What Scientists Found After Sifting Through Dust In The Solar System

Just as dust gathers in corners and along bookshelves in our homes, dust piles up in space too. But when the dust settles in the solar system, it’s often in rings. Several dust rings circle the Sun. The rings trace the orbits of planets, whose gravity tugs dust into place around the Sun, as it drifts by on its way to the center of the solar system.

The dust consists of crushed-up remains from the formation of the solar system, some 4.6 billion years ago — rubble from asteroid collisions or crumbs from blazing comets. Dust is dispersed throughout the entire solar system, but it collects at grainy rings overlying the orbits of Earth and Venus, rings that can be seen with telescopes on Earth. By studying this dust — what it’s made of, where it comes from, and how it moves through space — scientists seek clues to understanding the birth of planets and the composition of all that we see in the solar system.

Two recent studies report new discoveries of dust rings in the inner solar system. One study uses NASA data to outline evidence for a dust ring around the Sun at Mercury’s orbit. A second study from NASA identifies the likely source of the dust ring at Venus’ orbit: a group of never-before-detected asteroids co-orbiting with the planet.

“It’s not every day you get to discover something new in the inner solar system,” said Marc Kuchner, an author on the Venus study and astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This is right in our neighborhood.”

Another Ring Around the Sun

Guillermo Stenborg and Russell Howard, both solar scientists at the Naval Research Laboratory in Washington, D.C., did not set out to find a dust ring. “We found it by chance,” Stenborg said, laughing. The scientists summarized their findings in a paper published in The Astrophysical Journal on Nov. 21, 2018.

They describe evidence of a fine haze of cosmic dust over Mercury’s orbit, forming a ring some 9.3 million miles wide. Mercury — 3,030 miles wide, just big enough for the continental United States to stretch across — wades through this vast dust trail as it circles the Sun.

Ironically, the two scientists stumbled upon the dust ring while searching for evidence of a dust-free region close to the Sun. At some distance from the Sun, according to a decades-old prediction, the star’s mighty heat should vaporize dust, sweeping clean an entire stretch of space. Knowing where this boundary is can tell scientists about the composition of the dust itself, and hint at how planets formed in the young solar system.

So far, no evidence has been found of dust-free space, but that’s partly because it would be difficult to detect from Earth. No matter how scientists look from Earth, all the dust in between us and the Sun gets in the way, tricking them into thinking perhaps space near the Sun is dustier than it really is.

Stenborg and Howard figured they could work around this problem by building a model based on pictures of interplanetary space from NASA’s STEREO satellite — short for Solar and Terrestrial Relations Observatory.

Ultimately, the two wanted to test their new model in preparation for NASA’s Parker Solar Probe, which is currently flying a highly elliptic orbit around the Sun, swinging closer and closer to the star over the next seven years. They wanted to apply their technique to the images Parker will send back to Earth and see how dust near the Sun behaves.

Scientists have never worked with data collected in this unexplored territory, so close to the Sun. Models like Stenborg and Howard’s provide crucial context for understanding Parker Solar Probe’s observations, as well as hinting at what kind of space environment the spacecraft will find itself in — sooty or sparkling clean.

Two kinds of light show up in STEREO images: light from the Sun’s blazing outer atmosphere — called the corona — and light reflected off all the dust floating through space. The sunlight reflected off this dust, which slowly orbits the Sun, is about 100 times brighter than coronal light.

“We’re not really dust people,” said Howard, who is also the lead scientist for the cameras on STEREO and Parker Solar Probe that take pictures of the corona. “The dust close to the Sun just shows up in our observations, and generally, we have thrown it away.” Solar scientists like Howard — who study solar activity for purposes such as forecasting imminent space weather, including giant explosions of solar material that the Sun can sometimes send our way — have spent years developing techniques to remove the effect of this dust. Only after removing light contamination from dust can they clearly see what the corona is doing.

The two scientists built their model as a tool for others to get rid of the pesky dust in STEREO — and eventually Parker Solar Probe — images, but the prediction of dust-free space lingered in the back of their minds. If they could devise a way of separating the two kinds of light and isolate the dust-shine, they could figure out how much dust was really there. Finding that all the light in an image came from the corona alone, for example, could indicate they’d found dust-free space at last.

Mercury’s dust ring was a lucky find, a side discovery Stenborg and Howard made while they were working on their model. When they used their new technique on the STEREO images, they noticed a pattern of enhanced brightness along Mercury’s orbit — more dust, that is — in the light they’d otherwise planned to discard.

