a supernova soon after it exploded in the Messier 82, or M82, galaxy. Telescopes across the globe and in space turned their attention to study this newly exploded star, including Chandra. Astronomers determined that this supernova, dubbed SN 2014J, belongs to a class of explosions called “Type Ia” supernovas. These supernovas are used as cosmic distance-markers and played a key role in the discovery of the Universe’s accelerated expansion, which has been attributed to the effects of dark energy. Scientists think that all Type Ia supernovas involve the detonation of a white dwarf. One important question is whether the fuse on the explosion is lit when the white dwarf pulls too much material from a companion star like the Sun, or when two white dwarf stars merge. Credit: NASA/CXC/SAO/R.Margutti et al.

All of this makes for fascinating speculation on the SETI level, and I intend to get to that in a subsequent article, but the bulk of the new Ćirković paper deals with the far-future scenario by way of contrasting it with a culture not terribly more advanced than our own. The author dubs it humanity+, a civilization perhaps of the Kardashev 1 level or a bit beyond, that is capable of using the resources of the Solar System for industrial purposes, asteroid mitigation, exploration and colonization. This is a culture we could, barring various forms of intervening catastrophe, imagine emerging on and from our planet within centuries.

The question becomes, would a culture that had the means to do it protect itself against existential risk in the form of supernovae and GRBs? We’re currently just learning about what we can do to respond to the threat of impacts on Earth, by studying asteroids and comets to learn how we might alter a dangerous trajectory. We’re also learning about hazards like supervolcanoes, and the ways in which such activity has altered our planet in the past.

Supernovae and gamma ray bursts present what seems to be an entirely different kind of threat, and one that seems to play out on a galactic timescale. GRBs have been considered by some authors as offering a regulation mechanism preventing the spread of life in the distant past of the Milky Way, and it’s interesting that cosmic explosion rates have generally been declining over cosmic time, as shown in cosmological observations and models of star formation. I am not aware of any previous risk analysis on GRBs or supernovae of the sort that Ćirković and Vukotić undertake here, but the paper explains why this is understandable.

While we already have an extensive literature on impact prediction and mitigation, one reason for our attention is the existence of recent evidence, such as the 2013 Chelyabinsk air burst and the 1908 explosion that levelled thousands of acres in Siberia, not to mention our growing understanding of the Late Heavy Bombardment’s effects on the primordial Earth.

Likewise, supervolcanism has been little studied until recently, but while its effects may litter our past, we can also relate it to catastrophic eruptions in our own era, like Krakatoa in 1883 or Mount Tambora in 1815. Supernovae and GRBs are hardly as visible, but we do have reason to believe they can have disastrous effects on a nearby biosphere, and some researchers have argued for certain extinctions in Earth’s history to be the result of nearby cosmic explosions.

Will the threat of such catastrophes drive a future civilization to study mitigation efforts to prevent the worst of their effects? We have to consider the question in long timescales indeed:

…it is reasonable to assume – Earth’s single case notwithstanding – that evolving intelligent beings, not to mention technological civilizations, requires timescales on the order of several Gyr, during which a single close explosion could cut or derail the evolutionary chain of events leading to that outcome, this indicates that once a civilization emerges, it is only rational to seriously consider risk from such events and possibilities of its mitigation.

The paper goes on to refer to simulations reported within its pages by author Vukotić:

While the resolution of the simulation of Vukotić et al. is still insufficient for conclusions about number of individual stars and planetary systems, it is still indicative and motivating for further work in the area. For the present purposes, we note that no part of any spiral galaxy can be considered safe from cosmic explosions in the long run. And as the timeframe considered by an intelligent species grows longer, more relevant becomes the issue of mitigation. It is reasonable to hope that near-future simulations of habitability will offer more complete and precise account of the amount of risk faced by different parts of the Galactic Habitable Zone.


Image: GRB 111209A exploded on Dec. 9, 2011. The blast produced high-energy emission for an astonishing seven hours, earning a record as the longest-duration GRB ever observed. This false-color image shows the event as captured by the X-ray Telescope aboard NASA’s Swift satellite. Credits: NASA/Swift/B. Gendre (ASDC/INAF-OAR/ARTEMIS).

Timing the Event

Mitigation of the damage from a cosmic explosion would seem to be an impossibility, given our lack of knowledge of when one is going to occur. We would need to know not just where the explosion was centered but how strong it would be, and as the paper points out, how isotropic in terms of its emissions. We’re a long way in terms of supernovae, not to mention GRBs, from being able to work out timeframes for the explosion of even nearby stars like eta Carinae. Our present-day technology could do nothing to reduce the effects of a cosmic explosion, but Ćirković and Vukotić, remember, are speculating about a future humanity.

