Whether or not alien life exists has always interested people, and the more humans discover about space, the more the question burns. After all, the more you see, the harder it is to believe that the inhabitants of Earth are alone in the universe.

Also, that's just being arrogant, says former NASA astronaut Leroy Chiao.

Chiao was a NASA astronaut between 1990 and 2005 and flew four missions into space. Within his 15-year stint with the agency, he spent almost 230 days in space. Suffice it to say he's been in space long enough to have an opinion of his own about the whole alien life debacle.

So is there alien life out there?

While no aliens have been discovered, Chiao believes that there is life all over the universe. He's of the belief that somewhere life is always starting and ending in another.

"We don't know about each other simply because the distances are so vast," he said.

Take the nearest star to Earth, Proxima Centauri, for instance.

Proxima b is a recently discovered exoplanet orbiting Proxima Centauri. To send a spacecraft in the area, using current technology in place, it would take nearly 80,000 years.

It's extremely difficult to prove life (any form of life) exists in Proxima b because it's so far away, despite being "next-door neighbors" with Earth, but some scientists are pinning their hopes on the exoplanet.

For starters, it's about Earth's size, just slightly larger. Additionally, it is just the right distance from Proxima Centauri to support liquid water on its surface. And where there is water, there is a chance of life.

However, that life will have to contend with strong radiation, much harsher than what Earth is capable of. Proxima b also doesn't rotate on an axis so it has one side that is always facing the sun.

Just because it's Earth-like doesn't mean that it supports the same conditions as Earth.

Instead, Chiao is more confident that efforts to explore Mars will pay off more than focusing on Proxima b. He said that it's likely humans will find evidence of past life on the Red Planet within the century but the chance of discovering current microbial life is also there, given Mars has a thick atmosphere that offers protection from the sun and there is strong evidence that liquid water once flowed on the Martian surface. Again, where there is water, there is life.

Looking at Earth's next-door neighbor for clues is a good start but maybe scientists will fare better if they look even closer. Mars is just in Earth's backyard, after all.