“It wasn’t an isolated thing,” Howard said. “All around the Sun, regardless of the spacecraft’s position, we could see the same five percent increase in dust brightness, or density. That said something was there, and it’s something that extends all around the Sun.”

Scientists never considered that a ring might exist along Mercury’s orbit, which is maybe why it’s gone undetected until now, Stenborg said. “People thought that Mercury, unlike Earth or Venus, is too small and too close to the Sun to capture a dust ring,” he said. “They expected that the solar wind and magnetic forces from the Sun would blow any excess dust at Mercury’s orbit away.”

With an unexpected discovery and sensitive new tool under their belt, the researchers are still interested in the dust-free zone. As Parker Solar Probe continues its exploration of the corona, their model can help others reveal any other dust bunnies lurking near the Sun.

Asteroids Hiding in Venus’ Orbit

This isn’t the first time scientists have found a dust ring in the inner solar system. Twenty-five years ago, scientists discovered that Earth orbits the Sun within a giant ring of dust. Others uncovered a similar ring near Venus’ orbit, first using archival data from the German-American Helios space probes in 2007, and then confirming it in 2013, with STEREO data.

Since then, scientists determined the dust ring in Earth’s orbit comes largely from the asteroid belt, the vast, doughnut-shaped region between Mars and Jupiter where most of the solar system’s asteroids live. These rocky asteroids constantly crash against each other, sloughing dust that drifts deeper into the Sun’s gravity, unless Earth’s gravity pulls the dust aside, into our planet’s orbit.

At first, it seemed likely that Venus’ dust ring formed like Earth’s, from dust produced elsewhere in the solar system. But when Goddard astrophysicist Petr Pokorny modeled dust spiraling toward the Sun from the asteroid belt, his simulations produced a ring that matched observations of Earth’s ring — but not Venus’.

This discrepancy made him wonder if not the asteroid belt, where else does the dust in Venus’ orbit come from? After a series of simulations, Pokorny and his research partner Marc Kuchner hypothesized it comes from a group of never-before-detected asteroids that orbit the Sun alongside Venus. They published their work in The Astrophysical Journal Letters on March 12, 2019.

“I think the most exciting thing about this result is it suggests a new population of asteroids that probably holds clues to how the solar system formed,” Kuchner said. If Pokorny and Kuchner can observe them, this family of asteroids could shed light on Earth and Venus’ early histories. Viewed with the right tools, the asteroids could also unlock clues to the chemical diversity of the solar system.

Because it’s dispersed over a larger orbit, Venus’ dust ring is much larger than the newly detected ring at Mercury’s. About 16 million miles from top to bottom and 6 million miles wide, the ring is littered with dust whose largest grains are roughly the size of those in coarse sandpaper. It’s about 10 percent denser with dust than surrounding space. Still, it’s diffuse — pack all the dust in the ring together, and all you’d get is an asteroid two miles across.

Using a dozen different modeling tools to simulate how dust moves around the solar system, Pokorny modeled all the dust sources he could think of, looking for a simulated Venus ring that matched the observations. The list of all the sources he tried sounds like a roll call of all the rocky objects in the solar system: Main Belt asteroids, Oort Cloud comets, Halley-type comets, Jupiter-family comets, recent collisions in the asteroid belt.

“But none of them worked,” Kuchner said. “So, we started making up our own sources of dust.”

Perhaps, the two scientists thought, the dust came from asteroids much closer to Venus than the asteroid belt. There could be a group of asteroids co-orbiting the Sun with Venus — meaning they share Venus’ orbit, but stay far away from the planet, often on the other side of the Sun. Pokorny and Kuchner reasoned a group of asteroids in Venus’ orbit could have gone undetected until now because it’s difficult to point earthbound telescopes in that direction, so close to the Sun, without light interference from the Sun.

Co-orbiting asteroids are an example of what’s called a resonance, an orbital pattern that locks different orbits together, depending on how their gravitational influences meet. Pokorny and Kuchner modeled many potential resonances: asteroids that circle the Sun twice for every three of Venus’ orbits, for example, or nine times for Venus’ ten, and one for one. Of all the possibilities, one group alone produced a realistic simulation of the Venus dust ring: a pack of asteroids that occupies Venus’s orbit, matching Venus’ trips around the Sun one for one.

But the scientists couldn’t just call it a day after finding a hypothetical solution that worked. “We thought we’d discovered this population of asteroids, but then had to prove it and show it works,” Pokorny said. “We got excited, but then you realize, ‘Oh, there’s so much work to do.'”

