The search is on for the former Soviet Union's Luna 9 moon probe, which made history's first-ever successful soft landing on a body beyond Earth.
Luna 9 made it to the moon on Feb. 3, 1966, and shortly thereafter beamed home the first images taken from the lunar surface. When pieced together, those pictures offered a panoramic view of the moon's bleak terrain and the horizon less than a mile away.
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Now, nearly a half-century later, researchers are using NASA's sharp-eyed Lunar Reconnaissance Orbiter (LRO) in an attempt to locate the final resting place of Luna 9, which is less than 2 feet (0.6 meters) wide and weighed about 220 lbs. (100 kilograms) back on Earth. (The spherical probe weighs about 37 lbs. [17 kg] in the moon's low-gravity environment, though the craft's mass remains constant everywhere.) [The Moon: Space Programs' Dumping Ground (Infographic)]
Ingenious Landing System Getting Luna 9 safely onto the moon's surface required a great deal of engineering creativity.
"The method was ingenious," said Philip Stooke, an associate professor at the Department of Geography and the Centre for Planetary Science and Exploration at the University of Western Ontario in Canada.
Stooke said that the spacecraft descended under rocket power, slowing down just above the moon's surface. A long rod, projecting from under the spacecraft, eventually touched the lunar terrain. That contact triggered the landing probe's thrusters to turn off, which the Luna 9 landing capsule then ejected from the descent stage. The descent stage then fell to the ground.
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The Luna 9 landing capsule was surrounded by an air-bag-like cover that softened the impact on the moon and was then discarded. The egg-shaped capsule rolled to a stop nearby, unfolded its petal-like covers and began operating, Stooke said.
Coordinating the Coordinates Will people ever find Luna 9 in LRO images?
"Maybe," Stooke said. "The Luna 9 lander would be small, barely two pixels across in the best images."
But, Stooke added, the lander's rocket stage would be bigger than that, and a bright patch created by the rocket's blast might be visible; such patches are visible at most other lunar landing sites. The best evidence would come from a comparison of the craters near a possible site for the lander, he said, contrasted against those seen in the historical Luna 9 surface images. This would be a better method because these craters are bigger than the lander, and thus easier to spot.
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"The Soviets published maps, which we could compare with LRO images," Stooke said. "The Luna 9 landing site was always said to be at about 7.13 degrees north, 64.37 degrees west, based on tracking, but this doesn't fit with the surface photos."
Luna 9 captured a 360-degree panorama that shows more than 200 degrees of the horizon. That horizon is flat, as would be expected of the moon's dark volcanic plains regions, which are known as mare (plural maria).
"But the coordinates put it [the lander] pretty much on the edge of a range of hills, the remnants of an old crater rim. Those hills should be in the images, but they are not," Stooke said. "I have suggested that the landing must be further north or east, far enough away that the hills are over the horizon ... but there just is not enough in the Luna 9 images to help very much." [21 Most Marvelous Moon Missions]