"I was so excited about the news," the 41-year-old doctor told AFP in an interview on Friday, calling it "a major discovery that inspires dreams".

International astronomers announced Wednesday they had detected the largest body of liquid water ever found on the Red Planet, a breakthrough that may hold clues to whether life has ever formed on Mars -- or even exists today.

Kanai, who spent 168 days on the International Space Station, is firmly convinced that we're not alone in the universe and there is life out there.

"I believe there is," he said. "In the vast universe, anything could be possible."

"I have high hopes that finding extraterrestrial life forms could open a new page in learning."

The soft-spoken spaceman, nicknamed "Nemo" for his background as a diving medical officer in Japan's Maritime Self-Defense Force, blasted into space for the first time in December.

Read also: NASA's Mars rover drills up most complex organic matter yet

- Growing pains -

Following in the footsteps of other media-savvy astronauts, Kanai tweeted about his stay at the space station in Japanese.

But his social media foray came with some growing pains: he was forced to apologize and issue a correction after mistakenly claiming he had grown by nine centimeters just weeks after he arrived.

When a colleague suggested the growth was unlikely, despite the fact that astronauts' spines do extend in the zero-gravity environment of space, Norishige had himself remeasured.

It turned out a mix-up over centimeters and inches was to blame, and he said Friday that he had in fact grown by just two to three centimeters during his stay.

He has been shrinking since he arrived back on Earth on June 3, but is still one centimeter taller, he said.

"It's interesting to see how long it will take to get back to my original height."

Kanai, whose Twitter profile depicts him in cartoon form with a broad grin, concedes he wasn't always the likeliest candidate to join Japan's space agency JAXA, though he is now the agency's youngest astronaut.

He was a "reserved, cautious" boy, rather than adventurous.

"I was a granny's boy," he said. "When she was sewing, we did it together. I had a rather 'girlie' childhood."

But one of the skills he picked up as a child turned out to have a surprising application during the strict JAXA screening process.

In the final selection stage, 10 candidates spend a week in a capsule performing various tasks including folding paper cranes, which the agency says tests patience and steadiness under stress.

Luckily Kanai was a dab hand at origami from his childhood.

Read also: NASA astronauts install high-def cameras during spacewalk

- Space for all -

"I don't know if it gave me an advantage... but I knew how to do it. I'm dexterous and like to do repetitive small tasks. That task was easy for me," he said.

Even as he spoke, he deftly folded a piece of origami paper into a crane, without so much as leaning on a table for support.

He so enjoyed making small cranes that he folded more than 100 of them in the test capsule.

While Kanai now belongs to an elite group of astronaut alumni, he is eager to see space become more accessible.

"I think space is not only for astronauts and space-related corporations but is for everyone," he said.

"I welcome the idea of 'enjoyable' space or interesting ideas of private companies to use space."

He doesn't yet know if he'll be chosen for new missions, and admits that he had mixed emotions as he headed back to Earth last month.

"I felt sorry that it was ending. But I was also happy that I was finally going back to Japan, because six months is a long time.

"I had complex, half-happy, half-sad feelings."

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