According to a panel of high-ranking NASA scientists, humans may discover “definitive evidence” of extra-terrestrial life in the next two to three decades. NASA

Ever since our species discovered the existence of other planets beyond Earth, the question of whether we are alone in this universe has intrigued scientists and philosophers. Now, according to a panel of high-ranking NASA scientists, humans may discover “definitive evidence” of extraterrestrial life in the next two to three decades.

“In our lifetime, we may very well finally answer whether we are alone in the solar system and beyond,” NASA chief scientist Ellen Stofan said on Tuesday, during a panel discussion on the space agency’s search for habitable worlds. “We know where to look. We know how to look (for extraterrestrial life) … In most cases we have the technology, and we're on a path to implementing it. And so I think we're definitely on the road.”

However, these aliens probably wouldn’t be little green men. “We are talking about little microbes,” Stofan said.

The proclamation comes at a time when ground and space telescopes have detected the presence of liquid water -- considered essential to sustain life as we know it -- in several bodies in our solar system and beyond.

Thanks to recent discoveries, we now know that in addition to Jupiter’s moons Europa, Callisto and Ganymede, Saturn’s moon Enceladus also has massive underground oceans, adding to a growing list of bodies that could harbor life. And this is just within our solar system. Once we look beyond its confines, it would appear -- as Paul Hertz, director of NASA's Astrophysics Division said -- that the Milky Way is a “soggy place.”

“We can see water in the interstellar clouds from which planetary systems and stellar systems form. We can see water in the disks of debris that are going to become planetary systems around other stars, and we can even see comets being dissipated in other solar systems as their star evaporates them,” Hertz said during the panel discussion.

Given the apparent abundance of water in the Milky Way, and the possibility that life could even exist in conditions where water does not, aliens, it would seem, are just waiting to be discovered.

“It’s definitely not an if, it’s a when,” Jeffery Newmark, NASA’s interim director of heliophysics, said.