Are We all Alone, or could They be in the Asteroid Belt?
Michael D. Papagiannis
Department of Astronomy, Boston University, Boston, Massachusetts 02215, USA
(Received 1978 January 24)
The observations that life has a natural tendency to expand into all available space, that advanced technological civilizations should be able to engage with relative ease in interstellar traveling, and that once this threshold is crossed the complete colonization of the entire Galaxy will be accomplished in a very short interval relative to the age of the Galaxy, lead us to the following dilemma: either the entire Galaxy is teeming with intelligent life and hence our solar system must have been colonized hundreds of millions of years ago, or there are no other inhabitants in our solar system and hence most probably neither anywhere else in the Galaxy. Before accepting, however, the bleak verdict that we are all alone in the Galaxy, we must search carefully throughout the solar system for any signs of other technological civilizations. The most logical place to look for them seems to be the asteroid belt because of the many advantages it offers to a galactic society living in space colonies.
A Change Of Heart
The euphoric optimism of the sixties and the early seventies that communication with extraterrestrial civilizations seemed quite possible (Sagan 1973), is being slowly replaced in the last couple of years (Hart 1975; Jones 1976; Shklovskii 1977) by a pessimistic acceptance that we might be the only technological civilization in the entire Galaxy. This change of heart has been happening as a result of the following observations:
From the above it follows that if hundreds of millions of intelligent civilizations did evolve in our Galaxy over the past several billion years, as suggested by the integration of the Drake–Sagan probability formula over the entire history of the Galaxy (Freeman and Lampton 1975), then it seems inevitable that some of these galactic civilizations would have achieved interstellar traveling and the whole Galaxy, including our solar system, would have been teeming with advanced technological societies. Conversely, if we are the only technological inhabitants of our solar system, then most likely we are also the only ones of the entire Galaxy. This deduction implies that the values commonly used for one or more of the probability factors of the Drake formula (Shklovskii and Sagan 1966; Kreifeldt 1971; Sagan 1973; Oliver 1975) must have been grossly over-estimated (Papagiannis 1978).
Could They Be Around?
We have reached, therefore, the stage where the acid test for our dilemma seems to be whether or not our solar system is inhabited by an advanced extraterrestrial society. Of course there are in the literature several reports of UFO sightings and even stories of dramatic encounters with extraterrestrials. There are also several popular books, such as those of von Daniken (1969), in which the intervention of extraterrestrials in this planet is envisioned on countless occasions. Still, however, there is no convincing proof to any of these stories or suggestions; in accordance with the Shklovskii principle that "all events should be considered natural unless proven otherwise" the scientific community remains unconvinced about visits to Earth by extra-terrestrials. As a result, and in accordance with the presently available evidence, we tend to believe that we are the only advanced civilization inhabiting our solar system.
Absence of evidence however, should not be taken as evidence of absence. Before we resign therefore, to a pessimistic acquiescence that we might be the only technological inhabitants of our Galaxy, we have the responsibility to search exhaustively in our solar system for other advanced societies. The supposition that we are alone in the solar system is based essentially on the assumption that if others were here they would have already made contact with us, or at least we would have become aware of their existence. Neither of these assumptions, however, is necessarily true, though it is possible that some of the thousands of UFO sightings might deserve some further consideration, as suggested by Hynek (1972).
The most intriguing question in the whole problem is the following:
if our solar system is indeed inhabited by extraterrestrials, where are they most likely to be found? In earlier days people had tried to identify one of the other planets of our solar system, most frequently Mars (Lowell 1908), as the abode of an extraterrestrial society. From the above discussion however, it follows that the colonizers of our solar system are likely to continue to live in space colonies, probably at reasonably close distance to the Sun so as to have a sufficient supply of solar energy for their needs, and most likely near celestial bodies of weak gravity from which they would obtain all the natural materials needed for the continuous prosperity of their civilization.
The Asteroid Belt Choice
Within this framework, it seems that the asteroid belt would be an ideal place for the extraterrestrials to set up their space colonies. Not only would they have an easy access to all natural resources by mining the asteroids, but they would also be close enough to the Sun to have ample solar energy for their needs. Some years ago this suggestion would have sounded unreasonable, mainly because we used to think that the asteroid belt must be full of debris which can be very hazardous for any spaceships permanently stationed in their vicinity. The Pioneer 10 and 11 missions, however, (Kinard et al. 1974) have found that the density of meteroids in the asteroid belt hardly differs from any other place in the solar system, and therefore the colonization of the asteroid belt seems quite feasible. There are, of course, also the Kirkwood gaps in the asteroid belt which are practically free of any asteroids. A spaceship could remain there almost indefinitely by simply compensating against the tidal effects of Jupiter with its own propulsion system.
One can even consider the possibility that the large fragmentation of the components of the asteroid belt might be the result of mining projects by the extraterrestrial colonies. It is even conceivable that they have tried to keep the region clean of free floating debris for their safety. The identification of space colonies 1–10 km in size hidden in the asteroid belt would not be an easy task for a terrestrial observer because from a long distance these colonies would be practically indistinguishable from the thousands of natural asteroids. They would also follow the same orbits around the Sun as the asteroids, which would be much more numerous and therefore it would be almost like searching for a needle in a haystack. Still with careful observations in the radio domain we might be able to detect some leakage of radio noise, infrared observations might reveal a higher effective temperature than that which is justified by their distance from the Sun and finally, properly planned space missions to the asteroid belt might do some successful eavesdropping and might even return some direct photographic evidence. The search project, therefore, though admittedly quite difficult, is still within the capabilities of our present technology and in view of the far-reaching consequences of either positive or negative results, should be given a serious consideration.
Why Are They Silent?
As to why they have not yet made contact with us, one can think of several answers, including the zoo hypothesis of Ball (1973). The simplest explanation, however, and hence, maybe the most probable one, might be that of confusion and indecision. Our hypothetical neighbours were probably acquainted for millions of years with a lethargic Earth inhabited by life forms not worth any effort of communication. Suddenly, in the last 50 yr or so, which probably is a very short interval for a well-settled galactic society, they have been confronted with an exponentially mushrooming technological society. (aeroplanes, radio-communications, nuclear bombs, spacecraft) which undoubtedly must be causing them some serious concern. It is possible, however, that faced with such a sudden technological explosion, a serene cosmic civilization would be perplexed and undecided as to how to handle the situation. They might be debating on whether to crush us or to help us, and therefore they might be simply postponing their decision, waiting to see what we are going to do with ourselves. Meanwhile, the asteroid belt provides a natural hide-out where they can remain inconspicuous for a long time until we decide to search for them.
In conclusion, though the idea that the asteroid belt might be harbouring a number of extraterrestrial colonies sounds like science fiction, the arguments presented above suggest that if there are any extraterrestrial colonies in our solar system then the asteroid belt seems to be the most logical place to look for them. Before accepting, therefore, the bleak verdict that we are all alone in the Galaxy, we have an obligation carefully to investigate this possibility, remote as it might seem.
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