(CNN) Edgar Mitchell, one of just 12 human beings who walked on the moon, has died, according to his ex-wife, Anita Mitchell.

Mitchell was 85.

"On behalf of the entire NASA family, I would like to express my condolences to the family and friends of NASA astronaut Edgar Mitchell," NASA Administrator Charles Bolden said in a statement.

"He believed in exploration, having been drawn to NASA by President Kennedy's call to send humans to the moon. He is one of the pioneers in space exploration on whose shoulders we now stand."

Astronaut Harrison Schmitt is photographed next to the American flag while walking on the moon during Apollo 17.

Astronaut Harrison Schmitt is photographed next to the American flag while walking on the moon during Apollo 17.

Apollo 17 was the last of the Apollo missions. Humans have not been to the moon since.

Apollo 17 was the last of the Apollo missions. Humans have not been to the moon since.

An astronaut works in space as Apollo 17 orbits the moon in December 1972.

An astronaut works in space as Apollo 17 orbits the moon in December 1972.

The lunar module from Apollo 15 is seen in orbit.

The lunar module from Apollo 15 is seen in orbit.

Apollo 14 commander Alan Shepard poses next to the American flag while walking on the moon's surface in February 1971.

Apollo 14 commander Alan Shepard poses next to the American flag while walking on the moon's surface in February 1971.

Astronaut John Swigert, right, and the other two astronauts aboard Apollo 13 -- Fred Haise and Jim Lovell -- safely returned to Earth after improvising a solution to the craft's carbon-dioxide removal system.

Astronaut John Swigert, right, and the other two astronauts aboard Apollo 13 -- Fred Haise and Jim Lovell -- safely returned to Earth after improvising a solution to the craft's carbon-dioxide removal system.

This shot of the moon's surface was taken aboard Apollo 13, which famously had to abort its landing and return to Earth after an explosion threatened the crew.

This shot of the moon's surface was taken aboard Apollo 13, which famously had to abort its landing and return to Earth after an explosion threatened the crew.

Astronaut Alan Bean holds a sample of lunar soil during Apollo 12. Pete Conrad's reflection can be seen in Bean's visor as he takes the photo.

Astronaut Alan Bean holds a sample of lunar soil during Apollo 12. Pete Conrad's reflection can be seen in Bean's visor as he takes the photo.

A close-up view of an astronaut's boot on the moon's surface during Apollo 11.

A close-up view of an astronaut's boot on the moon's surface during Apollo 11.

Aldrin walks down the steps of the lunar module, codenamed "Eagle," as he prepares to walk on the moon.

Aldrin walks down the steps of the lunar module, codenamed "Eagle," as he prepares to walk on the moon.

Apollo 11 commander Neil Armstrong is photographed inside the lunar module after he and Buzz Aldrin walked on the moon's surface on July 20, 1969.

Apollo 11 commander Neil Armstrong is photographed inside the lunar module after he and Buzz Aldrin walked on the moon's surface on July 20, 1969.

During Apollo 10, the lunar module was flown around the moon as a "dress rehearsal" for a later landing.

During Apollo 10, the lunar module was flown around the moon as a "dress rehearsal" for a later landing.

Astronaut Russell Schweickart's feet are seen during one of Apollo 9's spaceflights.

Astronaut Russell Schweickart's feet are seen during one of Apollo 9's spaceflights.

Apollo 9 tested a lunar module above Earth to make sure it was ready to carry astronauts on a future trip to the moon.

Apollo 9 tested a lunar module above Earth to make sure it was ready to carry astronauts on a future trip to the moon.

The moon, as seen from Apollo 8 in December 1968. Apollo 8 orbited the moon and broadcast television images back to Earth. NASA used red and blue filters for the TV feed.

The moon, as seen from Apollo 8 in December 1968. Apollo 8 orbited the moon and broadcast television images back to Earth. NASA used red and blue filters for the TV feed.

Apollo 7 was a test flight around Earth that laid the foundation for future trips to the moon.

Apollo 7 was a test flight around Earth that laid the foundation for future trips to the moon.

With Earth in the background, NASA astronaut David Scott works in space during the Apollo 9 mission in March 1969. On July 20, 1969, Apollo 11 was the first manned mission to land on the moon. Here's a look at a few images from each Apollo mission.

With Earth in the background, NASA astronaut David Scott works in space during the Apollo 9 mission in March 1969. On July 20, 1969, Apollo 11 was the first manned mission to land on the moon. Here's a look at a few images from each Apollo mission.

Mitchell died Thursday in West Palm Beach, Florida, according to NASA . His death occurred on the eve of the 45th anniversary of his lunar landing, which took place on February 5, 1971.

Mitchell, Alan Shepard and Stuart Roosa were the crew of Apollo 14, which launched on January 31, 1971. Mitchell became the sixth man to walk on the lunar surface.

He and Shepard set foot on the moon two separate times during their mission, spending more than nine hours collecting rocks, taking measurements and (in Shepard's case) hitting a pair of golf balls. Mitchell also took a famous photograph of Shepard standing next to an American flag. All told, the two spent 33 hours on the moon.

(2/5/71) 45 years ago right now Alan Shepard and Edgar Mitchell begin EVA1 on the Moon at Fra Mauro. #Apollo14 pic.twitter.com/kJFFLmiUh4 — Max Winn (@max_winn) February 5, 2016

Mitchell, who was the lunar module pilot, found the trip to be a profound experience.

"Looking at Earth from space and seeing it was a planet in isolation ... that was an experience of ecstasy, realizing that every molecule in our bodies is a system of matter created from a star hanging in space," Mitchell told the UK Telegraph in 2014 . "The experience I had was called Samadhi in the ancient Sanskrit, a feeling of overwhelming joy at seeing the Earth from that perspective."

Fascinated and frustrated by the relationship between religion and science, he was very public about seeking links between the known and unknown.

He said he had conducted ESP experiments on the mission. He was also a believer in extraterrestrial activity, and was convinced UFOs had visited Earth.

JUST WATCHED 2008: Edgar Mitchell: 'I have a very satisfied life' Replay More Videos ... MUST WATCH 2008: Edgar Mitchell: 'I have a very satisfied life' 01:03

In one interview, he told Bloomberg Business that the 1947 Roswell incident , which to some people is evidence of an extraterrestrial crash landing, was covered up. (The U.S. government has said the incident involved the crash of a high-altitude balloon.)

"It's not just military. It's a cabal of organizations primarily for a profit motive," he told the publication

However, he drew the line when it came to an interview with the UK Mirror. The newspaper claimed Mitchell said UFOs had helped prevent nuclear war

"None of those statements were originated by me," he told the Huffington Post . (The Mirror stood by its story.)

The astronaut was born in Hereford, Texas, in 1930. A Navy pilot, he joined NASA in 1966 as part of the agency's astronaut corps. He was well-qualified: besides having served as a test pilot and college instructor, he earned a doctorate from MIT in aeronautics and astronautics.

Mitchell was part of the support crew for the Apollo 9 and Apollo 10 missions. A year after Apollo 14, in 1972, he left NASA to embark on his other activities.

He was in the news in 2011 when, threatened with a lawsuit from the U.S. government, he returned a camera he'd kept as a memento of the mission. NASA agreed to display the camera at the National Air and Space Museum.

With Mitchell's death, of the 12 men who have walked on the moon, seven survive: Buzz Aldrin, Alan Bean, David Scott, John W. Young, Charles Duke, Eugene Cernan and Harrison Schmitt.

Many have talked of their missions with joy and wonder. Mitchell went beyond, however: he believed we were all connected -- to everything.