Calculating The Odds Of Intelligent Alien Life
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The Search for Extraterrestrial Life
One of the most fundamental questions that humanity has always asked is, does life exist beyond Earth? Astrobiologists, scientists who study life in the universe, are currently trying to answer this question. While most are focused on the possibility of microbial life on Mars, under the frozen surface of Jupiter’s moon Europa, or in the liquid hydrocarbon lakes on Saturn’s moon Titan, a particular group of astrobiologists are working on SETI.
SETI, the Search for Extraterrestrial Intelligence, is a scientific endeavor aimed at detecting evidence of technological civilizations that may exist elsewhere in the universe. SETI researchers are trying to find evidence of intelligent life forms that have used technology to build a transmitter of some sort. However, the likelihood of finding such a signal is uncertain.
The Drake Equation
To help organize our thinking about the requirements for successful detection of extraterrestrial intelligence, scientists use the Drake equation. Named after Frank Drake, this equation doesn’t provide a definitive answer due to the many unknowns it contains. As we learn more about our universe and our place within it, some of the unknowns become better known, allowing us to estimate an answer a bit better. However, a definite answer to the Drake equation won’t be available until SETI succeeds or something else proves that Earthlings are the only intelligent species in our portion of the cosmos.
The Drake equation attempts to estimate the number of technological civilizations in the Milky Way Galaxy with whom we could make contact. It is usually written as: N equals R-star multiplied by f-sub-p multiplied by n-sub-e multiplied by f-sub-l multiplied by f-sub-i multiplied by f-sub-c and lastly, multiplied by capital L. All these factors multiplied together help to estimate the number of technological civilizations that we might be able to detect right now.
Understanding the Drake Equation
R-star represents the rate at which stars have been born in the Milky Way Galaxy over the last few billion years. The f-factors are fractions, each one must be less than or equal to one. F-sub-p is the fraction of stars that have planets. N-sub-e is the average number of habitable planets in any planetary system. F-sub-l is the fraction of planets on which life actually begins and f-sub-i is the fraction of all those life forms that develop intelligence. F-sub-c is the fraction of intelligent life that develops a civilization that decides to use some sort of transmitting technology. Lastly, L represents the longevity factor, or on average, how many years those transmitters continue to operate.
Currently, astronomers are almost able to tell us what the product of the first three terms is. We’re now finding exoplanets almost everywhere. The fractions dealing with life and intelligence and technological civilizations are ones that many experts ponder, but nobody knows for sure. So far, we only know of one place in the universe where life exists, and that’s right here on Earth.
The Importance of the Number Two
In the next couple of decades, as we explore Mars, Europa, and Titan, the discovery of any kind of life there will mean that life will be abundant in the Milky Way. Because if life originated twice within this one Solar System, it means it was easy, and given similar conditions elsewhere, life will happen. So the number two is a very important number here.
Scientists, including SETI researchers, often tend to make very crude estimates and acknowledge that there are very large uncertainties in these estimates, in order to make progress. We think we know that R-star and n-sub-e are both numbers that are closer to 10 than, say, to one, and all the f-factors are less than one. Some of them may be much less than one. But of all these unknowns, the biggest unknown is L, so perhaps the most useful version of the Drake equation is simply to say that N is approximately equal to L.
The Future of SETI and Humanity
The information in this equation is very clear. Unless L is large, N will be small. But, you can also turn that around. If SETI succeeds in detecting a signal in the near future, after examining only a small portion of the stars in the Milky Way, then we learn that L, on average, must be large. Otherwise, we couldn’t have succeeded so easily.
A physicist named Philip Morrison summarizes by saying that SETI is the archaeology of the future. By this, he meant that because the speed of light is finite, any signals detected from distant technologies will be telling us about their past by the time they reach us. But because L must be large for a successful detection, we also learn about our future, particularly that we can have a long future.
We’ve developed technologies that can send signals into space and humans to the moon, but we’ve also developed technologies that can destroy the environment, that can wage war with weapons and biological terrorism. In the future, will our technology help stabilize our planet and our population, leading to a very long lifetime for us? Or will we destroy our world and its inhabitants after only a brief appearance on the cosmic stage?
I encourage you to consider the unknowns in this equation. Why don’t you make your own estimates for these unknowns, and see what you come up with for N? Compare that with the estimates made by Frank Drake, Carl Sagan, other scientists or your neighbors. Remember, there’s no right answer. Not yet.
Discussion Questions
- Do you believe that there is life beyond Earth? Why or why not?
- How do you think the search for extraterrestrial intelligence (SETI) could impact our understanding of our place in the universe?
- What factors do you think are most important in determining the likelihood of finding technological civilizations in the Milky Way Galaxy?
- How do you think the discovery of life on Mars, Europa, or Titan would change our perception of the abundance of life in the universe?
- What do you think is the significance of the number two in the context of the search for extraterrestrial life?
- How do you think the Drake equation helps scientists organize their thinking about the search for extraterrestrial intelligence?
- What role do you think technology plays in determining the longevity of intelligent civilizations?
- Do you believe that our future as a species is dependent on our ability to stabilize the planet and our population? Why or why not?
Lesson Vocabulary
search – the action of looking systematically in order to find something or someone – I need to search for my keys before I can leave the house.
extraterrestrial – relating to or originating from outside the earth or its atmosphere – Scientists are studying the possibility of extraterrestrial life on other planets.
life – the condition that distinguishes animals and plants from inorganic matter, including the capacity for growth, reproduction, functional activity, and continual change – The discovery of water on Mars has raised hopes for the existence of life beyond Earth.
astrobiologists – scientists who study the possibility of life in the universe, including the origin and evolution of life on Earth and the potential for extraterrestrial life – Astrobiologists are conducting experiments to understand the conditions necessary for life to exist on other planets.
mars – the fourth planet from the sun in our solar system, often referred to as the Red Planet – NASA’s Perseverance rover is currently exploring the surface of Mars to gather data about its geology and potential for past habitability.
jupiter’s moon europa – one of Jupiter’s largest moons, believed to have a subsurface ocean and potential for supporting microbial life – Scientists speculate that Jupiter’s moon Europa may have the right conditions for life beneath its icy crust.
saturn’s moon titan – the largest moon of Saturn, known for its dense atmosphere and the presence of lakes and rivers of liquid methane and ethane – The Cassini spacecraft provided valuable data about the complex atmosphere and geology of Saturn’s moon Titan.
SETI – Search for Extraterrestrial Intelligence; the collective efforts and initiatives to detect signals or evidence of intelligent life beyond Earth – SETI scientists use radio telescopes to scan the universe for any potential communication signals from alien civilizations.
intelligence – the ability to acquire and apply knowledge and skills, or the ability to think and reason abstractly – Human intelligence has allowed us to explore the mysteries of the universe and search for signs of other intelligent beings.
technological civilizations – advanced societies capable of developing and utilizing advanced technologies – The existence of technological civilizations in the universe is a topic of great interest and speculation among scientists and science fiction enthusiasts.
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- Categories: Earth & Space Science, TED Ed, Video Lessons
- Keywords: astrobiologists, extraterrestrial, intelligence, Jupiter's moon Europa, life, Mars, Saturn's moon Titan, search, SETI, technological civilizations
