Evidence of 'oceans worth' of water in Earth's mantle detected

Schematic cross section of the Earth’s interior highlighting the transition zone layer (light blue, 410-660 km depth), which has an anomalously high water storage capacity. 

The study by Schmandt and Jacobsen used seismic waves to detect magma generated near the top of the lower mantle at about 700 km depth.

Dehydration melting at those conditions, also observed in the study’s high-pressure experiments, suggests the transition zone may be nearly saturated with H2O dissolved in high-pressure rock. 

Credit: Steve Jacobsen/Northwestern University

Researchers have found evidence of a potential "ocean's worth" of water deep beneath the United States.

Although not present in a familiar form, the building blocks of water are bound up in rock located deep in the Earth's mantle, and in quantities large enough to represent the largest water reservoir on the planet, according to the research.

For many years, scientists have attempted to establish exactly how much water may be cycling between the Earth's surface and interior reservoirs through the action of plate tectonics.

Northwestern University geophysicist Steve Jacobsen and University of New Mexico seismologist Brandon Schmandt have found deep pockets of magma around 400 miles beneath North America, a strong indicator of the presence of H₂O stored in the crystal structure of high-pressure minerals at these depths.

"The total H₂O content of the planet has long been among the most poorly constrained 'geochemical parameters' in Earth science. Our study has found evidence for widespread hydration of the mantle transition zone," says Jacobsen.

For at least 20 years geologists have known from laboratory experiments that the Earth's transition zone, a rocky layer of the Earth's mantle located between the lower mantle and upper mantle, at depths between 250 and 410 miles, can, in theory, hold about 1 percent of its total weight as H₂O, bound up in minerals called wadsleyite and ringwoodite.

However, as Schmandt explains, up until now it has been difficult to figure out whether that potential water reservoir is empty, as many have suggested, or not.

If there does turn out to be a substantial amount of H₂O in the transition zone, then recent laboratory experiments conducted by Jacobsen indicate there should be large quantities of what he calls "partial melt" in areas where mantle flows downward out of the zone.

This water-rich silicate melt is molten rock that occurs at grain boundaries between solid mineral crystals and may account for about 1 percent of the volume of rocks.

"Melting occurs because hydrated rocks are carried from the transition zone, where the rocks can hold lots of H₂O, downward into the lower mantle, where the rocks cannot hold as much H₂O."

"Melting is the way to get rid of the H₂O that won't fit in the crystal structure present in the lower mantle," says Jacobsen.

He adds:
"When a rock starts to melt, whatever H₂O is bound in the rock will go into the melt right away. So the melt would have much higher H₂O concentration than the remaining solid. We're not sure how it got there."

"Maybe it's been stuck there since early in Earth's history or maybe it's constantly being recycled by plate tectonics."

Seismic Waves
Melt strongly affects the speed of seismic waves, the acoustic-like waves of energy that travel through the Earth's layers as a result of an earthquake or explosion.

This is because stiff rocks, like the silicate-rich ones present in the mantle, propagate seismic waves very quickly.

According to Schmandt, if just a little melt, even 1 percent or less, is added between the crystal grains of such a rock it causes it to become less stiff, meaning that elastic waves propagate more slowly.

"We were able to analyse seismic waves from earthquakes to look for melt in the mantle just beneath the transition zone," says Schmandt.

Brandon Schmandt (University of New Mexico, left) and Steve Jacobsen (Northwestern University, right) combined seismic observations from the US-Array with laboratory experiments to detect dehydration melting of hydrous mantle material beneath North America at depths of 700-800 km. 

Credit: University of New Mexico/Northwestern University

"What we found beneath the U.S. is consistent with partial melt being present in areas of downward flow out of the transition zone."

"Without the presence of H₂O, it is very difficult to explain melting at these depths. This is a good hint that the transition zone H₂O reservoir is not empty, and even if it's only partially filled that could correspond to about the same mass of H₂O as in Earth's oceans," he adds.

Jacobsen and Schmandt hope that their findings, published in the June issue of the journal Science, will help other scientists to understand how the Earth formed and what its current composition and inner workings are, as well as establish how much water is trapped in mantle rock.

"I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades," says Jacobsen

Schematic representation of seismometers placed in the US-Array between 2004 and 2014 and used in the study by Schmandt and Jacobsen to detect dehydration melting at the top of the lower mantle beneath North America. 

