The signal of success has been received after many trials over the past decade, and the results of the study may complement future laser experiments used for space research.
A laser station in Grasse, France, sends laser beams towards NASA’s spacecraft, some 240,000 miles away. The beams must travel that distance to hit a reflective object in orbit the size of a paperback novel.
The orbiter has observed the moon since 2009 and its reflectors are a smaller version of the reflectors placed on the lunar surface during the Apollo 11, 14 and 15 moon landings. Soviet lunar landers sent in 1970 and 1973 also carried smaller reflectors.
But larger, older reflectors on the Moon’s surface are sending a weak signal, returning only about a tenth of what they expected. Scientists believe it may be due to the dust that has stuck to the five panels.
Micro-objects impact the moon all the time, flying up dust and settling. Not only can dust block the light from the mirror, but it also actually acts as an insulation layer that causes the reflector to overheat.
Testing the signal strength of a pristine reflector in orbit can help scientists determine what’s going on with reflective objects on the surface. So far, the scientific team is not sure if it is dust. But this success signal is a start to find out what’s going on in the moon’s reflector.
Lasers tell us nothing about the moon
Since the era of Apollo’s discovery and moon landing, scientists have used reflectors to get to know our moon companion.
By simply directing light at the reflectors, scientists have measured the time it takes the light to travel backwards from the moon to Earth. This reveals that the Earth and the moon are actually drifting over time, about 1.5 inches per year, caused by the way they interact gravely with each other.
“Now we’ve been collecting data for 50 years, we have,” said Erwan Mazarico, study author and a planetary scientist from NASA’s Goddard Space Flight Center in Greenbelt, Maryland. could see trends we wouldn’t have seen otherwise. , in a statement. “Long-range laser science is a long game.”
Scientists have also detected a slight oscillation, possibly even as the moon rotates, indicating that it has a liquid core. But is there a solid core inside the liquid? Scientists still do not know.
Vishnu Viswanathan, a NASA scientist Goddard who studies the inner structure of the Moon, said: “Knowing about the inside of the Moon has greater implications regarding the evolution of the Moon and interpretation of time. its magnetic field and how it dies. .
When the Apollo astronauts returned the samples from the moon back to Earth, they revealed that the moon had a magnetic field billions of years ago – this doesn’t exist to this day. This attracted the attention of scientists because they wanted to know what caused the moon to have a moon in the first place.
Laser science can determine if the moon has a solid core, which can provide that magnetic field. However, that would require more precise lasers to measure the distance between laser stations on Earth and objects that are reflected on the moon.
Xiaoli Sun, planetary scientist at Goddard, who helped design the orbital’s reflector, said: “The accuracy of this measurement has the potential to improve our understanding of gravity and development of the solar system.
Challenges of laser experiments
Targeting reflective objects on the moon sounds simple, but it means tracking them to specific locations when the moon is moving in orbit.
The particles called photons in the laser can also be scattered as they travel to and from the moon through the Earth’s thick atmosphere. So a laser beam 10 feet wide leaving Earth could become a mile wide when it reached the moon, and it could get even wider when it returned to Earth. This elongates the laser beam and its photons, making it more diffuse.
Therefore, the chances of photons emitted from Earth hitting a object that is reflected and returned is extremely small.
Given that the object that is reflected in orbit is smaller than that reflected on the moon and the fact that it is traveling much faster than the moon, the chances of hitting it and getting a signal back are even smaller.
Scientists at NASA’s Goddard Center found success when they collaborated with French researchers in the Géoazur group at Côte d’Azur University. They used a laser station in France to send an infrared laser, which could pass through the Earth’s atmosphere more efficiently.
Researchers received back 200 photons out of the tens of thousands of particles they sent to orbit over a few days in 2018 and 2019.
The success of this experiment could lead to the placement of new reflectors on the moon, the development of facilities with infrared lasers and more accurate measurements of the Earth and the moon to elucidate. the mysteries of the moon’s past.