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Study uses 560-kilometer-deep earthquake to make elusive measurements of the Earth's layers –



Credit: Pixabay/CC0 Public Domain

A new study from a University of Chicago scientist suggests there may be a layer of surprisingly fluid rock ringing the Earth, at the very bottom of the upper mantle.

The finding was made by measuring the lingering movement registered by GPS sensors on islands in the wake of a deep earthquake in the Pacific Ocean near Fiji. Published Feb. 22 in Nature, the study demonstrates a new method to measure the fluidity of the Earth’s .


“Even though the mantle makes up the largest part of Earth, there’s still a lot we don’t know about it,” said Sunyoung Park, a geophysicist with the University of Chicago and the lead author on the study. “We think there’s a lot more we can learn by using these deep earthquakes as a way to probe these questions.”

Mantle mysteries

We still know surprisingly little about the Earth beneath our feet. The furthest anyone has managed to dig down is about seven and a half miles before the increasing heat literally melts the drill. Thus scientists have had to use clues like how seismic waves move to infer the different layers that make up the planet, including the crust, mantle, and core.

One thing that has stymied scientists is a precise measurement of how viscous the mantle layer is. The mantle is the layer below the crust. It’s made of rock, but at the intense temperature and pressures at that depth, the rock actually becomes viscous—flowing very slowly like honey or tar.

“We want to know exactly how fast the mantle flows, because that influences the evolution of the entire Earth—it affects how much heat the planet retains for how long, and how the Earth’s materials are cycled over time,” explained Park. “But our current understanding is very limited and includes a lot of assumptions.”

Park thought there might be a unique way to get a measurement of the mantle’s properties by studying the aftermath of very deep earthquakes.

Most of the earthquakes we hear about on the news are relatively shallow, originating in the top crust of the Earth. But occasionally, there are earthquakes that originate deep within the Earth—down to 450 miles below the surface. These earthquakes are not as well-studied as shallower ones, because they’re not as destructive to human settlements. But because they reach down into the mantle, Park thought they might offer a way to understand the behavior of the mantle.

Park and her colleagues looked at one particular such earthquake, which occurred off the coast of Fiji in 2018. The quake was magnitude 8.2, but it was so deep—350 miles (560 kilometers) down—that it did not cause any major damage or deaths.

However, when the scientists carefully analyzed the data from GPS sensors on several nearby islands, they found the Earth kept moving—after the was over.

The data revealed that in the months following the quake, the Earth was still moving, settling in the wake of the disturbance. Even years later, Tonga is still moving slowly down at a rate of about 1 centimeter per year.

“You can think of it like a jar of honey that slowly comes back to level after you dip a spoon in it—except this takes years instead of minutes,” said Park.

This is the first solid observation of the deformation following deep quakes; the phenomenon had been observed before for , but experts thought the effect would be too small to be observable for deep earthquakes.

Park and her colleagues used this observation to infer the viscosity of the mantle.

By examining how the Earth deformed over time, they found evidence of a layer about 50-miles thick that is less viscous (that is, “runnier”) than the rest of the mantle, sitting at the bottom of the upper mantle layer. They think this layer may extend around the entire globe.

This low-viscosity layer could explain some other observations by seismologists that suggested there are “stagnant” slabs of rock that don’t move very much, located around the same depth at the bottom of the upper mantle. “It has been hard to reproduce those features with models, but the weak layer found in this study makes it easier to do so,” Park said.

It also has implications for how Earth transports heat, cycles and mixes materials between the crust, core, and mantle over time.

“We’re really excited,” Park said. “There’s a lot more to find out with this technique.”

The other co-authors on the paper were Jean-Philippe Avouac and Zhongwen Zhan of California Institute of Technology and Adriano Gualandi of Italy’s National Institute of Geophysics and Volcanology.

More information:
Sunyoung Park, Weak upper-mantle base revealed by postseismic deformation of a deep earthquake, Nature (2023). DOI: 10.1038/s41586-022-05689-8.

Study uses 560-kilometer-deep earthquake to make elusive measurements of the Earth’s layers (2023, February 22)
retrieved 22 February 2023

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Scientists discover water inside tiny beads of glass on moon



Analysis of lunar soil samples shows spheres of glass hold water inside them, scientists have said.

