Full Moon Has Magnetic Secret
Ponder this under tonight’s full moon. Scientists now say the moon once had a magnetic field stronger than Earth’s is now.
It’s a big surprise. How could the moon, much smaller than the Earth, have a strong magnetic field? Yet it did, a new analysis of Apollo moon rocks reveals, according to Benjamin Weiss, a professor of physics at MIT. In Science Magazine and other news outlets, he expressed his surprise that a body so small could generate this much power:
- Measurements of the intensity of the ancient lunar dynamo have shown that it was surprisingly intense and long-lived. (Science Magazine)
- It remains uncertain what might have powered this surprisingly intense lunar magnetic field. “It’s hard to understand how the moon’s magnetic field could be as strong as it seemed given how the moon has a very small core,” Weiss said. “The moon’s core is maybe one-fifth to one-seventh the radius of the moon, while Earth’s core is maybe one-half the planetary radius. This means the surface of the moon is much farther away from its core than you see with Earth. Since magnetic fields fall rapidly in strength with distance, it’s hard to understand how the moon could have had a magnetic field that was that strong all the way to its surface.” (Space.com)
- Q. Why is it so surprising that a lunar dynamo may have been so intense and long-lived? A. Both the strong intensity and long duration of lunar fields are surprising because of the moon’s small size. Convection, which is thought to power all known dynamos in the solar system today, is predicted to produce surface magnetic fields on the moon at least 10 times weaker than what we observe recorded in ancient lunar rocks. (PhysOrg)
This unexpectedly strong field, now detectable only in remnant magnetism in lunar rocks, is challenging current theories of how magnetic fields are created by convection-driven dynamos in liquid cores. Weiss said they are trying to think up “exotic” theories:
There are other more exotic mechanisms that scientists have suggested could have powered the lunar dynamo.
“One involves smacking the moon obliquely with large impacts from asteroids maybe a bunch of times,” Weiss said. “You could also use the fact that the moon’s spin wobbles over time, which is called precession, and it wobbled a lot more intensely in the past when it was closer to Earth, and that could also instill motion to power a dynamo. Both these mechanisms are not known in any planetary body today, and would represent new ways of generating magnetic fields.”
In science, it’s not good to dream up special cases to save a theory. Yet Weiss goes on: “Maybe there were multiple dynamo mechanisms operating at different times in lunar history,” he says, compounding the special pleading. It seems that the dynamo theory has some serious reckoning to do to fit the observations:
Much remains unknown about the moon’s magnetic field. “We still don’t know when the lunar dynamo turned off,” Weiss said. “There’s evidence it lasted until at least 3.3 billion years ago, and perhaps as long as 1.3 billion years ago, really pushing the limits of what we know can power the lunar dynamo.“
Those dates don’t come from the magnetic field signatures in the rocks, but rather from consensus ideas about the age of the moon. It would seem appropriate with this much surprise to consider alternative views. At CMI, for instance, Dr. D. Russell Humphreys analyzed lunar magnetization, and found that no dynamo is necessary to explain the field. The stronger-than-expected field is a problem for belief the moon is billions of years old, he showed. This is also true for Mercury, he wrote at CMI in 2012 based on results from the MESSENGER orbiter.
Other lunar mysteries
Lava-filled craters: Like Mercury, the moon has some craters with flat floors that appear to have been filled in with lava. Scientists publishing a paper in Icarus studied 170 craters with “anomalously shallow fractured floors” and concluded that they formed via magmatic intrusions followed by sills, indicating volcanic activity from deep inside near the surface in the past. This is not the same as volcanic activity caused by large impacts as hypothesized for the maria.
Dikes at depth: Geology published a paper about deep volcanic dikes, from 20 km down, evident in grabens on the lunar surface. “Such dike geometric properties are only plausible if a mechanically weak lunar lithosphere was under extension at the time of dike emplacement.”
Debris breakdown: Ejecta debris, including large rocks, breaks down faster than expected, according to another paper in Geology. “This result implies shorter rock survival times than predicted based on downward extrapolation of 100 m crater size-frequency distributions,” the scientists say, some from NASA and JPL.
Add this observational fact to the list of evidences for a young solar system. These observations are only a problem for the moyboys. One would expect an original magnetic field to decay rapidly, as it continues to do so for the Earth. Notice how the secular planetary scientists always reach for the favorite ad-hoc rescue device? (Impacts.) Not only are impacts unreproducible, they would have had to be finely tuned to achieve whatever effect is required to keep the moyboys from getting expelled from the science lab.