Frank D Drake (May 28, 1930 – September 2, 2022), one of the giants in the field of astronomy and astrophysics, left the bonds of Earth and headed for the stars yesterday. He was 92.
Drake was one of the most admired scientists, an exemplary human being and an inspiration to many. He was well-known for his pioneering efforts in the search for extraterrestrial intelligence, the Arecibo message and the famous Drake equation.
Frank Drake served as Professor of Astronomy and Astrophysics and Dean of Natural Sciences at the University of California, Santa Cruz, after having been at Cornell and serving as the founding Director of the National Astronomy and Ionosphere Center. He was the first president of the SETI Institute, and was President of the Astronomical Society of the Pacific during its Centennial.
The Drake Equation
The famous Drake equation is shown in this plaque, which adorns the wall of the conference room where the equation was presented on Nov 1, 1961, at the National Radio Astronomy Observatory site in Green Bank, West Virginia. It provides a mathematical approach to answering the question — is there intelligent life out there that can be detected by us?
In the Drake equation,
N = the number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light cone);
and
R∗ = the average rate of star formation in our Galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of planets that could support life that actually develop life at some point
fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space
Frank Drake wrote -
At the conference, we plugged in our best estimates for each of the factors, and found that the product of the first six factors on the right hand side came out to roughly the value of 1. Thus the value of N seemed to hinge solely on the value of L — how long intelligent, communicative civilizations could survive. At the end of the meeting, Struve offered a toast: “To the value of L. May it prove to be a very large number.”
L — how long intelligent, communicative civilizations could survive — that is difficult to estimate, since we have no real data points. We are still a fledging society, likely with a small L value, the way we are going, and we can hope that other civilizations will do or have done better and raise the average value of L.
Estimates of N vary from 0 to 15,600,000 for the Milky Way.
Note that R∗ is the number new stars formed per year, not the total number of stars. It is estimated to lie between 1.5 and 3.0 for the Milky Way.
Also, N is not the number of communicative civilizations that have ever existed; it is the number of civilizations whose communication would reach us in the present time.
Here is the esteemed Carl Sagan explaining the Drake Equation and performing some calculations to estimate N.
The Genesis of the Drake Equation
In 1960, soon after some new discussions about extraterrestrial civilizations, Drake made the first systematic search for radio signals from communicative extraterrestrial civilizations, using the 85-foot radio telescope at Green Bank, WV, as part of a project he named Ozma. It detected no signals, after 150 hours of observations over a 4-month period.
Soon thereafter, Drake hosted a "search for extraterrestrial intelligence" meeting at the Green Bank facility in 1961. Drake recalled -
As I planned the meeting, I realized a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it's going to be to detect extraterrestrial life. And looking at them it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy. This was aimed at the radio search, and not to search for primordial or primitive life forms.
The rest, as they say, is history.
Other Notable Contributions
Drake was the creator of the Arecibo Message, a digital encoding of an astronomical and biological description of the Earth and its lifeforms, broadcast via radio waves from the Arecibo Observatory in 1974, for whoever out there is listening for a signal from us.
Drake was also involved (with Carl Sagan and others) in the design of the plaques carried on the Pioneer 10 and 11 spacecraft and the “Golden Record” carried on the Voyager 1 and 2 spacecraft.
Frank Drake also coined the term “pulsar” in 60’s when he conducted some of the earliest work on these “highly magnetized rotating neutron stars.”
The starburst-like diagram in the lower left-hand corner of the cover of the Golden Record is the famous “pulsar map,” which shows the location of the solar system with respect to 14 pulsars, whose precise periods are well-known. Frank Drake designed the map, working with Carl Sagan and artist and writer Linda Salzman Sagan.
Tributes
Epilogue
RIP Frank Drake.
What are your memories of Frank Drake? Did his works have an effect on your thinking or your career?
Please share you knowledge and insights about the Drake Equation.
What is your estimate of L and N?
Further Reading
- The Origin of the Drake Equation, Frank Drake and Dava Sobel — astrosociety.org/…
- Frank Drake — en.wikipedia.org/…
- Drake Equation — en.wikipedia.org/…
- Frank Drake — www.famousscientists.org/...
- Life, the Universe and the Drake Equation (Sep 3, 2022) — telescoper.wordpress.com/…