Scientists from the SETI Institute were interested in the question of what would happen if there was a planet somewhere far away from us that was similar to Earth in every way and the scientists on it looked toward the solar system. What, in that case, could they see or hear? The answer was overwhelming.
Technosignatures
Recently, Sofia Sheikh of the SETI Institute, along with Characterizing Atmospheric Technosignatures and colleagues at the University of Pennsylvania, published a study answering the question of how visible our civilization was to intelligent beings living near other stars.
Generally speaking, the SETI Institute is the leading scientific institution dedicated to the search for extraterrestrial life. At the same time, scientists there are primarily looking for what is called by the general term “technosignatures” or “technomarkers”. This is the name given to every manifestation of extraterrestrial technology that we are able to spot from Earth or its orbit.
In doing so, researchers and enthusiasts usually start from the assumption that technosignatures can be found relatively easily in any star in the Milky Way, you just have to look at it closely enough. However, the warning has been repeatedly criticized by scientists who claim that radio signals or traces of industrial emissions in the exoplanet’s atmosphere become invisible to Earth observers with increasing distance.
To figure out what’s really going on there, Sofia Sheikh modeled what would happen if there was a twin Earth deep in space and the SETI Institute scientists were there with all the modern arsenal of astronomical instruments. From what distance would they be able to spot different kinds of technosignatures?
Is human civilization clearly visible?
In general, scientists distinguish several large groups of signs among technosignatures: radio signals, atmospheric traces, visual signs of the presence of intelligent beings and, finally, material artifacts in the form of various hardware that other intelligent beings send into space. Due to the recent development of space telescopes, it is the composition of atmospheres that has been talked about as the most reliable biomarker.
A new study has shown that the assumption that the distance from which observational tools comparable to ours can detect an Earth-like civilization is much smaller than the galactic disk is correct. Even our powerful technosignatures are visible from a distance of at most 12,000 light-years, which is even less than the distance to the center of the Milky Way.
And these technosignatures are exactly radio signals, or rather, a quite specific variety of them. We are talking about signals sent by radio telescopes. They are, in fact, narrow beams aimed at a certain part of the sky.
The most powerful military radars are next in terms of ease of technosignature detection. They “grope” the entire sky, but their signals carry no information at all. It is possible to detect such a source of radiation from a distance of several tens of light years.
And only from a distance of a few light years, that is, approximately from the nearest stars to us, we can confidently capture the rays of powerful lasers, conventional radio and television, as well as the most visible consequence of industry — nitrogen oxide in the Earth’s atmosphere.
As for city lights, heat islands, and non-directional lasers, they can be seen while at least within the Oort Cloud. As for satellites in orbit, they can only be viewed when the telescope is no farther away than Mars.
According to phys.org
