Alien tech signatures could be how we first encountered extraterrestrial life

If an a̳l̳i̳e̳n̳ were to look down on Earth, many human technologies, from cell towers to fluorescent light bulbs, could be a beacon indicating the presence of life.

We are two astronomers working on the search for ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ intelligence or SETI. In our research, we try to characterize and detect signs of technology originating from beyond Earth. These are called technology firms.

While scanning the sky for a TV broadcast of some ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ Olympics may seem straightforw̳a̳r̳d, looking for signs of distant, advanced c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳s is a much more nuanced and difficult task than it seems.

Say \’hello\’ with radios and lasers
The modern scientific search for ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ intelligence began in 1959 when astronomers Giuseppe Cocconi and Philip Morrison demonstrated that radio telescopes could detect radio transmissions from Earth at interstellar distances.

The same year, Frank Drake launched the first SETI search, Project Ozma, pointing a large radio telescope at two nearby Sun-like stars to see if he could detect any radio signals coming from them. Following the invention of the laser in 1960, astronomers showed that visible light could also be detected from distant planets.

These early foundational attempts to detect radio or laser signals from another c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳ were looking for focused and powerful signals that had been intentionally sent into the solar system and destined to be found.

Given the technological limitations of the 1960s, astronomers did not seriously think about looking for broadcast signals, such as radio and television broadcasts on Earth, that would leak into space.

But a beam of a radio signal, with all its power focused on Earth, could be detected from much further away: imagine the difference between a laser and a dim light bulb.

Searching for intentional radio and laser signals remains one of the most popular SETI strategies today. However, this approach assumes that ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳s want to communicate with other technologically advanced life forms.

H̳u̳m̳a̳n̳s̳ rarely send directed signals into space, and some scholars argue that intelligent species may deliberately avoid broadcasting their locations. This search for signals that no one can be sending is called the SETI Paradox.

radio wave leaks
Although humans do not transmit many intentional signals to the cosmos, many technologies that people use today produce many radio transmissions that leak out into space. Some of these signals would be detectable if they came from a nearby star.

The worldwide network of television towers constantly broadcast signals in many directions that leak out into space and can accumulate into a detectable, albeit relatively weak, radio signal.

Whether current emissions from cell towers at Earth\’s radio frequency would be detectable with current telescopes is being investigated, but the forthcoming Square Kilometer Array radio telescope will be able to detect even weaker radio signals with 50 times greater sensitivity than that of the current radio telescope. arrangements

However, not all human-made signals are so out of focus. Astronomers and space agencies use beams of radio waves to communicate with satellites and spacecraft in the solar system. Some researchers also use radio waves for radar to study asteroids.

In both cases, the radio signals are more focused and aimed at space. Any ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳ that was in the line of sight of these rays could probably detect these unmistakably artificial signals.

find megastructures
Aside from finding an actual a̳l̳i̳e̳n̳ spaceship, radio waves are the most common technological signatures to appear in science fiction movies and books. But they are not the only signs that could be out there.

In 1960, astronomer Freeman Dyson theorized that since stars are by far the most powerful source of energy in any planetary system, a technologically advanced c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳ could harvest a significant portion of the starlight as energy thereby it would essentially be a huge solar panel. Many astronomers call these megastructures, and there are a few ways to spot them.

After using the captured light energy, an advanced society\’s technology would re-emit some of the energy as heat. Astronomers have shown that this heat could be detected as additional infrared radiation from a star system.

Another possible way to find a megastructure would be to measure its dimming effect on a star. Specifically, large artificial satellites orbiting a star would periodically block some of its light.

This would appear as dips in the star\’s apparent brightness over time. Astronomers could detect this effect in a similar way to how distant planets are discovered today.

A lot of pollution
Another technology signature that astronomers have thought about is pollution.

Chemical pollutants, such as nitrogen dioxide and chlorofluorocarbons on Earth, are produced almost exclusively by human industry. It is possible to detect these molecules in the atmospheres of exoplanets with the same method that the James Webb Space Telescope uses to search for signs of biology on distant planets.

If astronomers find a planet with an atmosphere full of chemicals that can only be produced by technology, it may be a sign of life.

Finally, artificial light or heat from cities and industry could also be detected with large optical and infrared telescopes, as could a large number of satellites orbiting a planet. But a c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳ would need to produce much more heat, light, and satellites than Earth to be detectable in the vastness of space using the technology that humans currently possess.

Which signal is better?
No astronomer has ever found a confirmed technology signature, so it\’s hard to say what the first sign of ex̳t̳r̳a̳t̳e̳r̳r̳e̳s̳t̳r̳i̳a̳l̳ c̳i̳v̳i̳l̳i̳z̳a̳t̳i̳o̳n̳s will be.

While many astronomers have given a lot of thought to what might be a good sign, ultimately no one knows what a̳l̳i̳e̳n̳ technology might look like and what signs are out there in the Universe.

Some astronomers support a generalized SETI approach that looks for anything in space that current scientific knowledge cannot naturally explain. Some, like us, continue to look for both intentional and unintentional technology signatures.

The bottom line is that there are many ways to detect distant life. Since no one knows which approach is likely to succeed first, there is still a lot of interesting work to be done.

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