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Scientists Pin Down Timing of Lunar Dynamo’s Demise

A conventional compass would be of little use on the moon, which today lacks a global magnetic field. But the moon did produce a magnetic field billions of years ago, and it was likely even stronger than the Earth’s field today. Scientists believe that this lunar field, like Earth’s, was generated by a powerful dynamo — the churning of the moon’s core. At some point, this dynamo, and the magnetic field it generated, petered out.

Now scientists from MIT and elsewhere have pinned down the timing of the lunar dynamo’s end, to around 1 billion years ago. The findings appeared in the journal Science Advances.

The new timing rules out some theories for what drove the lunar dynamo in its later stages and favors one particular mechanism: core crystallization. As the moon’s inner iron core crystallized, the liquid core’s electrically charged fluid was buoyantly stirred, producing the dynamo.

“The magnetic field is this nebulous thing that pervades space, like an invisible force field,” says Benjamin Weiss, professor of earth, atmospheric, and planetary sciences at MIT. “We’ve shown that the dynamo that produced the moon’s magnetic field died somewhere between 1.5 and 1 billion years ago, and seems to have been powered in an Earth-like way.”

Weiss’ co-authors on the paper are co-lead authors Saied Mighani and Huapei Wang, as well as Caue Borlina and Claire Nichols of MIT, along with David Shuster of the University of California at Berkeley.

Over the past few years, Weiss’ group and others have discovered signs of a strong magnetic field, of around 100 microteslas, in lunar rocks as old as 4 billion years. For comparison, Earth’s magnetic field today is around 50 microteslas.

In 2017, Weiss’s group studied a sample collected from NASA’s Apollo project, and found traces of a much weaker magnetic field, below 10 microteslas, in a moon rock they determined to be about 2.5 billion years old. Their thinking at the time was that perhaps two mechanisms for the lunar dynamo were at play: The first could have generated a much stronger, earlier magnetic field around 4 billion years ago, before being replaced by a second, more long-lived mechanism that sustained a much weaker field, through to at least 2.5 billion years ago.

“There are several ideas for what mechanisms powered the lunar dynamo, and the question is, how do you figure out which one did it?” Weiss says. “It turns out all these power sources have different lifetimes. So if you could figure out when the dynamo turned off, then you could distinguish between the mechanisms that have been proposed for the lunar dynamo. That was the purpose of this new paper.”

Most of the magnetic studies lunar samples from the Apollo missions have been from ancient rocks, dating to about 3 billion to 4 billion years old. These are rocks that originally spewed out as lava onto a very young lunar surface, and as they cooled, their microscopic grains aligned in the direction of the moon’s magnetic field. Much of the moon’s surface is covered in such rocks, which have remained unchanged since, preserving a record of the ancient magnetic field.

However, lunar rocks whose magnetic histories began less than 3 billion years ago have been much harder to find because most lunar volcanism had ceased by this time.

“The past 3 billion years of lunar history has been a mystery because there’s almost no rock record of it,” Weiss says.

Nevertheless, he and his colleagues identified two samples of lunar rock, collected by astronauts during the Apollo missions, that appear to have suffered a massive impact about 1 billion years ago and as a result were melted and welded back together in such a way that their ancient magnetic record was all but erased.

The team took the samples back to the lab and first analyzed the orientation of each rock’s electrons, which Weiss describes as “little compasses” that either align in the direction of an existing magnetic field or appear in random orientations in the absence of one. For both samples, the team observed the latter: random configurations of electrons, suggesting that the rocks formed in an extremely weak to essentially zero magnetic field, of no more than 0.1 microteslas.

The team then determined the age of both samples using a radiometric dating technique that Weiss and Shuster were able to adapt for this study.

The team put the samples through a battery of tests to see whether they were indeed good magnetic recorders. In other words, once they were reheated by some massive impact, could they have still been sensitive enough to record even a weak magnetic field on the moon, if it existed?

To answer this, the researchers placed both samples in an oven and blasted them with high temperatures to effectively erase their magnetic record, then exposed the rocks to an artificially generated magnetic field in the laboratory as they cooled.

The results confirmed that the two samples were indeed reliable magnetic recorders and that the field strength they initially measured, of 0.1 microteslas, accurately represented the maximum possible value of the moon’s extremely weak magnetic field 1 billion years ago. Weiss says a field of 0.1 microteslas is so low that it’s likely the lunar dynamo ended by this time.

The new findings line up with the predicted lifetime of core crystallization, a proposed mechanism for the lunar dynamo that could have generated a weak and long-lived magnetic field in the later part of the moon’s history. Weiss says that prior to core crystallization, a mechanism known as precession may have powered a much stronger though shorter-lived dynamo. Precession is a phenomenon by which the solid outer shell of a body such as the moon, in close proximity to a much larger body such as the Earth, wobbles in response to the Earth’s gravity. This wobbling stirs up the fluid in the core, the way swishing a cup of coffee stirs up the liquid inside.

Around 4 billion years ago, the infant moon was likely much closer to the Earth than it is today, and much more susceptible to the planet’s gravitational effects. As the moon moved slowly away from the Earth, the effect of precession decreased, weakening the dynamo and the magnetic field in turn. Weiss says it’s likely that around 2.5 billion years ago, core crystallization became the dominant mechanism by which the lunar dynamo continued, producing a weaker magnetic field that continued to dissipate as the moon’s core eventually fully crystallized.

