Science

Moon's Magnetic Field Lasted A Billion Years Longer Than We Thought

Moon's Magnetic Field Lasted A Billion Years Longer Than We Thought”

Researchers at mit and Rutgers University found that the ancient magnetic field of the moon was generated giant Dynamo, similar to the earth.

"Whenever we look at exoplanets or the moons of exoplanets that could be in the habitable zone, we can consider the magnetic field-as an important player in habitability". These rocks melted from the heat of such impacts and recrystallized in orientations determined by the moon's magnetic field.

Following its formation in the wake of a massive collision between Earth Mark I and a Mars-sized object about 4.5 billion years ago, the Moon also had molten guts that rolled and churned enough to give it a relatively strong magnetic field of up to 70 microteslas.

At that point, the moon's magnetic field was the same strength as Earth's is today - about 50 microtesla.

This means that the moon's magnetic field, which was once as strong as the Earth's, lasted a lot longer than scientists thought.

"The Earth's magnetic field is a shield that protects us from risky solar wind particles and ionizing radiation, so magnetic fields play a key role in the habitability of planets and, possibly, moons", said Sonia Tikoo, lead author of a study published online in Science Advances and an assistant professor in Rutgers' Department of Earth and Planetary Sciences. Earth's magnetic field protects its oceans and its life from risky radiation from the sun; the death of Mars' magnetic field could help explain why the Red Planet is now dry and apparently lifeless.

United States researchers from MIT, Rutgers University, and University of California, Berkeley, found a rock sample brought back by Apollo 15 astronauts had captured evidence of a magnetic field measuring about 5 microteslas.

Weiss and his colleagues analyzed one such rock, known as Apollo 15 sample 15498, which was originally collected on August 1, 1971, from the southern rim of the moon's Dune Crater.

A number of lunar rocks such as 15498 recorded the strength and direction of the moon's ancient magnetic field.

Dynamo - a device to generate electricity that uses magnetic field and a rotating coil inside of it.

The lunar rock Tikoo tested, which is about 1 billion to 2.5 billion years old, recorded 5 microtesla.

Other coauthors are from the University of California, Berkeley and Massachusetts Institute of Technology.

Instead of forming from volcanic lava early in the moon's history, 15498 was born from the heat of a cosmic impact much later, the researchers found. She slowly demagnetized the rock to reveal its original magnetization, heating it to 1,436 degrees Fahrenheit in a controlled atmosphere chamber at MIT to keep the heat from altering the rock. MIT and Rutgers scientists studied the sample to glean new insights about the ancient moon's magnetic field.

Testing that magnetism showed that in spite of the time that had passed, there was still a weak but non-zero field present.

The find implies the Moon must have had two mechanisms powering its dynamo - one in its youth, and something else that dragged on the generation of a magnetic field for a lot longer. "We can figure this out by knowing the lifetime of the lunar dynamo".

"We didn't think that small planetary bodies could generate magnetic fields for a very long time because they have smaller cores that would cool quickly and crystallize early in their lifetimes", Tikoo says. It's possible that planets and moons smaller than Earth might be able to shelter life.

'Because the rate of crystallization depends on the core composition, our finding may challenge what we think the lunar core is made of. This happens to be right around the time the moon's magnetic field strength dropped. The strength of this field dropped off about three billion years ago, but the question remained whether it vanished or if it became much weaker. "We think this process could have generated enough energy to explain the strong field period". First, the field was maintained by rotation of the metallic core. As the moon moved away from the Earth, its core likely sustained a low boil via a slow process of cooling over at least 1 billion years.



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