In 2011, NASA's Gravity Recovery and Internal Lab (GRAIL) mission sent a pair of machine-sized satellites in low lunar orbit for nearly a year. Thanks to the precise dance of the spacecraft around the moon, scientists have been able to create the highest resolution gravity map ever made by any celestial body. The results revealed a wealth of never before seen lunar features in refined details.
"We are trying to understand how the moon has formed and how it has evolved over its history, this is one of the things we are trying to solve with the mission of GRACE", Maria Zuber, GRAIL's principal investigator and professor at the Massachusetts Institute of Technology . , a statement said before the launch of the mission. "But also, [we’re] trying to understand how the moon is an example of how earth planets were formed.
During the orbit around the moon, the spacecraft achieved both goals.
Path of precision
GRAIL's mission consisted of two medium sized ships, which were almost identical. Several differences between the ship stem from the need for a companion to fly before the other.
The spacecraft relied heavily on the success of the GRACE spacecraft, which began about nine years earlier in 2002 on a mission to explore Earth's gravity. GRAIL's useful information is a simplified form of GRACE, and the design of the new spacecraft was obtained from Lockheed Martin's experimental small satellite, launched in 2005.
The main instrument of the two spacecraft GRAIL was the Lunar Gravity Ranging System (LGRS). The LGRS transmitted radio signals that accurately determine the distance between the two spaceships. These signals allowed the spacecraft to accurately map the gravity of the moon's surface.
GRAIL was NASA's first planetary mission to bring instruments fully devoted to education and social work. Each spacecraft wore a small camera called GRAIL MoonKAM (the lunar knowledge acquired by high school students) that provided images and videos on the moon surface.
Thousands of students from the fifth to the eighth grade selected target areas on the moon surface and sent their orders to the MoonKAM Mission Center in San Diego. In general, MoonKAM captured more than 115,000 total images of the lunar surface required by high school students across the country.
Both GRAIL spacecraft launched on September 20, 2011, aboard a single Delta II Heavy missile built by the United Launch Alliance. Together, the pair weighed 1,600 pounds. (725 kilograms).
The spacecraft took 3.5 months to reach the moon, traveling on a path that reduced the spacecraft's fuel needs and allowed more time to observe the spacecraft and search for gas jets from the lunar surface.
The GRAIL spacecraft approached the moon beneath the lunar south pole and then entered the moon orbit – GRAIL-A on December 31, 2011 and GRAIL-B on January 1, 2012. The maneuvers put the couple in an almost polar elliptical orbit that sent them around The moon once every 11.5 hours, though eventually dropped to just under 2 hours. As of mid-January 2012, the spacecraft GRAIL received new names thanks to a group of creative fourth-graders from Montana. "Ebb and Flow" was the winning article in NASA's NASA national contest to name the spacecraft.
GRAIL completed its main mission ahead of schedule. From March 1, 2012 until May 29, 2012, the two spacecraft traveled in a low, polar lunar orbit just about 34 miles (55 kilometers) above the surface of the moon. During the extended mission, the average orbit height was 14 miles (23 km) above the moon's surface, placing the satellites within a radius of 8 km from some of the higher surface features of the moon.
"If Ebb and Flow had legs, I think, with a reflex, they would like to pull them every time they fly over the mountain," says Joe Beyer, GRAIL's mission manager.
They took a short pause, excluding between May 29th and August 30th, 2012, to avoid the expected lunar eclipse of June 4th that same year, when a revised orbit protects them from collecting solar energy.
"Before we started, we planned to make GRAIL's main mission to appear between lunar eclipses," said David Lehmann, head of the NASA GRAIL Nuclear Action Laboratory project.
GRAIL's extended mission was running from August 30 to December 17, 2012 when the spacecraft deliberately hit the moon's surface.
Map the moon
The main objectives of GRAIL's mission were to determine the structure of the lunar cortex to the core and to better understand the thermal history of the moon. To achieve this, the twin spacecraft created an extremely high gravity map on the high-resolution moon surface.
Since Ebb and Flow traveled through areas of greater or lesser gravity caused by visible and hidden features, the distance between the two spaceships changed slightly – about a tenth of a micron, or a little over half of the red blood cell.
– Gray twins [could] finds a change in its position to half of human hair, "NASA said in a statement.
Exact changes in the situation allowed the spacecraft to make a detailed map of how the moon's gravity tug changed as they floated above the surface.
These changes reveal the gravitational effects of not only famous mountains and craters, but also masons. Mascons are regions of a planet or lunar crust that contain positive anomalies of gravity, indicating the presence of additional mass in the region. The origin of the masons was a mystery since their discovery in 1968, although the researchers agree that they originated from ancient influences billions of years ago.
"GRAIL data confirms that lunar masks were generated when large asteroids or comets hit the ancient moon when its interior was much hotter than it is now," said a statement by Jay Melosh. The GRAIL map also reveals plenty of elements that have never been seen in detail, such as tectonic structures, volcanic relief forms, pool rings, central crater peaks, and numerous simple cup-shaped craters. GRAIL also revealed that the gravitational field of the Moon is different from that of any Earth planet in the solar system, NASA said.
"What this card tells us is that, more than any other body of heaven we know, the moon carries its gravitational field on its sleeve," said Zuber. "When we see a noticeable change in the gravitational field, we can synchronize this change with surface topography features like craters, reels, or mountains."
According to Zuber, the moon's gravitational field acts as a storm record of blows that have ever bombarded all Earth planetary bodies. This field also reveals evidence of the destruction of the lunar interior that extends to the deep bark and probably the mantle.
Ebb and Flow reveal that the density of the lunar mountain bark is significantly lower than the usual one, which is consistent with the data obtained during Apollo's final missions in the early 1970s. This suggests that lunar rock samples returned to Earth by Apollo astronauts are characteristic of global rather than regional processes.
GRAIL also found that the average thickness of the moon crust is about 6 to 12 miles (10 to 20 km) thinner than previously thought – between 21 and 27 miles (34 and 43 km).
"With this thickness of the Earth's crust, the volumetric composition of the moon is similar to Earth's," said Mark Victor, a GRAIL accomplice at the Globe de Paris Physics Institute. "This supports patterns where the Moon is extracted from earthly materials that were thrown out during a giant event at the beginning of the Solar System's history."
GRAIL also reveals the origin of a rocky contour on the moon surface, known as Oceanus Procellarum, or the ocean of storms. Early theories suggest that an asteroid impact creates the region. However, GRAIL has found evidence that the storm ocean is a rectangular region stretching about 1,600 miles (2,600 kilometers), which is actually the result of the formation of ancient decay valleys. Since the lunar surface here cooled and collapsed, it was withdrawing from its surroundings, creating large fractures similar to the cracks that formed in the mud until it dries up.
"The rectangular model of gravity anomalies is completely unexpected," said Jeff Andrews-Hanna, co-founder of GRAIL at the Colorado School of Mines in Colorado, Colorado and lead author. "Now we can clearly and completely see structures that have only been hinted at by superficial observations."
The end of the mission
GRAIL's mission ended with fuel depletion. The team decided to send the couple in a glamor of glory, deliberately pushing them to the moon's surface in the hope of revealing more about the moon's impact.
But before the GRAIL collision, one final experiment was completed. Fifty minutes before the impact on December 17, 2012, the two spacecraft launched their engines while their propellant was not exhausted, a maneuver designed to accurately determine the amount of fuel remaining in the tanks. This latest act helped NASA engineers validate computer models and improve fuel forecasts for future missions.
Since the Moon is about 380 miles from Earth, it would be a challenge to observe the influence of the grenade on our planet. Thus, three weeks before the planned impact, GRAIL researchers contacted NASA's LRD team, which was also studying the moon.
The LRO team was trying to take its orbit to prove GRAIL's burning death. When Ebb and Flow hit the surface, LRO was only about 100 miles (160 km) from the lunar surface. Since the place of the crash was in the shadows, the team had to wait to raise enough jets to be visible in sunlight. LRO tools reveal mercury and hydrogen in the track.
The resting areas of Ebb and Flow are relatively small, with a diameter of only 13 to 20 feet (4 to 6 meters). The material bursting with the blows created unusual dark patterns on the surface of the moon.
"The fresh shooters of the moon are usually bright, but they can be dark because the material on the spacecraft is mixed with discarding," said Marc Robinson, a member of the LRO team at the State University of Arizona.
Both shocks are located on the southern strip of an unnamed mountain and are about 2218 feet (2200 meters) wide. Ebb ran into the ground about 30 seconds before Flow, who set up his crater west and north of his twin.
Soon after the death of both of their craters were named in honor of the former astronaut and the head of the GRIL team, Sally Reid, who died in July 2012 as the mission was under way.
"Sally wanted to do her job, whether in exploring space, inspiring the next generation, or helping the GRAIL mission achieve great success today," Zuber said in a statement. "When we finish our lunar mission, we are proud to honor Sally Reid's contributions by calling that corner of the moon after it."
During its 15-month mission, GRAIL has improved our understanding of the moon by undertaking some of the steps necessary to bring people back to the moon's surface.
"As NASA moves forward with research endeavors, our missions in the lunar sciences will be the light buoys leading the way to future human activities," said Jim Greene, the then director of the Planetary Science Division at the Science Mission Directorate in Washington. declaration.