The group is looking next to measure the direction of the moon’s ancient magnetic field in hopes of gleaning more information about the moon’s evolution.

This research was supported, in part, by NASA.

Source: mit.edu

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Space

A “Meteorite” falls in Nigeria destroying more than 100 houses and leaving a huge crater

On the morning of Saturday 28 March 2020, a large meteorite crashed in Akure (Nigeria), destroying more than 100 houses and leaving a 21-meter crater on the ground. Experts from the Awbaowo University of Obafemi (Nigeria) denied the local police who initially claimed that a bomb explosion had created the 21-meter crater.

According to Nigerian sources, the explosion destroyed the Akure-OVO road and seriously damaged dozens of houses, from 50 to 100, as well as schools and churches.

It is interesting that initially the authorities denied the meteorite’s fall and claimed that the cause for the explosion was a truck with explosives, which was transported to a neighboring state. Ondo State Governor Rotimi Akeredolu said the blast was an accident.

Then the version changed and the truck was no longer just transporting explosives, but it was supposedly a terrorist act.

Now, a team of experts and scientists came to the conclusion that everything that happened was a fall of a large meteorite.

The blast that shook Akure, the state capital of Ondo, on Saturday, was caused by a giant cosmic rock, a team of experts concluded.

Led by Adepelumi Adekunle, a professor of geophysics and seismic engineering at Obafemi Avolovo University, the team said that the meteorite entered the atmosphere of our planet at a “43 degree angle”.

Adepelumi Adekunle’s report reads:

“My research team conducted a detailed analysis of the impact site. A round impact crater was discovered with a diameter of 21 m and a depth of 7.8 m, which indicates a natural phenomenon.

– It was found that water is oozing from the edges of the crater. Preliminary field studies of vibration, noise, seismicity, analysis of water, radioactivity, rocks and soil were carried out.

“Our findings suggest that the impact of the explosion covers a radius of 1 km from the vicinity of the crater.” No signs of fire or burning were found in the vicinity. “

“No signs of radioactive radiation were found within the crater and in the immediate vicinity of it. Field data indicate that a meteorite from the asteroid belt was moving at high speed from space, and fell at an angle of 43 degrees in the southwestern part of the country “

A local source said that after the incident, no one was missing and no one was killed. The most interesting thing in the report is the mention that “unusual stones and strange metal objects” were found inside the crater. So what actually fell in Nigeria – a meteorite or a UFO?

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Space

Something strange is happening with the interstellar comet 2I / Borisov

When astronomers see something in the Universe that at first glance seems to be one of a kind, this will certainly cause great excitement and attention.

This mysterious guest from the depths of space first attracted the attention of celestial observers at the end of August 2019, when it was officially discovered sweeping through the solar system along a trajectory indicating interstellar origin.

After analyzing the object, astronomers identified it as a comet called Comet 21 / Borisov, which is the first identified comet and the second observable interstellar alien after the infamous Oumuamua, who arrived here from another star.

NASA claims that they do not know where and when the comet began to move towards our Sun. Gravity of the Sun slightly deflects its trajectory, but cannot capture it due to the shape of the orbit and its high speed of about 160,934 km / h.

Hubble showed that the comet’s heart, a loose accumulation of ice and dust particles, was probably no more than 975 meters across, about the length of nine football fields.

Now, this month, astronomers have discovered that something strange is happening by checking the object.

In the next video, nemesis maturity explains what happens to this mysterious interstellar guest.

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Space

Hundreds of exoplanets with two suns discovered

Until recently, in search of inhabited exoplanets, binary star systems were completely undeservedly ignored. Exoplanets with two suns have long become familiar places where the events of science fiction novels and films are unfolding.

One of the most striking and well-known examples of this is the desert planet Tatooine, the birthplace of Anakin and Luke Skywalker in the famous Star Wars movie saga. But only in 2011, NASA scientists using the Kepler space telescope were able to provide clear evidence that such exoplanets that revolve around two stars at once really exist. The planet discovered then was called Kepler-16b.

Despite the impressive discovery, scientists continued to believe that such planetary systems are extremely rare due to the complex attraction of two suns at once. But this opinion turned out to be completely wrong, writes astrophysicist Paul M. Sutter in an article for Space.com. This was revealed as a result of a new analysis of millions of stars and the discovery of exoplanets that have been recorded and cataloged by the ESA space telescope since 2013.

In fact, there are only two scenarios in which planets cope with the complex gravitational forces of two stars. If the stars are located very far apart, the planet can rotate around one star – then the other will be visible from the surface of the planet as a brightly shining star in the sky. In another case, both stars are close to each other – then the planet rotates at a safe distance around its double sun, as if it were just one celestial body.
These seemingly unbelievable stellar constellations are likely to occur much more often than might be expected.

Researchers have discovered during their targeted search already 300 exoplanets that could “boast” of double suns. Until now, astronomical science has actually ignored binary stars to search for (inhabited) exoplanets, because scientists considered their occurrence extremely unlikely in principle. In the case of discovered 300 planets, it is most likely a question of constellations, in which binary stars were incorrectly interpreted by the telescope as single stars.

Sutter speaks of decades of scientific confusion and uncertainty: “Since we did not often pay attention to the search for planets in binary solar systems, we had little chance of finding them. We didn’t look for anything like that, therefore we didn’t find it. The researcher believes that the realization that such double suns are very common should definitely be considered when searching for new exoplanets.

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