(Sen) - Two space probes that successfully mapped variations in the Moon's gravity field have been deliberately crashed into the lunar surface in a dramatic end to their mission. They are just the latest in a string of probes to leave their shattered remains on the Moon.
The impacts of the GRAIL probes, Ebb and Flow, into a 2.4 km high (1.5 miles) mountain near the lunar north pole, was deliberate and planned in great detail.
NASA decided to destroy the craft in a controlled manouevre rather than take the risk, however tiny, that they might later hit one of the historic landing sites of Apollo and unmanned probes.
The two spacecraft, each the size of a washing machine, fired their thrusters one last time to burn up the last of their fuel. They dropped into a lower orbit and hit the peak's southern face, near a crater called Goldschmidt, at 6,050 kph (3,760 mph).
The crater was in darkness at the time of the impacts, so the collisions went unobserved. But NASA hopes to image the shallow craters produced in the impact when its Lunar Reconnaissance Orbiter flies over the site in several weeks time.
The space agency announced afterwards that it was naming the crash zone the Sally K Ride Impact Site in honour of the late astronaut who was the first US woman in space and who died in July after battling pancreatic cancer.
GRAIL project manager David Lehman, of NASA's Jet Propulsion Laboratory, said: "We will miss our lunar twins, but the scientists tell me it will take years to analyze all the great data they got, and that is why we came to the Moon in the first place."
These latest impacts by Ebb and Flow mean there is now man-made debris spread widely across the lunar surface. Here is a rundown on all the spacecraft to crash onto the Moon, not including the successful soft-landers.
The Soviet Union crashed its first spacecraft to reach the Moon, Luna 2, east of Mare Serenitatis, near the crater Archimedes, on September 14, 1959, followed by its third rocket stage.
The United States' first probe to get to the Moon was Ranger 4 which impacted on its far side on April 26, 1962, without sending back any scientific data.
An artist's impression of the LCROSS probe and Centaur rocket stage before hitting the Moon. Credit: NASA
It was followed by Ranger 6 which hit the eastern edge of Mare Tranquillitatis on February 2, 1964, and Ranger 7 which crashed between Mare Nubium and Oceanus Procellarum on July 31, 1964. It sent back 4,308 photographs before the collision.
Ranger 8 hit the Moon on February 20, 1965, in Mare Tranquillitatis after sending back 7,137 photographs of the approaching lunar surface. Then Ranger 9 crashed inside the crater Alphonsus a month later on March 24, returning 5,814 good images.
Luna 5 was the USSR's first attempt to soft-land on the Moon, but the probe went off course and crashed at a site that is still uncertain on May 12, 1965.
After Luna 6 missed the Moon entirely, Luna 7 again failed to soft-land and crashed at speed in Oceanus Procellarum on October 7, 1965. Follow-up Luna 8 also crashed into the same lunar sea on December 6, 1965, after an airbag punctured and sent it into a spin. (Luna 9 at last made a successful soft landing on February 3, 1966.)
Following the first successful US landing, by NASA's Surveyor 1, on June 2, 1966, Surveyor 2 attempted a second touchdown. Instead it suffered an engine failure and impacted on September 23, 1966, at roughly 5.5 N, 12 W.
Between August 10, 1966, and August 1, 1967, NASA launched five Lunar Orbiters that were eventually crashed into the Moon after months of mapping the surface to help prepare for the Apollo missions.
After three successful landings, Surveyor 4 crashed at an unknown location on the Moon on July 17, 1967, after possibly exploding on its descent.
Between 1970 and 1972, the third stages of five Saturn V rockets that launched Apollo 13, Apollo 14, Apollo 15, Apollo 16 and Apollo 17 were all fired into the Moon to produce "moonquakes" that seismometers on the surface could use to help study the lunar interior.
During that era, the Soviets' Luna 18 impacted with the Moon on September 11, 1971, after making 54 successful orbits.
NASA's very successful polar orbiter Lunar Prospector was sent crashing into the Moon near its south pole at the end of its 19-month mission on July 31, 1999, in the first attempt to look for signs of water ice. None was detected.
More than three years after launch, Japan crashed a satellite called Hiten into the Moon on April 10, 1993. It had had an unusual, highly elliptical orbit around the Earth that sent it flying close by the Moon ten times.
The European Space Agency's first lunar orbiter SMART-1 made a controlled crash into the Moon in Lacus Excellentiae on September 3, 2006. Then the Japanese space agency JAXA's Kaguya probe crashed near Gill crater on June 10, 2009, after orbiting for 20 months.
On October 9, 2009, NASA crashed another probe, LCROSS, and its two-ton Centaur rocket stage into a nearby 97 km-wide (60-mile) crater called Cabeus and detected clear signs of water in the cloud of debris produced by the impacts.