Is the Milky Way harboring dozens of intelligent alien civilizations?

Artist's illustration of what the surface of the newfound exoplanet Kepler-1649c might look like. (Image credit: NASA/Ames Research Center/Daniel Rutter)

Are dozens of intelligent extraterrestrial civilizations lurking right in our home galaxy?

According to a new study, there could be more than 30 civilizations capable of long-distance communication here in the Milky Way. This work, led by researchers at the University of Nottingham, assumed that intelligent life not only exists off-Earth, but develops on other planets similarly to how it does on Earth.

"There should be at least a few dozen active civilizations in our galaxy under the assumption that it takes 5 billion years for intelligent life to form on other planets, as it did on Earth," Christopher Conselice, an astrophysicist at the University of Nottingham who led this research, said in a statement. "The idea is looking at evolution, but on a cosmic scale."

To estimate the number of intelligent civilizations in our galaxy, the team took into account two major "Astrobiological Copernican limits", or conditions that such an "intelligent" civilization would depend on.

For one of these limiting factors, the researchers used Earth, where life began approximately 4.54 billion years ago, as an example. They assume that intelligent life most likely forms in less than 5 billion years (based on what has happened on Earth).

The second limiting criterion focused on stars. They estimate that a planet with intelligent life would orbit a star like our sun (because life has formed here on Earth, which orbits the sun). This sun-like star would have "a metal content equal to that of the sun … (the sun is relatively speaking quite metal-rich)," Tom Westby, an assistant professor at the University of Nottingham and first author on the paper said in the same statement.

In addition to these two Astrobiological Copernican limiting criteria, the scientists factored in technological capability. The researchers figured that the number of "intelligent" civilizations depends on technological prowess, specifically how long they have been sending out some sort of signal into space (anything from radio transmissions from orbiting satellites to television). So, using our civilization as an example for a potential extraterrestrial one, the researchers estimated that humans have been "technologically advanced" for about 100 years.

Taking these criteria into account and under these numerous assumptions, the researchers made an approximate estimation of the number of intelligent civilizations that could theoretically exist in the Milky Way.

"We calculate that there should be around 36 active civilizations in our galaxy," Westby said. However, the average distance to these alien worlds would be approximately 17,000 light-years, so much too far for humans to contact with existing technologies, according to the researchers.

"The classic method for estimating the number of intelligent civilizations relies on making guesses of values relating to life, where opinions about such matters vary quite substantially," Westby said, referring to "values relating to life" like proximity to a sun-like star.

Despite the new estimate, the researchers acknowledge it's still very possible that we could be alone: If other broadcasting civilizations exist, they might not survive for as long as humankind has and so we might not exist at the same time.

"If we find that intelligent life is common, then this would reveal that our civilization could exist for much longer than a few hundred years; alternatively, if we find that there are no active civilizations in our galaxy, it is a bad sign for our own long-term existence. By searching for extraterrestrial intelligent life — even if we find nothing — we are discovering our own future and fate," Conselice said.

This work was published today (June 15) in the Astrophysical Journal.

Email Chelsea Gohd at cgohd@space.com or follow her on Twitter @chelsea_gohd. Follow us on Twitter @Spacedotcom and on Facebook.

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Chelsea “Foxanne” Gohd joined Space.com in 2018 and is now a Senior Writer, writing about everything from climate change to planetary science and human spaceflight in both articles and on-camera in videos. With a degree in Public Health and biological sciences, Chelsea has written and worked for institutions including the American Museum of Natural History, Scientific American, Discover Magazine Blog, Astronomy Magazine and Live Science. When not writing, editing or filming something space-y, Chelsea "Foxanne" Gohd is writing music and performing as Foxanne, even launching a song to space in 2021 with Inspiration4. You can follow her on Twitter @chelsea_gohd and @foxannemusic.

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63 Comments Comment from the forums

rod

This is an interesting report. "The second limiting criterion focused on stars. They estimate that a planet with intelligent life would orbit a star like our sun (because life has formed here on Earth, which orbits the sun). This sun-like star would have "a metal content equal to that of the sun … (the sun is relatively speaking quite metal-rich)," Tom Westby, an assistant professor at the University of Nottingham and first author on the paper said in the same statement...Taking these criteria into account and under these numerous assumptions, the researchers made an approximate estimation of the number of intelligent civilizations that could theoretically exist in the Milky Way. "We calculate that there should be around 36 active civilizations in our galaxy," Westby said. However, the average distance to these alien worlds would be approximately 17,000 light-years, so much too far for humans to contact with existing technologies, according to the researchers."

