IT ISN’T a gold rush quite yet. But the launch of a second asteroid-mining venture in a year suggests that the allure of extraterrestrial prospecting may be as hard to resist for some as the Klondike was. On January 22nd a start-up called Deep Space Industries entered the fray. It joins Planetary Resources, a firm backed by Larry Page and Eric Schmidt of Google, which launched last year and promises to have its first asteroid-hunting spacecraft in orbit by late 2014.

The potential bonanza is, well, astronomical. A single 500-metre metal-rich asteroid might contain the equivalent of all the platinum-group metals mined to date. Icy bodies could provide water to sustain astronauts or be processed into rocket fuel for future missions to Mars.

Deep Space Industries might be thinking big, but it is starting small. Even smaller, in fact, than the relatively puny Planetary Resources. The firm is aiming to raise a mere $3m this year from venture capitalists, angels and private-equity funds, and another $10m next year. It will spend the money designing, building and launching three single-use spacecraft, called Firefly, to conduct fly-bys of small asteroids. Planetary Resources, for its part, intends to start by launching several constellations of tiny spacecraft into Earth orbit, where they will spend years observing and cataloguing nearby rocks.

The idea is to build Firefly on the cheap, forgoing extensive testing and using commercial off-the-shelf components rather than custom-built electronics. To reduce costs further, the Firefly probes will fly alongside larger payloads on scheduled launches. David Gump, the boss of Deep Space Industries, hopes to attract corporate sponsorship for his first missions. He is also counting on support from NASA, America’s space agency, and possibly its counterparts in other countries.

In this, Mr Gump has some form. Five years ago he co-founded Astrobotic Technology, a company which has booked a place on SpaceX’s Falcon 9 rocket for a lunar rover called Polaris. If all goes to plan, in October 2015 Polaris will embark on a one-way mission, carrying NASA instruments to hunt for water, oxygen and methane at the Moon’s north pole. Polaris benefited from $3.6m of NASA contracts and Mr Gump hopes Deep Space Industries will strike similar arrangements, especially as no one has ever studied the small asteroids that Firefly plans to visit. Mr Gump says NASA is interested.

If successful, the Firefly missions will be followed by a more sophisticated spacecraft called Dragonfly. This robotic vessel, which Mr Gump hopes to launch by 2016, would try to intercept a small asteroid and return a hefty 25-65kg sample to Earth within three to four years.

If all this sounds far-fetched, that’s because it is. Stardust, dispatched by NASA, and Hayabusa, launched by Japan’s space agency, took more than twice as long to bring back just a few specks of dust. Deep Space Industries’ proposed robotic 3D printer, for use in its mining operations, is if anything more fanciful still. It would accept crushed nickel-rich space rock at one end and churn out finished spacecraft parts at the other. None of the company’s technology has yet been demonstrated, however.

Most important, perhaps, the economic case for asteroid mining also remains far from clear. A doubling of supply from space might exert such downward pressure on the price of platinum on Earth as to undermine the whole business case for the venture. Asteroid mining seems likely to stay in the realm of science fiction for the time being.