Young Astronomers Blog, Volume 29, Number 1.
The universe is a big place. There might be some 200 billion to over a trillion galaxies in the visible universe, each with around 200 billion stars. Then here we are on this bluish/green planet orbiting a single yellowish star in a solar system around ½ way out from the center of one of those billions of galaxies.
So, the question is asked, are we alone in all this? For those of you who want the answer, I will let you know upfront, I don’t know what it is. However, it is still a great question, and, over the years, folks have tried to find an answer.
To find life and possibly intelligent life, astronomers have looked outside the solar system to the Milky Way and beyond. Setting the stage for this was physicist Enrico Fermi, who during a lunch time conversation at the Los Alamos laboratory asked the question, given the vast size of the galaxy, “Where is Everybody?” This has become known as “The Fermi Paradox”. Several ideas have been suggested to explain Fermi’s Paradox. Matt Williams and the folks at Universe Today have a series of articles discussing some of these in detail.
In advance of a meeting at the Green Bank Observatory in 1961, Frank Drake proposed a way to estimate the number of civilizations in the Milky Way. The equation, now known as “the Drake Equation”, is N = R* x Fp x Ne x Fl x Fi x Fc x L. It is not quite as complicated as it looks.
- N is the number of civilizations that exist today in the Milky Way. This is the answer we’re looking for.
- R* is the rate at which new stars form in the Milky Way (number per year).
- Fp is the fraction of stars that have planets. Based on exoplanet research, astronomers think this might be close to 1 (all of them).
- Ne is the average number of Earth-like planets per solar system.
- Fl is the fraction of Earth-like planets with life.
- Fi is the fraction of those planets with intelligent life.
- Fc is the fraction of those planets that have developed the capability to communicate. This could also be the fraction of technological civilizations.
- L is the number of years over which intelligent life communicates.
If you don’t want to do the calculations yourself, there are websites (e.g., PBS) that allow you fill in the numbers and they will calculate the answer for you.
To search for those alien civilizations that might (or might not) be out there, astronomers have turned to radio astronomy and a portion of the electromagnetic spectrum from 1 GHz to 10GHz. This is where there is minimal background noise and the Earth’s atmosphere is transparent. Cornell’s Giuseppe Cocconi and Philip Morrison set the stage for this with their 1959 paper. Bernard Oliver, in a 1974 book edited by Carl Sagan called Communication with Extraterrestrial Intelligence (CETI), suggested that SETI searches focus on the 1 to 2 GHz range where hydrogen (H) and hydroxyl (HO) spectral lines are found. He called this the “Water Hole.”, because when combined, hydrogen and hydroxyl result in water.
Credit: NASA Share the Science
The first SETI initiative was Project Ozma, which was a limited search of stars Tau Ceti and Epsilon Eridani in 1960 by Frank Drake at the Green Bank Observatory.
NASA slowly entered the search for ET and finally proposed a large scale, long-term, and expensive project called Cyclops in 1972. Funding for the project never materialized and the project faded from view, although the project’s report laid out some of the foundation for future searches.
A few SETI projects followed, including one at the Big Ear Observatory in Ohio. On August 15, 1977, Big Ear picked up a signal that stood out from the background noise. A few days later while reviewing a printout, astronomer Jerry Ehman noticed the signal and wrote the word “Wow!” next to it. Ehman eliminated all the possible terrestrial sources and concluded that it was coming from somewhere near the constellation Sagittarius. Unfortunately, the signal has never repeated and to this day no one knows exactly what it was.
Beginning in 1984, NASA started to look to the private sector and the newly formed SETI Institute for extraterrestrial searches. The Institute was founded by Tom Pierson and Jill Tarter, who was the inspiration for the main character in Carl Sagan’s book and movie Contact. Today the SETI Institute employs around 100 scientists as well as numerous other specialists.
Years later in 1992, NASA tried again with the High Resolution Microwave Survey Targeted Search (HRMS). Congress stepped in within a year and funding was cut. This time, the project was saved by the SETI Institute. It was renamed Project Phoenix and operated from 1994 to 2004.
Limited computing power constrained early SETI searches. To address this in 1999, scientists at UC Berkeley decided to harness the power of the internet and developed the SETI@home project. I tried it for a while years ago, but never did find ET. SETI@home has been “retired” as of early 2020.
Several other SETI searches have operated over the years.
- SERENDIP was a series of programs by UC Berkeley where searches were conducted in conjunction with traditional observations.
- Sentinel, META, and BETA were programs operated by Harvard.
- Project Argus is a search by a collaboration of amateur astronomers in coordination with the SETI League.
- Breakthrough Listen is a ten-year project funded by billionaire Yuri Milner and run by UC Berkeley. The $100 million initiative began in 2016 and will scan a million of the closest Milky Way stars along with a hundred of the closest galaxies for extraterrestrial signals.
SETI searches have utilized several world class radio observatories including Green Bank in West Virginia, Arecibo in Puerto Rico, Parkes in Australia, and the Very Large Array (VLA) in New Mexico. The SETI Institute built and is now operating the Allen Telescope Array in California, the first observatory dedicated to SETI. China might join the hunt with its Five-hundred-meter Aperture Spherical Telescope (FAST). Regrettably, the Arecibo observatory suffered the collapse of two cables followed by its instrument array in late 2020 and has been declared beyond repair.
Keeping up with all the SETI searches can be a daunting task. In 2019, Jill Tarter and the SETI Institute launched Technosearch, which is a database of all search projects from 1960 to the present.
