Experts puzzle over strange structure of Earth's asteroid

Deflecting an asteroid approaching Earth could be more complex than just blowing it up, new research suggests.

Deflecting an asteroid approaching Earth could be more complex than just blowing it up, new research suggests.

There is also a chance, though, that the interplanetary rocks' strange structure will one day make it easy to mine precious metals in space with almost no effort – except getting there. Data and images from Eros, a 21-mile-wide asteroid that is the second-largest "near-Earth object" (NEO) known, show it is made up of a loose mass of rocks and covered in "pools" of dust, grains of which are the size of a few atoms.

To predict what would happen if Eros had to be diverted from a collision with the Earth is nearly impossible. The risk of Eros hitting us was 5 per cent but, said Erik Asphaug of the University of California at Santa Cruz, "not anytime soon".

There are reckoned to be hundreds of asteroids in our solar system that could at some time be heading for Earth. An object just a few hundred yards wide could destroy a city; one as big as Eros could wipe out all life. There are international schemes to discover and monitor such NEOs, but no clear plan on how to deal with them.

The favoured theory for diverting an asteroid was to set off a nuclear blast near the surface, to push it off its orbit. But that might have no appreciable effect – or it could be unpredictable because its internal structure was so irregular.

The data emerged after Near, an unmanned spacecraft built by Nasa, was intentionally crashlanded on Eros in February, after a five-year mission during which it spent one year orbiting the asteroid taking photographs and readings.

The vista there was stranger than expected because the surface of Eros appeared eroded. Joseph Veverka, an astronomer at Cornell University writing about Eros in today's Nature, said: "It continues to surprise us, and to add to our amazement about how diverse the surface of an asteroid can be."

The mystery of the erosion and the pools hinders planning how to deflect asteroids heading for Earth. Professor Asphaug said the layer of dust could pose a problem for exploration. But it could also make relatively easy the mining of asteroids for their abundant metals, including precious metals such as gold and platinum. "They'll be making soda cans out of platinum if they're successful," the professor said.