Flashing some interplanetary gold bling and sipping "space water" might sound far-fetched, but both could soon be reality, thanks to a new US law that legalizes cosmic mining.

In a first, President Barack Obama signed legislation at the end of November that allows commercial extraction of minerals and other materials, including water, from asteroids and the moon.

That could kick off an extraterrestrial gold rush, backed by a private aeronautics industry that is growing quickly and cutting the price of commercial space flight.

The US Commercial Space Launch Competitiveness Act of 2015 says that any materials American individuals or companies find on an asteroid or the moon is theirs to keep and do with as they please.

While the Space Act breaks with the concept that space should be shared by everyone on Earth for scientific research and exploration, it establishes the rights of investors to profit from their efforts, at least under US law.

Christopher Johnson, a lawyer at the Secure World Foundation, which focuses on the long-term sustainable use of outer space, said the law sets the basis for the next century of activity in space.

"Now it is permissible to interact with space. Exploring and using space's resources has begun," he said.

The US move conjured visions of the great opening of the United States' Western frontier in the 19th century, which led to the California Gold Rush of 1849.

But for the moment, the costs of pioneering the economic exploitation of space remain exorbitant and the risks high.

Large companies are still studying their options, but smaller startups are impatient to get going, like Planetary Resources, launched in 2012 by Google co-founder Larry Page.