Tuesday, October 27, 2015

Interstellar Baggage – Part 2 – Probes

Part 1 of this series considered what data might be collected about a destination planet from observatories, mostly space-borne, in the originating star system. A long list of quantitative attributes about the destination star and planet, along with other large objects in that solar system, could be expected to be collected and verified, given that there was a long time available for the monitoring, and a large amount of assets devoted to building and then operating the observatories. But when all that is done, the data collected would be insufficient to completely inform the alien civilization about the planet they were considering colonizing.

Categories A1 and A3 alien civilizations are looking for sweet spot worlds. These are worlds which can be inhabited, without too much work, by the aliens themselves. They need to find out how closely the planet they have been investigating remotely matches their planet. Clearly there are limits to the match. They obviously do not want a planet which is already inhabited by another alien civilization, with equivalent capabilities. Overpowering another planet of roughly equivalent size and technology would be difficult for starship arriving with potential colonists.
If the inhabitants are not civilized, they would not have the capability of stopping the onset of the colonization, but might make expansion hazardous, if their numbers were large. Thus, one question that a probe must be able to answer concerns the inhabitants. We can assume that the remote observatories were used to see if there were any signs of a civilization there, but there might not be anything remotely detectable.

A second question that might be asked is in the list because of our own ignorance. We do not know if there are alternate routes for life origination, perhaps based on different fundamental chemicals, or based on different DNA in the coding schemes. If more than one might have arisen on the destination planet, the probe would have to be able to sample some life there, and determine the chemical makeup and the coding scheme used. The potential colonists would want to be sure that they would not be poisoned if they tried to eat or even interact with the flora and fauna existing on the new planet. Another gap in our knowledge here on Earth concerns what might be done if there was an alternate form of life on the new planet. Could the arriving aliens seed their own lifeforms, and expect that the old forms would be replaced? If indeed the originating aliens did not have the best of these, in other words, theirs would be replaced by the ones already inhabiting the new planet, then the alien travelers have a serious problem. Is this enough to eliminate a candidate sweet spot planet?

Besides the inhabitants question and the possible lifeform chemistry question, there is a third question the probe must investigate, but as before, it may be eliminated by technology and scientific modeling more advanced that we can do here on Earth. From a knowledge of the observable characteristics of the sun of the new planet, can the alien civilization estimate what the planetary surface will consist of? In other words, does solar content determine the chemical makeup of the primordial dust disk that surrounds it when it first fires off. Furthermore, if it does, it is possible to make good estimates of what the planet would be made of? And even further, if it is clear from these stellar measurements what the planet’s composition would be, is it possible to figure out what the surface would be showing, and in particular if the mineral resources that the alien civilization would need will be present and available in extractable form? If not, the probe would have to have some way of determining if there is sufficient accessible minerals, of several critical types, present on the planet.

A mineral survey would be by far the hardest task, as far as we can tell. Mineral surveys of Earth were done and are still done by physical presence and exploration. Our robots on Mars do the same. A sample of a rock has to be placed in a chemical laboratory and processed to tell the content. If the alien civilization’s probe has to become a mineral prospector, it is likely to be out of business. There are two alternatives. One is to automate the prospecting, possibly by using a laser vaporization bag of tricks, in which a very high power laser vaporizes some thin surface layer of rock, which then gives a brief pulse of near visible radiation, containing some clues as to the content of the rock. We can’t do it, but perhaps we will be able to do it in some decades of time. It might require a flexible frequency laser, able to compose a pulse with multiple wavelengths, or possible a chirp pulse with the wavelength changing through the length of the pulse. It might require much more knowledge about vaporized rocks than we have. And there may be much better ways to do this, which we are not schedule to figure out for a century or more, but which the aliens will have in their bag.

The second alternative to the impossible prospector concept depends on asking just what they need to know. They do not need their probe to find all the best mining sites on the planet’s surface. They simply need it to take the data that will allow them to figure to figure out if there are such sites, no matter where they are. This would be done by understanding the range of variation that is possible in a surface, if a few dozen or hundreds of measurements give this collection of data. In other words, would they know enough about the possible overall distribution of elements on the planet from such easy measurements to be able to predict that somewhere there will be an outcrop containing what they need? Let’s hope that between these two measurements, or something similar, the task of making sure the right minerals will be present can be done. Then we know that if a probe can take, say, a few hundred chemical samples from a wide variety of locations on the planet, it will have enough to answer the mineral availability question for the alien civilization.

All told, if we use the estimate in a previous post of a hundred metric tons to erect a large antenna capable of sending back to the home world, and of powering it for an extended time, and add to that another hundred tons for observers for inhabitants, samplers to go down for the biological chemistry and the rock compositions, and processing power for the sample data, a probe of a couple of hundred tons might be adequate. Some other time, figuring out if this is a doable probe mass will be done, but for now, it doesn’t look too bad. If necessary, it might be reduced somewhat by more careful estimation, but a probe doesn’t have to be too heavy.

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