(CNN) Aliens definitely exist, Britain's first astronaut has said -- and it's possible they're living among us on Earth but have gone undetected so far.

Helen Sharman, who visited the Soviet Mir space station in 1991, told the Observer newspaper on Sunday that "aliens exist, there's no two ways about it."

"There are so many billions of stars out there in the universe that there must be all sorts of different forms of life," she went on. "Will they be like you and me, made up of carbon and nitrogen? Maybe not."

Then, in a tantalizing theory that should probably make you very suspicious of your colleagues, Sharman added: "It's possible they're here right now and we simply can't see them."

Sharman was the first of seven Britons to enter space.

Sharman became the first Briton in space in 1992.