A new paper on technological signatures in the solar system highlights that our current technology is still unable to rule out the presence of extraterrestrial artificial objects – but also does not present evidence that they exist.
Humanity has already sent five spacecraft into escape orbit from the solar system: Pioneer 10 and 11, Voyager 1 and 2, and New Horizons. None of them will continue to operate when they approach another star system in the distant future, but their very existence proves that a technological civilization is capable of launching spacecraft to traverse interstellar space. This raises an intriguing, but entirely scientific, question: If we are doing this, is it possible that another civilization has done something similar—and one of its spacecraft has passed through or remained in our solar system?
In a new paper titled “Solar System Technosignatures,” astronomer T. Joseph W. Lazio proposes examining the question not as a claim for alien visitation, but as a problem of measurement: How far have we really searched for artificial objects of non-terrestrial origin within the solar system? His answer is cautious but disturbing: far from enough.
What is a technological signature?
A technological signature is a possible sign of the technological activity of an intelligent civilization. Typically, such signatures are searched for through radio signals, laser emissions, or anomalies in observations of distant stars. But there is another possibility: searching for physical objects – spacecraft, debris, automated stations, or technological remains – within the solar system itself. This field is sometimes called SETA, the Search for Extraterrestrial Artifacts, as opposed to the classic SETI that focuses on signals.
For the purposes of the discussion, Lazio divides the possibilities into four groups: passive objects moving through space, such as a spacecraft that is no longer operational; active objects capable of measuring, transmitting, or manipulating; passive relics on the surfaces of moons, planets, or asteroids; and active installations on the surface of a celestial body, such as a monitoring station or an automated mining rig. The question he examines is whether it is currently possible to rule out the possibility that at least one of these categories exists in the solar system. According to the article, the answer is no.
Partial observational coverage
The reason is not that there is positive evidence for such a presence, but that our observational coverage is very partial. Even when we discover an interstellar object or an object with an unusual orbit, it is difficult to distinguish between a natural and an artificial object. The case of 2020 SO illustrates this well: the object was initially discovered as an asteroid with a strange orbit, but further testing showed that it was probably a Centaur-type rocket stage from NASA's Surveyor 2 mission in 1966. That is, even human space debris can initially appear to be an unusual natural object.
The difficulty increases even more when it comes to searching across planetary surfaces. On the Moon, for example, there are very high-resolution photographs in some areas, to the point of identifying traces of lunar rovers or equipment left on the surface. But most of the solar system is not mapped at such a resolution. On Saturn's moons, for example, the average resolution of observations is sometimes around a kilometer per pixel – far from what is needed to detect an object the size of a spacecraft or a small facility.
Even an artificial object that landed or crashed a long time ago will not necessarily be preserved. On Mars, for example, dust, radiation, and micrometeorite impacts can erode remains over millions of years. On other bodies, conditions are different, but even there, preservation depends on location, material, and length of time.
Why is it difficult to distinguish between a spacecraft and an asteroid?
And what about active objects? They should be easier to detect, supposedly, because any active system must emit excess heat. Surveys like WISE have already detected objects with unusual thermal properties, but not every anomaly is technological. Asteroids, comets, and small bodies can exhibit complex thermal behavior, and it’s hard to draw a definitive conclusion without focused follow-up observations—or a spacecraft visit.
The paper points to a new generation of surveys that could improve the situation. The Vera Rubin Observatory, the SPHEREx mission, and the NEO Surveyor mission are expected to produce vast amounts of data on small objects in the solar system. Systematic analysis of anomalies in orbits, spectra, thermal emission, or temporal variations could greatly improve the ability to identify interesting candidates for investigation.
However, the main conclusion remains cautious: there is currently no evidence that extraterrestrial spacecraft are in the solar system. But we also do not have a strong observational basis to say that we have looked enough to rule it out. In this sense, the article is not a story about “aliens in the backyard,” but a reminder that the solar system is still large, complex, and only partially mapped.
To the article in UNIVERSE TODAY
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