WASHINGTON - The notion of landing astronauts on Mars has long been more fantasy than reality: The planet is, on average, 140 million miles from Earth, and its atmosphere isn't hospitable to human life.
But a human voyage to the planet is now, for the first time, within the realm of possibility, according to space advocates inside and outside government. As a result, plans for a mission around the planet have been sprouting like springtime flowers.
The new momentum, some space experts say, comes from the successful landing of the large rover Curiosity in a Martian crater last year, the growing eagerness of space entrepreneurs to mount and fund missions to Mars and encouraging new data about the radiation risks of such an expedition.
NASA is developing a heavy-lift rocket and a new space capsule to achieve this goal. It has even established an optimal time frame for this event - in the early 2030s, when the very different orbits of the two planets brings them closest to each other.
The challenges of space technology - including how to keep astronauts alive en route and on the planet - as well as government support and funding remain daunting, but the goal of landing humans on Mars is seeming less and less like a pipe dream.
"A human mission to Mars is a priority, and our entire exploration program is aligned to support this goal," said NASA Administrator Charles Bolden.
NASA has "overcome the technical challenges of landing and operating spacecraft on Mars" robotically, Bolden said. "We're developing today the technologies needed to send humans to Mars in the 2030s."
With both the promise and the obstacles in mind, Bolden and other top NASA planners and scientists, as well as leaders from the commercial space industry, are meeting through Wednesday at a conference at George Washington University.