It sounds like the stuff of science fiction, but Virgin Galactic's new partnership to mine asteroids in space might be less far-fetched than it seems.

On July 11, the Las Cruces-based company announced that its spacecraft will launch equipment for analyzing and eventually mining near-Earth asteroids—those that, like Earth, are within about 100 million miles of the Sun.

"We know the Earth is made from the same types of materials that asteroids are made of...both were originally created in the Sun and are debris of the original formation of the solar system," says David Yoel, CEO of American Aerospace Advisors, Inc. Based on that link and asteroids' orbital movements, scientists have some idea of their composition. Planetary Resources Inc., the Bellevue, Wash.-based company partnering with Virgin Galactic, has stated that a single asteroid could contain more platinum than the total amount ever mined on Earth. Space exploration technology expert Harvey Willenberg says that estimate is on target.

"If one asteroid is primarily platinum, and it's 10 miles in diameter, then we have an incredible amount of resources in a single asteroid," Willenberg writes SFR in an email.

But former US Senator from New Mexico, veteran NASA astronaut and geologist Harrison Schmitt, who is the last person to have walked on the moon, in 1972, remains skeptical.

"Planetary Resources would have to sample a number of asteroids to find one that can back up that claim," Schmitt tells SFR. Instead, he favors a permanent private facility on the moon.

"To visit an asteroid requires much more specialized spacecraft and processing equipment," he says. Asteroids have lower gravity than the moon, complicating robotic exploration and mining; in addition, while the moon orbits Earth, asteroids orbit the sun, so their distance from Earth varies dramatically over time.

Planetary Resources has a plan for reducing space travel costs, however. Before mining the asteroids for precious metals, the company plans to retrieve water ice from them that can be processed into rocket fuel, spokeswoman Stacey Tearne tells SFR. Scientists have proposed using such ice from celestial bodies both for this purpose and for life support for decades; with the financial backing of two Google executives, along with Titanic filmmaker James Cameron, Planetary Resources might have the muscle to pick up where that research left off.

If these companies' goals come to fruition, another question will likely take center stage: Whose asteroids are they, anyway? The main document prescribing international space law, 1967's Outer Space Treaty, prohibits countries from "appropriating" the moon or other celestial bodies. NASA's request earlier this year that other entities refrain from trampling on the Apollo landing site highlighted the murkiness of space law—there's no legal basis for NASA to actually enforce that friendly suggestion. But Schmitt says he believes the treaty permits commercial ventures like mining, so long as certain regulatory requirements are met.

As resources on Earth become scarcer and the cost of space travel declines, asteroid mining might become not only possible, but almost inevitable, Yoel says.

"Is this the time or not?" Yoel asks. "[Planetary Resources and Virgin Galactic] have taken a bold and strong step in saying they believe it is the time, and I really respect them for that. It's to be seen if it's real, but it very well could be the time."