Scientists say they have discovered water trapped inside tiny beads of glass scattered across the moon, suggesting a potential reservoir of this precious resource for future human activities on the lunar surface.

The moon was long believed to be dry, but over the last few decades, several missions have shown there is water both on the surface and trapped inside minerals.

Scientists said on Monday that an analysis of lunar soil samples retrieved in 2020 during China’s robotic Chang’e-5 mission showed that these spheres of glass – rock melted and cooled – bore within them water molecules formed through the action of the solar wind on the moon’s surface.


“The moon is constantly bombarded with impactors – for example micrometeoroids and large meteoroids – which produce impact glass beads during high-energy flash-heating events,” said planetary scientist Sen Hu of the Chinese Academy of Sciences’ Institute of Geology and Geophysics, a co-author of the study published in the journal Nature Geoscience.

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The solar wind is a stream of charged particles, primarily protons and electrons, emanating outward from the corona, the outermost part of the sun’s atmosphere, and permeating the solar system.

“Solar wind-derived water is produced by the reaction of solar hydrogen with oxygen present at the surface of the lunar glass beads,” Hu said, with these spheres then acting like a sponge for the water.

For future moon exploration, including potential long-term lunar bases staffed with astronauts, water is of vital importance not only as a drinking supply but as a fuel ingredient.

A screen shows footage of the spacecraft for the Chang’e-5 mission, during an event on China’s lunar exploration programme, at the National Astronomical Observatories of the Chinese Academy of Sciences in Beijing on January 18, 2021 [Tingshu Wang/Reuters]

‘Heat the glass beads to free the water’

The moon lacks the bodies of liquid water that are a hallmark of Earth. But its surface is thought to harbour a fairly substantial amount of water, for example in ice patches residing in permanently shadowed locales and trapped in minerals.

“Water is the most sought-after commodity for enabling sustainable exploration of planetary surfaces. Knowing how water is produced, stored and replenished near the lunar surface would be very useful for future explorers to extract and utilise it for exploration purposes,” Hu said.

Researchers see promise in obtaining water from the glass beads, perhaps through a heating process to release vapour that would then turn into liquid through condensation.

“We can simply heat these glass beads to free the water stored in them,” said Hu.

The capsule returning the soil samples to Earth landed in the northern Chinese region of Inner Mongolia.

About 3.8 pounds (1.7 kg) of soil were collected in the Chang’e-5 mission, with 32 glass beads – tens to hundreds of micrometres wide – examined in the study from the small amount of soil made available for this research, Hu said.

The glass beads were found to hold a water content of up to about 2,000 parts per million by weight. Hu said he believes that such impact glass beads are a common part of lunar soils, found globally and spread evenly.


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Webb Space Telescope found no atmosphere at faraway Earth-sized world, study says



This image shows an artist’s conception of what the surface of the exoplanet TRAPPIST-1f may look like, based on available data about its diameter, mass and distances from the host star.NASA/JPL-Caltech/The Associated Press

The Webb Space Telescope has found no evidence of an atmosphere at one of the seven rocky, Earth-sized planets orbiting another star.

Scientists said Monday that doesn’t bode well for the rest of the planets in this solar system, some of which are in the sweet spot for harbouring water and potentially life.

“This is not necessarily a bust” for the other planets, Massachusetts Institute of Technology astrophysicist Sara Seager, who wasn’t part of the study, said in an e-mail. “But we will have to wait and see.”

The Trappist solar system – a rarity with seven planets about the size of our own – has enticed astronomers ever since they spotted it just 40 light-years away. That’s close by cosmic standards; a light-year is about 9.6 trillion kilometres. Three of the seven planets are in their star’s habitable zone, making this star system even more alluring.


The NASA-led team reported little if any atmosphere exists at the innermost planet. Results were published Monday in the journal Nature.

The lack of an atmosphere would mean no water and no protection from cosmic rays, said lead researcher Thomas Greene of NASA’s Ames Research Center.

As for the other planets orbiting the small, feeble Trappist star, “I would have been more optimistic about the others” having atmospheres if this one had, Dr. Greene said in an e-mail.

If rocky planets orbiting ultracool red dwarf stars like this one “do turn out to be a bust, we will have to wait for Earths around sun-like stars, which could be a long wait,” said MIT’s Dr. Seager.