Apparently class G type stars were used in this study vs. class M, red dwarf stars. This exoplanet site shows 763 confirmed exoplanets found around stars with masses 0.95 to 1.05 solar masses in my MS SQL Query (most are class G stars), http://exoplanet.eu/ Another site I use shows 645 exoplanets for 0.95 to 1.05 solar mass stars, https://exoplanetarchive.ipac.caltech.edu/index.html
This new study indicating perhaps 36 *active civilizations in our galaxy*, places serious constraints on those who claim UFO sightings must be visitors from other star systems.
Reply
I_believe

I heard that report yesterday and was just about to ask about it.. Apparently it takes 5billion years for intelligent life to form? How do they come to that metric?
Reply
Cosmo47

I_believe said:
I heard that report yesterday and was just about to ask about it.. Apparently it takes 5billion years for intelligent life to form? How do they come to that metric?
They came to the "5 billion years to evolve intelligent life" number by looking at how long it took humans to become 'intelligent' after the formation of the Earth. Answer: 4.5 billion years (as microbial life appeared soon after Earth became Earth). I found this number to be sort of 'squishy' in that Earth is a sample size of 1. I'd much rather have 2 or 3. :)
Reply
Jason K

rod said:

Apparently class G type stars were used in this study vs. class M, red dwarf stars. This exoplanet site shows 763 confirmed exoplanets found around stars with masses 0.95 to 1.05 solar masses in my MS SQL Query (most are class G stars), http://exoplanet.eu/ Another site I use shows 645 exoplanets for 0.95 to 1.05 solar mass stars, https://exoplanetarchive.ipac.caltech.edu/index.html
This new study indicating perhaps 36 *active civilizations in our galaxy*, places serious constraints on those who claim UFO sightings must be visitors from other star systems.

Rod, I don't have access to the full article, but from the abstract, it appears the authors acknowledge that most of these potential civilizations would be found around class M red dwarf stars: "Furthermore, the likelihood that the host stars for this life are solar-type stars is extremely small and most would have to be M dwarfs, which may not be stable enough to host life over long timescales."

While I love the authors' optimism for intelligence in the universe, the article surely can only be another attempt to quantify the Drake equation. And the problem here is that there are massive unknowns in the terms of the Drake equation, mostly in what events in Earth's history represent major or minor filters on the biological progression that eventually allowed for the emergence of sentience. For instance, we know our large moon was certainly a factor in that it stabilizes our axial tilt over cosmological spans of time.... but is this a major filter that is crucial for long-term biological stability and diversification that only a very small percentage of potential habitable planets are likely possess, or a more minor filter? We don't know, because our current exemplar sample size is one. Another potential major filter is the presence of a large gas giant to keep debris strikes to habitable-zone planets relatively low enough to not completely disrupt biological evolution every few million years. Is Jupiter a major filter for the development of intelligence on Earth, or is it a more minor factor? Again, exemplar sample of one, so we don't know.

In the end, each attempt to quantify the Drake equation ends up showing the researchers' particular biases in regards to what they see as a significant versus a minor hurdles in the evolutionary chain. And to make matters worse, we cannot quantify those biases, because our only sample for intelligent life is one. In effect, we know that there is much that we don't know, but we don't know how lacking our knowledge might be, or how accurate or erroneous our assumptions really are. In short, the numerical solution to the Drake equation can be as low as one (us), or as high as several thousand, depending on the assumptions made about what constitutes major versus minor filters in the terms of the equation.

Still, it's always a fascinating thought experiment. And as I said, I applaud the authors' optimism in their assumptions which led to their answer of 36 civilizations. I personally am not as optimistic, but do believe the number to be greater than one ... although I'd be extraordinarily surprised if there were ever more than one active at the same time in our galaxy.

