Study: Self-replicating alien space probes in our solar system?

Posted Jul 19, 2013 by JohnThomas Didymus
A group of researchers from Edinburgh University have said that based solely on the age of the universe and feasible interstellar flight technology, "self replicating" probes from alien civilizations could already have arrived in our solar system.
Voyager spacecraft
Voyager spacecraft
The researchers proposed their argument in response to the Fermi paradox which asks why we have not already encountered extraterrestrial intelligence if it is common throughout the universe.
According to mathematicians Arwen Nicholson and Duncan Forgan, in a paper entitled "Slingshot Dynamics for Self Replicating Probes and the Effect on Exploration Timescales," published on July 5, 2013, in the journal Astrobiology, alien space probes propelled to the vicinity of our Sun using the gravitational field of stars rather than of planets, as humans have accomplished with the Voyager space probes, could already be in our solar system, but it could be that we are unable to detect them.
In theory, "self-replicating" space probes, otherwise known as von Neuman probes, sent to explore a nearby star could use mineral materials, stellar dust and gas in the local environment to create replicas of themselves. The fleet of space probes could then be launched to the nearest stars in the locality using the gravitational field of the local star to "slingshot" them into interstellar space while the "parent" probe continues its mission in the neighborhood of the first star. It could even be possible for the space probe to create replicas that are variants of itself modified for different missions. For instance, a probe sent to search for life in the next planetary system could have a special design different from one sent to search for new mineral deposits or one wholly on a science mission.
The argument that "self replicating" probes could already be in our solar system is based partly on the argument that given that planet Earth's young technological civilization already has a probe that has reached the edge of the solar system, older and more technologically advanced civilizations in the Milky Way galaxy could have launched probes thousands or even millions of years before Voyager.
In 1980, Robert Freitas published a paper in which he conducted a a quantitative analysis of the concept of self-replicating space probes that led to the widely accepted view that self-replicating probes launched from Earth could spread through the entire galaxy within a few million years travelling at 10 percent the speed of light.
The estimate led Frank Tipler to suggest in 1981 that absence of "self-replicating" probes in our solar system could be evidence that extraterrestrial intelligence does not exist.
Nicholson and Forgan, however, approached the problem by suggesting that alien civilizations with the technological capability and resources to conduct galaxy-wide explorations would be able to develop stealth probes invisible to humans.
In the study, the researchers point out the feasibility of launching galaxy-wide exploration using "slingshot maneuvers around the stars... gaining a boost in velocity by extracting energy from the star's motion around the Galactic Center."
The authors observed that "these maneuvers carry little to no extra energy cost" and that it has been shown in previous work that "a single Voyager-like probe exploring the galaxy does so 100 times faster when carrying out these slingshots than when navigating purely by powered flight."
The authors explored three scenarios of probe "behavior": "1. standard powered flight to the nearest unvisited star (no slingshot techniques used), 2. flight to the nearest unvisited star using slingshot techniques, and 3. flight to the next unvisited star that will give the maximum velocity boost under a slingshot trajectory," and concluded that: "In all three scenarios we find that as expected, using self-replicating probes greatly reduces the exploration time, by up to three orders of magnitude for scenario 1 and 3 and two orders of magnitude for 2."
The authors concluded that the "nearest-star slingshot" strategy remains "the most time effective way to explore a population of stars" and that "a fleet of self-replicating probes can indeed explore the Galaxy in a sufficiently short time to warrant the existence of the Fermi Paradox."
The authors observed that a speed of more than 10 percent of the speed of light could be achieved for a space probe using "slingshot maneuvers." They calculated that at 10 percent of the speed of light, self replicating space probes could explore the entire Milky Way galaxy in 10 million years. The study said: "We can conclude that a fleet of self-replicating probes can indeed explore the Galaxy in a sufficiently short time [that] are orders of magnitude less than the age of the Earth."
Forgan said: "The fact we haven't seen probes of this type makes it difficult to believe that probe building civilizations have existed in the Milky Way in the last few million years."
The authors (PDF) noted, however, that our solar system could be populated already by "self-replicating" probes but that we might have failed to detect them not only because we do not yet have the technology but also possibly because of the vastness of space in which they could hide and also possibly because the alien probes could be based on designs so novel that we do not know what to look for.
The Independent notes that the study's conclusion agrees with a 2011 study by Jacob Haqq-Misra of Rock Ethics Institute, who suggested that alien objects could already exist in our solar system and that we have not found them because we have not searched carefully enough.
However, questions may be asked why speculations by professionals and laymen alike tend to imagine that alien visitors would bother to hide evidence of their presence from us. Humans have sent two probes to the edge of the solar system and there is no evidence that we considered means to hide or conceal the probes from other civilizations that could detect and intercept them in the future. There is also no evidence in the context of the history of human exploratory activity that suggests that explorers routinely adopt a military stealth or espionage mindset.
The idea of a civilization conducting stealth explorations on a wide scale is conceivable, however, if we imagine an extremely advanced and experienced civilization that has been in contact with others cautiously expanding search within the galaxy by systematically targeting likely sectors of the universe.
The Fermi paradox, proposed by physicists Enrico Fermi and Michael H. Hart, arises from what some scientists believe is the apparent contradiction between what they consider the high probability of existence of extraterrestrial intelligence and the fact that we have not contacted any.
It appears, however, that physicists and mathematicians tend to take the most optimistic views about the existence of extraterrestrial life. Many biologists have contested scenarios about extraterrestrial intelligence based on claims of high probability of their existence by presenting low estimates of probability working solely on the neo-Darwinian theoretical notion of evolution by random mutations and natural selection. Indeed, the growing popularity in recent times of the theory of panspermia arises from the awareness that life on Earth, as far as the neo-Darwinian paradigm is concerned, is a statistical miracle with a very low probability of being reproduced elsewhere in the universe independently. It can be expected reasonably from the neo-Darwinian theory that life bearing planets, if they exist in the universe outside Earth, must be very rare and consequently so thinly distributed that the chances of interstellar voyage or communication is vanishingly small.
In fact, when one assesses the chances of any form of life at all; then the chances of any form of life evolving into intelligent life; and finally, separately, the chances of intelligent life advanced enough to conceive of the idea of space travel, not to mention building spaceships and sling-shooting them to the next star (!), it is amazing that we surprised that our solar system has not been visited by extraterrestrial beings.