By Margaret Harris at the European Planetary Science Congress in Riga, Latvia

If you wanted to mine an asteroid, what would you need? Right now, it’s a hypothetical question: only a handful of spacecraft have ever visited an asteroid, and fewer still have studied one in detail. As commercial ventures go, it’s not exactly a sure thing. But put that aside for a moment. If you wanted to create an asteroid-mining industry from scratch, how would you do it?

Well, for starters, you’d need to know which asteroids to target. “Not every mountain is a gold mine, and that’s true for asteroids too,” astrophysicist Martin Elvis told audience members at the European Planetary Science Congress (EPSC) yesterday. For every platinum-rich asteroid sending dollar signs into investors’ eyes, Elvis explained there are perhaps 100 commercially useless chunks of carbon whizzing around out there, and the odds for water-rich asteroids aren’t much better. Moreover, some of those valuable asteroids will be impractical to mine, either because of their speed and location or because they’re too small to give a good return on investment. “Smaller asteroids aren’t even worth a billion dollars,” Elvis scoffed. “Who’d get out of bed for that?”

Identifying the “right” asteroids is only the start. Last year, participants in the first ever joint conference between asteroid scientists and mining engineers identified several other key challenges. One is the need to understand how the surface and subsurface of an asteroid might behave when disturbed by a landing, sampling or digging robot. For the nascent asteroid-mining community, ESA’s Philae probe – which landed on the comet 67P/Churyumov–Gerasimenko in November 2014 – isn’t so much a success story as a cautionary tale. Tomas Kohout, a planetary scientist at the University of Helsinki, Finland, and one of the asteroid-mining session’s other speakers, reminded me during the evening poster session that all three of Philae’s tools for latching onto the comet had failed, and its shadowy landing site had rendered its solar panels useless, severely limiting its lifespan. That didn’t keep Philae from doing good science; indeed, its parent Rosetta mission was hailed as Physics World’s 2014 “Breakthrough of the Year”. But for a mining lander, it would have been disastrous.

Given the technical and knowledge barriers that must be overcome before anyone can turn a profit from asteroid mining, I was surprised to see that one of the session’s speakers, J L Galache, comes from a start-up firm, Aten Engineering. After the session, I asked how he’d managed to get funding to mine asteroids. “I’m not mining, I’m prospecting,” he replied immediately. “These are different things.” Galache also referred to a government initiative in Luxembourg, a country with a well-developed commercial space sector, that aims to boost R&D in the field. “That’s been a big deal for us,” he said, though he acknowledged that it was still difficult to find investors interested in such a long-term project.

Aside from the Luxembourg initiative, another factor tugging asteroid mining away from the realm of science fiction is a growing realization that the main goal is not to bring giant chunks of precious metals back to Earth (which would in any case cause the prices of these commodities to crash). The real prize is using material from asteroids to develop what the session’s first speaker, Luxembourg space policy officer Mathias Link, called “Earth-independent architecture.” Taking material from Earth and putting it into space is incredibly expensive; during his talk, Elvis joked that the water bottle on the lectern would be worth $5000 on the International Space Station. At those prices, it’s worth trying to exploit material that’s already in space, even if doing so requires techniques that would be economically unfeasible on Earth, such as extracting water from metal hydrides and turning it into hydrogen and oxygen fuel.

Although asteroids were the focus of the EPSC talks, the session’s organizer, Amara Graps, told me afterwards that they aren’t the only potential target for space mining. Many near-Earth orbits are currently occupied by defunct spacecraft, and although scavenging for parts in 1970s telecoms satellites might not get investors’ hearts pounding, it’s an avenue worth pursuing if we want to build structures in space – not least because we know where old satellites are, whereas near-Earth asteroids generally “disappear” within a week of being discovered. And wouldn’t it be great if space junk, one of space exploration’s ugliest legacies, could become part of a solution rather than a problem?