The successful signal was received after multiple attempts in recent decades, and the results of the study could complement future laser experiments used to study space.
A laser station in Grasse, France, sent the laser beams toward the NASA orbiter, some 240,000 miles away. The beams had to travel this distance to hit a reflector on the orbiter that was only about the size of a paperback novel.
The orbiter has been observing the moon since 2009, and its reflector is a smaller version of reflector panels placed on the lunar surface during the landing on Apollo 11, 14 and 15 on the moon. Soviet pay robot robots sent in 1970 and 1973 also carried smaller reflectors.
But the older, larger reflectors on the lunar surface send weak signals, delivering only about a tenth of what they expected. Scientists believe it may be dust that has accumulated on the five panels.
Micrometeorites affect the moon all the time, sending up dust which then sets downwards. Dust could not only block light from the mirrors, but actually act as an insulating layer that overheats the reflectors.
Testing the signal strength of the inertial reflector on the orbiter can help scientists determine what happens to the reflectors on the surface. So far, the science team is not sure if it is dust. But this successful signal is a start to learn what happens to the reflectors of the moon.
What lasers tell us about the moon
Since the Apollo era of lunar reconnaissance and landing, scientists have been using reflections to understand our lunar companion.
By simply directing light at the reflectors, scientists measure how long the light took to travel back from the moon to Earth. This showed that Earth and the moon actually run apart over time, about 1.5 inches per year, caused by the way they gravitationally interact with each other.
“Now that we’ve been collecting data for 50 years, we can see trends we could not otherwise have seen,” said Erwan Mazarico, a study author and a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. , in a statement. “Laser science is a long game.”
Scientists have also discovered a light, telltale wobble as the moon rotates, suggesting it has a liquid core. But is there a solid core within that fluid? Scientists do not know it yet.
“Knowledge about the moon’s interior has far-reaching implications that include the moon’s evolution and the timing of its magnetic field and how it died,” Vishnu Viswanathan, a NASA Goddard scientist, said in a statement. which studies the internal structure of the moon.
When Apollo astronauts returned monsters of the moon back to Earth, they revealed that the moon once had a magnetic field billions of years ago – that does not exist today. This has interested scientists because they want to know what caused the moon in the first place.
Laser science could determine if the moon has a solid core that could have provided that magnetic field. However, this will require more accurate lasers to measure the distance between the Earth’s laser stations and the reflectors on the moon.
“The accuracy of this one measurement has the potential to refine our understanding of gravity and the evolution of the solar system,” said Xiaoli Sun, a planetary scientist at Goddard who helped design the orbiter’s reflector. in a statement.
The challenges of laser experiments
Focusing on the reflectors on the moon may sound simple, but it does mean that they follow their specific locations as the moon moves in orbit.
Particles called photons in the lasers can also be scattered as they travel to and from the moon through the thick atmosphere of the earth. That a load of 10 feet from the earth can leave the earth a mile wide when it reaches the moon, and it can become even wider when it returns to Earth. This stretches the laser beam and its photons, causing it to diffuse.
That the chances that photons from Earth launch a reflector strike and return are incredibly small.
Given that the reflector on the orbiter is smaller than the reflectors on the moon and the fact that it moves much faster than the moon, the chance of hitting it and receiving a signal back was even smaller.
Scientists at NASA’s Goddard Center success once found them collaborating with French researchers on the Géoazur team at the Université Côte d’Azur. They used the laser station in France to send a laser of infrared light, which can pass more efficiently through the Earth’s atmosphere.
The researchers recovered 200 photons from the tens of thousands they sent to the orbiter over the course of a few days in 2018 and 2019.
The success of this experiment could lead to new reflectors placed on the moon, the development of facilities with infrared lasers and more accurate measurements of the Earth and the moon to discover the mysteries of the past of the moon.
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