Moon craters preserve billions of years of history. Scientists learned about the conditions of our early solar system by studying the composition, size and distribution of these holes in the surface of the Moon, which were created long ago by collisions with asteroids.
But instead of studying the properties of these holes directly, a team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, decided to try something different. Use computer simulationThey “erase” thousands of craters from the surface of the Moon, as if turning back the clock 4.25 billion years before craters formed. They found that the positions of the north and south poles of the moon moved quite a bit during this time period.
With the moon shifting in this way from the effects of asteroid collisions, the location of the poles “roamed” 10 degrees in latitude (or 186 miles/300 kilometers), scientists reported Sept. 19. Planetary Science Journal. The north and south geographic poles are located where the axis of rotation of a celestial body intersects with its surface. In this case, the Moon’s axis of rotation, the imaginary line that passes through its center and revolves around it, remains the same with the displacement of the Moon’s body.
Information about the wanderings of the poles can be useful for understanding the evolution of the moon; Specifically, the state of a resource, such as water, at its surface. Scientists have found frozen water in shaded areas near the moon’s poles, but they don’t yet know how much water is there. If the Moon shifted the positions of its poles significantly towards a warmer and less shaded region, such as the equator, it is possible that some of the frozen water would have risen (changed from solid state to the gaseous state) from the surface, with less time for new water to accumulate at the new poles.
But, says Vishnu Viswanathan, a NASA Goddard scientist who led the study, “Based on the history of craters, polar wandering appears to have been moderate enough for water near the poles to remain in the shadows and enjoy stable conditions over billions of years.”
The phenomenon behind the changing poles is known as the True Polar Wander, which is what happens under the laws of physics for an object, in this case, the moon trying to keep itself spinning when encountering obstacles, such as changes in the way its mass is distributed.
When the asteroid hits the drilled mass, leaving depressions in the surface – or pockets of low mass – the moon reorients itself to bring those pockets toward the poles, bringing regions of higher mass toward the equator through Centrifugal force. It’s the same force that acts on the dough when the pizza maker throws it and spins it in the air to stretch it.
To determine the degree of lunar wandering, Viswanathan partnered with several scientists, including David E. Smith, principal investigator for the Lunar Orbiter Laser (LOLA) altimeter, aboard NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft. Smith became interested in using gravity data To find out how far the Moon’s poles have traveled after serving as Deputy Principal Investigator for NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Grill mapped the moon’s gravitational field in great detail before the mission ended in 2012.
“If you look at the moon with all these craters, you can see the ones in the gravitational field data,” said Smith, of the Massachusetts Institute of Technology in Cambridge. “I thought, ‘Why can’t I just take one of those pits and suck it in, and completely remove the signature?’ “
Smith, Viswanathan and their team worked with about 5,200 craters ranging in size from 12 miles (20 km) to 746 miles (1,200 km) wide. They made computer models that took coordinates and displayed all these craters from lunar topographic maps made with LOLA data and then found the corresponding gravity signatures – or pockets of higher or lower gravity – on the GRAIL gravity map. Then the scientists ran simulations that removed the gravitational signals for each one crater Sequentially by age, essentially, the Moon’s evolution is rolled back and the poles slowly moved back toward their ancient positions with each influence removed.
While other researchers studying polar wandering have removed craters from the record, they have removed only a few dozen of the largest. “People assumed the little pits were negligible,” Viswanathan said. “They are hardly mentioned individually, but collectively they have a huge impact.”
Viswanathan said his team is getting close to figuring out the true degree of polar wandering on the moon, but scientists still need to revise their estimates. They plan to erase more small pits from the moon And to remove other features, such as volcanic eruptionscould have contributed to changing the poles.
“There are a few things we haven’t taken into account yet, but one thing we wanted to point out is those little craters that people have been overlooking, they really matter, so that’s the main point here,” said Sander, a planetary scientist. Goddard who participated in the study.
David E. Smith et al., Contribution of small craters to lunar wandering, Planetary Science Journal (2022). DOI: 10.3847 / PSJ / ac8c39
NASA’s Goddard Space Flight Center
the quoteNASA study (2022, September 20) finds small craters add up to wandering poles on the Moon, retrieved September 20, 2022 from https://phys.org/news/2022-09-small-craters-poles-moon- nasa.html
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