Could there be alien probes in the solar system?

In the unfolding drama of ideas surrounding the interstellar body 3I/ATLAS, in addition to the question of what this object is (which we will not discuss, as we have nothing new to add to what has already been said), of interest is the question of whether alien probes could, in principle, be present in the Solar System. It should be noted that science, and astrophysics in particular, assumes that the set of chemical elements and the laws of nature are the same everywhere in the Universe. In this sense, the fact that this combination allowed life to emerge on one planet makes it highly probable that it could also form on other planets, of which there are a huge number in the Universe. We also know from experience about the potentially high rates of development of technological civilizations, such as our own (just compare 1925 and 2025). Extrapolating these rates for thousands and tens of thousands of years into the future, we can hypothesize the possibility of the formation of technological supercivilizations.

Let’s now assume that a supercivilization exists in the Galaxy, capable of reliably determining the presence of planets (including their sizes and orbits) around all stars within, say, a sphere 10,000 light-years in diameter. For context, there would be approximately a billion such systems. Let’s assume that ten million of these could be selected as potentially life-forming. Sending out such a large number of manned expeditions at random would be odd, and the very idea of using automated probes to select from this list systems with actual life seems entirely reasonable. We will henceforth assume that the civilization can travel at superluminal speeds; otherwise, the very idea of exploring space at such distances would hardly have occurred to them.

A suitable probe could reach its destination—the planetary system being explored—in a short time, after which it would abruptly decelerate at its outer boundaries and, forming a ballistic trajectory in the plane of the planets, fly for a year at distances of tens or hundreds of millions of kilometers from them, collecting data. When this trajectory returns the probe to the outskirts of the planetary system, it resumes its previous mode of motion and returns with the data.

This scheme carries the risk that another technological civilization might be in the system being studied, which would detect the probe, something we would likely not want. A natural means of cloaking in this case would be cometary comas, which are effectively impenetrable to external observation and in which technological windows undetectable from the outside could be created for observation and data collection. Incidentally, a civilization could directly use comets from its Oort cloud (of which there are trillions) to create probes. In this case, no effort would even be required to create cloaking devices. A rock equipped with observation devices would form both a coma and a tail on its own when it approaches the target star.

Considering this, a number of questions arise that must be answered. The first, and most obvious, is why shape the probe’s hyperbolic trajectory, directly indicating its external origin. It was precisely this trajectory that attracted attention to 3I/ATLAS. There is a fairly obvious answer to this. With such trajectories and speeds, the probe passes through the planetary system in periods of approximately 1 to 3 years, which essentially leaves no time to assemble an expedition to it. Furthermore, the higher the probe’s speed, the more difficult it is to intercept. In particular, the speeds of 3I/ATLAS are fundamentally unattainable for our civilization, whereas we have already caught up with comets with ordinary speeds. Again, the apparent interstellar nature of the body helps explain the discrepancies between its characteristics and standard comets in this system. All questions about why the comet is so unusual can be answered by the fact that it is interstellar. Reconciling the coma’s composition with that of local comets may be impossible, since this composition is most likely unknown from the outside. If the probes are made from bodies in their Oort cloud, then the resulting discrepancy is simply inevitable.

The second question is why disguise a probe as a comet, thereby increasing its visibility. As is well known, ordinary asteroids without a tail or coma are much more difficult to detect. In this case, the answer may be that the technical means required to collect information about planets from distances of hundreds of millions of kilometers could be very large—on the order of a kilometer or more (let’s assume that for a technological supercivilization, creating such an instrument is not a problem). Asteroids of this size could undoubtedly be detected, and in this case, the very fact that the asteroid is a huge scientific instrument in the absence of a protective cometary coma could be revealed.

The question remains: what if such an expedition runs the risk of encountering a civilization advanced enough to intercept the probe, despite its rapid transit time and tremendous speed? It’s difficult to say in advance what might be planned for such a contingency. One possibility is that, having detected signs of such a civilization from the outskirts of the system, the probe simply returns. Another possibility is possible. It’s possible that such probes could serve as a means of contact, and the civilization that intercepts them would find information on them about the supercivilization that sent them. The very fact of interception in this case could be a test of their technological advancement. However, here we’re entering the realm of pure fantasy.

One question remains unanswered. Why did so many people turn against the unfortunate Avi Loeb, and is the criticism directed at him fair? Unfortunately, this is true, since the hypothesis of an extraterrestrial nature, no matter how appealing, is still less probable than the hypothesis that we are dealing with an ordinary celestial body. And basic scientific principles prohibit considering less probable hypotheses until a more probable one is rejected. One might, of course, ask how one could detect alien probes (assuming they exist) if they would be indistinguishable from comets. The answer is: no way, and, more importantly, it’s unclear why. The likelihood that this effort would result in finding a research probe from another civilization among the vast number of incoming celestial bodies is objectively very low (especially if that civilization has taken measures to prevent this from happening). Accordingly, in all remaining cases, the energy and money invested in the search would be wasted.

And finally, could it really be that 3I/ATLAS is precisely such a probe? The answer is yes, it can, but again, with a very low probability—the same as the chance of picking a single white ball out of thousands, or even millions, of balls of a different color. And until new information emerges that can objectively change these probability figures, science will continue to consider it an ordinary rock that accidentally flew into the solar system.