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 extra-terrestrial prospecting may be as hard to resist for some as the Klondike was. On January 22nd a Californian start-up called Deep Space Industries entered the fray. It joins Planetary Resources, a firm backed by Google executives Larry Page and Eric Schmidt, which promised to have its first asteroid-hunting spacecraft in orbit by the end of 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. Even humble ice could sustain astronauts or be processed into rocket fuel for future missions to Mars.

Deep Space Industries might be dreaming big but it is starting small. Smaller still, in fact, than the relatively puny Planetary Resources. The company 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 a fleet of three single-use spacecraft, dubbed Firefly, to conduct fly-bys of small asteroids. Planetary Resources, by comparison, intends to launch 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, it will fly alongside larger payloads on scheduled flights. David Gump, the company's boss, 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 Space X'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. According to Mr Gump, NASA seems interested.