Home > Clement's Game, Fermi Problems, Greg Benford, Hal Clement, Larry Niven, Worldbuilding > Your Turn, Round 2-2: Life In Vacuum

Your Turn, Round 2-2: Life In Vacuum


For the second alien species in the Fermi Problems setting, I decided to go with another take on the “Where are they?” line.  Fermi’s argument for a spacefaring civilization spreading across the galaxy in only a few million years depends on a long period of nearly exponential growth and on a travel speed that is a significant fraction of the speed of light.  My friend Jacob Haqq-Misra has worked out some limitations on the rapid growth of civilizations, but I decided to design aliens who could not travel at more than 0.001 c.  This requires two things: a species that cannot handle high acceleration, and a technology base that does not allow them to either engineer themselves or robotic emissaries to accelerate faster or to build a rocket that can continuously accelerate for a very long time.

The latter is a rather severe limitation.  Accelerating at 0.03 m/s^2, a spacecraft would still reach 0.003 c after 1 year and cover ~8 lightyears in a century if the acceleration was sustained.  The later is unlikely for something internally powered: fusion rockets are limited to maybe 0.1 c peak speed, given the requirement to stop at the destination.  Even a Bussard ramjet is limited to 0.119 c by the exhaust velocity of the fusion rocket.  But I have set a speed limit of 0.001 c or 300 km/s.  Even a fission-reactor-powered ion engine could in theory reach or somewhat exceed that speed.  So, I needed to design a species that cannot handle high acceleration and can travel interstellar distances with nothing fancier than a chemical rocket.  Taking some liberties with biochemistry, I propose a biosphere that evolved on small asteroids in the nominal habitable zone of a binary made of two M-dwarf stars.  I picked CM Draconis because there is a lot of data available on it, it doesn’t have any large planets in the habitable zone, and it isn’t too close to Earth.  Once again, I gave the fictional version of it a name in addition to the catalog listing: Druk.  It happens that CM Draconis forms a hierarchical triple system with a white dwarf, GJ 630.1B, several hundred AU away.  Continuing the theme, call it Wyvern.

Low-Pressure Biology

I fully confess that the following is far more improbable than the ursians are, because the reservoirs for biochemistry to develop in are far smaller if for no other reason.  With that caveat, I ask for any reasons why it is impossible, rather than merely incredibly improbable (levels of likelihood comparable to large-scale quantum tunneling may be counted as impossible).  The improbable makes for good science fiction; the impossible is not allowed.

Things started somewhere like this (main-belt asteroid 253 Mathilde, imaged by the NEAR spacecraft).

Things started somewhere like this (main-belt asteroid 253 Mathilde, imaged by the NEAR Shoemaker spacecraft).

Consider a water- and carbon-rich asteroid, between a few hundred meters and a few tens of kilometers across.  The particular object we are discussing doesn’t exist anymore, but it was like billions of others: a rubble-pile of variously-sized grains.  Fine-grained material accumulates in dust ponds on such objects, and on a carbonaceous-chondrite object those grains will be rich in a slew of various relatively complex carbon compounds.  This much is well-established.

The fictional assumption that I invoked was for there to be enough chemistry going on in those dust ponds (using monolayers of water molecules on the grain surfaces?) to produce small closed membranes durable enough to keep their contents separated from the surrounding grains and protected from being shaken off a grain into the surrounding vacuum while still being permeable enough to allow new molecules in.  From there, chemistry proceeds to something that is self-catalyzing and rather like a protocell – similar to the bubble model of abiogenesis.

