Astronaut Scott Kelly Says Mars Travel Is ‘Doable’

American astronaut Scott Kelly, who returned to Earth this week after spending a historic year on the International Space Station, said his journey proved to him it would be possible for astronauts to endure even longer journeys, including a trip to Mars.

“If there’s a good reason—whether it’s science or going to a certain destination—not just me, but I think people rise to the occasion,” Kelly said at a news conference Friday afternoon. “I personally think going to Mars—if it takes two years or two and half years, that’s doable.”

But if NASA ever does fly a Mars mission in the near future, Kelly doesn’t think he’ll be aboard.

“We have so many talented people in our office, there’s no reason to fly me again,” he said, adding that he’ll never completely retire from space because of the opportunities in the private sector. Kelly also predicted there will be more opportunities for commercial space travel for non-astronauts as well.

“I think everyone should be able to go to space,” he added. “Maybe in the next 20 years, you’ll be able to just buy a cheap ticket, go for a little visit.”

Kelly has spent 520 days in space, the most among U.S. astronauts.

Kelly said he hasn’t yet felt culture shock since his return, but the physical adjustment—sore muscles and fatigue—has been greater than it was when he went into space. His 340-day mission aimed to help scientists understand the effects of prolonged zero-gravity exposure on the human body. Kelly’s twin brother, a retired astronaut, participated in parallel studies on Earth.

“I think coming back to gravity is harder than leaving gravity, so I don’t know, maybe the aliens have got it a lot harder than we do,” he said.

Kelly answered questions in the news conference about the first food he ate upon return—a banana—and the one place in the world he wants to visit now that he’s seen it from a new perspective—a remote collection of lakes north of the Himalayas.

Read more: Inside the Gigantic Operation to Meet Astronauts Coming Home

His days on Earth this week have been filled with medical and fitness tests, but he made time to jump in his pool when he arrived home in Houston. “I hadn’t had running water in 340 days and it’s something you really miss,” he said.

Kelly said the past year made him an environmentalist because of all the time he spent looking down at Earth.

“The earth is a beautiful planet. It’s practically everything to us, and the space station is a great vantage point to observe it,” he said, also commenting on the large swaths of pollution he saw at times.

“We’ve got to take care of the environment,” he said, quoting “save the planet” advocates. “I think the planet will eventually recover. It’ll probably be without people.”

TIME chronicled the year-long mission for a documentary series, A Year in Space, which premiered Wednesday on PBS.