This is a civilization moving past Kardashev Level I that has learned a great deal more than we know about supernovae and GRBs, and the authors see no reason in principle why explosion times, energies, spectra, cosmic-ray acceleration power and other factors for these phenomena will not eventually be much better understood. Prediction is an essential, and while we are well on the way toward predicting dangerous asteroid encounters, we have much to do before we reach the level of understanding that GRB mitigation would involve.

While prediction of weather in its local detail is still notoriously uncertain, the trajectory and timing of hurricanes, cyclones and other storm systems storms is today routinely predicted, often enough in advance for efficient mitigation measures to be deployed. History of science offers many examples of the increase of reliability and accuracy of predictions in various other areas, from eclipses to neutrino pulse from supernova SN 1987 A. Even in the areas where predictions have not built a good track record so far (e.g., earthquakes, volcanic eruptions, economic crises), we are gradually focusing on the main obstacles to further progress and the development of massive numerical simulations did much to understand the related problems much better.

If such prediction could be mastered, then we or some hypothetical extraterrestrial civilization could investigate how to protect our planet or entire planetary system from the effects of a cosmic explosion. What kind of technologies would this most likely involve, and what kind of signature might it leave in our astronomical data? We’ll look at the possibilities tomorrow.

Centauri Dreams’ take: Learning how to predict events like these may be well beyond our understanding, but it is not unreasonable to think that a sufficiently advanced civilization may have found ways to assess their likelihood. Dysonian SETI looks at technologies, Dyson swarms being a classic example, that do not contradict physical law but are beyond conceivable human engineering. It makes sense to consider possible signatures of advanced civilizations even though we are ourselves unable to duplicate them. Thus I agree with Ćirković and Vukotić on this point from their paper:

It is important to emphasize from the outset that while details of the interaction of cosmic explosions with biospheres are still largely unknown, they are of minor importance for the central goal of this paper. As Ludwig Boltzmann [71] famously said: “It may be objected that the above is nothing more than a series of imperfectly proved hypotheses. But granting its improbability, it suffices that this explanation is not impossible. For then I have shown that the problem is not insoluble, and nature will have found a better solution than mine.” [present authors’ emphasis] We would add only that “nature” here should be expanded to encompass actions of advanced technological civilizations – which may or may not be recognizable as such.

The paper is Ćirković and Vukotić, “Long-term prospects: Mitigation of supernova and gamma-ray burst threat to intelligent beings,” accepted at Acta Astronautica. See also Vukotić et al., “‘Grandeur in this view of life'”: N-body simulation models of the Galactic habitable zone,” Monthly Notices of the Royal Astronomical Society published online 12 April 2016 (abstract / preprint).


Comments on this entry are closed.

  • Thomas Goodey November 7, 2016, 14:21

    “… the energies of the dying star bounce back and forth between these myriad reflecting surfaces until over aeons, they gradually leak out as infrared…”

    No. I don’t think so. That’s assuming virtually perfect reflectivity, which is impossible, especially as presumably the repurposed ringworlds weren’t even designed as mirrors in the first place. Actually what would happen is that the energies would leak out as infrared within hours, after the radiation bounced back and forth a few dozen times at most.

  • Alex Tolley November 7, 2016, 14:58

    “a civilization perhaps of the Kardashev 1 level or a bit beyond, that is capable of using the resources of the Solar System for industrial purposes”

    I think that should be Kardashev 2.

    • Paul Gilster November 7, 2016, 15:55

      The authors call it Kardashev 1.x and describe it this way:

      “We suppose that humanity+ is still mostly located on Earth in terms of population and industrial resources, while utilization of resources of the Solar System bodies, notably Moon, Mars, asteroids, comets, etc. is under way. Also, no revolutionary technological breakthroughs/miracles are assumed – no “warp rives”, “photon rockets”, or “zero-point energy engines”. In other words, humanity+ is a placeholder for a small civilization making its first serious steps into interplanetary space.”

      Their ‘humanity ++’ is described as Kardashev 2 and above.

      • Alex Tolley November 7, 2016, 16:05

        I see now. They are not KII as that future civilization isn’t harvesting the total solar output, just extending earth civilization into the solar system.

  • Michael November 7, 2016, 15:51

    The neutron flux is also quite high in a supernova and will transmute many materials damaging the structural integrity.

