The long lost lunar rover Lunokhod 1, has been rediscovered by astronomers using laser pulses, thirty-six years after it disappeared.
A team led by Associate Professor Tom Murphy at the University of California, San Diego worked out its position to within a few centimetres using data from NASA's Lunar Reconnaissance Orbiter (LRO).
Their paper, which has been submitted ot the journal Icarus, and appearing on the pre-press website ArXiv.org, says "the discovery will significantly advance gravitational and lunar science."
According to the researchers, it will improve sciences understanding of the Moon's orbit, position and movement through space.
Bathtub with a lid
Lunokhod 1 was launched from the Baikonur Cosmodrome aboard the then Soviet Union's Luna 17 mission, landing on the Moon on the 17 November 1970.
The rover, about the size of a small car and looking like a tin bathtub with a lid, travelled about 10 kilometres along the lunar landscape sending back tens of thousands of images and soil analyses from over 500 sites.
After it stopped working, scientists continued to bounce laser light off an array of French-built mirrors located on the rover's back.
Although range measurements were made, they were never published. The last recorded return signal was in May 1974, but the exact details of its position were never fully locked down.
Murphy's team regularly bounce laser light off the other known reflectors on the lunar surface left by Lunokhod 2 and the Apollo 11, 14 and 15 missions.
The more reflectors you have the more accurately you can measure the position of the Moon, so researchers enlisted the help of the LRO to search for Lunokhod 1.
In March the LRO spacecraft spotted the Luna 17 landing site. The rover's tracks helped the researchers to pinpoint its position to within a few hundred meters.
One month later, Murphy's team fired a laser from the Apache Point Observatory in New Mexico in that direction and detected a return.
They say the initial return was surprisingly bright.
"We found to our surprise that Lunokhod 1 is a much better reflector than its twin L2," they write.
The researchers say the Lunokhod 1 reflector is especially useful because it is closer to the Moon's limb than any of the other reflectors. And unlike the Lunokhod 2 reflector, it can be used during the lunar day.
Space analyst and writer Dr Morris Jones says the reflector's performance is not bad considering the rover's been on the exposed lunar surface for 40 years.
"While both reflectors were of the same design and materials, Lunokhod 1 seems to have suffered less space weathering, probably because of where it landed, its position and angle."
Jones says the Moon's environment is pretty hard on equipment. There are impacting micrometeorites that act like sand blasting and radiation that can cause chemical reactions in some materials, blackening the laser reflectors.
According to Jones, the failure of the N1 moon rocket program meant the Soviets abondaned their plans to send humans to the Moon and focus on lunar rovers instead.
"It was the first time anyone had tried to land and operate a rover on another world."