Given this admittedly out-there assumption, I can invoke evolutionary processes to expand this strange biosphere.  Cells with vacuum-tight walls, high radiation tolerance, and specialized molecule-sized valves survive better; on the surfaces of the ponds as well as beneath them and inside ejected meteoroids.  Photosynthesis takes over from feeding on primordial and cosmic-ray-seeded high-energy compounds.  Heterotrophs feed on the plants and on each other; larger and better-armored multicellular plants enjoy a survival advantage and larger animals evolve to feed on them.  Eventually, three-dimensional forests grow out from small cores – collecting a hundred times as much light as compared to if they only coated the rock.  I was inspired to this design by some speculation by Freeman Dyson and possibly by some of the pictures in Le Petit Prince.  Conveniently, these forests will be incredibly hard to observe over interstellar distances: they are dark in the visible, and infrared telescopes don’t have the same resolution as optical or radio arrays.  Even if they are seen, the forests will be confused for boring dead carbonaceous asteroids until and unless their orbits are known well enough to measure their masses from mutual perturbations – showing how low their densities are.

The first rock was destroyed in a collision within a few hundred million years of the first appearance of life, scattering microbes across the system in the debris.  Objects within the entire habitable zone have things growing on them; going too far out from the star causes un-insulated cells to freeze.  On a timescale of a hundred million years, each individual forest is destroyed.  On a much much shorter timescale, the plants break off rocket-propelled seed pods and solar-sail leaves that search for other objects using chemical-imaging tracers (the sail leaf idea was used by Larry Niven in the form of the ‘sail seed’).  The animals that don’t have sufficient hibernation and delta-v abilities of their own hitch rides.

And, because I said there would be one, an intelligent species of animal evolved in one of the larger forests and then spread.  I called them the neari – the etymology is a bit strained, but I hope it sounds cool enough.

Anatomy and Psychology

There is gravity, even on the smallest asteroids, although it can be effectively canceled for fast-spinning objects.  The neari can handle continuous loads of ~0.03 m/s^2 without having too many problems, and can do brief jerks up to several gees.  But they don’t have a physiologically preferred up and down or left-and-right, since the gravitational pull is a very gradual change as they navigate through the forests.  So I designed a body plan for them inspired by sea urchins, crabs, and T4-bacteriophage: an icosahedral central body with limbs (equally validly called ‘arms’ or ‘legs’) at the vertices.  The facets have specialized functions, but the neari are equally capable from all directions:

Concept art of a neari.  This one has mysteriously acquired a Rubik's Cube and a can of Pringles.  The top limbs to the upper left of the picture are holding on to a support (not pictured).

Concept art of a neari. This one has mysteriously acquired a Rubik’s Cube and a can of Pringles (that both of those were on my desk as I made this drawing is pure coincidence). It is looking directly at you with one of its optical eyes and obliquely with an infrared- and a nose-eye. The top limbs to the upper left of the picture are holding on to a support (not pictured).

Four facets contain mouths, with airlock throats leading into a central stomach (the mouths are also used to excrete waste).  Four are optical eyes, based around fish-eye lenses.  Four have lines of infrared-sensitive pits.  Four are blank on the surface, and underneath them are the neari’s central brain lobes.  And four have organs that work only in near-vacuum: nose-eyes.  This is an idea from Hal Clement: in vacuum, molecules travel long distances without collisions.  So a pinhole camera can make an image in molecules as easily as in light, as long as whatever it is looking at is putting out any detectable number of particles.  Neari exoskeletons and plant leaves smell only faintly.  A comet outgassing is detectable tens of thousands of kilometers away – far further along its tail.  An simpler version of this organ is used by the rocket pods and sail leaves to home in on objects.

The neari grow by molting and shedding their exoskeleton, a process which also allows the regeneration of limbs.  Molting grows less efficient with time, and eventually accumulated damage leads to death – although prompt injuries will kill a neari far more quickly.  The other way neari die is by giving birth.  To solve the problem of exchanging genetic material and maintaining a pressurized environment for the embryonic neari to grow in, two neari (of any two of the three different sexes) join along the blank faces and slowly fuse together.  The embryonic neari grow inside the merged exoskeleton, fed by their parents’ bodies.

