Tests performed by astronauts aboard the International Space Station (ISS) suggest bacteria can extract valuable minerals from rocks, opening a path to space-mining and human colonization of other worlds.
Getting heavy materials out of the Earth's gravity is exceptionally expensive. Advances in spaceflight may help somewhat, but the economics of large-scale colonies on other worlds are likely to depend on being able to find most of what we need locally, rather than shipping from home. Although asteroids and the Moon offer rich sources of many metals we will want, the question of how to extract them in such a different environment has weighed on the minds of those planning such projects.
Indeed, if the challenges OSIRIS-REx experienced trying to grab a piece of the asteroid Bennu are anything to go by, getting rocks off asteroids may not be as easy as it sounds, and processing adds an extra complication. Scientists wondered if bacteria might help, and an international collaboration developed biomining reactors to explore the possibility.
Eighteen of these matchbox-sized reactors were carried to the ISS in 2019, where they were supplied with basalt and submerged in solutions of three bacterial species for three weeks.
Bacteria are already used to extract metals such as copper and gold from rocks on Earth in a process known as biomining, but no one knew how they would respond to microgravity. The ISS also used centrifuges to simulate Martian gravity (30 percent of Earth's) and Earth-like gravity. Each was compared to experiments run at home.
In Nature Communications, the makers report the success of the reactor with Sphingomonas desiccabilis at any gravity, extracting cerium and neodymium with 70 percent efficiency, up to four times as much as non-biological methods. For all 14 studied metals, extraction was higher in Martian than Earth gravity. The other bacteria were unsuccessful, but at least they got a ride into space.
"Microorganisms are very versatile and as we move into space, they can be used to accomplish a diversity of processes. Elemental mining is potentially one of them,” said Dr Rosa Santomartino, from the University of Edinburgh, in a statement.
Although some love to dream of mining asteroids for use on Earth – even touting the value of space rocks if all the metals could be extracted – Professor Charles Cockell is more realistic. “While it is not economically viable to mine these elements in space and bring them to Earth, space biomining could potentially support a self-sustaining human presence in space,” he said.
“Our results suggest that the construction of robotic and human-tended mines in the Oceanus Procellarum region of the Moon, which has rocks with enriched concentrations of rare earth elements, could be one fruitful direction of human scientific and economic development beyond Earth,” Cockell added. Oceanus Procellarum is a long way from the lunar poles, where water is most abundant, but perhaps some site will be found that combines the best of both worlds.