The question as to whether or not we are alone in the universe has been one of the greatest and most difficult to answer in the history of mankind.
Is the appearance of life a cosmic accident, or commonplace in the universe?
The incredible vastness of space make these challenging questions to answer. The possibility that life, primitive or advanced, might exist in other places in the universe has occupied human thought for thousands of years.
Although proposals to communicate with extraterrestrial intelligences go back a few centuries, true scientific investigation began shortly after the advent of radio in the early 1900s, and focused efforts have been ongoing since the 1980s. The search for extraterrestrial intelligence (SETI) started in 1959 with the proposal to use radio telescopes to search for special patterns in radio waves that could have been sent by another civilization in space. The overall SETI effort continues today under the auspices of the SETI Institute.
In 1961, astronomer Frank Drake created a formula for estimating the number of intelligences that could exist within our galaxy. The Drake Equation demonstrated that even by conservative estimates, our galaxy was likely to host a few advanced civilizations at any given time.
What do we look for?
To start, we would look for signs of a distant technology, such as electromagnetic emissions, or indicators of biological processes, such as gases, that could be released by living organisms.
Where do we look?
Astronomers have long proposed that planets in “habitable zones,” orbital regions around stars where liquid water, a requirement for life as we know it, could exist are the most likely places for life.
Could there be life in the oceans of planets and moons in our own solar system?
Some bodies in our solar system, particularly those with possible subsurface oceans, have the potential for life. Candidates include several of the larger moons of Jupiter and Saturn, and dwarf planets Pluto and Ceres. Mars probably had liquid water at one time and thus may have harbored life.
Could there be life on Earth-like planets circling other stars?
We are now discovering planets by the thousands orbiting other stars in our Milky Way galaxy. There are billions to trillions of other galaxies in the universe. Most of them likely have stars with planets.
Life or No Life Elsewhere?
To many, it seems unlikely that, as vast as the universe is, intelligent life could have emerged only once… but, that same vastness makes it unlikely that we are going to find it anytime soon. The nearest star to Earth is 25 trillion miles away.
To quote the cosmologist Carl Sagan: “The universe is a pretty big place. If it's just us, seems like an awful waste of space.”
Western Slope Skies is produced by the Black Canyon Astronomical Society. This episode was written and recorded by Nancy McGuire.