The possibility of finding intelligent life on other planets has long stoked our imaginations. Movies and television series about space adventure, in addition to government-funded space exploration, raise curiosity and cause us to gaze skyward with wonder.

A recent poll in of over 400,000 respondents found 66% saying they believe life exists elsewhere in the universe. Scientists at NASA think humanity could discover alien life in our solar system or beyond within the next 10 to 20 years.

They cite observations from planetary probes that show evidence of water throughout the Milky Way, along with nitrogen and other organic molecules necessary for sustaining Earth-like life.

The idea of the possibility of intelligent alien beings will continue to challenge our human inquisitiveness. The creation consists of billions and billions of galaxies and trillions and trillions of stars.

When considering the possibility of alien life, there is a litany of considerations. There’s an absurdly large number of just-right requirements for a planet like Earth, particularly for intelligent life.

At the top of any list of considerations are three conditions. Chief among them is for a planet to reside in a Galactic Habitable Zone (GHZ). Many in science believe there’s an area within a galaxy that’s likely to be more advantageous than others for a planetary system to reside that could support life. Ideally this area should be just the right distance from the center of the galaxy. This would be close enough to where the available metallicity is sufficiently rich, a necessity for a newly-forming planetary system to be able to form rocky planets like Earth, as well as in a relatively quiet galactic neighborhood sufficiently out of harm’s way, i.e. free of cosmic IED’s such as supernovae.

Science estimates a range of 50 billion to 800 billion planets that are in the GHZ of just the Milky Way. Of that, an amazing 1% (500 million to 8 billion) are estimated to be located in the habitable zone of their respective sun. This translates to an astonishing number of planets with potential for some kind of life form just within the Milky Way.

Water is universally regarded to be essential for life. A planet must also be capable of creating internal heat, an occurrence most likely to be caused by volcanism and/or tectonic activity, but not so much heat that could deplete it of its water. It needs a strong magnetic field to protect the planet from the solar wind of its sun.

The third condition regards the atmospheric composition. This consists mostly of molecules. Earth’s life forms require oxygen for respiration, carbon dioxide for photosynthesis, and nitrogen. Most people don’t realize that nitrogen comprises 78% of the troposphere, the atmosphere closest to the surface that we live in, and is by far its largest component.

In addition to this life-sustaining collection of molecules, our atmosphere works like a protective shield by absorbing ultraviolet radiation emitted by the sun and by retaining heat. This greenhouse effect warms the planet’s surface, as well as reduces the difference between our night and day temperatures.

In spite of the concept of habitable zones and the sheer quantity of numbers, there are substantial additional criteria that exponentially reduce the number of planets that could support intelligent life.

Interestingly, because of so many precursors as well as so many potentials, the probability of there not being intelligent alien life forms is every bit as great as the probability that it could exist, so take your pick!

J.C. Faris is the author of Once Upon a Time 13.81 Billion Years Ago (, an examination of the universe, its creation and how it all works from the perspectives of both religion and science. A graduate of Ball State University with a B.S. in anthropology, Faris did graduate school work in biology, chemistry and human anatomy at the University of Louisville. A man with diverse interests, he’s a former U.S. Army officer, has owned large businesses and has been a guest instructor at Ball State. He’s been a frequent speaker and TV guest and hosted a weekly radio show.

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