A former NASA astronaut and commander aboard the International Space Station who has logged nearly 230 days in space says it's arrogant for humans to assume there aren't aliens sharing the universe with us.

Leroy Chiao has completed four missions into space and performed six spacewalks. In an article published in the Christian Science Monitor Friday, he said the recent discovery of a possible Earth-like planet confirms his suspicions that the universe is full of alien life. Scientists said the planet, called Proxima b, is orbiting the closest star to our sun and is located about 4.2 light years away.

He also detailed his bleak vision for Earth's future. 

"I believe that there is life all over our universe, since it would be the height of arrogance to think that we are alone. Moreover, I believe that at some point, life on Earth will die out, either from natural causes, or from our own doing. To me, this is a natural progression, just like individual lives on our planet. Unlike many people, including several of my astronaut colleagues, I don't think that technology will save us," he wrote. "I believe that life is always starting in some parts of the universe at the same time that it is dying out in others. We don't know about each other, simply because the distances are so vast."

He is not alone in his thinking. Scientists informed Congress in 2014 that the components and conditions necessary for life are “perhaps ubiquitous” in the Milky Way galaxy. 

"At least a half-dozen other worlds (besides Earth) that might have life are in our solar system," Seth Shostak, a senior astronomer at the California-based Search of Extraterrestrial Intelligence Institute told the U.S. House of Representatives’ Committee on Science, Space, and Technology at the time. "The chances of finding it, I think, are good, and if that happens, it’ll happen in the next 20 years, depending on the financing."

Popular TV astrophysicist Neil deGrasse Tyson also believes in aliens. 

"At the moment, life on Earth is the only known life in the universe, but there are compelling arguments to suggest we are not alone. Indeed, most astrophysicists accept a high probability of there being life elsewhere in the universe, if not on other planets or on moons within our own solar system. The numbers are, well, astronomical: If the count of planets in our solar system is not unusual, then there are more planets in the universe than the sum of all sounds and words ever uttered by every human who has ever lived. To declare that Earth must be the only planet in the cosmos with life would be inexcusably egocentric of us," he wrote in 2003 in NASA's Astrobiology magazine.

Other scientists, however, have dismissed the long debate over extraterrestrial life as nothing more than science fiction.

William Borucki, a world-renowned NASA scientist whose research led to the discovery of new planets, told the South China Morning Post last year that humans would know for certain by now if there were aliens. 

"Up till now, it was just an intellectual question. It isn’t anymore. There could be 10 billion civilizations or none. The evidence certainly is none," Borucki said. "The evidence says no one’s out there."