  • Geoffrey Hillend November 7, 2016, 17:30

    I think the House of the Sun is completely science fiction. It lacks a scientific foundation for the following reasons. 1) Supernovas require a star of with a mass of at least eight solar masses. The lifetime of a star is based on it’s solar mass and the larger the mass of the star the shorter the life of a star. A star with eight solar masses can only last 80 millions years which is far too short for life to evolve on a planet around it. Consequently no such civilizations can ever evolve on a planet in orbit around a supernova since any planets are destroyed or made inhabitable by lost of ocean, atmosphere and radiation from the supernova explosion.

    Larger Stars have a shorter life because the greater mass causes a greater compression and movement of the atoms in the core and a much higher temperature there and faster burning of nuclear fuel. http://cseligman.com/text/stars/mldiagram.htm

    How long would it take to build a Dyson sphere around a 8 solar mass star with such primitive space technology?

    Finally, I don’t think a Dyson sphere or the technology proposed in House of the Suns would fare too well in a super nova explosion if we consider the relativistic cosmic rays, gamma rays and the entire matter of the star, iron core and gas that is expelled at one fifth light velocity in every direction from the center of the star.

    • Cambias November 8, 2016, 10:00

      Well, the novel does say “science fiction” on the dust jacket, so that’s a tip-off, right there.

      Note that in the novel, the “stardams” are not built by a civilization on a world orbiting the incipient supernova. They are built by an interstellar civilization (based on absurdly efficient relativistic starships) and the purpose is to protect worlds in neighboring star systems which would be harmed by the supernova.

      My problem with the stardams is the description of them as a nested set of non-co-orbital “ringworlds.” It was demonstrated back in the 1970s that a ringworld is not stable over the long term — unlike a sphere, the net attraction around a ring doesn’t equal out if you move it. Perhaps there is some kind of active position-controlling method.

  • Douglas Dwyer November 7, 2016, 17:37

    The reflecting surface would work at a a single Microwave? frequency employing a naturally ocurring echoing gallery within a plasma sphere generated by a stellar gravitational collapse. A naturally occurring Dyson sphere/Collapse of the mode would release cosmic levels of energy detectable over light years.

  • James Franklin November 7, 2016, 17:43

    Whilst all science is filled with speculation, it’s that very speculation that drives our knowledge forward, there is speculation here that is way beyond acceptable.

    If these myriad ringworlds were positioned around a star so as to act as a barrier to its emissions I can see numerous issues.

    Firstly, the sheer logistic nightmare of putting all these ringworlds in place around the star would be a monumental challenge by itself, especially as all those suggesting such structures seem to conveniently forget about gravitational forces, dynamical stresses and the pressure of material being ejected from the star.

    Next we have the rather large white elephant in the room..when the star explodes there is no way these polished ringworld’s could possibly contain the enormous forces of the explosion, they would be vapourised along with all other material in the stars vacinity.

    Now let’s take another issue. The emergence of a technically advanced civilisation. We have no idea why a given species comes to dominate it’s environment in such a way it goes beyond nature and becomes what we may class as sentient. There is reason to conclude that environmental pressures are the driving forces, pushing a creature well beyond its ‘comfort zone’ so it’s adaptability becomes a cornerstone of its ability to survive. It appears on Earth that the most intelligence species appear to be predatory in nature, no surprise really as they need to outfox their prey. Some of the most successful are territorial predatory omnivores, and perhaps here is a clue from nature as too the nature of dominant species. The period of time from the rise to the fall of a particular species seems to be about 5 million years, though some exceed this 100 fold and others barely make a few hundred thousand years. Our species has been around perhaps 250,000 to 300,000 years, but it would appear that only in the last 10,000 has humanity managed to rise from mediocrity to where we are now. The Ice ages and other events clearly held humanity back, other species may rise faster, and perhaps die faster or live longer.

    Humanity is on the cusp of overcoming the threats posed by nature, rising to a status and position where we alone could completely eradicate humanity, but even here we cannot do that, there will always be survivors.

    What we have to consider is that technically capable species are the norm on world’s where complex biospheres exist, that if they survive to a point where their technology takes them off their home pla net then the only thing that can kill them will be the death of their star or a massive cosmic event such as a supernova or GRB

  • Sean Robert Meaney November 7, 2016, 23:43

    A Kardishev 3 civ might require the mass production capacity energy needed to build a bunch of rings in their lifetime but we need to build that first space prope needed to collect solar hydrogen and three dee print a ring from the captured protons.

  • Eniac November 7, 2016, 23:48

    There is really no plausible cosmic “explosion” that would affect life on Earth much at all. A GRB focused exactly on us may have some destructive potential if no further than ~50 ly away. Very unlikely, as these things are rare and almost always focused elsewhere. A mere supernova would have very little impact on Earth, even if it was one of the Centauri stars. Space is really, really big, and the stars really, really far away. That saves us from cosmic catastrophes.

