Obtaining minerals in space may be a little easier than we'd thought - with the help of some of Earth's tiniest inhabitants.
Experiments aboard the International Space Station have shown that bacteria can improve space mining efficiency by over 400 percent, offering a much easier way to access materials such as magnesium, iron, and the rare-earth minerals we widely use in electronics and alloys.
Here on Earth, bacteria play a very important role in extracting minerals from the ground. They are involved in the natural weathering and breakdown of rocks, releasing minerals contained therein.
This bacterial ability to leach metals from their environment has been harnessed to aid in human mining operations; called biomining, it has a number of benefits. It can help to reduce the reliance on cyanide for mining gold, for example. The bacteria can also help to decontaminate polluted soils.
In space environments, such as asteroids, the Moon, and even Mars, mining will be a valuable tool as we set up human outposts. Ferrying material from Earth is costly; even the least expensive option, SpaceX's Falcon Heavy, costs US$1,500 per kilogram (2.2 pounds) of payload. So scientists have been investigating the feasibility of biomining in space.
"Microorganisms are very versatile and as we move into space, they can be used to accomplish a diversity of processes," explained astrobiologist Rosa Santomartino of the University of Edinburgh in the UK. "Elemental mining is potentially one of them."
Over a period of 10 years, the team developed a small, matchbox-sized device called a biomining reactor that could be easily transported and installed on the International Space Station. Then, in July 2019, 18 of these biomining reactors were shipped to the ISS for low-Earth orbit experiments.
Each biomining reactor contained a bacterial solution that submerged a small piece of basalt, a type of volcanic rock abundant on the Moon. For a three-week period, the basalt in each reactor was exposed to the bacterial solution to determine if bacteria could perform the same rock-weathering function in a low-gravity environment.
In simulated Mars gravity, simulated Earth gravity (using a centrifuge) and microgravity, the team performed experiments with separate solutions of three different bacteria: Sphingomonas desiccabilis, Bacillus subtilis and Cupriavidus metallidurans. A control solution with no bacteria was used as a baseline.
The researchers found that there were no significant differences in bacterial leaching performance based on the gravity conditions, and for B. subtilis and C. metallidurans, the rare-earth mineral extraction was lower than and not significantly different from the control solution, respectively.
However, the S. desiccabilis solution resulted in the extraction of significantly more rare-earth minerals from the basalt than the control solution.
"For S. desiccabilis, across all individual rare earth elements and across all three gravity conditions on the ISS, the organism had leached 111.9 percent to 429.2 percent of the non-biological controls," the researchers wrote in their paper.
Since microgravity has been previously shown to influence microbial processes, the similarity between the concentrations of minerals extracted in all three gravity conditions was something of a surprise. However, the team noted that all three bacteria reached similar concentrations in all three gravity conditions, probably because they had enough nutrients to do so.
They concluded that, with enough nutrients, biomining is therefore possible under a range of gravity conditions.
"Our experiments lend support to the scientific and technical feasibility of biologically enhanced elemental mining across the Solar System," said astrobiologist Charles Cockell of the University of Edinburgh.
"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.
"For example, 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."
The research has been published in Nature Communications.