Thursday, June 25, 2015

Reconnaissance in Star-traveling Alien Civilizations

Reconnaissance is the collecting of information.  This blog is about what an alien civilization, either an expanding one or a contracting or stable one, would want to do.  The focus is on a civilization that has achieved the ability to travel across interstellar distances, and has already reached asymptotic technology, where they can do everything that can be done, in the most effective way.  Recall that the transition happens fast, going from virtually no scientific and technical knowledge beyond some agricultural know-how to having it all, in understandable and organized form, in millennia at the most, an instant in the life of the universe.  Recall also that the scientific theory part of the asymptotic technology transition does not provide data about the universe, only about the laws that govern it.  Reconnaissance is the getting of the data.

For a civilization that has the meme of interstellar dispersion and is either on the verge of their first expedition to another solar system, or has already done it and is going to continue doing it, reconnaissance is mandatory.  Reconnaissance at the earliest stage is simply another name for astronomy of nearby solar systems, and would be done so they can find the one that is best suited for their first or next interstellar voyage.  We can project that a civilization at this stage can build an array of large telescopes in space, isolated from their own planet and other planets in the solar system, operating in the UV to IR range, of sufficient size to look at exo-planets orbiting nearby stars.  Think of the size of each reflector as kilometers and the whole array strung around an orbit the size of Earth’s, which determines the aperture.  With this aperture, and as long to look as they want to, they could possibly determine continent-sized details on the planet.  More importantly, they can do spectroscopic analysis of the atmosphere, learn something about the winds, see if there are oceans, and in general get many other chunks of information. 

With all science already learned, the data can be used to fill in the details of models of planets.  With the star understood well, and the planets to some degree, knowledge of how planets form can be used to fill in more information about the planets.  A consistent picture of each observed planet can be developed, and some good estimates of what is there built up.

One of the interesting chunks of data is about the signatures of life on an exo-planet.  Life as we know it has some chemical signatures that might be detected.  With asymptotic technology passed, meaning science is known, the question of what forms of life are possible should be answered completely.  If there are multiple forms, they might have multiple types of signatures, which can be independently checked.  There might even be some indication of what stage life was in, whether it was simply single celled or whether there were animals walking on any dry surfaces.  Perhaps the signatures for animal life are not sufficiently distinct to be discerned remotely. 

While  telescopic reconnaissance from the home solar system can continue, this much information allows a selection of targets to be found for reconnaissance voyages.  Assuming their meme is directing them toward a future habitat, they would select those planets that most closely match what they require, or which could be altered using the technology they can transport to the exo-planet into something close to what they need.  It would be nice to have a Garden of Eden awaiting their arrival, but the bottom line is that the exo-planet must have resources available to sustain their form of life.  They can build hermetically sealed shelters and vehicles if necessary, but they cannot truck all the materials needed to sustain a civilization in large numbers across interstellar distances.  This is the deciding criteria.  Does it have the resources needed?

Resources include an energy supply and materials needed for every aspect of life.  Any space-faring civilization would need to master at least D-D fusion to power their spaceships, so as long as there is hydrogen around in the atmosphere of some planet in the new solar system or in water or another chemical on the surface of some planet, preferably the one they chose for their possible habitat, they can have fuel for a fusion reactor.  They also need all the minerals needed for life support, for habitat construction, for infrastructure construction, and eventually for a spaceport and a spaceship construction facility.  To find out if there are such minerals available, a closer look is needed. 
Sending a reconnaissance ship out to observe at a closer distance might be sufficient, provided that the knowledge of how planets form is so robust that some better data taken by the ship can decide what the planet is composed of and how accessible the minerals might be.  We don’t know at this point in our scientific trajectory if planets can be easily categorized, and, for example, the crust is predictable from the knowledge of the orbital radius, the observable details of the sun, perhaps some details from other planets in the same solar system, and what can be observed from the planet itself. 

There is a question of how accurate the information must be to fully inform the model.  Is a fly-by at a few astronomical units sufficient to get whatever is needed, or is it necessary to get closer or perhaps go into an orbit around the planet itself?  Perhaps the type of atmosphere present controls what is necessary.  A planet with a permanent cloud cover would not give off any information about the surface, just the atmospheric layer where the clouds resided, and for this, sending some vehicle under the cloud layer would likely be necessary.  Perhaps having a cloud layer is sufficient to eliminate the planet from consideration, or perhaps it is a good sign that something valuable lies under the clouds. 

Another facet is how much time is needed for observations.  If the planet has seasons, it might be necessary to have a whole year of data collection, to make sure there are not killer storms that occur during one of the seasons, or that the distribution of temperatures is reasonable throughout the year, or that flooding isn’t an issue, or something else.  This would require the surveillance craft to slow down from the travel speed it used to get to the new solar system.  A previous blog post has indicated that a reasonable speed range is 0.1 to 10% of light speed, and that would have the craft across the planetary orbit too quickly.  If deceleration is not needed, the ship is much more efficient, as the fuel needed for deceleration is about what is needed for acceleration alone, and this much more than doubles the ship size. 

The other aspect of efficient reconnaissance involves whether the craft has to be ‘manned’ with aliens or whether it can be fully autonomous.  Having a crew, even a sleeping crew, raises the payload mass greatly, so if the ship can be made autonomous, it would be.  If the culture of the alien civilization was such that the crew needed to be returned, fuel and mass requirements grow to many, many times what they would be for the minimal reconnaissance voyager, a full speed fly-by.  Probably the alien civilization is forced into the same pattern of travel that we might use in interplanetary travel, if we ever accomplish it.  Autonomous reconnaissance robots first, and then, crewed vessels. 

Our planet might be high on any nearby civilization’s selection list as potential habitats.  We have been able to make observations of our solar system only for a very, very short time, so it is not likely that a spaceship would be traveling through on a high speed flyby while we are able to witness it.  It is also not clear that we have thought through how to detect such a reconnaissance vehicle as it sped by, perhaps at an orbital radius like Jupiter’s.  

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