In December 2020, The Breakthrough Listen project identified an interesting signal coming from Proxima Centauri, the closest star to the Sun. Before any scientific papers could be written, the story leaked to The Guardian, which published an article in mid-December. The news quickly spread to other news outlets and several additional articles followed. Despite the interest, everyone is urging caution. The signal, dubbed BLC-1 (Breakthrough Listen Candidate-1), could be the next “WOW” signal, but most likely, it is some stray terrestrial noise picked up by the Parkes observatory during the observation session. In October 2021, The Breakthrough Listen team announced that this signal was most likely a “false positive” and is terrestrial in origin.
SETI searches have just scratched the surface. The Universe is huge and SETI projects have focused on only a small portion of it. If we assume there are 200 billion stars in the Milky Way and 200 billion galaxies in the visible universe, we need to search 4 x 1022 stars (that is 40,000,000,000,000,000,000,000 stars). For each one, we need to search all possible EM frequencies. Jill Tarter and others use the analogy that searches so far are equivalent to investigating the oceans using only a glass or hot tub size sampling of water.
Who knows if an advanced civilization is out there? The answer might come tomorrow, next month, next year, or maybe never. We will just have to keep searching to find out.
Selected Sources and Further Reading
“Beyond ‘Fermi’s Paradox’.” Universe Today. (accessed December 5, 2020). https://www.universetoday.com/?s=%22Beyond+%22Fermi%27s+Paradox%22%22
Matt Williams. “What is the Drake Equation?” Universe Today. June 13, 2017. https://www.universetoday.com/39966/drake-equation-1/
“Drake Equation.” PBS, Life Beyond Earth. (accessed December 5, 2020). https://www.pbs.org/lifebeyondearth/listening/drake.html
Jason Davis. “Is There Anybody Out There?” The Planetary Society. October 25, 2017. https://www.planetary.org/articles/20171025-seti-anybody-out-there
Matt Ransford. “The Search For Extraterrestrial Life: A Brief History.” Popular Science. June 17, 2008. https://www.popsci.com/military-aviation-space/article/2008-06/et-phone-earth/
“What Is the Water-Hole?” SETI League. (accessed December 15, 2020). http://www.setileague.org/general/waterhol.htm
Eric Betz. “The Wow! Signal: An alien missed connection?” Astronomy. September 30, 2020. https://astronomy.com/news/2020/09/the-wow-signal-an-alien-missed-connection
“WOW!”. Ohio History Connection, Collections, Blog Posts. July 3, 2010. https://www.ohiohistory.org/learn/collections/history/history-blog/2010-(1)/july-2010/wow
Alan MacRobert. “SETI Searches Today.” Sky & Telescope. December 20, 2018. https://skyandtelescope.org/astronomy-news/seti-searches-today/
Sarah Scoles. Making Contact, Jill Tarter and the Search for Extraterrestrial Intelligence. Pegasus Books. New York. 2017. http://www.sarahscoles.com/making-contact.html
“SETI Institute.” (accessed December 7, 2020). https://seti.org/
“SETI@home is in hibernation.” SETI@home. (accessed December 7, 2020). https://setiathome.berkeley.edu/
“Project Argus, Project Update.” SETI League. (accessed December 15, 2020). http://www.setileague.org/argus/
“Breakthrough Listen.” (accessed December 14, 2020). https://breakthroughinitiatives.org/initiative/1
“The First Comprehensive Interactive Tool to Track SETI Searches.” SETI Institute. January 9, 2019. https://seti.org/press-release/first-comprehensive-interactive-tool-track-seti-searches
Phil Plait. “Watch Footage of the Devastating Collapse of the Arecibo Observatory Telescope.” SyFy Wire/Bad Astronomy. December 3, 2020. https://www.syfy.com/syfywire/footage-arecibo-observatory-telescope-collapse
Ian Sample. “Scientists looking for aliens investigate radio bean ‘from nearby star’.” The Guardian. December 18, 2020. https://www.theguardian.com/science/2020/dec/18/scientists-looking-for-aliens-investigate-radio-beam-from-nearby-star
Robert Naeye. “Here’s what we know about the signal from Proxima Centauri.” Astronomy. December 28, 2020. https://astronomy.com/news/2020/12/heres-what-we-know-about-the-signal-from-proxima-centauri
“Breakthrough Listen Releases Analysis of Previously Detected Signal.” Breakthrough Initiatives. October 25, 2021. https://breakthroughinitiatives.org/news/33
Videos
Jill Tarter. “Join the SETI search.” TED. 2009. https://www.ted.com/talks/jill_tarter_join_the_seti_search
Jill Tarter. “Calculating the Odds of Intelligent Alien Life – Jill Tarter.” TED-Ed/YouTube. July 2, 2012. https://youtu.be/6AnLznzIjSE
“What Was The Wow Signal? The Most Interesting Signal SETI Has Ever Seen.” Fraser Cain/YouTube. September 21, 2015. https://youtu.be/mDT8xDtliS8
Technical Reading
Giuseppe Cocconi and Philip Morrison. “Cosmic Search Vol. 1, No. 1. Searching For Interstellar Communication.” Cosmic Search Magazine / Nature. Volume 184, Number 4690. Pages 844-846. September 19, 1959. http://www.bigear.org/vol1no1/interste.htm
Bernard M. Oliver and John Billingham (Co-Directors). “Project Cyclops: a Design Study of a System for Detecting Extraterrestrial Intelligent Life.” NASA NTRS. CR 114445. January 1, 1972. https://ntrs.nasa.gov/citations/19730010095 & https://archive.org/details/projectcyclopsde00stan
You must be logged in to post a comment.