How many detectable alien civilizations are out there in our galaxy? In 1961, astronomer Frank Drake developed an equation to estimate the number. Now data journalist David McCandless, who gave the talk “The beauty of data visualization” at TEDGlobal 2010, has created an information graphic for the BBC calculating the Drake Equation — with a twist. It’s interactive, and you can be as optimistic or skeptical as you like as you set the value of each variable in the equation. Any tinkering leads to highly different conclusions.

Jill Tarter, the head of the SETI Institute, would no doubt set her variables on the optimistic side. Tarter gave the wonderful TED-Ed lesson “Calculating the Odds of Intelligent Alien Life,” which explains the Drake Equation and its many variables. Tarter won the TED Prize in 2009 and called for more people to join the search for extraterrestrial life. “From my perspective, we live on a fragile island of life in a universe of possibilities,” says Tarter in her talk. “So what exactly is SETI? Well, SETI uses the tools of astronomy to try and find evidence of someone else’s technology out there. Our own technologies are visible over interstellar distances, and theirs might be as well … SETI doesn’t presume the existence of extraterrestrial intelligence; it merely notes the possibility, if not the probability in this vast universe, which seems fairly uniform.”

Chris Anderson, TED’s intrepid curator who made the TED-Ed lesson “Why can’t we see evidence of alien life?,” would be optimistic too. “In the past year, the Kepler space observatory has found hundreds of planets just by nearby stars. If you extrapolate that data, it looks like there could be half a trillion planets just in our own galaxy,” he says. “If only one in 10,000 has conditions that might support a form of life, that’s still 50 million possible life-harboring planets right here in our Milky Way.”

But the real question is — how optimistic or skeptical will you be as you play with McCandless’ interactive data set? View the full chart here >>