The radio astronomer and astrophysicist Frank Drake, who has died aged 92, was a pioneer of the search for extraterrestrial intelligence. He carried out the first search for signals from extraterrestrial civilisations, Project Ozma, in 1960 and shortly afterwards invented the “Drake equation”, which estimates the number of extraterrestrial civilisations in our galaxy.
As a radio astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, he made the first observations of Jupiter’s radiation belts, analogous to the Van Allen belts around the Earth, and was one of the first astronomers to measure the intense surface temperature on Venus, a consequence of the greenhouse effect of its thick atmosphere. But it is for Project Ozma, named after Princess Ozma in L Frank Baum’s Wizard of Oz books and carried out with Green Bank’s 85ft radio telescope, that he will be remembered.
For three months Drake observed the sun-like stars Tau Ceti and Epsilon Eridani for radio signals that might be from planets with extraterrestrial civilisations. None were found, but as Drake recalled in a 2012 interview: “It was a start – and it did stimulate a lot of other people to start searching.”
Project Ozma quickly attracted public attention and in 1961 Drake was given funding by the US Academy of Sciences to lead a workshop at Green Bank to discuss the search for life beyond Earth – colleagues from across the US attended. Realising he needed to organise this discussion, he started to write down the factors that astronomers would need to estimate how many detectable civilisations there might be throughout the Milky Way.
This came together as the Drake equation: “The number of detectable civilisations in the Milky Way galaxy = the rate at which stars are born x the fraction of stars that host planets x the number of habitable planets per planetary system x the fraction of those planets on which life evolves x the fraction of life that evolves intelligence x the fraction of intelligent life that develops communicative technologies x the average length of time civilisations are detectable.”
At the time, only the first of the seven factors was known. Since then, enormous progress has been made with the next two factors, with the discovery of thousands of extraterrestrial planets, dozens of which are in the habitable or “Goldilocks” zone in which life is feasible. The final three factors in the equation could probably only be determined if we detected extraterrestrial civilisations. The Drake equation has been called “the second most-famous equation in physics” after E = mc2.
Project Ozma and the Drake equation, together with a 1959 Nature paper on interstellar communications by Giuseppe Cocconi and Philip Morrison, stimulated a series of ever more ambitious searches for extraterrestrial intelligence (Seti) and the founding of the Seti Institute, in California, in 1984. The Seti programme has not been without its critics, perhaps because no matter how many searches fail, its advocates can never entertain the possibility that we are alone. After Congress finance was withdrawn in the 1990s, private funding supported Seti research.
Drake was born in Chicago. His father, Richard, was a chemical engineer and his mother, Winnifred (nee Thompson), was a music teacher. When Frank was eight his father told him there were other worlds in space, meaning the other planets of the solar system, but the young boy imagined other planets like Earth strewn through the galaxy.
He enrolled at Cornell University on a Naval Reserve Officer Training Corps scholarship. Once there he started studying astronomy, and he heard about the possibility of a search for extraterrestrial life from Otto Struve. After graduating with a BA in engineering physics, Drake served briefly as an electronics officer on the heavy cruiser USS Albany. He then did a PhD in astronomy at Harvard University, where his doctoral adviser was Cecilia Payne-Gaposchkin, famous for the discovery that stars are mainly made of hydrogen and helium.
After receiving his PhD in 1955, Drake went to the Green Bank Observatory, where he set up new radio telescopes and carried out his studies of Jupiter and Venus.
In 1960 he set up Project Ozma and embarked on his pioneering searches for radio transmissions from extraterrestrial civilisations. He worked briefly at the Jet Propulsion Laboratory in Pasadena before joining the faculty at Cornell. He was director of the Arecibo Observatory in Puerto Rico from 1966 to 1968, and of Cornell’s National Astronomy and Ionosphere Center, which managed Arecibo, from 1971 to 1981.
During his stewardship of Arecibo, Drake oversaw improvements to the telescope, originally built to monitor the upper atmosphere for missile defence research, to make it better suited to astronomical studies. A new surface was installed on the radio telescope’s massive dish, making it more sensitive, and a powerful new radar was added to detect the motion of asteroids and other planetary bodies.
In 1972, with the astronomer Carl Sagan and Sagan’s wife, Linda, he designed the Pioneer Plaque, a picture message that travelled out of the solar system on the Pioneer 10 and 11 spacecraft. If it were ever found by aliens, they would be able to work out the location of Earth. He also designed the “Arecibo message”, a radio signal that was beamed to a star cluster 22,000 light-years away.
Drake left Cornell in 1984 and moved with his family to California, becoming dean of the Division of Natural Sciences at the University of California, Santa Cruz. He retired from teaching there in 1996.
His hobbies were making red wine and jewellery, and cultivating orchids. He continued to be involved with Seti, and was on the advisory board of one of its most recent searches, Breakthrough Listen, begun in 2015.
Drake is survived by his second wife, Amahl (nee Shakhashiri), whom he married in 1978, and their daughters, Nadia and Leila; by three sons, Steve, Richard and Paul, from his first marriage to to Elizabeth Proctor Bell, which ended in divorce; and by four grandchildren.
• Frank Donald Drake, astrophysicist, born 28 May 1930; died 2 September 2022