Credit: NSF-Earthscope

Crystals of laboratory-grown hydrous ringwoodite, a high-pressure polymorph of olivine that is stable from about 520-660 km depth in the Earth’s mantle. 

The ringwoodite pictured here contains around one weight percent of H2O, similar to what was inferred in the seismic observations made by Schmandt and Jacobsen. 

Credit: Steve Jacobsen/Northwestern University

NuSTAR telescope takes observes core of supernova

Cassiopeia A is among the best-studied supernova remnants. 

This image blends data from NASA's Spitzer (red), Hubble (yellow), and Chandra (green and blue) observatories. 

Credit: NASA /JPL-Caltech /STScI /CXC /SAO

Astronomers have peered for the first time into the heart of an exploding star in the final minutes of its existence.

The feat by the high-energy X-ray satellite NuSTAR provides details of the physics of the core explosion inaccessible until now, says team member Steven Boggs of UC Berkeley.

NuSTAR mapped radioactive titanium in the Cassiopeia A supernova remnant, which has expanded outward and become visible from Earth since the central star exploded in 1671.

Astronomers for the first time have peered into the heart of an exploding star in the final minutes of its existence.

The feat is one of the primary goals of NASA's NuSTAR mission, launched in June 2012 to measure high-energy X-ray emissions from exploding stars, or supernovae, and black holes, including the massive black hole at the center of our Milky Way Galaxy.

The NuSTAR team reported in this week's issue of the journal Nature the first map of titanium thrown out from the core of a star that exploded in 1671.

That explosion produced the beautiful supernova remnant known as Cassiopeia A (Cas A).

The well-known supernova remnant has been photographed by many optical, infrared and X-ray telescopes in the past, but these revealed only how the star's debris collided in a shock wave with the surrounding gas and dust and heated it up.

NuSTAR has produced the first map of high-energy X-ray emissions from material created in the actual core of the exploding star: the radioactive isotope titanium-44, which was produced in the star's core as it collapsed to a neutron star or black hole.

The energy released in the core collapse supernova blew off the star's outer layers, and the debris from this explosion has been expanding outward ever since at 5,000 kilometers per second.

Steven Boggs

"This has been a holy grail observation for high energy astrophysics for decades," said coauthor and NuSTAR investigator Steven Boggs, UC Berkeley professor and chair of physics.

"For the first time we are able to image the radioactive emission in a supernova remnant, which lets us probe the fundamental physics of the nuclear explosion at the heart of the supernova like we have never been able to do before."

"Supernovae produce and eject into the cosmos most of the elements are important to life as we know it," said UC Berkeley professor of astronomy Alex Filippenko, who was not part of the NuSTAR team.

Alex Filippenko

"These results are exciting because for the first time we are getting information about the innards of these explosions, where the elements are actually produced."

Boggs says that the information will help astronomers build three-dimensional computer models of exploding stars, and eventually understand some of the mysterious characteristics of supernovae, such as jets of material ejected by some.

Previous observations of Cas A by the Chandra X-ray telescope, for example, showed jets of silicon emerging from the star.

Fiona Harrison

"Stars are spherical balls of gas, and so you might think that when they end their lives and explode, that explosion would look like a uniform ball expanding out with great power," said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology.

"Our new results show how the explosion's heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating."

More information: Study paper: dx.doi.org/10.1038/nature12997

Astrophysicists propose 'Planck star' are core of black holes

This artist's concept depicts a supermassive black hole at the center of a galaxy. 

The blue colour here represents radiation pouring out from material very close to the black hole. 

The grayish structure surrounding the black hole, called a torus, is made up of gas and dust. 

Credit: NASA/JPL-Caltech

Two astrophysics, Carlo Rovelli, Centre de Physique Theorique de Luminy and Francesca Vidotto, Radboud University Nijmegen, have uploaded a paper to the preprint server arXiv in which they suggest that a structure known as a Planck star exists at the center of black holes, rather than a singularity.

Carlo Rovelli

This would suggest, they note, that black holes at some point return all the information they have pulled in, to the universe.

The current thinking regarding black holes is that they have two very simple parts, an event horizon and a singularity.

Because a probe cannot be sent inside a black hole to see what is truly going on, researchers have to rely on theories.

