Is the Moon moving away from Earth? Laser beams unveil a new mystery

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While the Moon has always been a source of mystery to people across the world, a new observation has sparked even more curiosity in astronomical circles: Is the Moon moving away from Earth?

On several occasions over the past decade, scientists have fired laser beams at reflector panels placed about 240,000 miles (385,000 kilometers) from Earth on the Moon. By measuring the time it takes for laser light to return to Earth – about 2.5 seconds on average – researchers calculate the distance between Earth’s laser stations and lunar reflectors.

The signals they received this time around indicate that the Earth and the Moon are slowly moving apart at the rate that fingernails grow – 1.5 inches (3.8 centimeters) per year. This widening gap is the result of gravitational interactions between the two bodies.

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The results were published this month in the Journal Earth, planets and space.

“Now that we’ve been collecting data for 50 years, we can see trends that we might not have seen otherwise,” said Erwan Mazarico, a planetologist at NASA’s Goddard Space Flight Center, who coordinated the LRO experiment. .

Analysis of lunar laser data shows that the Moon has a fluid core. (NASA)

There are five reflective panels on the Moon. Two were delivered by the crews of Apollo 11 and 14 in 1969 and 1971, respectively. They are each made up of 100 mirrors that scientists call “corner cubes” because they are the corners of a glass cube; these mirrors reflect light in any direction it comes from. Another panel with 300 corner cubes was put down by the Apollo 15 astronauts in 1971. Soviet robotic rovers called Lunokhod 1 and 2, which landed in 1970 and 1973, carry two additional reflectors, with 14 mirrors each. Collectively, these reflectors constitute the last scientific experiment of the Apollo era still active on the natural satellite.

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Is dust to blame on the moon?

Some experts suspect that the reason some of the reflectors only return a tenth of the expected signal could be dust. They suspect that dust may have settled on the panels for decades after being lifted by micrometeorite impacts. These dust particles could block light from reaching the mirrors, isolating them, causing them to overheat and reducing their efficiency.

Moon

There are five reflective panels on the Moon. Two were delivered by the crews of Apollo 11 and 14 in 1969 and 1971. (NASA)

As a result of the research, scientists hope to use the Lunar Reconnaissance Orbiter (LRO) reflector to determine if this is true by trying to find a deviation in the light returned by the LRO reflector from surface ones they could use. computer models to test whether dust or something. else, is responsible.

The reflector the scientists wanted was mounted on the LRO, a spacecraft that has studied the Moon from orbit since 2009. The reflectors were placed on the spacecraft so that it could serve as a target to help test the reflective power of the panels left on the surface of the moon by the Apollo missions about 50 years ago.

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The art of beams

The laser experiment on the Moon has continued since astronaut Neil Armstrong and Buzz Aldrin landed on its surface in 1969. Four observatory telescopes in New Mexico, France, Italy and Germany fire lasers at the retro-reflector arrays, measuring the time it takes for a laser pulse to bounce off the reflectors and return to Earth. In addition to measuring distance, the beams have helped determine the orbit, rotation and orientation of the Moon over the years, which is essential for spacecraft that orbit and land on the lunar surface.

Lunar reflectors

They are each made up of 100 mirrors that scientists call “corner cubes” because they are the corners of a glass cube. (NASA)

The beams have helped understand the natural phenomenon of the tides on the planet, which are highest not when the Moon is overhead, but hours later. The highest tide is east of the Moon. They helped identify Earth’s gravitational tugs on the Moon, causing two tidal bulges in the moon rock. According to NASA, the positions of the reflective arrays have varied up to six inches (15 centimeters) up and down each month as the moon flexes.

Analysis of lunar laser data shows that the Moon has a fluid core. Additionally, laser experiments could help reveal if there is any solid material in the Moon’s core that may have helped fuel the now-extinct magnetic field. “The accuracy of this measurement has the potential to refine our understanding of gravity and the evolution of the solar system,” said Xiaoli Sun, a Goddard planetary scientist who helped design the LRO reflector.

Laser rays

Laser beams fired at the moon to study lunar properties. (NASA Goddard)

Getting more photons on the Moon and coming back and better accounting for those lost to dust are two ways to improve accuracy in the future. But it is a Herculean task.

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