    • ljk November 8, 2016, 9:42

      And perhaps lots of other beings throughout the space as well.

    • Alex Tolley November 8, 2016, 13:11

      This paper by Hartmann et al might change your mind.

      • Nelson Bridwell November 8, 2016, 16:12

        The premise of that paper is that the increased UV levels from a nearby GRB/supernova would increase DNA mutation rates, which would slowly change the biological mix of lifeforms. Sorry, but to me that does not sound especially life-threatening for any advanced civilization that has access to sunblock, window shades, and is not overly dependent (as we are) upon the fragile planetary surface ecology.

  • Nelson Bridwell November 8, 2016, 2:51

    From my very casual research it appears to me that a few inches of soil would be more than sufficient to protect a Kardashev Type 0 civilization from the worst that a local neighbor supernova or GRB could throw at them, although there could be some unpleasant side-effects (ozone-depletion induced UV) for those who choose to live in houses built of straw.
    And speaking as an engineer, the “stardam” proposal sounds absurdly inefficient. The two most important factors for mitigating radiation exposure are distance and shielding, so if you build your shield immediately around your population, rather than shielding the entire Universe, the amount of shielding and the corresponding costs will be much less. Furthermore, such a shield would protect them from almost anything else in the rest of the universe, rather than just one troublesome star,

    • ljk November 8, 2016, 10:14

      And ice works even better against radiation, which bodes well for all those worlds with global oceans covered with icy crusts, of which we know more than a few in our Sol system alone.


  • Alastair Reynolds November 8, 2016, 7:30

    Just to pick up on Geoffrey’s first point, although it’s not clear from the extract in the article, the endangered civilisation isn’t on a planet orbiting the star likely to go supernova, it’s in a nearby but separate solar system. All the galactic civilisations (with the exception of the long-vanished Priors) are in any case human or posthuman cultures that have spread out from Earth.

    Thank you to Paul for picking up on this reference to my book in the paper.

    • Michael Spencer November 9, 2016, 7:31

      I was frankly far more intrigued by the handling of human relationships where spaceships making galactic orbits are nearly commonplace, and where experiential time has stretched so far as to have very little meaning.

      The splendidly provocative tech in Mr. Reynolds’ novels places puny humans in extraordinary situations; this is where SF really shines. So it is with “House”.

  • ljk November 8, 2016, 12:24

    Thanks to Breakthrough Listen, the CSIRO Parkes radio telescope in Australia has been fired up to conduct SETI again. Parkes joins the Green Bank Telescope in West Virginia and the Automated Planet Finder at Lick Observatory in California in this effort to see if there is at least someone in this galaxy who has at least some intelligence.

    Its first target is Proxima Centauri:


    To quote:

    CSIRO’s Parkes radio telescope is perfectly positioned to observe parts of the sky that can’t be seen from the northern hemisphere, including the centre of our own Milky Way galaxy, large swaths of the Galactic plane, and numerous other galaxies in the nearby Universe.

    Dr Douglas Bock, Director of CSIRO Astronomy and Space Science, said the Parkes telescope was one of the most highly cited radio telescopes in the world.

    “The Parkes radio telescope has a long list of achievements to its credit, including the discovery of the first ‘fast radio burst’,” Dr Bock said.

    “Its unique view of the southern hemisphere sky and cutting-edge instrumentation means it now also has a great opportunity to contribute to the search for extra-terrestrial life.”


    Breakthrough Listen will use 25 per cent of the science time available on the Parkes radio telescope over the next five years. [This certainly beats the table scraps of the past when SETI had to take what it could get from radio observatories scanning the skies for other purposes.]

  • RobFlores November 8, 2016, 12:28

    Looking at Khar 2 type civilization, that has colonized it’s local 1,000 LY.
    I remember G. Benford’s novel Beyond Infinity.

    In the novel, among some of the more interesting side effects of 1 billion year technological presence of humans was their genetically engineered Space adapted life forms. You see while human civ’s were technological there was an ebb an flow and space faring “kingdoms” rose and fell.

    Left alone these space faring life forms evolved in a myriad of ways beyond their purpose., which leaves one to wonder, if we ever travel to another galaxy, will find life forms that could not have colonized space w/0 genetic design by a super civilization, (lately falling into ruin)
    Would some of them turn Virulent.

    I recall the Episode “Doomsday Machine” in Star Trek,
    maybe that planet destroyer was not originally a menace.
    maybe it was a series of semi-sentient Heavy Terraforming Units
    that went wild.

