Lasers on the Moon Could Find Subtle Gravity Deviations

NASA is becoming more and more interested in future scientific applications based on the Moon. The agency asked the US National Research Council (NRC) in 2006 to advise it on what kinds of science could be tackled from the Moon and what projects should be given top priority.

They liked the idea of an American astronomer to build a giant liquid-mirror telescope on the Moon, saying that it will be hundreds of times more accurate and sensitive than even the Hubble Space Telescope.

They also liked the one about building a radio observatory on the far side of the Moon, in the form of metallic antennas plated onto a flexible plastic film that can be rolled up for transport to the Moon, then unrolled on the lunar surface like a carpet, creating an instant array of radio receivers.

Now, they're funding a research on developing lasers that could be placed on the Moon to check for subtle deviations from the standard theory of gravity. Lasers have been previously used for extremely precise measurements of the distance between Earth and the Moon, since the Apollo astronauts left reflectors on the surface of the Moon, in three distinct sites, and with a fourth being attached to a robotic lander belonging to the former Soviet Union.

The measurements are made by calculating how long it takes a ray of light, bounced from Earth-based lasers off of these reflectors, to get back to Earth. Moon's gravity is affecting these lasers, so by studying minute changes in the response time, subtle deviations from Einstein's general theory of relativity could accurately describe the motion.

Some astrophysicists believe that the string theory, involving exotic particles called dilatons - also known as the radions or graviscalars - could predict deviations from general relativity.

Slava Turyshev of NASA's Jet Propulsion Laboratory in Pasadena, California, US, and colleagues want to put a suitcase-sized laser transponder that astronauts could bring with them on future missions to the Moon.