These biological differences led to some important psychological differences between neari and humans (or ursians).  Neari never know their parents – they are raised by their aunts/uncles and cousins.  The individual is generally seen as less important compared to the family than it is for us.  And sex is not a recreational activity.  I have not fully explored how such different psychology will be reflected in neari culture.  There is one other relevant psychological trait, from the hazard of being stuck in space just out of reach of a claw-hold: neari get very anxious if they aren’t holding onto something.

Culture, Technology, and Starships

The neari culture at Druk is in many senses less fragmented than that of the ursians, even though they’re spread out over cubic astronomical units.  As of 70,000 BCE, you might have been tempted to call them a bronze-age culture.  But there is no such thing as technological levels – real technological developments are spurred by the environment, the available resources and knowledge, and random moments of inspiration.  The neari may have not have any metal other than nickel-iron, but they formed it into knives and hooks and parabolic focusing mirrors.  Reflecting telescopes and heliographs gave light-speed communication across all of Druk, at least at telegraph-equivalent bandwidth.  Writing preserved information.  The neari had chemical rocketry, using rocket pods, and solar sails, made by cultivating and then trimming the leaves of sail plants.  Travel between the forests, while slow and mass-limited, was inexpensive, and the neari understood Newtonian mechanics, radiation pressure, and numerical integration.

That said, the forests were isolated enough from each other that they retained very different cultures.  Wars were not unknown, although they were limited in scope by the very low population density.  Enough cooperation between forests did happen to organize large scale projects, including starships.

Druk has two red dwarf stars very close to each other, with an orbital velocity of ~75 km/s.  With a little extra help from the super-jovian gas giant (>5 AU from the stars) and Wyvern (~500 AU), a careful gravitational slingshot maneuver past both stars can give an escaping interstellar spacecraft a velocity of ~300 km/s.  And the neari already have things that can be turned into starships: comets (I got this idea from Greg Benford and David Brin).  Several cubic kilometers of comet ice/organics contain ~3e16 J of usable chemical energy, enough to support 100 neari and their life-support system for tens of thousands of years.  Select a comet about to make a close flyby of the stars, trim its orbit with high-speed impactors so that it gets ejected at high speed, jump on board before the flyby, afterwards adjust your trajectory using the gas giant or the white dwarf, and then burrow down under the surface for the long ride.

The problem with these comet boats is that they can only be targeted onto a certain range of trajectories, only a small fraction of comets are suitable (e.g. the comet has to be big enough to survive the stellar flybys), and the accuracy of the navigation can only be so good.  The comets jet out gas unpredictably at perihelion, and even if the comet boat’s trajectory was known perfectly that of the destination star isn’t.  The neari can measure parallax and proper motion accurately, but radial velocity is only approximate.  A 0.1 km/s error at launch would be 1000 AU at arrival, and the comet boat can’t change its velocity by too much more than that en route.

For purposes of the setting:

The neari did start to spread across interstellar space ~70000 years ago – launching comet boats every few thousand years.  But only one of them got close enough to its target star for the neari then on board to ditch the comet and stop.  The others are either confirmed to be dead, still flying through the void, or unknown in status because they stopped replying to heliograph calls centuries ago.  So Druk and Wyvern (the latter has a small debris disc out to a few hundredths of an AU from the star that the neari have settled) are still the main place to find the neari and there they are hard to see from parsecs away.

Does all of this work for a species that can travel over interstellar distances without being readily detectable, while simultaneously not spreading so fast that we should expect them to be here already?

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  1. 2012/12/29 at 3:53 pm

    This is a very interesting scenario. The only thing I’m worried about, biologically, is the loss of volatiles. Can asteroids in the habitable zone retain water over geological times? Also, if we are to be strict about the ~0.003 g limit, then the life forms could not withstand much pressure, and you would need to choose a biochemistry that does not require free gases.

    My other concern is self-consistency with the rocket pods. They could exert a lot more acceleration than 0.003 g, and they probably would at least during launch to escape a larger asteroid’s gravity well quickly. But I suppose it’s only improbable that the neari are that delicate, not impossible.

