KentuckyFC writes: In 2012, various billionaires such as Richard Branson, Larry Page and Eric Schmidt announced the launch of Planetary Resources, an ambitious start up with the goal of mining nearby asteroids for natural resources. Now an academic survey of ore-bearing asteroids estimates that only about 10 are likely to have resources worth mining. The new approach is to create a Drake-like equation that starts with the total number of asteroids and determines the percentage that are close enough to Earth, the percentage of these that contain valuable resources, the percentage of these large enough to pay for a space mining mission and so on. Each of these factors is filled with uncertainty but the bottom line is that when it comes to platinum group metals such as platinum, palladium and iridium, there are likely to be very few worth exploiting. That has significant implications for the future of space exploration. With so few commercially-viable space rocks out there, knowing which ones to pursue will be hugely valuable information, concludes the study. And that means the prospecting of asteroids is likely to become a highly secretive commercial endeavour in the not too distant future.