The Apollo 11 astronauts returned from the moon 40 years ago today, but they left behind more than footprints. An experiment they placed on the moon?s surface is still running to this day.
The Lunar Laser Ranging Experiment is the only moon investigation to continuously operate since the Apollo 11 mission. The experiment studies the Earth-Moon system and beams the data to labs around the world, including NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
"Yes, we are still going," said James Williams, a JPL scientist involved with the experiment, in an e-mail interview.
Data from the ranging experiment has been used to learn ? among other things ? that the moon has a fluid core and is moving away from the Earth, and that Einstein's Theory of Relativity is accurate.
The instrument itself, called a lunar laser ranging reflector, was originally intended to accurately calculate the distance between the Earth and moon by measuring the round-trip time of a laser fired from Earth to a reflector on the instrument.
The average distance from the centers of the Earth and the moon was calculated to be 238,897 miles (384,467 km). NASA scientists say the measurement is one of the most precise distance measurements ever made and is equivalent to determining the distance between Los Angeles and New York to one-hundredth of an inch.
The accuracies will continue to improve as observatories on Earth improve their technology.
"Technical improvements at the observatories rejuvenate the lunar laser ranging effort," Williams said in 2004, when the experiment turned 35. Williams is one of four JPL scientists that analyze the data from the Lunar Laser Ranging Experiment. "When the range accuracy improves, it is like getting a new experiment on the Moon."
The instrument itself does not require any power to operate on the moon (only the lasers on Earth do), so it's likely to be in service for many years to come. Scientists at the University of California, San Diego and the University of Washington are working with a new lunar ranging instrument that has significantly improved accuracy at the Apache Point Observatory in New Mexico.
"The usefulness of continued improvements in range determinations for further advancing our understanding of the Earth-moon system will keep the lunar reflectors in service for years to come," Williams said.
The lunar measuring, ongoing for 40 years now, is by no means the longest-running experiment. Physicist Thomas Parnell set up a slow pitch-drop experiment in 1927 that has continued long after his death, with about one drop of the gooey stuff falling each decade. Other experiments still underway date back to the mid-1800s.
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