- Impact was not be visible from Earth, scientists said, as small probes had no fuel to cause explosion on impact
- Action follows end to a successful year-long mission
- Landing site named in honor of Sally Ride, the first American woman in space, who died earlier this year
By Nick Mcdermott, Science Reporter
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They have danced around the moon for almost a year, making detailed maps of its interior.
Flying in formation over the lunar surface, the two NASA probes - named Ebb and Flow - helped further our understanding of the early solar system.
But Monday, in a dramatic climax to their mission, the two spacecraft plunged seconds apart into a mountain near the moon's North Pole.
Afterward, NASA said it had dedicated the impact site in honor of mission team member, Sally Ride, the first American woman in space who died earlier this year.
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Projection: The Ebb and Flow Satellites' trajectory to crash into the moon on December 17
Heavenly bodies: An artist's depiction of the twin spacecraft (Ebb and Flow) that comprise NASA's Gravity Recovery And Interior Laboratory (GRAIL) mission.
Mapping the moon: Using a precision formation-flying technique, the twin GRAIL spacecraft -- Ebb and Flow -- have mapped the Moon's gravity field, as depicted in this artist's rendering.
By design, the spot was far away from the Apollo landings and other historical sites.
With their fuel running low, NASA was keen to prevent them from crashing near the historically important Apollo landing sites.
Honoring: NASA said it had dedicated the impact site in honor of mission team member, Sally Ride, the first American woman in space who died earlier this year
And even the keenest stargazer would not have spotted the two-washing machine sized probes as they impacted at a speed of 3,800mph, as the collisions occurred on the dark side of moon.
But NASA's Lunar Reconnaissance Orbiter which circles the moon will soon be passing over the site and will attempt to photograph the skid marks after the craft slammed into the surface.
The mission, codenamed Grail - Gravity Recovery and Interior Laboratory - was launched in September 2011 from Cape Canaveral and has been deemed a success.
The twin craft collected data about the moon's gravity while orbiting at an average altitude of 34 miles, revealing its surface is much thinner than previously thought, gouged out by the impact of thousands of asteroids and comets.
'It is going to be difficult to say goodbye to our little robotic twins,' says MIT professor Maria Zuber, Grail principal investigator. 'Planetary science has advanced in a major way because of their contributions.' Ebb and Flow conducted one final experiment before their mission ends, firing their main engines until their propellant tanks are empty in a bid to determine precisely the amount of fuel left in their tanks.
NASA engineers hope this information will help improve predictions of fuel needs for future missions.
'Our lunar twins may be in the twilight of their operational lives, but one thing is for sure, they are going down swinging,' said Grail project manager David Lehman of NASA's Jet Propulsion Laboratory in California.
Trajectory: The twin lunar-orbiting NASA spacecrafts went on a controlled crash into a site named after Sally Ride
Crash landing site: The map shows the region where the twin spacecraft of NASA's Gravity Recovery and Interior Laboratory mission will impact on Monday
A successful mission: The map created by Ebb and Flow has revealed an incredibly pulverized lunar crust, suggesting the moon, Earth, Mars, Mercury and Venus were pounded by long-ago impacts far more violently than previously thought.
Blast Off: The $496 million Grail mission - short for Gravity Recovery and Interior Laboratory - launched in September 2011, and Ebb and Flow reportedly arrived in lunar orbit about three months later.
'Even during the last half of their last orbit, we are going to do an engineering experiment that could help future missions operate more efficiently.' The twin craft focused exclusively on measuring the moon's lumpy gravity field in a bid to learn more about its interior and early history.
'After flying in formation for months, they produced the most detailed gravity maps of any body in the solar system.
Since the dawn of the Space Age, more than 100 missions have involved the moon, including Nasa's six Apollo landings that put 12 astronauts on the surface.
The last time the US space agency intentionally fired a man-made object at the moon was in 2009, but it was for the sake of science. Spectators on Earth barely saw the faintest of flashes, but the experiment proved that the moon contained water.
'Grail has produced the highest-resolution, highest-quality gravity field for any planet in the solar system, including Earth,' Zuber reportedly said.
The resulting map has revealed an incredibly pulverized lunar crust, Zuber added, suggesting that the moon, Earth, Mars, Mercury and Venus were pounded by long-ago impacts far more violently than previously thought.
Mission managers on Friday turned off Ebb and Flow's science instruments and ordered a maneuver putting them on course for the rim of the crater, which reportedly sits at a latitude of 75.62 degrees north and a longitude of 26.63 degrees east.
New moon: This locations on the moon that NASA considers 'lunar heritage sites' and the path GRAIL will take to avoid hitting any of them
Impact: These 3D renderings show the lunar mountain targeted by the GRAIL mission for controlled impact of the Ebb and Flow spacecraft
LUNAR GRAVEYARD: HOW THE EBB AND FLOW WILL BE IN GOOD COMPANY
More than 100 missions have been flung to Earth's nearest neighbor since the dawn of the Space Age including NASA's six Apollo moon landings that put 12 astronauts on the surface.
The demise of Ebb and Flow comes on the same month as the 40th launch anniversary of Apollo 17, the last manned mission to the moon.
Ebb and Flow focused exclusively on measuring the moon's lumpy gravity field in a bid to learn more about its interior and early history. After flying in formation for months, they produced the most detailed gravity maps of anybody in the solar system.
Secrets long held by the moon are spilling out. Ebb and Flow discovered that the lunar crust is much thinner than scientists had imagined. And it was severely battered by asteroids and comets in the early years of the solar system - more than previously realized.
Data so far also appeared to quash the theory that Earth once had two moons that collided and melded into the one we see today.
Besides a scientific return, the mission allowed students to take their own pictures of craters and other lunar features as part of collaboration with a science education company founded by Ride, who died in July of pancreatic cancer at age 61.
bout 3,600 classrooms around the world participated, sending back 114,000 photos.
Scientists expect to sift through data and images from the $487 million mission for years.
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