They needed to show that the very existence of the asteroids makes sense in the solar system. It would be unlikely, they realized, that asteroids in these special, circular orbits near Venus arrived there from somewhere else like the asteroid belt. Their hypothesis would make more sense if the asteroids had been there since the very beginning of the solar system.

The scientists built another model, this time starting with a throng of 10,000 asteroids neighboring Venus. They let the simulation fast forward through 4.5 billion years of solar system history, incorporating all the gravitational effects from each of the planets. When the model reached present-day, about 800 of their test asteroids survived the test of time.

Pokorny considers this an optimistic survival rate. It indicates that asteroids could have formed near Venus’ orbit in the chaos of the early solar system, and some could remain there today, feeding the dust ring nearby.

The next step is actually pinning down and observing the elusive asteroids. “If there’s something there, we should be able to find it,” Pokorny said. Their existence could be verified with space-based telescopes like Hubble, or perhaps interplanetary space-imagers similar to STEREO’s. Then, the scientists will have more questions to answer: How many of them are there, and how big are they? Are they continuously shedding dust, or was there just one break-up event?

Dust Rings Around Other Stars

The dust rings that Mercury and Venus shepherd are just a planet or two away, but scientists have spotted many other dust rings in distant star systems. Vast dust rings can be easier to spot than exoplanets, and could be used to infer the existence of otherwise hidden planets, and even their orbital properties.

But interpreting extrasolar dust rings isn’t straightforward. “In order to model and accurately read the dust rings around other stars, we first have to understand the physics of the dust in our own backyard,” Kuchner said. By studying neighboring dust rings at Mercury, Venus and Earth, where dust traces out the enduring effects of gravity in the solar system, scientists can develop techniques for reading between the dust rings both near and far.

Researchers Uncover Additional Evidence For Massive Solar Storms

Our planet is constantly being bombarded by cosmic particles. However, at times the stream of particles is particularly strong when a solar storm sweeps past. Solar storms are made up of high-energy particles unleashed from the sun by explosions on the star’s surface.

For the past 70 years, researchers have studied these solar storms by direct instrumental observations, which has led to an understanding of how they can pose a risk to the electrical grid, various communication systems, satellites and air traffic. Two examples of severe solar storms in modern times that caused extensive power cuts took place in Quebec, Canada (1989) and Malmö, Sweden (2003).

Now, an increasing amount of research indicates that solar storms can be even more powerful than measurements have shown so far via direct observations.

The researchers behind the new, international study led by researchers from Lund University have used drilled samples of ice, or ice cores, to find clues about previous solar storms. The cores come from Greenland and contain ice formed over the past about 100,000 years. The material contains evidence of a very powerful solar storm that occurred in 660 BCE.

“If that solar storm had occurred today, it could have had severe effects on our high-tech society,” says Raimund Muscheler, professor of geology at Lund University.

The new study means that a third known case of a massive solar storm dating back in time has been discovered via indirect observations in nature’s own archive. Raimund Muscheler also took part in research that confirmed the existence of two other massive solar storms, using both ice cores and the annual growth rings of old trees. These storms took place in 775 and 994 CE.

Raimund Muscheler points out that, even though these massive solar storms are rare, the new discovery shows that they are a naturally recurring effect of solar activity.

“That’s why we must increase society’s protection again solar storms,” he says.

Today’s risk assessment is largely based on direct observations made over the past 70 years, but Raimund Muscheler suggests that there is a need for a reassessment in view of the three massive solar storms that have now been discovered. He argues that there is a need for greater awareness of the possibility of very strong solar storms and the vulnerability of our society.

“Our research suggests that the risks are currently underestimated. We need to be better prepared,” concludes Raimund Muscheler.

Solar Mystery Starts To Unravel As NASA Detects ‘Tadpole’ Jets Coming From Sun’s Surface

One of the biggest mysteries of the Sun is why its upper atmosphere—also known as the corona—is over 200 times hotter than its surface. For some unknown reason, this region that extends millions of miles into space is superheated—while the surface temperature hovers around 5,500 degree Celsius, the corona can reach two million degrees Celsius.

In a study published in Nature Astronomy, scientists with NASA are now edging closer to understanding this weird phenomenon.

While analyzing data taken by one of the space agency’s solar observation satellites, researchers discovered jets emerging from sunspots and shooting up to 3,000 miles into the inner corona. The jets had bulky heads and slim tails, so they looked like tadpoles swimming through the layers of the Sun.

Sunspots are regions that temporarily appear on the surface of the Sun. They are much cooler than the surrounding areas and are highly magnetized.

Previously, there were two main hypotheses about what was heating the Sun’s corona. The first relates to nanoflares, where explosions caused by the reconnection of magnetic lines release energy into the atmosphere, heating it in the process. The second involves electromagnetic waves, with charged particles being pushed into the Sun’s atmosphere. The tadpole discovery adds a third possibility to the mix.

Scientists found the tadpoles were made up entirely of plasma—the fourth state of matter, consisting of electrically conducting material made up of charged particles. The tadpoles (also known as ‘pseudo shocks’) may help heat up the Sun’s corona at specific times in its 11 year cycle—specifically during the solar maximum, when there is increased activity on the Sun’s surface.

The pseudo-shocks are thought to occur when magnetic field lines become tangled and produce explosions. This often happens around sunspots, but may well take place in other magnetized regions of space.

Computer simulations showed that the tadpoles could carry enough energy to heat the inner corona.

“We were looking for waves and plasma ejecta, but instead, we noticed these dynamical pseudo-shocks, like disconnected plasma jets, that are not like real shocks but highly energetic to fulfill Sun’s radiative losses,” lead author Abhishek Srivastava, from Indian Institute of Technology, said in a statement.

The Sun is currently coming to the end of its latest cycle—known as sunspot cycle 24—and will enter the next one at some point this year. As the new cycle begins, sunspot activity will begin to increase before reaching a peak, known as the solar maximum—currently expected to be around 2024.

Previously, scientists suggested that sunspot cycle 25 could be weaker than the current cycle, potentially meaning a period of global cooling could ensue. However, this has largely been ruled out, with a team of scientists in India recently predicting that the next solar cycle could be even stronger than the current one.

In their paper published in Nature Astronomy, the authors said: “We conclude that near-Earth and inter-planetary space environmental conditions and solar radiative forcing of climate over sunspot cycle 25 (i.e., the next decade) will likely be similar or marginally more extreme relative to what has been observed during the past decade over the current solar cycle.”

LOFAR Radio Telescope Reveals Secrets Of Solar Storms

An international team of scientists led by a researcher from Trinity College Dublin and University of Helsinki announced a major discovery on the very nature of solar storms in the journal Nature Astronomy.

The team showed that solar storms can accelerate particles simultaneously in several locations by combining data from the Low Frequency Array, LOFAR, with images from NASA, NOAA and ESA spacecraft.

The sun is the closest star to Earth, and like many stars, it is far from quiet. Sunspots many times the size of Earth can appear on its surface and store enormous reservoirs of energy. And it is within these regions that huge explosions called solar storms occur. Solar storms are spectacular eruptions of billions of tonnes of hot gas traveling at millions of kilometres an hour. The Nature Astronomy paper reports on a particularly large solar storm that occured on September 10, 2017, soon after the LOFAR station in Ireland came online.

How to predict space weather

“Our results are very exciting, as they give us an amazingly detailed insight into how solar storms propagate away from the sun and where they accelerate fast particles with speeds close to the speed of light,” says Dr. Diana Morosan, the lead author on the publication, and affiliated with Trinity College Dublin and the University of Helsinki.

These results may in the future help researchers to produce more accurate forecasts of solar radio bursts and determine how solar storms impact the Earth—they can produce beautiful displays of the aurora, but they can also cause problems with communication and navigation systems and power grids. Society is now even more dependent on technology, and solar storms have the potential to cause significant effects on their performance.

In 1859, the largest solar storm ever observed – the so-called Carrington Event – occurred. Within hours, it generated displays of aurora as far south as Italy and Cuba and caused interruptions in early telegraph systems in Europe and the U.S.

During a 2003 event, transformers in South Africa were damaged, and Swedish air traffic control systems were closed down in 2015 for more than an hour due to effects associated with a solar storm. More than 50 satellites reported problems. More recently, emergency response communications were interrupted during hurricane season in September 2017 in the Caribbean.

“We used data from the Low Frequency Array, LOFAR, together with images from NASA, NOAA and ESA spacecraft to show where solar storms accelerate fast particles,” says Morosan.

Spacecraft Measurements Reveal Mechanism Of Solar Wind Heating

Queen Mary University of London has led a study which describes the first direct measurement of how energy is transferred from the chaotic electromagnetic fields in space to the particles that make up the solar wind, leading to the heating of interplanetary space.

The study, published in Nature Communications and carried out with University of Arizona and the University of Iowa, shows that a process known as Landau damping is responsible for transferring energy from the electromagnetic plasma turbulence in space to electrons in the solar wind, causing their energisation.

