In Science and Space: A new study shows that the moon’s poles have moved over billions of years due to asteroid impacts.
Researchers at his NASA Goddard Space Flight Center in Maryland found that when the moon was hit by an asteroid, its north and south poles moved about 10 degrees of latitude (equivalent to about 186 miles (300 kilometers)). I discovered that
Astronomers have long used lunar craters to illustrate the history of both the moon and the entire solar system. Because the distribution of destruction left by asteroid impacts paints a picture of the violent conditions seen in young solar systems. A new study turns those studies upside down by simulating the removal of thousands of craters and explaining the effects of even smaller craters, rewinding the moon’s history by 4.25 billion years.
The geographic poles of the moon are where its axis of rotation (the imaginary line around which the moon rotates) intersects the lunar surface. Simulations have shown that the axis of rotation remains fixed while the lunar body moves.
Polar migration is caused by a phenomenon called “true polar migration” that occurs when a rotating object encounters obstacles such as: B. A change in the distribution of its mass. In the case of the Moon, this happened when an asteroid impact carved a deep depression into the Moon’s surface, redistributing mass and leaving regions of lower mass.
The Moon realigned and moved these low-mass “pockets” toward the poles. As this happened, centrifugal force, “the same force that flattens dough and stretches it into a pizza crust,” moved the region of greater mass toward the moon’s equator. “If you look at the moon with all these craters, you can see them in the gravitational field data,” said David E. Smith, a Massachusetts Institute of Technology researcher and co-author of the new study. increase. “I thought, why can’t he of these craters blot one dry and completely remove the signature?”
Smith is the principal investigator of the Lunar Orbiter Laser Altimeter (LOLA) instrument on NASA’s Lunar Reconnaissance Orbiter, and has experience using gravity data to assess the shift of the Moon’s pole. Smith, Viswanathan, and their team used LOLA data to design a computer model to obtain the coordinates and latitudes of his 5,200 lunar craters ranging from 12 to 746 miles (19 to 1,200 km) in diameter. The team then matched impact craters to high- or low-gravity pockets found in lunar gravity maps created using NASA gravity recovery and internal laboratory data. They ran these simulations in reverse, removing these high- and low-gravity pockets and chronologically erasing the craters. This unwinding of the moon’s evolution has gradually moved the poles back to the positions they occupied billions of years ago.
Researchers have attempted a similar process before, but by focusing only on the Moon’s largest craters, these efforts failed to account for the net impact of smaller impacts on the Moon’s poles. “People thought the small crater was negligible,” Viswanathan said. “Individually they are insignificant, but together they have a big impact.”
The researchers plan to continue simulating the removal of small craters from the moon’s surface, removing features caused by volcanic eruptions in the lunar history. The team hopes that these additional steps will help paint a more complete picture of the Moon’s polar wander.