During the 19th and early 20th Centuries many astronomers believed the galaxy teemed with life, much of it intelligent. Some of the world's foremost stargazers were certain that sister worlds Mars and Venus harbored intelligent life. But as the 20th Century moved closer to the 21st Century, many astronomers became jaded. Some even postulated that the Earth was unique and intelligent life—if it existed anywhere beyond Earth—was so rare that humans would never encounter it.
Then the space telescopes. like Kepler, were launched. As the orbiting telescopes peered into the depths of the galaxy world after world was discovered…a surprising number were found to be able to support life as we know it. Some might even support intelligent life.
As the decades progressed and the calendar pushed past the new millennium, astronomers became more positive again about their outlook for intelligent life in the galaxy. Soon, many scientists began predicting that the norm for a star was to have planets orbiting about it. Even binary and trinary star systems were discovered that had planets.
100 billion planets
Astronomers 150 years ago would be thrilled: the latest study from Caltech's exolab researchers has determined that as many as 100 billion planets exist in the Milky Way Galaxy. Extrapolating on the number that could support life based on those already discovered, astronomers conclude that as many as 17 billion are Earth-sized and a good number of those probably support life—some even intelligent life.
Their study is published in an upcoming issue of the The Astrophysical Journal.
The Drake Equation
Astronomer Frank Drake, now 82, launched the first Search for Extraterrestial Intelligence (SETI) experiment during 1960. More than 50 years later the octogenarian has not let up in his quest to discover signs of intelligence in the galaxy.
The creator of a popular scientific equation known as "The Drake Equation," the astronomer created a mathematical model to create a yardstick measuring the likelihood of extraterrestrial civilizations in the galaxy. "The equation was devised in 1961 by Frank Drake while at the National Astronomy and Ionosphere Center."
CBS News observes that ""The Fermi Paradox [the supposed lack of evidence for extraterrestrial intelligence] isn't exactly the sort of thing you can answer in the traditional sense, rather it highlights an apparent contradiction in what we could reasonably expect from the universe given it's size and age, and what we actually observe (or fail to). The Drake Equation is actually a sort of partial 'answer' in that it attempts to at least formalize the specific unknowns that affect the number of potentially detectable civilizations that might currently exist in our galaxy."
For many decades afterward, researchers at SETI used the Drake equation to assist their efforts in seeking telltale traces of intelligent life.
Drake believes there may be as many as 10,000 civilizations in the galaxy advanced enough to be broadcasting artificial radiowaves.