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Until 2006 our Solar System consisted essentially of a star, planets, moons, and very much smaller bodies known as asteroids and comets. In 2006 the International Astronomical Union’s (IAU) Division III Working Committee addressed scientific issues and the Planet Definition Committee address cultural and social issues with regard to planet classifications. They introduced the “pluton” for bodies similar to planets but much smaller.

The IAU set down three rules to differentiate between planets and dwarf planets. First, the object must be in orbit around a star, while not being itself a star. Second, the object must be large enough (or more technically correct, massive enough) for its own gravity to pull it into a nearly spherical shape. The shape of objects with mass above 5×1020 kg and diameter greater than 800 km would normally be determined by self-gravity, but all borderline cases would have to be established by observation.

Third, plutons or dwarf planets, are distinguished from classical planets in that they reside in orbits around the Sun that take longer than 200 years to complete (i.e. they orbit beyond Neptune). Plutons typically have orbits with a large orbital inclination and a large eccentricity (noncircular orbits). A planet should dominate its zone, either gravitationally, or in its size distribution. That is, the definition of “planet” should also include the requirement that it has cleared its orbital zone. Of course this third requirement automatically implies the second. Thus, one notes that planets and plutons are differentiated by the third requirement.

As we are soon to become a space faring civilization, we should rethink these cultural and social issues, differently, by subtraction or addition. By subtraction, if one breaks the other requirements? Comets and asteroids break the second requirement that the object must be large enough. Breaking the first requirement, which the IAU chose not address at the time, would have planet sized bodies not orbiting a star. From a socio-cultural perspective, one could suggest that these be named “darktons” (from dark + plutons). “Dark” because without orbiting a star, these objects would not be easily visible; “tons” because in deep space, without much matter, these bodies could not meet the third requirement of being able to dominate its zone.

Taking this socio-cultural exploration a step further, by addition, a fourth requirement is that of life sustaining planets. The scientific evidence suggest that life sustaining bodies would be planet-sized to facilitate a stable atmosphere. Thus, a life sustaining planet would be named “zoeton” from the Greek zoe for life. For example Earth is a zoeton while Mars may have been.

Again by addition, one could define, from the Latin aurum for gold, “auton”, as a heavenly body, comets, asteroids, plutons and planets, whose primary value is that of mineral or mining interest. Therefore, Jupiter is not a zoeton, but could be an auton if one extracts hydrogen or helium from this planet. Another auton is 55 Cancri e, a planet 40 light years away, for mining diamonds with an estimated worth of $26.9x1030. The Earth is both a zoeton and an auton, as it both, sustains life and has substantial mining interests, respectively. Not all plutons or planets could be autons. For example Pluto would be too cold and frozen for mining to be economical, and therefore, frozen darktons would most likely not be autons.

At that time the IAU also did not address the upper limit for a planet’s mass or size. Not restricting ourselves to planetary science would widen our socio-cultural exploration. A social consideration would be the maximum gravitational pull that a human civilization could survive, sustain and flourish in. For example, for discussion sake, a gravitational pull greater the 2x Earth’s or 2g, could be considered the upper limit. Therefore, planets with larger gravitational pulls than 2g would be named “kytons” from the Antikythera mechanical computer as only machines could survive and sustain such harsh conditions over long periods of time. Jupiter would be an example of such a kyton.

Are there any bodies between the gaseous planet Jupiter and brown dwarfs? Yes, they have been named Y-dwarfs. NASA found one with a surface temperature of only 80 degrees Fahrenheit, just below that of a human. It is possible these Y-dwarfs could be kytons and autons as a relatively safe (compared to stars) source of hydrogen.

Taking a different turn, to complete the space faring vocabulary, one can redefine transportation by their order of magnitudes. Atmospheric transportation, whether for combustion intake or winged flight can be termed, “atmosmax” from “atmosphere”, and Greek “amaxi” for car or vehicle. Any vehicle that is bound by the distances of the solar system but does not require an atmosphere would be a “solarmax”. Any vehicle that is capable of interstellar travel would be a “starship”. And one capable of intergalactic travel would be a “galactica”.