This process, named after the Nobel-prize winning physicist Lev Landau (1908-1968), occurs when a wave travels through a plasma and the plasma particles that are travelling at a similar speed absorb this energy, leading to a reduction of energy (damping) of the wave.

Although this process had been measured in some simple situations previously, it was not known whether it would still operate in the highly turbulent and complex plasmas occurring naturally in space, or whether there would be a different process entirely.

All across the universe, matter is in an energised plasma state at far higher temperatures than expected. For example, the solar corona is hundreds of times hotter than the surface of the Sun, a mystery which scientists are still trying to understand.

It is also vital to understand the heating of many other astrophysical plasmas, such as the interstellar medium and the disks of plasma surrounding black holes, in order to explain some of the extreme behaviour displayed in these environments.

Being able to make direct measurements of the plasma energisation mechanisms in action in the solar wind (as shown in this paper for the first time) will help scientists to understand numerous open questions, such as these, about the universe.

The researchers discovered this using new high-resolution measurements from NASA’s Magnetospheric Multi-Scale (MMS) spacecraft (recently launched in 2015), together with a newly-developed data analysis technique (the field-particle correlation technique).

The solar wind is the stream of charged particles (i.e., plasma) that comes from the Sun and fills our entire solar system, and the MMS spacecraft are located in the solar wind measuring the fields and particles within it as it streams past.

Lead author Dr Christopher Chen, from Queen Mary University of London, said: “Plasma is by far the most abundant form of visible matter in the universe, and is often in a highly dynamic and apparently chaotic state known as turbulence. This turbulence transfers energy to the particles in the plasma leading to heating and energisation, making turbulence and the associated heating very widespread phenomena in nature.

“In this study, we made the first direct measurement of the processes involved in turbulent heating in a naturally occurring astrophysical plasma. We also verified the new analysis technique as a tool that can be used to probe plasma energisation and that can be used in a range of follow-up studies on different aspects of plasma behaviour.”

University of Iowa’s Professor Greg Howes, who co-devised this new analysis technique, said: “In the process of Landau damping, the electric field associated with waves moving through the plasma can accelerate electrons moving with just the right speed along with the wave, analogous to a surfer catching a wave. This first successful observational application of the field-particle correlation technique demonstrates its promise to answer long-standing, fundamental questions about the behavior and evolution of space plasmas, such as the heating of the solar corona.”

This paper also paves the way for the technique to be used on future missions to other areas of the solar system, such as the NASA Parker Solar Probe (launched in 2018) which is beginning to explore the solar corona and plasma environment near the Sun for the first time.

Earth’s Magnetic Shield Booms Like A Drum When Hit By Impulses

The Earth’s magnetic shield booms like a drum when it is hit by strong impulses, according to new research from Queen Mary University of London.

As an impulse strikes the outer boundary of the shield, known as the magnetopause, ripples travel along its surface which then get reflected back when they approach the magnetic poles.

The interference of the original and reflected waves leads to a standing wave pattern, in which specific points appear to be standing still while others vibrate back and forth. A drum resonates like this when struck in exactly the same way.

This study, published in Nature Communications, describes the first time this effect has been observed after it was theoretically proposed 45 years ago.

Movements of the magnetopause are important in controlling the flow of energy within our space environment with wide-ranging effects on space weather, which is how phenomena from space can potentially damage technology like power grids, GPS and even passenger airlines.

The discovery that the boundary moves in this way sheds light on potential global consequences that previously had not been considered.

Dr Martin Archer, space physicist at Queen Mary University of London, and lead author of the paper, said: “There had been speculation that these drum-like vibrations might not occur at all, given the lack of evidence over the 45 years since they were proposed. Another possibility was that they are just very hard to definitively detect.

“Earth’s magnetic shield is continuously buffeted with turbulence so we thought that clear evidence for the proposed booming vibrations might require a single sharp hit from an impulse. You would also need lots of satellites in just the right places during this event so that other known sounds or resonances could be ruled out. The event in the paper ticked all those quite strict boxes and at last we’ve shown the boundary’s natural response.”

The researchers used observations from five NASA THEMIS satellites when they were ideally located as a strong isolated plasma jet slammed into the magnetopause. The probes were able to detect the boundary’s oscillations and the resulting sounds within the Earth’s magnetic shield, which agreed with the theory and gave the researchers the ability to rule out all other possible explanations.

