Searching for Extraterrestrial Artifact in Our Solar System
December 11, 2010 2 Comments
What sort of physical evidence might be available for us to find? In my previous articles, as I’ve argued that the best way to explore the entire galaxy is, to launch the self replicating Interstellar probes. The only true compelling categoryof evidence is physical observables. For instance, we might observe their spacecraft, their self-replicating machinery, their habitats or strip mines, or a host of other physical manifestations which are the hallmark of technological activity. If an exploitative Type II civilization exists or had ever existed in our vicinity, then the Solar System would have been wholly converted to replicating machines mass, our planets sorted into their constituent elements for transshipment or industrial use and the Sun-stripped of its fuel – and of course we would not be here to discuss the outcome of these activities. Since humanity exists, rapacious nearby stellar civilizations are ruled out, much as exploitative galactic civilisations are provisionally excluded by the observational evidence.
Detection of probes would be especially challenging, as these could in theory be located almost anywhere. Robert A. Freitas argues that a typical alien probe might be 1-10 metres in size – this is large enough to house a microwave antenna to report back to the senders, and to survive micrometeorite impacts for millions of years, but light enough to fly across the interstellar gulf without consuming unreasonable amounts of energy. A spherical Solar System boundary enclosing the orbit of Pluto consists of 260,000 AU3 of mostly empty interplanetary space and 10^11square km of planetary and asteroidal surface area. To be able to say with any certainty thatthere is no alien presence in the Solar System, you have to have carefully combed most of this space for artifacts.
Currently the sky has been exhaustively surveyed to perhaps magnitude 14, the Palomar Schmidt Sky Survey extends to 21, and the best available magnitude limit for any telescope on Earth is about mv= 24. This means that at best, current surveys from Earth might have detected an unmoving, mirror-shiny, optimally-oriented 10-metre object orbiting 0.01, 0.25, and 1 AU from Earth, respectively. If the artifact is smaller, moving, black, or canted at a different angle then it will be even harder to see. So we can only scan the nearest 4AU3 of space for probes, but we have at least 260,000 AU3 to search. Even if the Palomar 200-inch telescope was employed exclusively to search for alien artifacts it could reach atmost one-millionth of the necessary volume. Orbital space, in other words, isat least 99.999% unexplored for 1-10 metre objects. A more realistic assessment suggests that the visual detection threshold for alien probes for present-day humanity includes only 10-5-10-11of the potential probe residence volume. This estimate assumes a random search pattern typical of past serendipitous observations which might have discovered alien artifacts if they were present. Radar and infrared measurements can’t substantially improve this current limit.
How about probes parked on planetary surfaces? Of the 0.1 trillion square kilometres of Solar System territory other than Earth, less than 50 million has been examined to 1-10 metre resolution. So 99.95% is still virgin territory as far as a search for extraterrestrial artifacts is concerned. If objects are buried somewhere or floating in a Jovian atmosphere, there is almost zero chance we could have found them up to now. Even huge 1-10 kilometre artificial alien habitats occupying the asteroid belt would appear visually indistinguishable from asteroids to terrestrial observers, and the Belt population itself is poorly catalogued. So it is exceedingly unlikely that we would have spotted an extraterrestrial artifact anywhere in the Solar System unless it was desperately trying to get our attention. And why should it bother to do that?
The total mass of probes needed to explore even the entire Galaxy is astonishingly small. If each self-replicating probe, mass fully-fueled about 10^10kg, makes 10 replicas during each of 11 generations, enough to span the entire Galaxy, that is 10^11x 10^10kg = 10^21kg or about the mass of Ceres, the largest known asteroid. If the Solar System carried the burden of manufacturing all 10^11probes to explore the entire Galaxy, how could we know if one Ceres-size asteroid had ever been removed from the Asteroid Belt? And take the argument one step further. Assume that one million extraterrestrial civilisations each pillage the Solar System for materials to build and launch their own million independent probe networks, each covering every star in the Galaxy. The total requirement is still only 10^6×10^21kg = 10^27kg, about the mass of Jupiter. It is doubtful we could say for certain if even this much matter had been stolen away sometime in the remote past.
Don’t we need some better approach?
[Source: Robert A. Freitas]