History of collisions with tiny asteroids made our moon “wander” around its axis

(ORDO NEWS) — New data has shown how asteroids that crashed into the moon changed the position of its poles.

Over the past 4.25 billion years, asteroid impacts have caused the body of the Moon to “roam”, rolling about 10 degrees with respect to its axis of rotation.

This is a relatively small shift, meaning that any ice hidden in craters at the lunar poles is unlikely to be significantly impacted. In turn, this means that lunar exploration can continue accordingly in the future.

“Based on the history of crater formation on the Moon,” says planetary scientist Vishnu Vishwanathan of NASA’s Goddard Space Flight Center, “polar wandering appears to have been moderate enough. water at the poles remained in the shadow and was in stable conditions for billions of years.

Much of the history of the moon is written in its craters. Earth’s largest natural satellite is scarred by collisions spanning billions of years, carefully mapped and dated by lunar scientists. And these impacts changed the distribution of mass on the Moon, a measure that is directly related to gravity.

Thus, every time a piece of space rock crashes into the lunar surface, it changes the lunar gravity profile, even if only slightly. Together, over a very long time, this can change how an object moves and orients itself in space.

The empty space created by asteroid impacts causes the Moon to reorient itself, bringing these lower-mass holes closer to the poles. Meanwhile, higher concentrations of mass are attracted closer to the equator. Think about how the hammer thrower spins to exert centrifugal force on the hammer to throw it a greater distance.

Thanks to a NASA mission called the Gravity and Internal Organ Recovery Laboratory (GRAIL), we have an extremely detailed map of the Moon’s gravitational field; so detailed that you can see the effect of craters. This gave MIT planetary scientist David Smith the idea.

History of collisions with tiny asteroids made our moon wander around its axis
A map of the Moon showing how the GRAIL data relates to the distribution of impact craters

“If you look at the Moon with all these craters, you will see them in the gravitational field data,” explains Smith. “I thought, ‘Why can’t I just take one of these funnels and suck it out, completely removing the signature?’

Here’s what the team decided to do in an attempt to erase the craters. wider than 20 kilometers (12 miles) across. They identified nearly 5,200 craters and depressions, matched them to GRAIL’s gravity data, and then worked backwards to erase them.

They initially worked by hand before handing over the work to computers to virtually rewind the Moon’s data. story.

The impact of each individual crater was negligible. But there were many of them, and with each subtraction, the lunar poles returned to the position in which they were billions of years ago.

Combined, the gravitational effect of all these small craters was nearly equal to that of the South Pole-Aitken Basin, a colossal impact zone about 2,500 kilometers (1,550 miles) in diameter, nearly a quarter of the Moon’s surface.

“People thought small craters were insignificant,” says Viswanathan. “Individually they are small, but collectively they have a big impact.”

This is important: if the effect were large enough, it could push the polar regions of the moon towards the places where the craters are. illuminated by sunlight.

If that were to happen, any frozen volatiles harbored in the previously shaded crater floor would sublimate, leaving less ice (or even none at all) as a durable record. As scientists want to explore the poles to find these ice patches, it will have implications for future lunar exploration, including NASA’s upcoming Artemis crewed mission.

The team has shown that the effect is not large enough for this, which is a good thing. But there is still a lot of work to be done.

The end result of the analysis is impressive, but that’s not all. There are many craters on the Moon that are not within the parameters included by the team; they too would have had an influence, though perhaps less so.

In addition, the Moon has not always been as geologically calm as it is now. Volcanic activity may also have changed its gravity profile over time.

However, previous work has only focused on craters larger than 200 kilometers (125 miles) in diameter. This work, according to the team, shows that every little thing matters.

“There are a few things we haven’t accounted for yet,” says planetary scientist Sander Goossens of NASA Goddard Space. Flight Center, “but we wanted to point out one thing: those little craters that people have been neglecting actually matter, so that’s the point here.”


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