When you imagine an alien, what do you think of? A green, slimy creature with jagged teeth? Or maybe a cute little E.T.-like figure?

Generally, we envision aliens as somewhat like us -- slightly more bizarre or fearsome versions of ourselves, but humanlike nonetheless. These perceptions reflect our own fears and desires and imaginings.

Now, thanks to nonprofit studio Blank on Blank, we can listen to astronomer Carl Sagan explain why it makes perfect sense that humans would "project their hopes and fears upon the cosmos." Blank and Blank recently published author Studs Terkel's 1985 interview with Sagan as part of its "Experimenter" series.

Kirill Yeretsky Human-alien interaction, animated by Blank on Blank.

Sagan explains that our galaxy is one of probably hundreds of billions of other galaxies, and throughout these galaxies, there is an abundance of the carbon-rich complex molecules that are the building blocks for life as we know it.

"There's a lot of potential abodes for life," Sagan says in the interview, "and the stuff of life is everywhere.

Add to this equation billions of years for biological evolution on each planet and, Sagan adds, "It seems very hard to believe that our paltry little planet is the only one that's inhabited."

So, while we might not have a very good idea what extraterrestrials look like, it seems likely that they exist.

Sagan also touches on the age-old conflict between science and religion, rejecting a literal interpretation of the Bible as scientifically wrong, but noting that the two ways of thinking are ultimately about finding answers to life's biggest questions -- answers that may ultimately be less important than the questions themselves.