Supporting Life

[Robert Maxwell]

As a hobby project, I am working on a simulation system that involves simulating star systems, planets, life forms, etc. I am doing my best to incorporate sound science--not all stars will be able to have planets supporting life, for instance, and all stars will go through stages and have lifespans based on their mass.

One issue I am struggling with a bit is the basis for life, though.

Other concerns aside (such as the habitable zone, gravity, etc.), each planet will have an atmosphere, hydrosphere, and lithosphere. Each of these will be composed of three dominant elements. Earth, for instance, would have an atmosphere that is predominantly nitrogen, oxygen, and argon; a hydrosphere that is predominantly hydrogen, oxygen, and sodium; and a lithosphere that is predominantly oxygen, silicon, and aluminum.

Given the relative abundance of carbon in the rocky planets of our own solar system, I think it would be generally safe to assume its abundance in the solar systems of other main sequence stars. The same can be said for silicon, too, which has been hypothesized as a basis for life. Are there any other elements with properties similar to carbon or silicon that could be used as a basis for life? I have seen nitrogen, phosphorous, and a few others suggested, but how plausible are they?

Second, I have to consider solvents. Water is, of course, the one we are most familiar with, but ammonia also seems to be a popular alternative. Are there any others?

For my simulation, I intend to evaluate the chemical suitability for life on a planet based on whether it has an abundance of appropriate elements. So, I would need a list of "primary" elements (carbon, silicon, etc.) for the biochemical basis and then a list of "secondary" elements (hydrogen, oxygen, nitrogen, etc.) for the solvent basis. If a planet has at least one of the primary elements in abundance, and at least two of the secondary elements, that seems like a reasonable enough basis to say the planet, at least chemically, could support life. That's no guarantee life will emerge there through the course of the simulation, I'm just looking for a baseline to say "this planet could develop life."

Asking my question more broadly, what would be sane parameters to use to determine whether a planet can chemically support life?

 

[Pauln6]

Awesome project - a potentially useful tool for any Star Trek roleplaying game! I have no useful information personally but I found this to be interesting:

http://www.newuniverse.co.uk/Astrobiology.html
http://www.xenology.info/Papers/Xenobiology.htm

I don't think it adds anything useful to what you already know though. It looks as though the 'habitable zone' could be wider than first thought once you take into account heat generated by tidal forces and the greenhouse effect of distant planets and moons with thick atmospheres. Silicon and boron seem to be the most likely candidates for the basis of organic life so far, although not at Earthly temperature and pressure ranges.

The Xenobiology paper also notes this:

"We can imagine four broad classes of metabolic entities – chromodynamic or nuclear lifeforms, electromagnetic lifeforms (e.g., all Earth life, including humans), weak lifeforms, and gravitational lifeforms. Each is most likely to evolve in those environments where the forces upon which they most depend predominate over all others.
For example, gravitational lifeforms, should they exist, survive by making use of the most abundant form of energy in the universe. Gravity is also the most efficient – this is why a hydroelectric power station which converts the energy of falling water into electricity (essentially a controlled gravitational contraction of the Earth) can have an efficiency close to 100%. In theory, gravity beings could be the most efficient creatures in the universe. Their energy might be derived by arranging encounters of collisions between black holes, galaxies or other celestial objects, or by carefully regulating the contraction of various objects such as stars or planets. These beings need not be astronomical in size. Rotational and orbital motions of planetary bodies could serve as sources of gravitational power. Comparatively small lifeforms might survive by harnessing the energy of waterfalls, wind patterns, tides and ocean currents, or even seismic disturbances.
Chromodynamic creatures may evolve in an environment where nuclear forces are predominant. While the chromodynamic force is the strongest in nature, it is effective only over ranges of about 10-15 meter, so very special conditions might be required for such life to exist. These conditions possibly could be found inside a neutron star.
Neutron stars are heavy, rapidly spinning objects 10-20 kilometers in diameter with approximately the mass of a star. They have densities like nuclear matter, tremendous magnetic fields. surface gravities in excess of 100 billion Earth-gees, and are thought to be the energy source for pulsars. Neutron stars have atmospheres half a centimeter deep and mountains at most one centimeter high. Under the three-kilometer crust of crystalline iron nuclei a sea of neutrons circulates at a temperature of hundreds of millions of degrees. In this sea float a variety of nuclear particles including protons and atomic nuclei. Scientists believe that there may be neutron-rich “supernuclei” or “macronuclei” dissolved in the neutron sea. These macronuclei might contain thousands of nucleons (as compared to only a couple of hundred in normal matter) which could combine to form still larger supernuclei analogous to the macromolecules which make up earthly life. The neutron sea may be the equivalent of water in the primordial oceans of Earth, with macronuclei serving as the equivalents of amino acids, carbohydrates, and nucleotides in the prebiotic origin of life. It is possible to conceive of life evolving in neutron stars much as it did on our own planet nearly five billion years ago, but substituting atomic nuclei, supernuclei and neutrons for atoms, molecules and water.
Weak force lifeforms would be creatures unlike anything we can readily imagine. Weak forces are believed to operate only at subnuclear ranges, less than 10-17 meter. They are so weak that unlike other forces, they don't seem to play a role in actually holding anything together. They appear in certain kinds of nuclear collisions or decay processes which, for whatever reason, cannot be mediated by the strong, electromagnetic or gravitational interactions. These processes, such as radioactive beta decay and the decay of the free neutron, all involve neutrinos.
A weak lifeform might be a living alchemist. By carefully controlling weak interactions within its environment, such a creature could cause its surroundings to change from a state of relatively high “weak potential” to a condition of low “weak potential” and absorb the difference into itself. A state of high “weak potential” might be characterized by extreme instability against beta decay – perhaps these beings are comprised of atoms laden with an excess of neutrons and become radioactive only when they die.
Electromagnetic lifeforms also may assume many different shapes. Any creature that makes use of electromagnetic atomic bonding, electron flows, or electric and magnetic fields is a member of this class. All biochemical life on Earth or any other planet meets this test, but there may be many other kinds of alien living systems which also qualify. For instance, the advancing intelligence and versatility of electronic computers suggests that some sort of solid state “machine life” may be plausible. Such entities would survive by manipulating electron flows and fields in order to process matter-energy and patterns of information.
Another outré possibility is the proposal by Jean Schneider of the Groupe d'Astrophysique at the Meudon Observatory in France that a crystalline nonchemical form of life is theoretically feasible using arrangements of crystal dislocations. Schneider describes a primitive memory process that provides a rich, stable information storage system, using what he calls “dislocation loops” which can react and interlock and are capable of being diffused into the surrounding medium in coherent form. Such crystalline physiologies might be found in any of four different places: (1) the rocks on Earth and other planets; (2) interplanetary or interstellar dust grains; (3) in the dense matter of white dwarf stars; and (4) in the crust or core of neutron stars.
Venturing still further afield, someday we may meet electromagnetic creatures such as those described in astronomer Fred Hoyle's The Black Cloud. In this science fiction classic, a great cloud of ionized gas approaches our Solar System and engulfs the Sun, shutting out its light and warmth. Scientists eventually discover that the Cloud is a giant living creature operating on the principles of plasma physics rather than the usual molecular biochemistry. Memory and intelligence are stored on an electrically conductive substrate of various solid materials. Streams of ionized gases carry “nutrients” to wherever they are needed within the Cloud, controlled purely by means of electromagnetic forces."

 

[Robert Maxwell]

Nice site, but you're right, it doesn't tell me much I don't already know.

 

[SamuraiBlue]

Although not within the parameters you had seted, you'll also need a magnetosphere to shield the planet's atmosphere from being blown away from solar wind which means the planet needs an iron core with radioactive material to maintain heat within the core.
You'll also need strong electrolyte substances like H,O,Na,K,Cl,etc for life to develop an energy transfer mechanism.
A counter balance like are own moon is also recommended to stabilize the rotating axis of the planet.

 

[Robert Maxwell]

I'm handwaving the magnetosphere issue. Is it not true that a rocky planet with a weak magnetosphere would also have most of its atmosphere blown away? So, if I generate a planet with (almost) no atmosphere, one could attribute that to the lack of a strong magnetosphere, and thus the lack of an iron core.

The electrolyte and moon stuff is useful, too! I'm sure this will all end up in some SupportsLife method to determine one way or the other whether the planet could have life emerge.

 

[SamuraiBlue]

I'm handwaving the magnetosphere issue. Is it not true that a rocky planet with a weak magnetosphere would also have most of its atmosphere blown away? So, if I generate a planet with (almost) no atmosphere, one could attribute that to the lack of a strong magnetosphere, and thus the lack of an iron core.

Not always, if the planet is too small or absence of radioactive material to maintains the heat within the core then the core cease to rotate that powers the dynamo effect that creates the magnetosphere.

 

[Robert Maxwell]

I'm handwaving the magnetosphere issue. Is it not true that a rocky planet with a weak magnetosphere would also have most of its atmosphere blown away? So, if I generate a planet with (almost) no atmosphere, one could attribute that to the lack of a strong magnetosphere, and thus the lack of an iron core.

Not always, if the planet is too small or absence of radioactive material to maintains the heat within the core then the core cease to rotate that powers the dynamo effect that creates the magnetosphere.

Then I refer back to my original plan to ignore the issue.

I am willing to handwave a fair amount of stellar parameters because the focus of the simulation is on the life aspect. Once life emerges on a planet, a whole different set of logic is involved. Species will have (rather simple) DNA, there will be frequent speciation (since I'll deal with large timescales), and some species may evolve the right traits to become a civilization (a combination of high intelligence, a high place on the food chain, and toolmaking). An advanced enough civilization will spread beyond its home planet, and perhaps encounter other civilizations. It is the rise and fall of species and civilizations, as well as their interactions, that is the focus of the simulation.

