By Macy Huston and Jason Wright, Penn State University Park, Oct. 22 (The Conversation) If an alien gazed down at Earth, many human technologies—from cell phone towers to fluorescent lights—could be a beacon of the presence of life indicates.
We are two astronomers working on the search for extraterrestrial intelligence – or SETI. In our research we try to characterize and detect signs of technology coming from beyond Earth.
These are called technosignatures. While scanning the skies after a televised broadcast of some alien Olympic Games may sound easy, searching for signs of distant, advanced civilizations is a much more nuanced and difficult task than it might seem.
Saying hello with radios and lasers The current scientific search for extraterrestrial intelligence began in 1959 when astronomers Giuseppe Cocconi and Philip Morrison showed that radio transmissions from Earth could be detected with radio telescopes at interstellar distances.
That same year, Frank Drake launched the first SETI search, Project Ozma, by pointing a large radio telescope at two nearby sun-like stars to see if he could detect radio signals coming from them.
After the invention of the laser in 1960, astronomers showed that visible light can also be detected from distant planets.
These first, fundamental attempts to detect radio or laser signals from another civilization all looked for focused, powerful signals that were being sent intentionally to the solar system to be found.
Given the technological limitations of the 1960s, astronomers didn’t seriously consider looking for broadcast signals — like TV and radio broadcasts on Earth — that would make their way into space.
But a beam of radio signal with all its power directed towards the earth could be detectable from a much further distance – just imagine the difference between a laser and a dim lightbulb.
Searching for intentional radio and laser signals remains one of the most popular SETI strategies today. However, this approach assumes that extraterrestrial civilizations want to communicate with other technologically advanced beings.
Humans very rarely send targeted signals into space, and some scientists argue that intelligent species may deliberately avoid broadcasting their locations. This search for signals that no one might be sending is called the SETI paradox.
Leaking Radio Waves Although humans do not send many intentional signals into the cosmos, many technologies that humans use today create many radio transmissions that leak into space. Some of these signals would be detectable if they came from a nearby star.
The worldwide network of television towers constantly radiates signals in many directions that can leak out into space and accumulate into a detectable, albeit relatively weak, radio signal.
Research is ongoing to determine whether current emissions from cell towers would be detectable at Earth’s radio frequency range with today’s telescopes, but the forthcoming Square Kilometer Array radio telescope will be able to detect even weaker radio signals with 50 times the sensitivity of current radio telescope arrays.
However, not all man-made signals are so unfocused. 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 will be more focused and directed into space.
Any extraterrestrial civilization that happened to be in the line of sight of these beams could likely detect these clearly artificial signals.
Finding Megastructures Next to finding a real alien spacecraft, radio waves are the most common technosignatures in science fiction movies and books. But they’re not the only signals that might 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 civilization could collect a significant portion of the star’s light as energy using what would essentially be a massive solar panel.
Many astronomers call these megastructures, and there are a few ways to spot them.
After harnessing the energy of the captured light, the technology of an advanced society would release some of the energy as heat.
Astronomers have shown that this heat could be detectable as additional infrared radiation from a star system.
Another way to find a megastructure would be to measure its dimming effect on a star. In particular, large artificial satellites orbiting a star would regularly block some of its light.
This would appear as a dip in the star’s apparent brightness over time. Astronomers have been able to detect this effect, similar to how distant planets are discovered today.
A Whole Lot of Pollution Another techno-signature that astronomers have pondered 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 using the same method that the James Webb Space Telescope uses to scan distant planets for signs of biology.
When astronomers find a planet whose atmosphere is filled with chemicals that can only be made through technology, it can be a sign of life.
Finally, artificial light or heat from cities and industries could also be detected with large optical and infrared telescopes, as could large numbers of satellites orbiting a planet.
But a civilization would have to produce far more heat, light, and satellites than Earth to be detectable in the vast expanses of space with the technology humans currently have.
Which signal is best? No astronomer has ever found a confirmed techno-signature, so it’s hard to say what the first sign of extraterrestrial civilizations will be.
Ultimately, while many astronomers have given much thought to what might make a good signal, no one really knows what extraterrestrial technology might look like and what signals are out there in the universe.
Some astronomers support a generalized SETI approach, which looks for anything in space that current scientific knowledge cannot explain naturally. Some, like us, continue to search for both intentional and unintentional technosignatures.
The bottom line is that there are many ways to discover distant life. Since no one knows which approach is likely to succeed first, there is still a lot of exciting work to be done.
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)