On the 45th anniversary of NASA's Apollo 11 mission to the moon, the two living members of the expedition met with President Barack Obama.

According to USA Today, Buzz Aldrin and Michael Collins accompanied Carol Armstrong, Neil Armstrong's widow, in an Oval Office meeting Tuesday morning. Reporters and television crews were not allowed in the meeting, but news photographers were.

On July 20, 1969, Armstrong, Aldrin and Collins became the first humans to travel to the moon. Armstrong commemorated the achievement by stepping foot on the lunar surface and delivering one of the most iconic statements in American history.

"That's one small step for [a] man, one giant leap for mankind."

Sunday marked the 45th anniversary to the day of the Apollo 11 mission's success and the U.S. has been celebrating the achievement since. Aldrin has also used the attention to praise NASA's innovation since and also to urge the space agency to strive to put a man on Mars.

"The three brave astronauts of Apollo 11 -Neil Armstrong, Buzz Aldrin, and Michael Collins - took the first small steps of our giant leap into the future," Obama said in a statement released by the White House after the meeting. "And for all the years since, they and their families have served as testaments to American ingenuity and human achievement.

"Today, I was honored to welcome Buzz, Michael, and Neil's wife, Carol, to the White House to mark this historic anniversary - and to thank them for serving as advocates, role models, and educators who've inspired generations of Americans - myself included - to dream bigger and reach higher."

NASA held a panel discussion at its D.C. headquarters early last week and some of their top scientists suggested the agency is close to finding alien life on a distant, habitable exoplanet. NASA has also said it does in fact plan to send astronauts to Mars.

Read Obama's statement, "The United States of America is stronger today thanks to the vision of President Kennedy, who set us on a course for the moon, the courage of Neil, Buzz, and Michael, who made the journey, and the spirit of service of all who've worked not only on the Apollo program, but who've dared to push the very boundaries of space and scientific discovery for all humankind."