The first time Peggy Whitson left Earth and rode a rocket into outer space in 2002 she was awestruck by what she saw.
“Looking out the window,” Whitson—one of PEOPLE’s 25 Women Changing the World — says in an interview in this week’s magazine, “it seemed like I’d lived my whole life in semi-darkness and somebody turned on the lights.”
Over the course of the next 16 years as an astronaut, Whitson, 58, who retired from NASA in June, chalked up an impressive string of records —including spending more cumulative time (655 days, to be exact) living in outer space than any other American.
A biochemist by training, she was named NASA’s first science officer for the International Space Station before being tapped (twice!) to command the space station.
“I wanted to be an astronaut ever since watching the Apollo 11 moon landing,” says Whitson, who grew up on an Iowa farm. “I’m lucky to have never quite recognized how the odds were stacked against me.”
Floating in a laboratory 250 miles above the earth, Whitson has worked on hundreds of experiments (“Everything from superconductor crystals,” she says, “to soybeans and stem cells”) that have had led to breakthroughs in artificial intelligence, medicine and agriculture.
About the only thing that Whitson hasn’t done in outer space is catch a glimpse of an alien—although she doesn’t rule out the idea that intelligent life exists in other parts of the cosmos.
“I just think it would be naïve to believe there’s not other life out there,” she says. “It may not look like us, it may not think like us, we may not recognize it as such, but I just think that there’s gotta be other life out there.”
Her best advice for earthlings? “You can do even more than you’ve ever dreamed of,” says the planet’s oldest female spacewalker, “when you just keep pushing yourself—and keep on pushing.”
For full coverage of PEOPLE’s 25 Women Changing the World, pick up this week’s issue, on newsstands Friday.