A new study might contain some bad news for companies hoping to mine asteroids for their valuable ores.
In the last couple of years, start-ups – including one backed by Sir Richard Branson – have announced plans to extract resources from space rocks.
But calculations by Dr Martin Elvis suggest our cosmic neighbourhood might not be such a treasure trove after all.
The Harvard astrophysicist suggests just 10 near-Earth asteroids would be suitable for commercial-scale mining.
Dr Elvis, from the Harvard-Smithsonian Center for Astrophysics in Cambridge, US, has developed an equation that estimates the number of asteroids in the Solar System that could be exploited in a cost-effective way.
“All-in-all, asteroid mining may be a plausible future space industry. But it would require significant capital investment”
His research paper is in press at the journal Planetary and Space Science and has been published on the pre-print server Arxiv.org.
But other researchers said there were still many uncertainties about what was in the many thousands of sizeable space rocks near our planet.
In 2012, Planetary Resources, backed by billionaire investors including Hollywood director James Cameron as well as Google executives Larry Page and Eric Schmidt, unveiled their vision of using robotic spacecraft to squeeze the chemical components of fuel as well as minerals out of asteroid rocks.
Several months later, the company was joined by a competitor – Deep Space Industries – which plans to use low-cost spacecraft called Fireflies and Dragonflies to reconnoitre and return samples from near-Earth asteroids.
Advocates of asteroid mining say it could turn into a trillion-dollar business, but some experts have always been sceptical of the idea.
Making the grade
In the latest study, Dr Elvis worked out the factors that would make an asteroid commercially viable to mine and what fraction of known space rocks met these requirements. Though he emphasised large uncertainties in the values and called for more thorough surveys of what’s out there.
He assumed that mining operations would want to focus on iron-nickel asteroids (known as M-type), considered the most promising targets for finding so-called platinum-group metals – which include platinum, along with iridium, palladium and others.
These are rare in the Earth’s crust because they dissolve in molten iron, instead being mainly concentrated in the planet’s core. Platinum and palladium are the most economically important, having a wide range of uses in industry. But according to the analysis, just 1% of near-Earth asteroids are rich in platinum-group metals.
In addition, suitable asteroids also need to be relatively easy to reach, further narrowing the pool by ruling out all but the nearest objects to Earth. The operative parameter here is delta-v – the change in velocity needed to send mining equipment to the target and return with a larger mass of ore.
The size of the target is also a factor; the paper suggests it wouldn’t be worth mining asteroids smaller than 100m because the total value of the ore they would produce wouldn’t be enough to cover the costs of a space mission.
However, Dr Elvis points out that the ore values in his analysis ranges from a low of US$0.8bn to US$8.8bn.
“Such a large range of values could greatly change the profitability of a venture, making more accurate assays necessary,” he explained.
The analysis also looked at the number of asteroids that could be profitably mined for water – which could be used in space for life support or separated into hydrogen and oxygen for rocket fuel. The number of suitable water-bearing asteroids larger than 100m was around 18.
Shift of emphasis
Prof Alan Fitzsimmons, from Queen’s University Belfast, who was not involved with the study, said the calculations were “plausible”, but that he would have placed even more emphasis on the uncertainties.
“The make-up of small Near-Earth asteroids is still relatively unknown,” he told BBC News.
“There are large uncertainties in the total number of platinum group-rich asteroids that come near the Earth. This is because it is still difficult to unambiguously determine the mineral makeup of small asteroids.
“We know they exist, as pieces are found as meteorites on Earth. The small asteroid that formed meteor crater in Arizona some 50,000 years ago was one such object.”
In his analysis, Dr Elvis wrote: “The apparently limited supply of potentially profitable [near-Earth objects] argues strongly for an accelerated rate both for discovery and especially for characterisation, which is lagging badly behind.”
Prof Fitzsimmons added: “All-in-all, asteroid mining may be a plausible future space industry. But it would require significant capital investment to start such an industry. The practical problems of mining, refining and transport back to Earth are still unsolved right now.”