We now have socio-cultural handles to be a space faring civilization. A vocabulary that facilitates a common understanding and usage. Exploration implies discovery. Discovery means new ideas to tackle new environments, new situations and new rules. This can only lead to positive outcomes. Positive outcomes means new wealth, new investments and new jobs. Let’s go forth and add to these cultural handles.

Ben Solomon is a Committee Member of the Nuclear and Future Flight Propulsion Technical Committee, American Institute of Aeronautics & Astronautics (AIAA), and author of An Introduction to Gravity Modification and Super Physics for Super Technologies: Replacing Bohr, Heisenberg, Schrödinger & Einstein (Kindle Version)

It is interesting to note that the technical possibility to send interstellar Ark appeared in 1960th, and is based on the concept of “Blust-ship” of Ulam. This blast-ship uses the energy of nuclear explosions to move forward. Detailed calculations were carried out under the project “Orion”. http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) In 1968 Dyson published an article “Interstellar Transport”, which shows the upper and lower bounds of the projects. In conservative (ie not imply any technical achievements) valuation it would cost 1 U.S. GDP (600 billion U.S. dollars at the time of writing) to launch the spaceship with mass of 40 million tonnes (of which 5 million tons of payload), and its time of flight to Alpha Centauri would be 1200 years. In a more advanced version the price is 0.1 U.S. GDP, the flight time is 120 years and starting weight 150 000 tons (of which 50 000 tons of payload). In principle, using a two-tier scheme, more advanced thermonuclear bombs and reflectors the flying time to the nearest star can reduce to 40 years.
Of course, the crew of the spaceship is doomed to extinction if they do not find a habitable and fit for human planet in the nearest star system. Another option is that it will colonize uninhabited planet. In 1980, R. Freitas proposed a lunar exploration using self-replicating factory, the original weight of 100 tons, but to control that requires artificial intelligence. “Advanced Automation for Space Missions” http://www.islandone.org/MMSG/aasm/ Artificial intelligence yet not exist, but the management of such a factory could be implemented by people. The main question is how much technology and equipment should be enough to throw at the moonlike uninhabited planet, so that people could build on it completely self-sustaining and growing civilization. It is about creating something like inhabited von Neumann probe. Modern self-sustaining state includes at least a few million people (like Israel), with hundreds of tons of equipment on each person, mainly in the form of houses, roads. Weight of machines is much smaller. This gives us the upper boundary of the able to replicate human colony in the 1 billion tons. The lower estimate is that there would be about 100 people, each of which accounts for approximately 100 tons (mainly food and shelter), ie 10 000 tons of mass. A realistic assessment should be somewhere in between, and probably in the tens of millions of tons. All this under the assumption that no miraculous nanotechnology is not yet open.
The advantage of a spaceship as Ark is that it is non-specific reaction to a host of different threats with indeterminate probabilities. If you have some specific threat (the asteroid, the epidemic), then there is better to spend money on its removal.
Thus, if such a decision in the 1960th years were taken, now such a ship could be on the road.
But if we ignore the technical side of the issue, there are several trade-offs on strategies for creating such a spaceship.
1. The sooner such a project is started, the lesser technically advanced it would be, the lesser would be its chances of success and higher would be cost. But if it will be initiated later, the greater would be chances that it will not be complete until global catastrophe.
2. The later the project starts, the greater are the chance that it will take “diseases” of mother civilization with it (e.g. ability to create dangerous viruses ).
3. The project to create a spaceship could lead to the development of technologies that threaten civilization itself. Blast-ship used as fuel hundreds of thousands of hydrogen bombs. Therefore, it can either be used as a weapon, or other party may be afraid of it and respond. In addition, the spaceship can turn around and hit the Earth, as star-hammer — or there maybe fear of it. During construction of the spaceship could happen man-made accidents with enormous consequences, equal as maximum to detonation of all bombs on board. If the project is implementing by one of the countries in time of war, other countries could try to shoot down the spaceship when it launched.