-Jason
Reply
rod

FYI, the quote you provide Jason appears to focus on M class or red dwarfs but the space.com report and others I read make it clear that the focus was G class stars similar to our Sun, "The second limiting criterion focused on stars. They estimate that a planet with intelligent life would orbit a star like our sun (because life has formed here on Earth, which orbits the sun). This sun-like star would have "a metal content equal to that of the sun … (the sun is relatively speaking quite metal-rich)," this from the space.com report. Another report shows the same criteria, https://phys.org/news/2020-06-intelligent-life-galaxy.html. However you are correct about the abstract, https://iopscience.iop.org/article/10.3847/1538-4357/ab8225, "Furthermore, the likelihood that the host stars for this life are solar-type stars is extremely small and most would have to be M dwarfs, which may not be stable enough to host life over long timescales. We furthermore explore other scenarios and explain the likely number of CETI there are within the Galaxy based on variations of our assumptions."

If the model tosses out class G type stars like our Sun and focuses on M, red dwarf stars, it seems the constraints placed on UFO reports claiming they come from the stars is even more restricted and difficult with so many red dwarf stars and only 36 likely civilizations arising, mostly on red dwarf stars with exoplanets. This assumes that abiogenesis works similar to model(s) for abiogenesis on Earth and natural selection will work similar too, creating an evolutionary tree of life that results in intelligent life emerging and flourishing to create a civilization.
Reply
rod

FYI, I find M dwarf star hosts very intriguing when it comes to extrapolating the emergence of intelligent life on an exoplanet orbiting such stars (and the assumption that abiogenesis and natural selection will work similar to our Earth). Here is a recent example with a 3.14 day period, http://exoplanet.eu/catalog/epic_249631677_b/ The planet is about 0.0234 AU from the red dwarf star.
Reply
FrankT

Recently, there were a few video footage declassified by the Pentagon, showing UFO flying with our fighter jets in mid air. One of them was narrated as suddenly dropping from 28,000 ft to sea level in 0.7 seconds. A few clicks on the calculator said that roughly equals to falling at 27,000 mph, with instantaneous acceleration and deceleration, as if inertia did not exist. Whoever or whatever inside that vehicle or controlling it, has to be pretty intelligent.
Reply
rod

So applying the 36 civilizations model for the red dwarf stars in our galaxy using the science in the new report, which red dwarf star did the UFOs come from flying around the fighter jets? We have 261 confirmed exoplanets reported around stars with masses 0.08 to 0.5 solar masses, and this includes the TRAPPIS-1 system, http://exoplanet.eu/
Reply
George B.

This research did not use the Drake equation, which I've always thought was too optimistic to begin with because the 7th term L ( the length of time for which such civilizations release detectable signals into space) should be the fraction of time a civilization is releasing detectable signals into space over possible time the civilization could exist (this would reduce the number of possible civilizations by the Drake equation by several orders of magnitude...a possible answer to the Fermi Paradox).

This new research does acknowledge the question about how long such a civilization could exist (better yet...how long it would use electromagnetic emissions (i.e. radio) to communicate information, which would be shorter than its time of existence). In short, what is the probability of these 36 civilizations existing (i.e. overlapping) simultaneously?

"Despite the new estimate, the researchers acknowledge it's still very possible that we could be alone: If other broadcasting civilizations exist, they might not survive for as long as humankind has and so we might not exist at the same time. "
Reply
rod

George B. said:
This research did not use the Drake equation, which I've always thought was too optimistic to begin with because the 7th term L ( the length of time for which such civilizations release detectable signals into space) should be the fraction of time a civilization is releasing detectable signals into space over possible time the civilization could exist (this would reduce the number of possible civilizations by the Drake equation by several orders of magnitude...a possible answer to the Fermi Paradox). This new research still does not account for how long such a civilization could exist, or even how long it would use electromagnetic radiation (i.e. radio) to communicate information, which would be shorter than its time of existence. In short, what is the probability of these 36 civilizations existing (i.e. overlapping) simultaneously? The report does account for this possibility:
"Despite the new estimate, the researchers acknowledge it's still very possible that we could be alone: If other broadcasting civilizations exist, they might not survive for as long as humankind has and so we might not exist at the same time. "

And this quote provided from the report shows more constraints for those claiming the UFOs are space ships visiting from the stars.
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