Silver found among moon’s treasure trove of elements

Poets who wax lyrical about the silvery moon may be on to something.

Scientists who blasted a spent rocket into a lunar crater last year released an unexpected treasure trove of elements – including traces of silver.

But the levels are far too low to make it worth opening a lunar silver mine. More importantly from the point of view of space exploration, large amounts of water were discovered at the bottom of the Cabeus crater.

Making up around 5.6 per cent of the surface material, it was present in sufficient quantities to be useful to future manned missions.

Less welcome was the detection of surprisingly high levels of mercury in the soil, posing a potential risk to explorers.

The Lunar Crater Remote Observation and Sensing Satellite mission involved deliberately crashing a spent Centaur rocket into a crater near the moon’s south pole.

Material thrown up by the impact could then be analysed by instruments on the American space agency Nasa’s Lunar Reconnaissance Orbiter probe.

The chosen target was the cabeus crater, which lies in a permanently shaded region of the moon where temperatures fall as low as 35 Kelvin (-238ºC).

When the rocket struck the bottom of the crater on October 9 last year, it blasted out a hole 70ft to 100ft in diameter and 6ft deep.

An estimated two tons of material was thrown into a plume which reached a height of more than half a mile.

As the debris and vapour was illuminated by sunlight, its properties were measured for almost four minutes by the LRO’s instruments.

The findings, reported in the journal Science, showed that the crater soil was far more complex than expected.

Not only did it contain water, but a plethora of other compounds and elements including mercury, calcium, magnesium, carbon monoxide and dioxide, ammonia, sodium – and small traces of silver.

Planetary geologist Peter Schultz, one of the US scientists from Brown University in Providence, Rhode Island, said: “This place looks like it’s a treasure chest of elements, of compounds that have been released all over the moon, and they’ve been put in this bucket in the permanent shadows.”

He believes elements liberated by meteor impacts right across the moon may have migrated to the cold poles driven by the energy of sunlight.

There they had remained trapped within dark and frigid craters that never see the sun. Atoms of silver may have been part of that migration. But Dr Schultz stressed that the discovery of minute traces of the precious metal “doesn’t mean we can go mining for it”.

Fellow expert Kurt Retherford, from Southwest Research Institute in San Antonio, Texas, one of the scientists operating the LRO instruments, said the biggest surprise was finding mercury at about the same abundance as water.

“Its toxicity could present a challenge for human exploration,” he said.