Frank Drake speaking at Cornell University, October 2017. Photo: Amalex5/Wikimedia Commons, CC BY-SA 4.0
- Even before the discovery of other planetary systems, astronomers believed there must be plenty of exoplanets across the cosmos, and that the chemistry of life isn’t unique to Earth.
- The universe is so immense that it is almost impossible for Earthlings to be alone, and the laws of evolution suggest that technically-capable civilisations could be the norm rather than the exception.
- Frank Drake formulated an equation (which bears his name) in 1961 in the first major attempt to determine the probability of intelligent life elsewhere.
- It remains one of the finest ways to ponder ET – from the likelihood of life emerging from chemicals to the chances of such life being able to communicate across the universe.
- Drake also coined the word ‘pulsar’ to describe some neutron stars, discovered Jupiter’s radiation belts, and mapped the centre of the Milky Way for the first time.
Frank Drake, one of the most celebrated astronomers of all time, who passed away peacefully at 92 in his California home last Friday, leaves behind a priceless legacy: the Search for Extraterrestrial Intelligence (SETI).
Regarded as the father of SETI, Drake – along with a few others like Carl Sagan – enriched popular science and sparked the interest of generations in astronomy and wonder with the question, ‘are we alone in the cosmos?’.
Even before the discovery of other planetary systems, astronomers believed exoplanets must be scattered plentifully across the cosmos, and that the chemistry of life is not unique to Earth. The universe is so immense that it is almost impossible for Earthlings to be alone, and the laws of evolution suggest that technically-capable civilisations could be the norm rather than the exception.
The math is compelling: of the 200-400 billion stars in the Milky Way galaxy alone, half of them probably have planets. And there are more than 200 billion other galaxies in the observable universe.
Drake formulated an equation (which bears his name) in 1961 in the first major attempt to determine the probability of intelligent life elsewhere. It is based on the probabilities of variables: the likely occurrence of planets around stars, the number of planets per star where conditions are suitable for life, the aggregate of life-bearing planets where intelligent civilisations develop and the fraction of intelligent civilizations with communications technology humans could detect.
This remains one of the finest ways to ponder extraterrestrial (ET) life – from the likelihood of life emerging from chemicals to the chances of such life being intelligent and able to communicate across the universe.
Curiously, this iconic equation eclipsed some of Drake’s other great achievements. Not so well-known is the fact that he coined the word ‘pulsar’ to describe rapidly rotating neutron stars, discovered Jupiter’s radiation belts (similar to Earth’s Van Allen belts), and mapped the centre of the Milky Way for the first time, to name some.
Long before Drake popularised modern-day SETI, there were attempts to send signals to potential ETs in outer space. In the 1800s, radio inventor Guglielmo Marconi searched in vain for radio signals from space. In the 19th century, the mathematician Carl Friedrich Gauss (possibly) suggested drawing geometric symbols on the surface of Earth to attract attention from what he believed were aliens.
The idea of listening in on ET signals gained currency in 1900 when Nikola Tesla mistook electrical disturbances in his receiver as alien transmissions – only to discover later that the signals were from Earth’s magnetic field.
In 1959, when physicists Philip Morrison and Giuseppe Cocconi suggested that alien civilisations could be using radio signals to reach across the galaxy, a young Drake conducted Project Ozma the next year using the 26-metre radio telescope at Green Bank, West Virginia, to eavesdrop on two Sun-like stars, Epsilon Eridani and Tau Ceti. He ‘listened’ on the frequency of 21 cm (1,420 MHz) emitted by hydrogen gas.
Drake reasoned that since hydrogen is the most abundant element in the universe, any alien would pick this frequency for communication.
But after more than 150 hours of observations, Drake could not detect any tell-tale signals and wound up the project. Over the next 10 years, other planet-hunters carried out similar searches on various frequencies and with different stars, but failed to record any ET call-signs. These efforts, however, helped astronomers develop better signal-processing methods to weed out false alarms like the natural cosmic static.
Drake advocated for people using their limited technological means to reach out to ET life. In 1972, along with Carl Sagan and Linda Salzman Sagan, he attached plaques with information about where aliens could find Earth to NASA’s Pioneer 10 and 11 space probes.
Later, in 1974, he beamed a message at a likely star cluster 23,000 light-years from Earth using the Arecibo radio telescope in Puerto Rico. The message comprised a string of bits (1s and 0s) that could be assembled into a two-dimensional array to show the figure of a man, a telescope, the numbers from one to 10, the structure DNA and the Solar System.
Drake and Sagan teamed up again in 1977 to make a gold phonograph with the sights and sounds of Earth for the Voyager 1 and 2 missions. The record affixed to the spacecraft is now sailing the seas of interstellar space like a message in a bottle, in the hope that someday it will be intercepted by intelligent beings in a faraway star system.
Drake always believed that humans would, sooner or later, detect the first whispers of sentient life elsewhere in the universe as discernible radio waves or bursts of light. A strong advocate of hunting for ETs using pulsed laser emissions, he inspired the Pulsed All-sky Near-infrared Optical SETI project at the University of San Diego. It uses hundreds of telescopes to simultaneously hunt for flashes of optical or infrared light.
Who knows, one day in the near or far future, Earth-bound searchers will recognise the equivalent of a faint ‘hello’ amid the crackle of radio waves or a burst of light from outer space.
Frank Drake, quintessential explorer of the universe, RIP. You will be much missed.
Prakash Chandra is a science writer.