Why the Moon really IS silvery: Lunar surface contains traces of precious metal and is 6% water
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.
Anthony Colaprete, from the US space agency’s Ames research centre said it was a ‘significant amount of water’.
‘And it’s in the form of water-ice grains. That’s good news because water-ice is very much a friendly resource to work with. You don’t have to warm it very much; you just have to bring it up to room temperature to pull it out of the dirt real easy.
‘Just as a point of reference – in about a tonne of material, at about 5 per cent, you’re talking 11-12 gallons of water that you could extract’.
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 (LCROSS) 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 (LRO) probe.
The chosen target was the Cabeus crater, which lies in a permanently shaded region of the Moon where temperatures fall as low as -238c.
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 today 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 Dr Peter Schultz, one of the U.S. 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.’
Astronauts sent as part of NASA’s Apollo missions found trace amounts of silver, along with gold, on the near-side (Earth-facing side) of the Moon. The discovery of silver at Cabeus crater suggests that silver atoms throughout the moon migrated to the poles.
Dr Shultz 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.
‘There’s a balance between delivery and removal,’ explained Schultz, who has been on the Brown faculty since 1984 and has been studying the Moon since the 1960s.
‘This suggests the delivery is winning. We’re collecting material, not simply getting rid of it.’
Fellow expert Dr 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.
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’.
‘There’s this archive of billions of years (in the Moon’s permanently shadowed craters),’ Schultz said. ‘There could be clues there to our Earth’s history, our solar system, our galaxy. And it’s all just sitting there, this hidden history, just begging us to go back.’