  • Geoffrey Hillend November 8, 2016, 18:19

    Quote by Eniac: ” There is really no plausible cosmic “explosion” that would affect life on Earth much at all. A GRB focused exactly on us may have some destructive potential if no further than ~50 ly away. Very unlikely, as these things are rare and almost always focused elsewhere. A mere supernova would have very little impact on Earth, even if it was one of the Centauri stars. Space is really, really big, and the stars really, really far away. That saves us from cosmic catastrophes. ”

    A supernova at the distance Alpha Centauri would wipe out all life on the surface of the Earth. A supernova has to be at least thirty light years away for us to be safe. The Earth’s surface would be bathed in gamma radiation and x -rays. People would have to live underground fifty feet. There would also be relativistic cosmic ray atoms which would be following shortly in time behind the electromagnetic black body radiation. Then in thirty years, a relativistic cloud(one fifth light velocity) of highly radioactive atoms from the stars matter would move through our solar system. The Crab nebula, the remains of a supernova explosion, is ten light years in diameter.

  • Dmitry Novoseltsev November 8, 2016, 22:55

    “Planetary size structures with unusually small mass and non-Keplerian motion. In other words, find something the size of a terrestrial planet but with a mass as little as 10-8 Earth mass and suspicion should mount that it is an artifact.”

    See http://lnfm1.sai.msu.ru/SETI/koi/articles/Arhipov_1SWASP.pdf

    1SWASP-J161732.90+242119.0 (TYC 2042-7-1) ?

  • Dmitry Novoseltsev November 9, 2016, 3:33

    In this case in the foreseeable near future, “Shielding Swarms” to protect against the ion flow may consist of a multilayer stack of thin electric solar sails like this (https://jour.space/issues/issue-8-2014/). This will take a little mass and they can be quickly deployed to protect the Earth from the distant flash of a supernova, or, more important, from powerful solar emissions. And to the place of deployment, they all can be delivered quickly to traditional rocket engines with high thrust.

  • Douglas F Dwyer November 9, 2016, 4:54

    You perform a service in trailing these ideas to ignite our imagination; thanks. An idea that explains Fast Radio Bursts, solves other problems.
    A naturally occurring plasma sphere could be a bi product of supernova gravitational collapse, or a black hole. A sphere could store energy as a cosmic resonator at a variety of wavelengths. The collapse of the resonance would give rise to the electromagnetic pulse that we see as an FRB.

  • Dmitry Novoseltsev November 23, 2016, 23:13
  • Nelson Bridwell November 28, 2016, 15:44


    Mass extinctions and supernova explosions.
    Crutzen PJ1, Brühl C.

    In a recent contribution to this journal Ellis and Schramm [Ellis, J. & Schramm, D. N. (1995) Proc. Natl. Acad. Sci. USA 92, 235-238] claim that supernova explosions can cause massive biological extinctions as a result of strongly enhanced stratospheric NOx (NO + NO2) production by accompanying galactic cosmic rays. They suggested that these NOx productions which would last over several centuries and occur once every few hundred million years would result in ozone depletions of about 95%, leading to vastly increased levels of biologically damaging solar ultraviolet radiation. Our detailed model calculations show, however, substantially smaller ozone depletions ranging from at most 60% at high latitudes to below 20% at the equator.

  • Nelson Bridwell November 28, 2016, 15:50


    What we’re really asking is, what stars near us can explode? And it turns out the answer is that there are a lot within a thousand light years, a handful within 500, and none within the hard 50 – 100 light year limit.

    In other words: you can take supernovae off your things-to-be-scared-of list. They’re all too far away, at least for the next few million years.You can breathe easy.

  • Nelson Bridwell November 28, 2016, 16:06

    There is an enormous difference between an event that could cause mass extinctions and an event that could kill off an advanced technological civilization.
    Because most plants and animals are dependent upon fairly fixed environment conditions, any event that significantly disrupts food chains, rainfall, or temperatures is likely to kill off a very significant fraction (but not all) of the biosphere. However, killing off all life is nearly impossible because there are some organisms that live underground or underwater, that are relatively immune to almost anything.
    And an advanced technological civilization, because it has the potential to survive and thrive in space, if prepared, should be able to engineer habitats that can withstand the worst that nature can dish our.

  • ljk December 30, 2016, 14:24

    People, especially space fans, say they want to live in space. But do they really?


  • ljk December 30, 2016, 14:26

    Maybe we won’t find living ETI but the remains of their civilizations:


  • ljk December 30, 2016, 14:33

    The main reason for humans colonizing other worlds – staying alive: