According to the study, an asteroid impact shifted the moon’s poles over billions of years

A new study shows that the poles of the moon shifted billions of years after an asteroid impact.

Astronomers have long used lunar craters to look at the history of the moon and the entire solar system, because the pattern of destruction left behind by asteroid impacts paints a picture of the violent conditions in the young solar system.

A new study published Monday in The Planetary Science Journal “turns the tables” on those studies, simulating the removal of thousands of craters and also taking into account the impact of smaller craters, pushing the moon’s history back 4.25 billion years.

Researchers based at NASA’s Goddard Space Flight Center in Maryland found that when the moon collided with asteroids, its north and south poles wandered about 10 degrees of latitude, or about 300 kilometers.

The Moon’s geographic poles are located where its axis of rotation—the imaginary line around which it rotates—crosses the surface of the Moon. The simulation showed that the axis of rotation remained fixed during the movement of the lunar body.

The discovery could shed light on the evolution of Earth’s natural satellite and help researchers find water and other resources that could be used for future manned space missions. Scientists have found frozen water in the cold, dark regions at the moon’s poles, but how much water is there is a mystery.

By understanding how and where the poles moved, researchers can determine how much of the frozen water turned directly from solid ice to gas—a process called sublimation. An extreme shift in the location of the Moon’s poles—especially toward hotter, less cloudy regions of the Moon—would cause water to sublimate rapidly and be lost to space, giving less time for new water to accumulate at the poles.

Asteroid collisions shifted the poles of the moon
This view of the moon’s cratered south pole was seen by NASA’s Clementine spacecraft in 1996 (Image: NASA/JPL/USGS)

“Based on the lunar cratering history, the polar shift appears to have been moderate enough that water near the poles remained in the shadow and enjoyed stable conditions for billions of years,” said NASA researcher Vishnu Viswanathan. Studying the Moon’s Wandering Poles, the statement said.

The pole shift is caused by a phenomenon called “true polar drift”, which occurs when a rotating object encounters obstacles such as a change in its mass distribution. In the case of the Moon, this occurred when an asteroid impact carved out deep depressions in the Moon’s surface, redistributing the mass and leaving lower mass regions.

The Moon has moved and these low-mass “pockets” have moved poleward. When that happened, centrifugal force—the same force that flattens and stretches dough on a pizza crust—pulled the high-mass regions toward the moon’s equator.

“If you look at a moon with all these craters, you can see them in the gravitational field data,” said David E. Smith, a researcher at the Massachusetts Institute of Technology and co-author of the new study.

“I thought to myself, ‘Why can’t I just take one of these craters, pull it out, and completely remove the signature?’ Smith is the principal investigator for the Lunar Orbiter Laser Altimeter (LOLA) instrument on NASA’s Lunar Reconnaissance Orbiter and has experience using gravity data to estimate the motion of the Moon’s poles.

Smith, Viswanathan and their team used the LOLA data to create computer models that obtained the coordinates and widths of 5,200 lunar craters ranging from 19 to 1,200 km in diameter. Next, the team matched the impact craters with pockets of higher or lower gravity found in a gravity map of the moon created using data from NASA’s Gravity and Interior Recovery Laboratory.

1663730853 880 Asteroid impact shifted the poles of the Moon
A close-up view of many lunar craters (Image: NASA)

They ran these simulations backwards, removing these high- and low-gravity pockets and thereby deleting the craters in order of their age. This reversal of the Moon’s evolution has returned the poles to the positions they occupied billions of years ago.

Researchers have tried a similar process before, but by focusing only on the moon’s largest craters, those efforts failed to account for the net effect of smaller impacts on the moon’s poles. “People assume that small craters are insignificant,” Viswanathan said. “Individually they are insignificant, but collectively they have a great effect.” »

The researchers will continue to simulate the removal of small craters from the lunar surface and plan to remove features caused by volcanic eruptions in the moon’s history. The team hopes these additional steps will help paint a more complete picture of the polar pilgrimage to the Moon.

with space information

Feature image: Marcelo Zurita/Netcost-Security

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