William Shatner's trip to outer space left him with mixed emotions.
In an excerpt from his new book Boldly Go: Reflections on a Life of Awe and Wonder obtained by Variety, Shatner detailed that he was surprised by how he reacted to the adventure.
"You can only prepare so much for a trip out of Earth's atmosphere!" Shatner said, per Variety.
"I love the mystery of the universe. I love all the questions that have come to us over thousands of years of exploration and hypotheses," he wrote.
All of that became secondary when he gazed out into space. "There was no mystery, no majestic awe to behold... all I saw was death," said Shatner.
When his attention returned to Earth, he recognized all that he was leaving behind — and how important it was to him.
"It was life. Nurturing, sustaining, life. Mother Earth. Gaia. And I was leaving her," Shatner continued.
"Everything I had thought was wrong," Shatner then detailed. "I had thought that going into space would be the ultimate catharsis of that connection I had been looking for between all living things — that being up there would be the next beautiful step to understanding the harmony of the universe."
RELATED VIDEO: William Shatner and Blue Origin Passengers Float In Space
Comparing his experience to Jodie Foster's character in the movie Contact, Shatner added, "I discovered that the beauty isn't out there, it's down here, with all of us. Leaving that behind made my connection to our tiny planet even more profound."
In the excerpt, Shatner wrote that he later learned he "was not alone in this feeling," which is called the "Overview Effect" and is "not uncommon among astronauts."
Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.
Coined by space author and philosopher Frank White, the powerful phenomenon describes how seeing the planet from space can change a person's perspective on Earth — and life.
"It reinforced tenfold my own view on the power of our beautiful, mysterious collective human entanglement, and eventually, it returned a feeling of hope to my heart," he wrote.
In October 2021, the Emmy Award-winning actor also told Amazon billionaire Jeff Bezos about his experiences high above the blue planet.
"In a way, it's indescribable," Shatner told Bezos, 58, who made his own trip to space in July 2021.
"Not only is it different from what you thought, it happens so quickly," he added during a Blue Origin live stream.
Want to get the biggest stories from PEOPLE every weekday? Subscribe to our new podcast, PEOPLE Every Day, to get the essential celebrity, entertainment and human interest news stories Monday through Friday.
"When I was there [in space], everything I thought might be clever to say [about the trip] went out the window," he said. "I was struck so profoundly by it."
Boldly Go: Reflections on a Life of Awe and Wonder, which is co-authored by Josh Brandon, is available for purchase now.