4. The spaceship is a means of protection against Doomsday machine as strategic response in Khan style. Therefore, the creators of such a Doomsday machine can perceive the Ark as a threat to their power.
5. Should we implement a more expensive project, or a few cheaper projects?
6. Is it sufficient to limit the colonization to the Moon, Mars, Jupiter’s moons or objects in the Kuiper belt? At least it can be fallback position at which you can check the technology of autonomous colonies.
7. The sooner the spaceship starts, the less we know about exoplanets. How far and how fast the Ark should fly in order to be in relative safety?
8. Could the spaceship hide itself so that the Earth did not know where it is, and should it do that? Should the spaceship communicate with Earth? Or there is a risk of attack of a hostile AI in this case?
9. Would not the creation of such projects exacerbate the arms race or lead to premature depletion of resources and other undesirable outcomes? Creating of pure hydrogen bombs would simplify the creation of such a spaceship, or at least reduce its costs. But at the same time it would increase global risks, because nuclear non-proliferation will suffer complete failure.
10. Will the Earth in the future compete with its independent colonies or will this lead to Star Wars?
11. If the ship goes off slowly enough, is it possible to destroy it from Earth, by self-propelling missile or with radiation beam?
12. Is this mission a real chance for survival of the mankind? Flown away are likely to be killed, because the chance of success of the mission is no more than 10 per cent. Remaining on the Earth may start to behave more risky, in logic: “Well, if we have protection against global risks, now we can start risky experiments.” As a result of the project total probability of survival decreases.
13. What are the chances that its computer network of the Ark will download the virus, if it will communicate with Earth? And if not, it will reduce the chances of success. It is possible competition for nearby stars, and faster machines would win it. Eventually there are not many nearby stars at distance of about 5 light years — Alpha Centauri, the Barnard star, and the competition can begin for them. It is also possible the existence of dark lonely planets or large asteroids without host-stars. Their density in the surrounding space should be 10 times greater than the density of stars, but to find them is extremely difficult. Also if nearest stars have not any planets or moons it would be a problem. Some stars, including Barnard, are inclined to extreme stellar flares, which could kill the expedition.
14. The spaceship will not protect people from hostile AI that finds a way to catch up. Also in case of war starships may be prestigious, and easily vulnerable targets — unmanned rocket will always be faster than a spaceship. If arks are sent to several nearby stars, it does not ensure their secrecy, as the destination will be known in advance. Phase transition of the vacuum, the explosion of the Sun or Jupiter or other extreme event can also destroy the spaceship. See e.g. A.Bolonkin “Artificial Explosion of Sun. AB-Criterion for Solar Detonation” http://www.scribd.com/doc/24541542/Artificial-Explosion-of-Sun-AB-Criterion-for-Solar-Detonation
15. However, the spaceship is too expensive protection from many other risks that do not require such far removal. People could hide from almost any pandemic in the well-isolated islands in the ocean. People can hide on the Moon from gray goo, collision with asteroid, supervolcano, irreversible global warming. The ark-spaceship will carry with it problems of genetic degradation, propensity for violence and self-destruction, as well as problems associated with limited human outlook and cognitive biases. Spaceship would only burden the problem of resource depletion, as well as of wars and of the arms race. Thus, the set of global risks from which the spaceship is the best protection, is quite narrow.
16. And most importantly: does it make sense now to begin this project? Anyway, there is no time to finish it before become real new risks and new ways to create spaceships using nanotech.
Of course it easy to envision nano and AI based Ark – it would be small as grain of sand, carry only one human egg or even DNA information, and could self-replicate. The main problem with it is that it could be created only ARTER the most dangerous period of human existence, which is the period just before Singularity.