A study claims that rocks in the lunar mantle could be the answer to why the magnetic field of our moon satellite seems to have been present at one time.
While the moon may not be large enough for a magnetic field to surround it like that surrounding Earth, NASA astronauts returned rock samples to Earth from 50 years back to confirm this.
This is a mystery that has baffled planetary scientists for decades, but a new study, by experts from Brown University Providence, Rhode Island may have the answer.
They suggest that the early moon may have been able to generate intermittent, powerful magnetic fields as a result of giant rocks sinking through the liquid mantle during its first billion years — before it became a solid body.
The team stated that this would explain why some moon rock formations occurred under a magnetic field despite the lack of evidence to the contrary.
Study has shown that rock fragments from the moon’s early days could help explain why there is no magnetic field on our satellite.
The Apollo Program, 1968-72, saw rock fragments return to Earth, providing a lot of historical information on the moon’s past.
These discoveries have allowed planetary scientists to better understand the formation of this planet, what its composition is, and how it lost its magnetic field.
Analysis of the rocks revealed that some seemed to have formed in the presence of a strong magnetic field — one that rivalled Earth’s in strength — and others didn’t.
It was not clear for many decades how a half-moon-sized moon, with a size quarter of Earth’s, could create a strong magnet field.
Geoscientists found that huge rock formations that sank through the Moon’s crust could have caused strong magnetic fields by interior convection.
Researchers believe that the processes may have created intermittently strong magnetic field for the first billion year of the history of the moon.
Alexander Evans from Brown, co-author of the study, stated that “everything we have thought about how magnetic field are generated by planet cores tells me that a moon size body should not be capable to generate a force that is as strong as Earth.”
“But rather than thinking about how to continuously power strong magnetic fields over many billions, perhaps there is a way of getting a high intensity field intermittently.
“Our model illustrates how this can occur, and is consistent with our knowledge of the interior of the moon.”
The core dynamo is a method by which planetary bodies create magnetic fields. Slowly dissipating heat results in convection and molten metals within the core.
A magnetic field is created when electrically conductive materials are constantly churned. This process works in the same way that the Earth’s core creates the magnetic field.
Today’s moon doesn’t have a magnetic field. However, models of its core show that the moon was too small and lacking in convective forces to ever produce one.
Evans stated that the early moon’s mantle was not much cooler than its core. Because the heat from the core didn’t have a place to travel, Evans said there was no convection within the core.
But this new study, in partnership with Sonia Tikoo from Stanford University, shows how sinking rocks could have provided intermittent convective boosts.
This mystery has been a puzzle for planet scientists for over a century. However, experts at Brown University Providence, Rhode Island, have just released a study that may help them to solve it.
According to researchers, this story begins just a few thousand years after the birth of the Moon.
It is believed that the moon was covered in molten rocks at an early stage of its history. This happened within one billion years.
This vast magma ocean started to cool down and to solidify. Minerals like pryoxene and olivine, which were denser than liquid magma, began to sink to the bottom.
A crust formed when less dense minerals like anorthosite floated to top.
It took longer for the liquid magma to cool because it was high in both titanium and heat-producing elements such as thorium, radiation, and potassium.
The titanium layer that finally formed just under the crust was denser and more dense than any of the solidifying minerals.
Gravitational overturn refers to the gradual sinking of the mantle rock beneath, which is less dense than the titanium.
Evans and Tikoo created a model of the way that these titanium formations might sink, as well the possible effect on how they would reach the core of the moon.
Based on current moon composition and estimated viscosity in its mantle, they predict that formations will be broken into small blobs measuring 37 miles wide and then slowly sink for about a billion year.
Researchers discovered that each one of the blobs would eventually reach its bottom and give a significant jolt the core dynamo.
Perched below the Moon’s crust the titanium formations would be relatively cold in temperature. This is far more than what the core temperature estimates to be between 2,600-3,800 F.
The temperature mismatch between the core and the cold blobs after they had sunk would have led to increased core convection.
According to the team, this could explain why certain moon rocks were formed in a magnetic field, even though there is no evidence for one.
It would have been sufficient to generate a magnetic field on the moon’s surface that was as strong, if not stronger than Earth’s.
Evans stated that it can be compared to a drop of liquid hitting a hot pan.
“You can suddenly have a lot heat flux out of the core if something very cold touches it.” This causes the core’s temperature to rise, which in turn creates magnetic fields that are intermittently strong.
Researchers predicted that there could have been up to 100 such downwelling events in the first billion years of the moon’s existence. Each one of them could have created a strong magnetic field for a hundred years.
Evans claims that the intermittent magnetic model is responsible for both the strength and variability of magnetic signatures in Apollo rocks samples.
Geologists and planetary scientists have found out that certain rock samples carry strong magnetic signatures while others lack it.
‘This model is able to explain both the intensity and the variability we see in the Apollo samples — something that no other model has been able to do,’ Evans said.
“It gives us time limitations on the founding of this titan material, which allows us to get a better understanding of the moon’s early evolution.
Evans stated that the idea can also be tested. This implies there must be evidence for a weak magnetic background at the moon punctuated with high-strength phenomena.
This should be apparent in the Apollo collection. The team says that closer examination of the rocks will reveal the truth.
Evans says that although the Apollo samples’ strong magnetic signatures stood out, those with weaker signatures were less prominent.
This new idea would benefit from the presence of both weak and strong signatures, which might finally solve the Moon’s mysterious magnetic field.
These findings were published in Nature Astronomy.