Because the Trappist system’s innermost planet is bombarded by solar radiation – four times as much as Earth gets from our sun – it’s possible that extra energy is why there’s no atmosphere, Dr. Greene noted. His team found temperatures there hitting 230 degrees Celsius on the side of the planet constantly facing its star.

By using Webb – the largest and most powerful telescope ever sent into space – the U.S. and French scientists were able to measure the change in brightness as the innermost planet moved behind its star and estimate how much infrared light was emitted from the planet.

The change in brightness was minuscule since the Trappist star is more than 1,000 times brighter than this planet, and so Webb’s detection of it “is itself a major milestone,” the European Space Agency said.

More observations are planned not only of this planet, but the others in the Trappist system. Looking at this particular planet in another wavelength could uncover an atmosphere much thinner than our own, although it seems unlikely it could survive, said Taylor Bell of the Bay Area Environmental Research Institute, who was part of the study.

Further research could still uncover an atmosphere of sorts, even if it’s not exactly like what’s seen on Earth, said Michael Gillon of the University of Liege in Belgium, who was part of the team that discovered the first three Trappist planets in 2016. He did not take part in the latest study.

“With rocky exoplanets, we are in uncharted territory” since scientists’ understanding is based on the four rocky planets of our solar system, Dr. Gillon said in an e-mail.

Launched in late 2021 to an observation post 1.6 million kilometres away, Webb is considered the successor to the Hubble Space Telescope, orbiting Earth for more than three decades.

In the past, Hubble and the Spitzer Space Telescope scoured the Trappist system for atmospheres, but without definitive results.

“It is just the beginning, and what we can learn with the inner planets is going to be different from what we can learn from the other ones,” MIT’s Julien de Wit, who was not involved in the study, said in an e-mail.

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.


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Large asteroid to zoom between Earth and Moon




A large asteroid will safely zoom between Earth and the Moon on Saturday, a once-in-a-decade event that will be used as a training exercise for planetary defence efforts, according to the European Space Agency.

The asteroid, named 2023 DZ2, is estimated to be 40 to 70 metres (130 to 230 feet) wide, roughly the size of the Parthenon, and big enough to wipe out a large city if it hit our planet.

At 19:49 GMT on Saturday it will come within a third of the distance from the Earth to the Moon, said Richard Moissl, the head of the ESA’s planetary defence office.


Though that is “very close”, there is nothing to worry about, he told AFP.

Small asteroids fly past every day, but one of this size coming so close to Earth only happens around once every 10 years, he added.

The asteroid will pass 175,000 kilometres (109,000 miles) from Earth at a speed of 28,000 kilometres per hour (17,400 miles per hour). The moon is roughly 385,000 kilometres away.

An observatory in La Palma, one of Spain’s Canary Islands, first spotted the asteroid on February 27.

Last week, the UN-endorsed International Asteroid Warning Network decided it would take advantage of the close look, carrying out a “rapid characterisation” of 2023 DZ2, Moissl said.

That means astronomers around the world will analyse the asteroid with a range of instruments such as spectrometers and radars.

The goal is to find out just how much we can learn about such an asteroid in only a week, Moissl said.

It will also serve as training for how the network “would react to a threat” possibly heading our way in the future, he added.

‘Scientifically interesting’ 

Moissl said preliminary data suggests 2023 DZ2 is “a scientifically interesting object”, indicating it could be a somewhat unusual type of asteroid. But he added that more data was needed to determine the asteroid’s composition.

The asteroid will again swing past Earth in 2026, but poses no threat of impact for at least the next 100 years — which is how far out its trajectory has been calculated.

Earlier this month a similarly sized asteroid, 2023 DW, was briefly given a one-in-432 chance of hitting Earth on Valentine’s Day 2046.

But further calculations ruled out any chance of an impact, which is what normally happens with newly discovered asteroids. Moissl said 2023 DW was now expected to miss Earth by some 4.3 million kilometres.

Even if such an asteroid was determined to be heading our way, Earth is no longer defenceless.

Last year, NASA’s DART spacecraft deliberately slammed into the pyramid-sized asteroid Dimorphos, significantly knocking it off course in the first such test of our planetary defences.


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