    Some other observations:

    The problem of being stranded without a handhold could be mitigated by throwing or expelling some kind of reaction mass.

    If we are to be strict about the 0.003 g limit, the neari could not move very fast. This is not necessarily bad, but it could be important.

    We can measure radial velocities to much better precision than 0.1 km/s (as in planet hunting), and the neari should be able to as well with reasonable spectroscopic tools.

    The neari are definitely not readily detectable over interstellar distances both because they don’t live in the obvious places to look and because of the small scale of their constructions.

    • michaelbusch
      2012/12/30 at 2:43 am

      In order:

      1. Some objects in the near-Earth population are ~20% water by mass. The water is held as chemically-bonded H2O and OH integrated into the carbonaceous and silicate grains. It doesn’t escape to space. The out-there assumption that I have made here is that there is enough chemistry going on on the surfaces of those grains for abiogenesis to happen.

      2. The rocket pods can and do accelerate at much more than 0.03 m/s^2, although not to escape from the asteroid they start on (escape velocities are meters per second and surface gravities are millimeters to centimeters per second squared). The higher acceleration is necessary to match velocities with a destination object when it gets in range of a pod’s chemical sensors. To use a pod, the neari cover the sensors and ignite the rocket artificially. They’re using them for trajectory correction of a much more massive system (pod+neari+cargo), so the acceleration is bearable.

      3. Neari anxiety about handholds is mitigated if they are holding a hook with a line, or even a just a rock to throw themselves onto a new trajectory.

      4. As I said above, the neari can handle brief episodes of high acceleration, ~1 g for ~3 s, much as how humans can survive shocks of many tens of gravities. This lets them jump and land. They can swing on lines, although not particularly quickly or for too long. They can also handle internal pressure. Their insides are pressurized well enough to allow water-dominated fluids to be stable; and the stomach and throats can be at anything from zero pressure to several tens of kilopascals. The problem with higher gravity is that if the pressure inside the neari’s central body is more than ~100 Pa higher on one side than on the other, its circulatory system isn’t able to work against the pressure difference. Its hearts aren’t very strong.

      5. It is true that _we_ can measure stellar velocities to very high precision. Alpha Cen Bb perturbs Alpha Cen B’s velocity by ±0.5 m/s, and it is neatly detected by the HARPS spectrometer. But if I give the neari the technical expertise to do that, they will be able to do many other things that make the ‘stone-age starship’ idea invalid. Even a spectrometer accurate enough to give radial velocities to 100 m/s is pushing things in terms of technology that the neari wouldn’t also use to make themselves very visible to everyone. I had the neari do that by putting a grating in the line of a big cooking mirror and figuring out that there was a hot spot in the focal plane that moved as the velocity of the star it was pointed at changed, and not extending that technology to a quantitative understanding of spectroscopy. A perhaps less-disruptive alternative is for them to have plotted stellar positions to ~0.1″ for two thousand years; that will give the line-of-sight velocities of stars within 10-20 parsecs to the necessary precision from the changing angle between the star’s velocity vector and the line-of-sight.

  2. michaelbusch
    2013/01/03 at 10:08 pm

    Note:

    The neari and the ursians also avert a problem Hal Clement noted with a lot of mid-20th-century science fiction, called Clement’s Paradox: “The universe is old, and alien civilizations should have been around a long time in diverse environments. Why then do scifi aliens have technological capabilities similar to the humans that encounter them?”

    The neari avert this by having only the simplest of tools (and yet still manage to launch starships).

    The ursians avert this by being very advanced in some areas, such as hydration-based organic chemistry and aerogel manufacturing, but not doing much in terms of nuclear physics or anything in terms of space travel.

  1. 2013/05/25 at 12:35 am
  2. 2013/11/27 at 4:45 am
  3. 2015/11/22 at 8:27 am

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