So, I am willing to omit significant detail in terms of stellar and planetary dynamics. I may bring the magnetosphere issue down to a simple boolean--either it has a sufficient one or it doesn't, and if it doesn't, bye-bye life.

 

[SamuraiBlue]

If you are focusing on development and evolution of life then I suggest a stress parameter since change within the environment is the driving force for evolution and advancement of technology.
Bio diversity is also something you need to consider. Lack of bio diversity may result to mass extinction of one species creating a cascade failure of the entire eco-system.

 

[Robert Maxwell]

Yup, I have considered that. Individual species will rely on types of food sources rather than a specific species. But since each species will have its own types to feed on, it is conceivable that one species could find itself in a niche where it has nothing to feed on, and die out. Say, a species that is carnivorous but manages to eat all other animals--they will be left in a world full of plants, and unless some of them develop the ability to subsist herbivorically (which would require enough DNA drift to consider them a new species), their lineage would die out entirely.

I'm curious about this "stress parameter," though. Is that basically what I just described above? The loss of a food source, a catastrophic environmental change, etc.?

Something this makes me consider is that, the larger a species' population gets, the lower its overall mutation rate should be. It would still speciate, but the populations of new species would be rather small, presumably from geographically-isolated pockets of the original species. If population crashes, however, the mutation rate should increase and allow rapid speciation. Not all species to come out of this will survive--it is a given that most will die out, in fact.

That seems fairly consistent with how evolution works in nature, at least.

 

[Pauln6]

I suppose you might even have to factor in the occasional interference from an extra-terrestriel species too although in the grand scheme of things, if you want to remain reasonably scientifically accurate, the odds of an intelligent species having technology to reach a nearby solar system are infinitessimal - unless you are the borg.

 

[Robert Maxwell]

Civilizations will have "technology levels," and they can indeed reach a level where they can travel to other star systems, terraform planets, etc. However, I'm going to make it a difficult level to reach!

Spacefaring civilizations may encounter one another, and depending on their dispositions, they could trade and coexist, or make war until one wipes out the other.

 

[SamuraiBlue]

Stress is not always catastrophic, for example the periodical change in temperature, amount of sun light, tidal level, etc. Hypothetically periodical change in gravity intensity, amount of radioactivity, electromagnetism, etc. should also provoke change.
Migration,hibernation,etc are means in copping with stress of lack of food supply.

 

[Pauln6]

Spacefaring civilizations may encounter one another, and depending on their dispositions, they could trade and coexist, or make war until one wipes out the other.

Sweet! Make sure you factor in the possibility of space bikinis.

 

[Robert Maxwell]

Stress is not always catastrophic, for example the periodical change in temperature, amount of sun light, tidal level, etc. Hypothetically periodical change in gravity intensity, amount of radioactivity, electromagnetism, etc. should also provoke change.
Migration,hibernation,etc are means in copping with stress of lack of food supply.

True. This is a very macro-level simulation, though, so seasonal effects (such as hibernation) will not be taken much into account. I will certainly have random disturbances in environmental norms, though, like those you mentioned. Depending on the traits of individual species, they might find the changes beneficial, devastating, or completely benign.

 

[SamuraiBlue]

I remember reading a short story written by Hoshino Yukinobu a Japanese Si-Fi author about a planet orbiting a trinary star system and every 300 years or so the stars align themselves creating a devastating heat surge upon the planet.
A fish like creature native to this planet develops a method to jump through time to escape the periodic heat surge.
Without stress, a life form would not need to adapt resulting to no evolution of species.

 

[Zachary Smith]

Don't forget to consider the possibility of methane acting as solid, liquid and gas in a low-temperature biosphere, taking the role of water in our own system.

 

[Canadave]

You may want to take a look at Noctis, which features a procedurally generated galaxy with a radius of 90,000 light years. There are no civilizations in the game, but there are planets with life (though they are relatively rare and hard to find). I know the source code is available online, so that may give you some clues for what you're looking for.

 

[Robert Maxwell]

I love Noctis! I didn't realize the source code had been released, though. That's awesome.

Thanks for the methane tip, Zachary. It makes sense that CH4 could be an H2O analogue, considering NH4 is in the same boat.

 

[Lindley]

Noctis sounds kind of cool. Is there a point to it?

Sucks that it doesn't have black holes.....I'd love it if a space sim went to the trouble of actually doing the math to show what a fall into a black hole would look like.

 

[Robert Maxwell]

I believe the "point" of Noctis is to chart the myriad the stars and star systems in it. It is a pure exploration game. You fly around, see what's out there, and if you come across a star system that hasn't been charted yet, you can name it. People submit their charts to the maintainer and it gets added to the master star chart. It's pretty cool, although I don't know if the charts are still maintained.