The singularity theory suffers from what has come to be known as the "information paradox"—black holes appear to destroy information, which would seem to violate the rules of general relativity, because they follow rules of quantum mechanics instead.

This paradox has left deep thinking physicists such as Stephen Hawking uneasy—so much so that he and others have begun offering alternatives or amendments to existing theories. In this new effort, a pair of physicists suggest the idea of a Planck star.

Francesca Vidotto

The idea of a Planck star has its origins with an argument to the Big Bang theory, this other idea holds that when the inevitable Big Crunch comes, instead of forming a singularity, something just a little more tangible will result, something on the Planck scale.

And when that happens, a bounce will occur, causing the universe to expand again, and then to collapse again and so on forever back and forth.

Rovelli and Vidotto wonder why this couldn't be the case with black holes as well—instead of a singularity at its center, there could be a Planck structure, a star, which would allow for general relativity to come back into play.

If this were the case, then a black hole could slowly over time lose mass due to Hawking Radiation, as the black hole contracted, the Planck star inside would grow bigger as information was absorbed.

Eventually, the star would meet the event horizon and the black hole would dematerialise in an instant as all the information it had ever sucked in was cast out into the universe.

This new idea by Rovelli and Vidotto will undoubtedly undergo close scrutiny in the astrophysicist community likely culminating in debate amongst those who find the idea of a Planck star an answer to the information paradox and those who find the entire idea implausible.

More information: Planck stars, arXiv:1401.6562 [gr-qc] arxiv.org/abs/1401.6562

The Earth's Magnetic Field Is Wonky

The solution to a long-standing puzzle, why magnetic north sits off the coast of Canada, rather than at the North Pole, may have been found in the strange, lopsided nature of Earth's inner core.

The inner core is a ball of solid iron about 760 miles (1,220 kilometers) wide.

It is surrounded by a liquid outer core (mostly iron and nickel), a rocky, viscous mantle layer and a thin, solid crust.

As the inner core cools, crystallizing iron releases impurities, sending lighter molten material into the liquid outer core.

This upwelling, combined with the Earth's rotation, drives convection, forcing the molten metal into whirling vortices.

These vortices stretch and twist magnetic field lines, creating Earth’s magnetic field. Currently, the center of the field, called an axis, emerges in the Arctic Ocean west of Ellesmere Island, about 300 miles (500 kilometers) from the geographic North Pole.

In the last decade, seismic waves from earthquakes revealed the inner core looks like a navel orange, bulging slightly more on its western half.

Geoscientists recently explainedthe asymmetry by proposing a convective loop: The inner core might be crystallizing on one half and melting on the other.

Peter Olson and Renaud Deguen, geophysicists at Johns Hopkins University, set out to test this theory, called translational instability.

They ran numerical models simulating the forces that generate Earth’s magnetic field, and included a lopsided inner core.

Olson and Deguen found that adding inner-core asymmetry shifted magnetic north away from the center of the Earth, into the cooling hemisphere. Convection was stronger there, as was the magnetic field.

"The lopsided growth of the inner core makes convection in the outer core a little bit lopsided, and that then induces the geomagnetic field to have this lopsided or eccentric character too," Olson stated.

Olson and Deguen's research was detailed online July 1 in the journal Nature Geoscience.

Geophysicist Bruce Buffett said Olson and Deguen’s research is intriguing, but there are still questions about the underlying theory. "It's an interesting result, but we don't know for sure the inner core is translating.

The model does a good job at explaining some but not all of the features of the inner core," said Buffett, a professor at the University of California, Berkeley, who was not involved with the research.

Olson points out that his numerical model offers a real-world proof of the theory. Magnetic particles trapped and aligned in rocks reveal that the magnetic north pole wandered around the Western Hemisphere over the past 10,000 years, and circled the Eastern Hemisphere before that — a result mirrored by the numerical test.

Gathering a longer, more detailed record of the magnetic field's behavior, Olson said, could reveal whether the inner core acts as researchers predict.

"The key question for interesting ideas like translational instability is, 'Can we test it?'" Olson said. "What we're doing is proposing a test, and we think it's a good test because people can go out and look for eccentricity in the rock record and that will either confirm or shoot down this idea."

