Nasa has said that the first people to walk on the surface of Mars are already living on Earth.
Ahead of the 45th anniversary of Apollo 11, Nasa said that it will continue to push for manned exploration of the solar system, despite budget constraints.
In a post on its website titled "Nasa's Next Giant Leap", it said that "the first humans who will step foot on Mars are walking the Earth today".
"The Apollo missions blazed a path for human exploration to the moon and today we are extending that path to near-Earth asteroids, Mars and beyond.
"Technology drives exploration and we're building on the Apollo program's accomplishments to test and fly transformative, cutting-edge technologies today for tomorrow's missions. As we develop and test the new tools of 21st century spaceflight on the human Path to Mars, we once again will change the course of history."
The Path to Mars program is designed to frame many different research projects and investments, focused mainly on the work of the International Space Station where astronauts are "teaching us how humans can live, work and thrive for longer periods in space".
Nasa is also looking to explore asteroids, launching missions designed to help it eventually capture and redirect an asteroid into orbit around Earth, while finalising its new Space Launch System rocket -- the largest since Apollo and the "most advanced" ever built.
"The new technologies we test through the Asteroid Redirect Mission, and the new human spaceflight capabilities we prove by sending astronauts to study the asteroid, will make important advances to safely send humans to Mars," it said. "Sending humans to deep space around the moon also will help advance techniques for space operations on and around Mars and its moons."
"Mars beckons us to explore. Missions to Mars could answer some of the fundamental questions of humanity: Does life exist beyond Earth? Could humans live on Mars in the future? The journey to answer these questions has risks, but the rewards for humanity are worth it. Meeting the remaining challenges ahead of us to send humans to Mars will take the ingenuity and innovation of the entire nation and our international partners."
Unfortunately for Nasa - and humanity - the path to Mars is still largely unknown. Despite various private attempts to launch manned missions to land on or orbit the planet, many technical issues remain firmly in place, including how to build and stock an inter-planetary craft, how to avoid radiation poisoning from cosmic and solar rays on the way, how to land safely on the harsh Martian surface and how to get back home once the mission is over.