ST/ Strange radio waves from heart of Milky Way

Paradigm

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Paradigm

33 min readOct 20, 2021

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Space biweekly vol.37, 6th October — 20th October

TL;DR

Astronomers have detected a very unusual variable radio signal from towards the heart of the Milky Way, which is now tantalizing scientists.
Scientists find evidence the early solar system harbored a gap between its inner and outer regions. The cosmic boundary, perhaps caused by a young Jupiter or a wind from the solar system emerging, likely shaped the composition of infant planets.
With future space exploration in mind, a team of astronomers has published the final maps of Titan’s liquid methane rivers and tributaries — as seen by NASA’s late Cassini mission — so that may help provide context for Dragonfly’s upcoming 2030s expedition.
Astrophysicists have investigated the past of Venus to find out whether Earth’s sister planet once had oceans.
Evidence of superionic ice provides new insights into unusual magnetic fields of Uranus and Neptune.
A compositional link between planets and their respective host star has long been assumed in astronomy. Scientists now deliver empirical evidence to support the assumption — and partly contradict it at the same time.
A new study proposes that space probes could hitch a ride with ‘centaurs’ as they become comets. Along the way, the spacecraft would gather data that would otherwise be impossible to record — including how comets, Earth-like planets, and even the solar system formed.
Astronomers have imaged 42 of the largest objects in the asteroid belt, located between Mars and Jupiter. The observations reveal a wide range of peculiar shapes, from spherical to dog-bone, and are helping astronomers trace the origins of the asteroids in our Solar System.
Solar prominences hover above the visible solar disk like giant clouds, held there by a supporting framework of magnetic forces, originating from layers deep within the Sun. The magnetic lines of force are moved by ever-present gas currents — and when the supporting framework moves, so does the prominence cloud. A research team has observed how magnetic forces lifted a prominence by 25,000 kilometers within ten minutes.
It has long been theorized that hydrogen, helium, and lithium were the only chemical elements in existence during the Big Bang, and that supernova explosions are responsible for transmuting these elements into heavier ones. Researchers are now challenging this and propose an alternative model for the formation of nitrogen, oxygen, and water based on the history of Earth’s atmosphere. They postulate that the 25 elements with atomic numbers smaller than iron were created via an endothermic nuclear transmutation of two nuclei, carbon and oxygen.
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Space industry in numbers

The global smart space market size is projected to grow from USD 9.4 billion in 2020 to USD 15.3 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 10.2% during the forecast period. The increasing venture capital funding and growing investments in smart space technology to drive market growth.

Analysts at Morgan Stanley and Goldman Sachs have predicted that economic activity in space will become a multi-trillion-dollar market in the coming decades. Morgan Stanley’s Space Team estimates that the roughly USD 350 billion global space industry could surge to over USD 1 trillion by 2040.

Source: Satellite Industry Association, Morgan Stanley Research, Thomson Reuters. *2040 estimates

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Latest research

Discovery of ASKAP J173608.2–321635 as a Highly Polarized Transient Point Source with the Australian SKA Pathfinder

by Ziteng Wang, David L. Kaplan, Tara Murphy, Emil Lenc, Shi Dai, Ewan Barr, Dougal Dobie, B. M. Gaensler, George Heald, James K. Leung, Andrew O’Brien, Sergio Pintaldi, Joshua Pritchard, Nanda Rea, Gregory R. Sivakoff, B. W. Stappers, Adam Stewart, E. Tremou, Yuanming Wang, Patrick A. Woudt, Andrew Zic in The Astrophysical Journal

Astronomers have discovered unusual signals coming from the direction of the Milky Way’s centre. The radio waves fit no currently understood pattern of variable radio source and could suggest a new class of stellar object.

“The strangest property of this new signal is that it is has a very high polarisation. This means its light oscillates in only one direction, but that direction rotates with time,” said Ziteng Wang, lead author of the new study and a PhD student in the School of Physics at the University of Sydney.

ASKAP images of ASKAP J173608.2321635 (centered at 888 MHz). Each image is 100 on a side, with north up and east to the left.

“The brightness of the object also varies dramatically, by a factor of 100, and the signal switches on and off apparently at random. We’ve never seen anything like it.”

Many types of star emit variable light across the electromagnetic spectrum. With tremendous advances in radio astronomy, the study of variable or transient objects in radio waves is a huge field of study helping us to reveal the secrets of the Universe. Pulsars, supernovae, flaring stars and fast radio bursts are all types of astronomical objects whose brightness varies.

“At first we thought it could be a pulsar — a very dense type of spinning dead star — or else a type of star that emits huge solar flares. But the signals from this new source don’t match what we expect from these types of celestial objects,” Mr Wang said.

The Gemini J-band (1.2 m) image (3000 on a side, 2 times the ASKAP synthesized beam) of ASKAP J173608.2321635.

Mr Wang and an international team, including scientists from Australia’s national science agency CSIRO, Germany, the United States, Canada, South Africa, Spain and France discovered the object using the CSIRO’s ASKAP radio telescope in Western Australia. Follow-up observations were with the South African Radio Astronomy Observatory’s MeerKAT telescope. Mr Wang’s PhD supervisor is Professor Tara Murphy also from the Sydney Institute for Astronomy and the School of Physics.

Professor Murphy said: “We have been surveying the sky with ASKAP to find unusual new objects with a project known as Variables and Slow Transients (VAST), throughout 2020 and 2021. “Looking towards the centre of the Galaxy, we found ASKAP J173608.2–321635, named after its coordinates. This object was unique in that it started out invisible, became bright, faded away and then reappeared. This behaviour was extraordinary.”

After detecting six radio signals from the source over nine months in 2020, the astronomers tried to find the object in visual light. They found nothing. They turned to the Parkes radio telescope and again failed to detect the source.

Professor Murphy said: “We then tried the more sensitive MeerKAT radio telescope in South Africa. Because the signal was intermittent, we observed it for 15 minutes every few weeks, hoping that we would see it again. “Luckily, the signal returned, but we found that the behaviour of the source was dramatically different — the source disappeared in a single day, even though it had lasted for weeks in our previous ASKAP observations.”

However, this further discovery did not reveal much more about the secrets of this transient radio source.

Duty cycle lower limit for a non-detection in the pulsar search for the MeerKAT data from 2021 February 07 (at 856{1712 MHz).

Mr Wang’s co-supervisor, Professor David Kaplan from the University of Wisconsin-Milwaukee, said: “The information we do have has some parallels with another emerging class of mysterious objects known as Galactic Centre Radio Transients, including one dubbed the ‘cosmic burper’. “While our new object, ASKAP J173608.2–321635, does share some properties with GCRTs there are also differences. And we don’t really understand those sources, anyway, so this adds to the mystery.”

The scientists plan to keep a close eye on the object to look for more clues as to what it might be.

“Within the next decade, the transcontinental Square Kilometre Array (SKA) radio telescope will come online. It will be able to make sensitive maps of the sky every day,” Professor Murphy said. “We expect the power of this telescope will help us solve mysteries such as this latest discovery, but it will also open vast new swathes of the cosmos to exploration in the radio spectrum.”

Fluvial Features on Titan and Earth: Lessons from Planform Images in Low-resolution SAR

by J. W. Miller, S. P. D. Birch, A. G. Hayes, M. J. Malaska, R. M. C. Lopes, A. M. Schoenfeld, P. M. Corlies, D. M. Burr, T. G. Farr, JT Perron in The Planetary Science Journal

With future space exploration in mind, a Cornell-led team of astronomers has published the final maps of Titan’s liquid methane rivers and tributaries — as seen by NASA’s late Cassini mission — so that may help provide context for Dragonfly’s upcoming 2030s expedition.

Like water on Earth, liquid methane and ethane fill Titan’s lakes, rivers and streams. But understanding those channels — including their twists and branch-like turns — is key to knowing how that moon’s sediment transport system works and the underlying geology.

“The channel systems are the heart of Titan’s sediment transport pathways,” said Alex Hayes, associate professor of astronomy in the College of Arts and Sciences. “They tell you how organic material is routed around Titan’s surface, and identifies locations where the material might be concentrated near tectonic or perhaps even cryovolcanic features. “Further, those materials either can be sent down into Titan’s liquid water interior ocean, or alternatively, mixed with liquid water that gets transported up to the surface,” Hayes said.

(A) Elvigar Flumina: a network of radar-bright channels near Menrva Crater in Titan’s equatorial region. (B) Saraswati Flumina: a liquid-filled channel draining into Ontario Lacus, with two potential deltas at the river−sea margin.

Larger than the planet Mercury and fully shrouded in a dense nitrogen and methane atmosphere, Titan is the only other place in the solar system with an active hydrologic system, which includes rain, channels, lakes and seas.

“Unlike Mars, it’s not 3.6 billion years ago when you would have seen lakes and channels on Titan. It’s today,” Hayes said. “Examining Titan’s hydrologic system represents an extreme example comparable to Earth’s hydrologic system — and it’s the only instance where we can actively see how a planetary landscape evolves in the absence of vegetation.”

Julia Miller ’20 led the detailed work of examining Cassini’s Synthetic Aperture Radar (SAR) images of Titan’s surface, looking for fluvial characteristics and then comparing those images to those available on Earth.

On Earth, fluvial geomorphology is typically studied with topographic data and high-resolution visible images, but that was not available for Titan. Instead, Miller used Earth-based radar images and degraded them to match the Cassini radar images of Titan. This way, Miller could understand the limits of the Cassini dataset and know which results are robust for analysis using low, roughly 1-kilometer resolution data.

(A) SPOT visible image of an area in northern Quebec at the scale it was mapped (1:60,000). (B) Sentinel-1 SAR-C data in the same area with a spatial resolution of 30 m pixel−1. (c) The same data downgraded to 350 m pixel−1 by calculating mean pixel values. (D) Downgraded data with added speckle noise.

“Although the quality and quantity of Cassini SAR images put significant limits on their utility for investigating river networks,” Miller said, “they can still be used to understand Titan’s landscape at a fundamental level.”
River shapes say a lot. “You can use sort of what the river looks like to try to say some things about the type of material that it’s flowing through, or like how steep the surfaces, or just what went on in that region,” Miller said. “This is using the rivers as a starting point, to then, ideally, learn more about the planet.”

The Dragonfly mission to Titan is slated to launch in 2027 and is scheduled to arrive at Titan in 2034.

Said Hayes: “These maps will provide context for understanding things that Dragonfly finds locally and regionally, and will help to place Dragonfly’s result into global context.”

Day–night cloud asymmetry prevents early oceans on Venus but not on Earth

by Martin Turbet, Emeline Bolmont, Guillaume Chaverot, David Ehrenreich, Jérémy Leconte & Emmanuel Marcq in Nature

The planet Venus can be seen as the Earth’s evil twin. At first sight, it is of comparable mass and size as our home planet, similarly consists mostly of rocky material, holds some water and has an atmosphere. Yet, a closer look reveals striking differences between them: Venus’ thick CO2 atmosphere, extreme surface temperature and pressure, and sulphuric acid clouds are indeed a stark contrast to the conditions needed for life on Earth. This may, however, have not always been the case. Previous studies have suggested that Venus may have been a much more hospitable place in the past, with its own liquid water oceans. A team of astrophysicists led by the University of Geneva (UNIGE) and the National Centre of Competence in Research (NCCR) PlanetS, Switzerland, investigated whether our planet’s twin did indeed have milder periods. The results suggest that this is not the case.

Venus has recently become an important research topic for astrophysicists. ESA and NASA have decided this year to send no less than three space exploration missions over the next decade to the second closest planet to the Sun. One of the key questions these missions aim to answer is whether or not Venus ever hosted early oceans. Astrophysicists led by Martin Turbet, researcher at the Department of Astronomy of the Faculty of Science of the UNIGE and member of the NCCR PlanetS, have tried to answer this question with the tools available on Earth.

“We simulated the climate of the Earth and Venus at the very beginning of their evolution, more than four billion years ago, when the surface of the planets was still molten,” explains Martin Turbet. “The associated high temperatures meant that any water would have been present in the form of steam, as in a gigantic pressure cooker.”

Using sophisticated three-dimensional models of the atmosphere, similar to those scientists use to simulate the Earth’s current climate and future evolution, the team studied how the atmospheres of the two planets would evolve over time and whether oceans could form in the process.

**Day and night water cloud feedbacks.**

“Thanks to our simulations, we were able to show that the climatic conditions did not allow water vapour to condense in the atmosphere of Venus,” says Martin Turbet. This means that the temperatures never got low enough for the water in its atmosphere to form raindrops that could fall on its surface. Instead, water remained as a gas in the atmosphere and oceans never formed.
“One of the main reasons for this is the clouds that form preferentially on the night side of the planet. These clouds cause a very powerful greenhouse effect that prevented Venus from cooling as quickly as previously thought,” continues the Geneva researcher.

Surprisingly, the astrophysicists’ simulations also reveal that the Earth could easily have suffered the same fate as Venus. If the Earth had been just a little closer to the Sun, or if the Sun had shone as brightly in its ‘youth’ as it does nowadays, our home planet would look very different today. It is likely the relatively weak radiation of the young Sun that allowed the Earth to cool down enough to condense the water that forms our oceans. For Emeline Bolmont, professor at UNIGE, member of PlaneS and co-author of the study, “this is a complete reversal in the way we look at what has long been called the ‘Faint Young Sun paradox’. It has always been considered as a major obstacle to the appearance of life on Earth!” The argument was that if the Sun’s radiation was much weaker than today, it would have turned the Earth into a ball of ice hostile to life. “But it turns out that for the young, very hot Earth, this weak Sun may have in fact been an unhoped-for opportunity,” continues the researcher.

**Water clouds and thermal emission horizontal maps.**

“Our results are based on theoretical models and are an important building-block in answering the question of the history of Venus,” says study co-author David Ehrenreich, professor in the Department of Astronomy at UNIGE and member of the NCCR PlanetS. “But we will not be able to rule on the matter definitively on our computers. The observations of the three future Venusian space missions will be essential to confirm — or refute — our work.”

Paleomagnetic evidence for a disk substructure in the early solar system

by Cauê S. Borlina et al. in Science Advances

In the early solar system, a “protoplanetary disk” of dust and gas rotated around the sun and eventually coalesced into the planets we know today.

A new analysis of ancient meteorites by scientists at MIT and elsewhere suggests that a mysterious gap existed within this disk around 4.567 billion years ago, near the location where the asteroid belt resides today.

“Over the last decade, observations have shown that cavities, gaps, and rings are common in disks around other young stars,” says Benjamin Weiss, professor of planetary sciences in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “These are important but poorly understood signatures of the physical processes by which gas and dust transform into the young sun and planets.”

Likewise the cause of such a gap in our own solar system remains a mystery. One possibility is that Jupiter may have been an influence. As the gas giant took shape, its immense gravitational pull could have pushed gas and dust toward the outskirts, leaving behind a gap in the developing disk.

AF demagnetization of CO dusty olivine chondrules.

Another explanation may have to do with winds emerging from the surface of the disk. Early planetary systems are governed by strong magnetic fields. When these fields interact with a rotating disk of gas and dust, they can produce winds powerful enough to blow material out, leaving behind a gap in the disk.

Regardless of its origins, a gap in the early solar system likely served as a cosmic boundary, keeping material on either side of it from interacting. This physical separation could have shaped the composition of the solar system’s planets. For instance, on the inner side of the gap, gas and dust coalesced as terrestrial planets, including the Earth and Mars, while gas and dust relegated to the farther side of the gap formed in icier regions, as Jupiter and its neighboring gas giants.

“It’s pretty hard to cross this gap, and a planet would need a lot of external torque and momentum,” says lead author and EAPS graduate student Cauê Borlina. “So, this provides evidence that the formation of our planets was restricted to specific regions in the early solar system.”

Weiss and Borlina’s co-authors include Eduardo Lima, Nilanjan Chatterjee, and Elias Mansbach of MIT, James Bryson of Oxford University, and Xue-Ning Bai of Tsinghua University.

Over the last decade, scientists have observed a curious split in the composition of meteorites that have made their way to Earth. These space rocks originally formed at different times and locations as the solar system was taking shape. Those that have been analyzed exhibit one of two isotope combinations. Rarely have meteorites been found to exhibit both — a conundrum known as the “isotopic dichotomy.”

Direction of the HC components of the dusty olivine chondrules from CO chondrites.

Scientists have proposed that this dichotomy may be the result of a gap in the early solar system’s disk, but such a gap has not been directly confirmed. Weiss’ group analyzes meteorites for signs of ancient magnetic fields. As a young planetary system takes shape, it carries with it a magnetic field, the strength and direction of which can change depending on various processes within the evolving disk. As ancient dust gathered into grains known as chondrules, electrons within chondrules aligned with the magnetic field in which they formed.

Chondrules can be smaller than the diameter of a human hair, and are found in meteorites today. Weiss’ group specializes in measuring chondrules to identify the ancient magnetic fields in which they originally formed.

In previous work, the group analyzed samples from one of the two isotopic groups of meteorites, known as the noncarbonaceous meteorites. These rocks are thought to have originated in a “reservoir,” or region of the early solar system, relatively close to the sun. Weiss’ group previously identified the ancient magnetic field in samples from this close-in region.

In their new study, the researchers wondered whether the magnetic field would be the same in the second isotopic, “carbonaceous” group of meteorites, which, judging from their isotopic composition, are thought to have originated farther out in the solar system.

They analyzed chondrules, each measuring about 100 microns, from two carbonaceous meteorites that were discovered in Antarctica. Using the superconducting quantum interference device, or SQUID, a high-precision microscope in Weiss’ lab, the team determined each chondrule’s original, ancient magnetic field. Surprisingly, they found that their field strength was stronger than that of the closer-in noncarbonaceous meteorites they previously measured. As young planetary systems are taking shape, scientists expect that the strength of the magnetic field should decay with distance from the sun.

Comparison between paleomagnetic constraints and model predictions for the solar nebula magnetic field intensity.

In contrast, Borlina and his colleagues found the far-out chondrules had a stronger magnetic field, of about 100 microteslas, compared to a field of 50 microteslas in the closer chondrules. For reference, the Earth’s magnetic field today is around 50 microteslas. A planetary system’s magnetic field is a measure of its accretion rate, or the amount of gas and dust it can draw into its center over time. Based on the carbonaceous chondrules’ magnetic field, the solar system’s outer region must have been accreting much more mass than the inner region.

Using models to simulate various scenarios, the team concluded that the most likely explanation for the mismatch in accretion rates is the existence of a gap between the inner and outer regions, which could have reduced the amount of gas and dust flowing toward the sun from the outer regions.

“Gaps are common in protoplanetary systems, and we now show that we had one in our own solar system,” Borlina says. “This gives the answer to this weird dichotomy we see in meteorites, and provides evidence that gaps affect the composition of planets.”

Structure and properties of two superionic ice phases

by Vitali B. Prakapenka, Nicholas Holtgrewe, Sergey S. Lobanov, Alexander F. Goncharov in Nature Physics

Not all ice is the same. The solid form of water comes in more than a dozen different — sometimes more, sometimes less crystalline — structures, depending on the conditions of pressure and temperature in the environment. Superionic ice is a special crystalline form, half solid, half liquid — and electrically conductive. Its existence has been predicted on the basis of various models and has already been observed on several occasions under — very extreme — laboratory conditions. However, the exact conditions at which superionic ices are stable remain controversial. A team of scientists led by Vitali Prakapenka from the University of Chicago, which also includes Sergey Lobanov from the German Research Center for Geosciences GFZ Potsdam, has now measured the structure and properties of two superionic ice phases (ice XVIII and ice XX). They brought water to extremely high pressures and temperatures in a laser-heated diamond anvil cell. At the same time, the samples were examined with regard to structure and electrical conductivity. They provide another piece of the puzzle in the spectrum of the manifestations of water. And they may also help to explain the unusual magnetic fields of the planets Uranus and Neptune, which contain a lot of water.

Ice is cold. At least type I ice from our freezer, snow or from a frozen lake. In planets or in laboratory high-pressure devices, there are different species of ice, type VII or VIII, for example, which exist at several hundred or thousand degrees Celsius. However, this is only because of very high pressures of several ten Gigapascal.

Pressure and temperature span the space for the so-called phase diagram of a substance: Depending on these two parameters, the various manifestations of water and the transitions between solid, gaseous, liquid and hybrid states are recorded here — as they are predicted theoretically or have already been proven in experiments.

**Phase diagram of water at extreme P–T conditions.**

The higher the pressure and temperature, the more difficult such experiments are. And so the phase diagram of water — with ice as its solid phase — still has quite a few inaccuracies and inconsistencies in the extreme ranges.

“Water is actually a relatively simple chemical compound consisting of one oxygen and two hydrogen atoms. Nevertheless, with its often unusual behaviour, it is still not fully understood. In the case of water, the fundamental physical and geoscientific interests come together because water plays an important role inside many planets. Not only in terms of the formation of life and landscapes, but — in the case of the gaseous planets Uranus and Neptune — also for the formation of their unusual planetary magnetic fields,” says Sergey Lobanov, geophysicist at GFZ Potsdam.

Sergey Lobanov is part of the team led by first author Vitali Prakapenka and Nicholas Holtgrewe, both from the University of Chicago, and Alexander Goncharov from the Carnegie Institution of Washington. They have now further characterized the phase diagram of water at its extremes. Using laser-heated diamond anvil cells — the size of a computer mouse — they have generated high pressures of up to 150 Gigapascal (about 1.5 million times atmospheric pressure) and temperatures of up to 6,500 Kelvin (about 6,227 degrees Celsius). In the sample chamber, which is only a few cubic millimetres in size, conditions then prevail that occur at the depth of several thousand kilometres inside Uranus or Neptune.

The scientists used X-ray diffraction to observe how the crystal structure changes under these conditions. They carried out these experiments using the extremely bright synchrotron X-rays at the Advanced Photon Source (APS) of the Argonne National Laboratory at the University of Chicago. A second series of experiments at the Earth and Planets Laboratory of the Carnegie Institution of Washington used optical spectroscopy to determine the electronic conductivity.

**XRD patterns measured on laser heating (LH).**

The researchers first produced ice VII or X from water at room temperature by increasing the pressure to several tens of Gigapascal (see the phase diagram). And then, at constant pressure, they increased the temperature by heating it with laser light. In the process, they observed how the crystalline ice structure changed: First, the oxygen and hydrogen atoms moved a little around their fixed positions. Then only the oxygen remained fixed and formed its own cubic crystal lattice. As the temperature rose, the hydrogen ionised, i.e. gave up its only electron to the oxygen lattice. Its atomic nucleus — a positively charged proton — then whizzed through this solid, making it electrically conductive. In this way, a hybrid of solid and liquid is created: superionic ice.

Its existence was predicted on the basis of various models and has already been observed on several occasions under laboratory conditions. The scientists have now been able to synthesize and identify two superionic ice phases — ice XVIII and ice XX -, and to delineate the pressure and temperature conditions of their stability.

“Due to their distinct density and increased optical conductivity, we assign the observed structures to the theoretically predicted superionic ice phases,” explains Lobanov.

In particular, the phase transition to a conducting liquid has interesting consequences for the open questions surrounding the magnetic field of Uranus and Neptune, which presumably consist of more than sixty percent water. Their magnetic field is unusual in that it does not run quasi parallel and symmetrically to the axis of rotation — as it does on Earth — but is skewed and off-centre. Models of its formation therefore assume that it is not generated — as on Earth — by the motion of molten iron in the core, but by a conductive water-rich liquid in the outer third of Uranus or Neptune.

“In the phase diagram, we can draw the pressure and temperature in the interiors of Uranus and Neptune. Here, the pressure can roughly be taken as a measure of the depth inside. Based on the refined phase boundaries we have measured, we see that about the upper third of both planets is liquid, but deeper interiors contain solid superionic ices. This confirms the predictions about the origin of the observed magnetic field,” Lobanov sums up.

A compositional link between rocky exoplanets and their host stars

by Vardan Adibekyan et al. in Science

A compositional link between planets and their respective host star has long been assumed in astronomy. For the first time now, a team of scientists, with the participation of researchers of the National Centre of Competence in Research (NCCR) PlanetS from the University of Bern and the University of Zürich, deliver empirical evidence to support the assumption — and partly contradict it at the same time.

Stars and planets are formed from the same cosmic gas and dust. In the course of the formation process, some of the material condenses and forms rocky planets, the rest is either accumulated by the star or becomes part of gaseous planets. The assumption of a connection between the composition of stars and their planets is therefore reasonable and is confirmed, for example, in the solar system by most rocky planets (Mercury being the exception). Nevertheless, assumptions, especially in astrophysics, do not always prove to be true. A study led by the Instituto de Astrofísica e Ciências do Espaço (IA) in Portugal, which also involves researchers from the NCCR PlanetS at the University of Bern and the University of Zürich provides the first empirical evidence for this assumption — and at the same time partially contradicts it.

To determine whether the compositions of stars and their planets are related, the team compared very precise measurements of both. For the stars, their emitted light was measured, which bears the characteristic spectroscopic fingerprint of their composition. The composition of the rocky planets was determined indirectly: Their density and composition were derived from their measured mass and radius. Only recently have enough planets been measured so precisely that meaningful investigations of this kind are possible.

The iron content (percentage) of the analyzed planets and the protoplanetary disks where the planets are formed. (Credit; Earth Core: Mats Halldin; Mercury Core: Joel Holdsworth; Earth: Public Domain; Mercury: NASA/Johns Hopkins U. Applied Physics Laboratory/Arizona State U./Carnegie Institution of Washington; Protoplanetary Disk: ESO/L. Calçada)

“But since stars and rocky planets are quite different in nature, the comparison of their composition is not straightforward,” as Christoph Mordasini, co-author of the study, lecturer of astrophysics at the university of Bern and member of the NCCR PlanetS begins to explain. “Instead, we compared the composition of the planets with a theoretical, cooled-down version of their star. While most of the star’s material — mainly hydrogen and helium — remains as a gas when it cools, a tiny fraction condenses, consisting of rock-forming material such as iron and silicate,” explains Christoph Mordasini.

At the University of Bern, the “Bern Model of Planet Formation and Evolution” has been continuously developed since 2003.

Christoph Mordasini says: “Insights into the manifold processes involved in the formation and evolution of planets are integrated into the model.” Using this Bern model the researchers were able to calculate the composition of this rock-forming material of the cooled-down star. “We then compared that with the rocky planets,” Christoph Mordasini says.
“Our results show that our assumptions regarding star and planet compositions were not fundamentally wrong: the composition of rocky planets is indeed intimately tied to the composition of their host star. However, the relationship is not as simple as we expected,” lead author of the study and researcher at the IA, Vardan Adibekyan, says.

What the scientists expected, was that the star’s abundance of these elements sets the upper possible limit.

“Yet for some of the planets, the iron abundance in the planet is even higher than in the star” as Caroline Dorn, who co-authored the study and is a member of the NCCR PlanetS as well as Ambizione Fellow at the University of Zurich, explains. “This could be due to giant impacts on these planets that break off some of the outer, lighter materials, while the dense iron core remains,” according to the researcher. The results could therefore give the scientists clues about the history of the planets.

“The results of this study are also very useful to constrain planetary compositions that are assumed based on the calculated density from mass and radius measurements,” Christoph Mordasini explains. “Since more than one composition can fit a certain density, the results of our study tell us that we can narrow potential compositions down, based on the host star’s composition,” Mordasini says.

And since the exact composition of a planet influences, for example, how much radioactive material it contains or how strong its magnetic field is, it can determine whether the planet is life-friendly or not.

Velocity Difference of Ions and Neutrals in Solar Prominences

by E. Wiehr, G. Stellmacher, H. Balthasar, M. Bianda in The Astrophysical Journal

Solar prominences hover above the visible solar disk like giant clouds, held there by a supporting framework of magnetic forces, originating from layers deep within the Sun. The magnetic lines of force are moved by ever-present gas currents — and when the supporting framework moves, so does the prominence cloud. A research team from the University of Göttingen and the astrophysics institutes at Paris, Potsdam and Locarno observed how magnetic forces lifted a prominence by 25,000 kilometres — about two Earth diameters — within ten minutes.

This uplift corresponds to a speed of 42 kilometres per second, which is about four times the speed of sound, in the prominence. Oscillations occurred with a period of 22 seconds, during which positively charged ions of iron were up to 70 per cent faster than neutral helium atoms. The charged iron ions have to follow the movement of the magnetic field but the uncharged helium atoms are not affected in the same way. In fact, the helium atoms are carried along by the ions, but only partly because there are not enough collisions between the two types of particle since the gas pressure is too low.

H image sequence of the prominence at the east limb, 5 north from June 28, 2019, (Learmouth observatory); north direction is upwards; the 100” bar corresponds to 73.4 Mm.

Such conditions — where partially ionised gas exists with few collisions — play an important role in astrophysics. Their role is not just demonstrated in solar prominences, but also in the following: the huge gas clouds from which stars and planets form; the gas that fills the vast expanse between stars; and in the gas between galaxies. Theoretical astrophysicists have already simulated such conditions as two fluids interacting only weakly with each other.

“Some of the previous assumptions used in model calculations can now be verified thanks to these new measurements in our results,” says Dr Eberhard Wiehr from the Institute for Astrophysics at the University of Göttingen.

The team carried out the observations at the solar telescope in Locarno, where it is only possible to measure two emission lines simultaneously. Now the scientists are planning extended observations at the French telescope on Tenerife, where several lines can be measured at the same time. In addition, the light intensity for this telescope is increased four-fold, which will enable such a short exposure time for the light-sensitive cameras that even shorter oscillation periods will be measurable.

“We may then find even higher velocity differences between the charged ions and the neutral atoms,” added Wiehr.

A Sublime Opportunity: The Dynamics of Cometary Bodies Transitioning into the Inner Solar System and the Feasibility of In Situ Observations of The Evolution of Their Intense Activity

by Seligman, Kratter, Levine, and Jedicke in Planetary Science Journal

Deep in the solar system, between Jupiter and Neptune, lurk thousands of small chunks of ice and rock. Occasionally, one of them will bump into Jupiter’s orbit, get caught and flung into the inner solar system — towards the sun, and us.

This is thought to be the source of many of the comets that eventually pass Earth. A new study lays out the dynamics of this little-understood system. Among the findings: it would be doable for a spacecraft to fly to Jupiter, wait in Jupiter’s orbit until one of these objects gets caught in the planet’s gravity well, and hitch a ride with the object to watch it become a comet in real time.

“This would be an amazing opportunity to see a pristine comet ‘turn on’ for the first time,” said Darryl Seligman, a postdoctoral researcher with the University of Chicago and corresponding author of the paper. “It would yield a treasure trove of information about how comets move and why, how the solar system formed, and even how Earth-like planets form.”

The Gateway depicted in eccentricity verses semi-major axis space.

Thanks in part to discoveries of several major asteroid belts, scientists over the last 50 years have revamped their theories of how our solar system came to be. Rather than big planets quietly evolving in place, they now envision a system that was much more dynamic and unstable — chunks of ice and rock scattered and smashing into each other, re-forming and moving around within the solar system.

Many of these objects eventually coalesced into the eight major planets, but others remain loose and scattered in several regions of space. “These minor bodies show you the solar system is actually this very dynamic and almost living place that’s constantly in a state of flux,” said Seligman.

Scientists are very familiar with the asteroid belt near Mars, as well as the larger one out past Neptune called the Kuiper belt. But between Jupiter and Neptune, there lurks another, lesser-known population of objects called the centaurs (named after the mythical hybrid creatures due to their classification halfway between asteroids and comets). Occasionally, these centaurs will get sucked into the inner solar system and become comets.

“These objects are very old, containing ice from the early days of the solar system that has never been melted,” said Seligman. “When an object gets closer to the sun, the ice sublimates and produces these beautiful long tails. “Therefore comets are interesting not only because they’re beautiful; they give you a way to probe the chemical composition of things from the distant solar system.”

In this study, scientists examined the centaur population and the mechanisms by which these objects occasionally become comets bound for the sun. They estimate that about half of the centaurs-turned-comets are nudged into the inner solar system by interacting with both Jupiter and Saturn’s orbits. The other half come too close to Jupiter, then get caught in its orbit and flung toward the center of the solar system.

The latter mechanism suggested a perfect way to get a better look at these soon-to-be comets: Space agencies, the scientists said, could send a spacecraft to Jupiter and have it sit in orbit until a centaur bumps into Jupiter’s orbit. Then the spacecraft could hitch a ride alongside the centaur as it heads toward the sun, taking measurements all the way as it transforms into a comet.

The geometry of a scattering event of an object with Jupiter.

This is a beautiful but destructive process: A comet’s beautiful tail is produced as its ice burns off as the temperature rises. The ice in comets is made up of different kinds of molecules and gases, which each start to burn up at different points along the way to the sun. By taking measurements of that tail, a spacecraft could learn what the comet was made up of.

“You could figure out where typical comet ices turn on, and also what the detailed internal structure of what a comet is, which you have very little hope of figuring out from ground-based telescopes,” Seligman said. Meanwhile, the surface of the comet erupts as it heats up, creating pockmarks and craters. “Charting all of this would help you understand the dynamics of the solar system, which is important for things like understanding how to form Earth-like planets in solar systems,” he said.

While the idea sounds complicated, NASA and other space agencies already have the technology to pull it off, the scientists said. Spacecraft routinely go to the outer solar system; NASA’s Juno mission, currently taking wild photos of Jupiter, only took about five years to get there. Other recent missions also show that it’s possible to visit objects even as they’re moving: OSIRIS-REx visited an asteroid 200 million miles away, and Japan’s Hayabusa 2 spacecraft brought back a handful of rocks from another asteroid.

There’s even a possible target: A year and a half ago, scientists discovered that one of the centaurs, called LD2, will likely be sucked into Jupiter’s orbit in about the year 2063. And as telescopes become more powerful, scientists may soon discover many more of these objects, Seligman said: “It’s very possible there would be 10 additional targets in the next 40 years, any of which would be attainable by a spacecraft parked at Jupiter.”

VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis

by P. Vernazza, M. Ferrais, L. Jorda, et al. in Astronomy & Astrophysics

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile, astronomers have imaged 42 of the largest objects in the asteroid belt, located between Mars and Jupiter. Never before had such a large group of asteroids been imaged so sharply. The observations reveal a wide range of peculiar shapes, from spherical to dog-bone, and are helping astronomers trace the origins of the asteroids in our Solar System.

The detailed images of these 42 objects are a leap forward in exploring asteroids, made possible thanks to ground-based telescopes, and contribute to answering the ultimate question of life, the Universe, and everything.

“Only three large main belt asteroids, Ceres, Vesta and Lutetia, have been imaged with a high level of detail so far, as they were visited by the space missions Dawn and Rosetta of NASA and the European Space Agency, respectively,” explains Pierre Vernazza, from the Laboratoire d’Astrophysique de Marseille in France, who led the asteroid study. “Our ESO observations have provided sharp images for many more targets, 42 in total.”

VLT/SPHERE images of all D > 210 km asteroid targets deconvolved with the MISTRAL algorithm (Fusco et al. 2003). The relative sizes are respected, and the scale is indicated on the plot. The objects are ordered according to decreasing values of their volume equivalent diameter.

The previously small number of detailed observations of asteroids meant that, until now, key characteristics such as their 3D shape or density had remained largely unknown. Between 2017 and 2019, Vernazza and his team set out to fill this gap by conducting a thorough survey of the major bodies in the asteroid belt.

Most of the 42 objects in their sample are larger than 100 km in size; in particular, the team imaged nearly all of the belt asteroids larger than 200 kilometres, 20 out of 23. The two biggest objects the team probed were Ceres and Vesta, which are around 940 and 520 kilometres in diameter, whereas the two smallest asteroids are Urania and Ausonia, each only about 90 kilometres.

By reconstructing the objects’ shapes, the team realised that the observed asteroids are mainly divided into two families. Some are almost perfectly spherical, such as Hygiea and Ceres, while others have a more peculiar, “elongated” shape, their undisputed queen being the “dog-bone” asteroid Kleopatra.

By combining the asteroids’ shapes with information on their masses, the team found that the densities change significantly across the sample. The four least dense asteroids studied, including Lamberta and Sylvia, have densities of about 1.3 grams per cubic centimetre, approximately the density of coal. The highest, Psyche and Kalliope, have densities of 3.9 and 4.4 grammes per cubic centimetre, respectively, which is higher than the density of diamond (3.5 grammes per cubic centimetre).

This large difference in density suggests the asteroids’ composition varies significantly, giving astronomers important clues about their origin. “Our observations provide strong support for substantial migration of these bodies since their formation. In short, such tremendous variety in their composition can only be understood if the bodies originated across distinct regions in the Solar System,” explains Josef Hanuš of the Charles University, Prague, Czech Republic, one of the authors of the study. In particular, the results support the theory that the least dense asteroids formed in the remote regions beyond the orbit of Neptune and migrated to their current location.

Density distribution of our large programme asteroid targets. The density distribution appears strongly bimodal (see text) with volatile-poor bodies on the left of the gray zone and volatile-rich bodies on its right. Two multiple systems imaged outside of our observing program were also added because of their accurate density determination. Asteroids are grouped following their spectral classification. The relativesizes of the dots follow the relative diameters of the bodies in logarithmic scale. Error bars are one sigma. In the center of the figure, the gray zone shows the average density of the main asteroid groups (left) and of their likely meteoritic analogs (right).

These findings were made possible thanks to the sensitivity of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument mounted on ESO’s VLT.

“With the improved capabilities of SPHERE, along with the fact that little was known regarding the shape of the largest main belt asteroids, we were able to make substantial progress in this field,” says co-author Laurent Jorda, also of the Laboratoire d’Astrophysique de Marseille.

Astronomers will be able to image even more asteroids in fine detail with ESO’s upcoming Extremely Large Telescope (ELT), currently under construction in Chile and set to start operations later this decade.

“ELT observations of main-belt asteroids will allow us to study objects with diameters down to 35 to 80 kilometres, depending on their location in the belt, and craters down to approximately 10 to 25 kilometres in size,” says Vernazza. “Having a SPHERE-like instrument at the ELT would even allow us to image a similar sample of objects in the distant Kuiper Belt. This means we’ll be able to characterise the geological history of a much larger sample of small bodies from the ground.”

Earth factories: Creation of the elements from nuclear transmutation in Earth’s lower mantle

by Mikio Fukuhara, Alexander Yoshino, and Nobuhisa Fujima in AIP Advances

It has long been theorized that hydrogen, helium, and lithium were the only chemical elements in existence during the Big Bang when the universe formed, and that supernova explosions, stars exploding at the end of their lifetime, are responsible for transmuting these elements into heavier ones and distributing them throughout our universe.

Researchers in Japan and Canada are now challenging a piece of the Big Bang puzzle. Do all of the elements heavier than iron really originate from stars exploding, or are some created deep within the Earth’s mantle, thanks to convection dynamics driven by plate tectonics? The group proposes an alternative model for the formation of nitrogen, oxygen, and water based on the history of the Earth’s atmosphere.

Structure of γ-orthopyroxene (Mg0.44Fe0.56) SiO3 mineral under a high pressure of 32 GPa. (a) Network of oxygen tetrahedra and octahedra. (b) Unit cell, where the shortest Mg–Fe distance is indicated by d1.

They postulate that the 25 elements with atomic numbers smaller than iron (26) were created via an endothermic nuclear transmutation of two nuclei, carbon and oxygen. These nuclei could be confined within the natural aragonite lattice core of the Earth’s lower mantle at high temperatures and pressures during lithosphere subduction, which occurs when two tectonic plates converge.

The group describes the endothermic nuclear transformation process as being “aided by the physical catalysis of excited electrons generated by the stick-slipping movement of mineral compounds of geoneutrinos produced deep within the Earth’s mantle by nuclear fusion of deuterons or radioactive decay of elements.” “Our study suggests that the Earth itself has been able to create lighter elements by nuclear transmutation,” said Mikio Fukuhara, a co-author from Tohoku University’s New Industry Creation Hatchery Center in Japan.

Cross section of the Earth’s interior showing the crust, upper mantle, lower mantle, and outer and inner cores. The formation of lighter elements can be interpreted as the result of endothermic nuclear transmutation of two atom nuclei in natural minerals carried by lithosphere subduction. The process is aided by the physical catalysis of excited electrons (e*) generated by stick slipping of mineral compounds and geoneutrinos produced deep in the Earth’s mantle by nuclear fusion of deuterons and/or radioactive decay of elements.

If accurate, this is a revolutionary discovery because “it was previously theorized that all of these elements were sourced from supernova explosions, whereas we postulate a supplementary theory,” