Researchers from The University of Western Australia have uncovered answers to a mystery that has puzzled scientists for half a century.
The researchers discovered the reasons for ‘horizon glow’ (a bizarre glow occurring on the Moon’s western horizon just after sunset) relate to two new phenomena concerning dust movements on the Moon’s surface - ‘sunrise dust storms’ and ‘horizon brightening’.
Adjunct Professor Brian O’Brien from the UWA School of Physics said the discoveries were made using a matchbox-sized dust detector he invented in 1966.
“In 2011 we published two reasons that doubted the popular belief that horizon glow occurred due to fine dust particles being lifted by electric fields very high above the surface of the Moon,” he said.
“Then in mid-2015 a sophisticated NASA dust detector on The Lunar Atmosphere and Dust Environment Explorer (LADEE) in orbit around the Moon confirmed there was no evidence of the predicted dust at altitudes between three kilometres and 250 kilometres.”
Professor O’Brien said his team’s dust detector was mounted just one metre about the surface of the Moon.
“It found that sunrise dust-storms had resulted from the Apollo 12 mission rockets freeing up dust particles on the Moon's smooth surface and then sunrise lifting them to this height,” he said.
Professor O’Brien also developed a model explaining sunrise dust storms and the resulting new phenomenon of ‘horizon brightening’, which occurs when the dawn horizon becomes one to four per cent brighter than sunlight at the end of sunrise.
Dust is the largest environmental problem on the Moon, and Professor O’Brien’s invention is the only one to measure it directly.
Dust storms are an unexpected hazard and can clog up machinery during surface missions in the vacuum of the Moon, and may have caused the Chinese lunar rover Yutu to stall in 2014.
The sunrise effects may also help reduce dust effects from mining on the Moon.
The research has been published in the Journal of Planetary and Space Science.