The most detailed study of an asteroid shows that it contains precious metals worth at least $20,000bn.

The data were collected last December by the Near Earth Asteroid Rendezvous (Near) spacecraft which passed close to the asteroid Eros.

It provided an unprecedented look at one of the mountains of rock that fly around the solar system.

The first conclusions from that encounter are now published the journal Science.

Eros: A "banana" in space

Near, which due to a computer malfunction will not be able to go into orbit around Eros until next year, revealed that the asteriod is shaped like a 33 km by 13 km by 13 km banana.

Over a thousand images of Eros were transmitted back to Earth that allowed scientists to estimate its size and mass. The results are startling.

Gold mine in space

Eros is believed to have been formed from the wreckage of a collision with a larger body. Its composition appears to be similar to the stony meteorites that frequently fall to Earth.

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That means Eros is a goldmine in space, as well as a platinum mine, a zinc mine and many more minerals besides.

If Eros is typical of stony meteorites, then it contains about 3% metal. With the known abundance's of metals in meteorites, even a very cautious estimate suggests 20,000 million tonnes of aluminium along with similar amounts of gold, platinum and other rarer metals.

Controllers briefly lost contact with the Near craft

In the 2,900 cubic kms of Eros, there is more aluminium, gold, silver, zinc and other base and precious metals than have ever been excavated in history or indeed, could ever be excavated from the upper layers of the Earth's crust.

That is just in one asteroid and not a very large one at that. There are thousands of asteroids out there.

Astronomic value

How much is Eros worth? Today's trading price for gold is about $250 per ounce or about $9m per tonne.

It means the value of the gold in asteroid Eros is about $1,000bn. That is just the gold. Platinum is even more expensive, $350 per oz. Work it out yourself.

Since it contains a lot of rare elements and metals that are of use in the semiconductor industry for example, at today's prices Eros is worth more than $20,000bn.

Market busting

But there are two problems with this analysis.

Eros partially illuminated by the Sun

Firstly, such a dramatic influx of metals to Earth could crash the global market for such commodities. Secondly, the resources are way out in space.

But in the week we celebrate the 30th anniversary of the first footprint on the Moon can we not contemplate mining what is just another big chunk of rock in space?

One way to get the metals back would be to mine them on Eros and send the refined iron back to Earth.

Solar powered

It takes about 2,000 calories to boil a gram of iron so the equivalent of between 20 to 200 thousand megatons of TNT would be needed to start liberating substantial quantities of iron from the asteroid.

But this energy could be obtained from the Sun.

If you wanted to mine only a section of Eros at a time then a huge solar energy collector - a sheet only a few kilometres in size - could collect enough energy from sunlight to power a smelting plant on the surface of Eros.

These are all "guesstimate" figures. But they serve to demonstrate just how plentiful are the resources of the Solar System, in terms of minerals, metals and energy, once we decide to go out and get them.

It shows how mining one fairly small asteroid like Eros would revolutionise the availability of many raw materials on Earth.

No one knows how much a robot mission to mine an asteroid would cost but I am willing to bet it would be the best return on an investment since Leonardo da Vinci bought a sketch pad or Paul McCartney a guitar.