Dusty mirrors on Moon obstruct tests of Einstein's theory of relativity

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London, Feb 16 (ANI): Scientists have said that as a result of moon dust covering a network of mirrors placed on the lunar surface, tests of Albert Einstein's general theory of relativity are being obstructed.

Many of the best tests of relativity come from lunar ranging experiments.

Several times a month, teams of astronomers from three observatories blast the moon with pulses of light from a powerful laser and wait for the reflections from a network of mirrors placed on the lunar surface by the Apollo 11, 14 and 15 missions, as well as two Soviet Lunokhod landers.

By timing the light's round trip, they can pinpoint the distance to the moon with an accuracy of around a millimetre - a measurement so precise that it has the potential to reveal problems with general relativity.

But now, according to a report in New Scientist, Tom Murphy from the University of California, San Diego, who leads one of the teams at the Apache Point Observatory in Sunspot, New Mexico, thinks the mirrors have become coated in moon dust.

"The lunar reflectors are not as good as they used to be by a factor of 10," he said.

The fainter light is a problem for lunar ranging experiments.

Out of every 100 million billion (1017) photons, Murphy's team fires at the moon, only a handful make it back to Earth.

Most of are absorbed by Earth's atmosphere on the way to the moon and back, or miss the mirrors altogether.

Murphy first suspected two years ago that the dust problem was cutting the light down even further.

He was puzzled to detect far fewer photons than he expected, even when the atmospheric conditions were perfect.

His team also saw a further drop when the moon was full and used to joke about the full moon curse.

This gave Murphy some clues.

He suspects that moon dust is either coating the surface of the mirrors or has scratched them.

Both scenarios would increase the amount of heat the mirrors absorb, and so during a full moon, sunlight falling on the mirrors would heat them up and change their optical properties.

As a result, the mirrors would not reflect light as efficiently.

Even though the moon has no atmosphere, dust can be stirred up from the surface by the impact of micrometeorites.

Murphy has scoured measurements stretching back to the 1970s and found that the problem first appeared between 1979 and 1984, and has been getting worse. (ANI)

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