Many impulses which can impact our magnetic shield originate from the solar wind, charged particles in the form of plasma that continually blow off the Sun, or are a result of the complicated interaction of the solar wind with Earth’s magnetic field, as was technically the case for this event.

The interplay of Earth’s magnetic field with the solar wind forms a magnetic shield around the planet, bounded by the magnetopause, which protects us from much of the radiation present in space.

Other planets like Mercury, Jupiter and Saturn also have similar magnetic shields and so the same drum-like vibrations may be possible elsewhere.

Further research is needed to understand how often the vibrations occur at Earth and whether they exist at other planets as well. Their consequences also need further study using satellite and ground-based observations.

Innovative Method Enables New View Into Earth’s Interior

An innovative X-ray method enables new high-pressure investigations of samples under deep mantle conditions. The technique, which was developed by a team led by Georg Spiekermann from DESY, the German Research Centre for Geosciences GFZ and the University of Potsdam, extends the range of instruments available to high-pressure researchers. Successful tests of the new method at DESY’s X-ray light source PETRA III support the idea that heavy elements have to accumulate in magmas so that they could be stable at depths of Earth’s lower mantle. The scientists present their work in the journal Physical Review X.

The so-called standard conditions of chemistry, i.e. a temperature of 25 degrees Celsius and a pressure of 1013 millibar, are actually rare in nature. Most of the matter in the universe exists under completely different conditions. In Earth’s interior, for example, pressure and temperature rise rapidly to many times the standard conditions. “However, even with the most elaborate deep drilling, only the uppermost part of the Earth’s crust is accessible,” Spiekermann emphasises. Researchers therefore simulate the conditions of Earth’s interior in the laboratory in order to investigate the behaviour of matter under these conditions.

Such experiments often involve determining the inner structure of the samples, which in many materials changes with increasing pressure. This inner structure can be explored with X-rays that are energetic enough to penetrate the sample and short enough in wavelength to resolve the tiny details of atomic distances. For this purpose, usually two X-ray based methods exist in high-pressure research: absorption and diffraction of X-rays through the sample.

Based on X-ray emission, Spiekermann and his team have now developed a third method that can be used to determine both the bonding distances in compressed amorphous (disordered) matter and the so-called coordination number, which indicates how many direct neighbours an atom has. These parameters can be read from the energy and intensity of the radiation of a certain emission line of the sample, called Kβ” (“K-beta-doubleprime”). The Kβ” radiation is generated when the sample is excited with X-rays. The energy of the emission line depends on the coordination number, the intensity on the bonding distance.

Experiments at the experimental station P01 at DESY’s X-ray source PETRA III have confirmed the new method. “We have shown this, using the spectrum of germanium in compressed amorphous germanium dioxide, but this procedure can also be applied to other chemical systems,” says Spiekermann.

The method will provide scientists with an additional technique for investigating the structure of high-pressure samples. “The insight provided by a new measuring method is particularly welcome when different methods have so far produced significantly different results so far, as in the case of compressed amorphous germanium dioxide,” explains DESY researcher Hans-Christian Wille, head of the measuring station P01 at which the experiments took place.

For their experiments, the researchers exposed samples of germanium dioxide (GeO2) to a pressure of up to 100 gigapascals, about one million times as much as the atmospheric pressure at sea level. This pressure corresponds to a depth of 2200 kilometres in the lower mantle of Earth. The measurements show that the coordination number of germanium dioxide does not rise higher than six even under this extreme pressure. This means that even in the high-pressure phase, the germanium atoms each still have six neighbouring atoms as already at 15 gigapascals.

This result is of great interest for the exploration of Earth’s interior, because germanium dioxide has the same structure and behaves like silicon dioxide (SiO2), which is the main component of natural magmas in general. Since melts such as magma generally have a lower density than the solid form of the same material, it has long been a mystery why magmas at great depth do not rise towards the surface over geological periods.

“There are two possible explanations for this, one chemical, the other structural,” Spiekermann explains. “Either heavy elements such as iron accumulate in the melt, or there is a special compacting mechanism in melts that makes melts denser than crystalline forms of the same composition.” The latter would be noticeable, among other things, by an increase in the coordination number under high pressure.

“Our investigations show that up to 100 gigapascals the coordination number in non-crystalline germanium dioxide is not higher than in the corresponding crystalline form,” reports the researcher. Applied to silicon dioxide, this means that magma with a higher density can only be produced by enriching relatively heavy elements such as iron. The composition and structure of the lower mantle have far-reaching consequences for the global transport of heat and the propagation of Earth’s magnetic field.