The Earth’s Core: An Enigma 1,800 Miles Below Our Feet

Geologists have long known that Earth’s core, some 1,800 miles beneath our feet, is a dense, chemically doped ball of iron roughly the size of Mars and every bit as alien. 

It’s a place where pressures bear down with the weight of 3.5 million atmospheres, like 3.5 million skies falling at once on your head, and where temperatures reach 10,000 degrees Fahrenheit — as hot as the surface of the Sun. 

It’s a place where the term “ironclad agreement” has no meaning, since iron can’t even agree with itself on what form to take. It’s a fluid, it’s a solid, it’s twisting and spiraling like liquid confetti.

Researchers have also known that Earth’s inner Martian makes its outer portions look and feel like home. The core’s heat helps animate the giant jigsaw puzzle of tectonic plates floating far above it, to build up mountains and gouge out seabeds. 

At the same time, the jostling of core iron generates Earth’ magnetic field, which blocks dangerous cosmic radiation, guides terrestrial wanderers and brightens northern skies with scarves of auroral lights.

Now it turns out that existing models of the core, for all their drama, may not be dramatic enough. Reporting recently in the journal Nature, Dario Alfè of University College London and his colleagues presented evidence that iron in the outer layers of the core is frittering away heat through the wasteful process called conduction at two to three times the rate of previous estimates. 

The theoretical consequences of this discrepancy are far-reaching. The scientists say something else must be going on in Earth’s depths to account for the missing thermal energy in their calculations. 

They and others offer these possibilities:

• The core holds a much bigger stash of radioactive material than anyone had suspected, and its decay is giving off heat.
• The iron of the innermost core is solidifying at a startlingly fast clip and releasing the latent heat of crystallization in the process.
• The chemical interactions among the iron alloys of the core and the rocky silicates of the overlying mantle are much fiercer and more energetic than previously believed.
• Or something novel and bizarre is going on, as yet undetermined.

“From what I can tell, people are excited” by the report, Dr. Alfè said. “They see there might be a new mechanism going on they didn’t think about before.”

Researchers elsewhere have discovered a host of other anomalies and surprises. They’ve found indications that the inner core is rotating slightly faster than the rest of the planet, although geologists disagree on the size of that rotational difference and on how, exactly, the core manages to resist being gravitationally locked to the surrounding mantle.

Miaki Ishii and her colleagues at Harvard have proposed that the core is more of a Matryoshka doll than standard two-part renderings would have it. 

Not only is there an outer core of liquid iron encircling a Moon-size inner core of solidified iron, Dr. Ishii said, but seismic data indicate that nested within the inner core is another distinct layer they call the innermost core: a structure some 375 miles in diameter that may well be almost pure iron, with other elements squeezed out. 

Against this giant jewel even Jules Verne’s middle-Earth mastodons and ichthyosaurs would be pretty thin gruel.

Core researchers acknowledge that their elusive subject can be challenging, and they might be tempted to throw tantrums save for the fact that the Earth does it for them. Most of what is known about the core comes from studying seismic waves generated by earthquakes.

As John Vidale of the University of Washington explained, most earthquakes originate in the upper 30 miles of the globe (as do many volcanoes), and no seismic source has been detected below 500 miles. But the quakes’ energy waves radiate across the planet, detectably passing through the core.

Granted, some temblors are more revealing than others. “I prefer deep earthquakes when I’m doing a study,” Dr. Ishii said. “The waves from deep earthquakes are typically sharper and cleaner.”

Read more of this article here: Earth’s Core - The Enigma 1,800 Miles Below Us

Jupiter's heart is dissolving

Even the mighty can lose heart. New calculations suggest that Jupiter's rocky core is dissolving like an antacid tablet plopped in water.

The work could help explain why its core appears smaller and its atmosphere richer in heavy elements than predicted.

Giant planets like Jupiter and Saturn are thought to have begun their lives as solid bodies of rock and ice. 

When they grew to about 10 times the mass of Earth, their gravity pulled in gas from their birth nebula, giving them thick atmospheres made mainly of hydrogen.

Curiously, some studies have suggested that Jupiter's core may weigh less than 10 Earths, while the core of its smaller sibling Saturn packs a bigger punch at 15 to 30 Earths. Last year, researchers led by Shu Lin Li of Peking University in China offered a grisly explanation – a rocky planet bigger than Earth slammed into Jupiter long ago, vaporising most of the giant planet's core.

That scenario could also explain another mystery – why Jupiter's atmosphere contains a higher fraction of heavy elements than the sun, whose composition is thought to mirror that of the nebula that gave birth to the solar system's planets.

Now Hugh Wilson and Burkhard Militzer of the University of California, Berkeley, suggest a competing – though no less macabre – explanation: Jupiter's core has gradually been dissolving since its formation 4.5 billion years ago.

Read More at Jupiter's heart is dissolving

Jupiter's Eroding Core: Large Exoplanets Have no Cores

A new study indicates that the hydrogen and helium gases that made Jupiter a gas giant are destroying the planet's very core, leading astronomers to believe that most massive extrasolar planets have no cores at all and changing the view scientists have long held of these distant worlds.

Jupiter has been called a gas giant because it consists mostly of hydrogen and helium surrounding a central core of iron, rock, and ice.

The core, which weighs roughly 10 times as much as Earth, is a small component in a planet that weighs 318 Earths.

These same gases are causing the solid rock in Jupiter's core to dissolve into liquid, the researchers said.

Planetary scientists Hugh Wilson and Burkhard Militzer of the University of California, Berkeley, performed quantum mechanical calculations on the outcome if magnesium oxide (MgO), which is a key ingredient in the rock of Jupiter's core, is submerged in a hydrogen-helium fluid at the planet's heart.

According to the researchers, with MgOs high solubility, the core's temperature, which is hotter than the sun at approximately 16,000 degrees Kelvin, will make the solid rock in Jupiter's core melt into liquid.

In a paper submitted to Physical Review Letters, the scientists said that although the exact rate of erosion is unknown, it is also calculated that the ice in the core also dissolves, so Jupiter's present core may not be as large as it was when the planet formed.

While the new findings are important, a planetary scientist, Jonathan Fortney, said the big question is whether the convection in Jupiter's interior is vigorous enough to dredge up dissolved core material and toss it into the hydrogen-helium envelope.

Fortney said that if this was the case, then Jupiter's core could be smaller today than it was at birth; if not, the dissolved rock and ice will simply remain at Jupiter's center although the boundary between the core and mantle may not be so distinct.

"I think we've made much more progress in the past year than people had made in the previous 20 years," said Fortney, adding that those calculations have implications far beyond Jupiter since many of the planets orbiting other stars are more massive than Jupiter, so their cores are even hotter.

"For these planets, core erosion would be faster," says Militzer, which could support the theory that gas giants several times heavier than Jupiter might be completely coreless.

In 2016, NASA's Juno spacecraft will start orbiting Jupiter, which could provide data on the planet's interior by measuring its gravitational field.

X-rays Unravels Mysteries of Earth’s Core

The window of opportunity for implementing radical changes to combat global warming may be as narrow as five years, warns a new report by the International Energy Agency. (Photo: NASA/Reuters)

The Earth's core, which is some 3,000km (1,900 miles) below sea level, will never be reached by scientists but a new experiment will attempt to unravel the mysterious processes at the center of the planet.

The European Synchrotron Radiation Facility's ID24 beam line will use X-ray beams to subject iron and other materials to extraordinary temperatures and pressures to recreate the extreme conditions at the center of the Earth as it investigate on the origin of the Earth's magnetic field, and how shock waves from earthquakes propagate through it.

The ID24 will utilize what is known as a diamond anvil cell - an established and remarkably simple means to create high pressures by confining tiny samples between the points of two carefully cut diamonds.

These samples are then compressed at a pressure millions of times higher than that on the Earth's surface after which high-power lasers are fired through the diamonds to heat them to higher than 10,000C.

The newly upgraded ID24 makes it possible to focus the X-rays to a much smaller spot than existing facilities to determine the precise composition and chemistry of the samples.

The X-rays are also able to monitor the reactions that happen as matter is heated and squeezed with a resolution several hundreds higher, and "snapshots" taken every millionth of a second.

The microsecond time resolution makes the ID24 unique, according to Sakura Pascarelli, chief scientist on the ID24 beam line.

Located in Grenoble, France, the ID24 is the first of eight beam lines at the ESRF that will be radically overhauled as part of the eight year 180 million euro project.

Memory Magic: What's in Store?

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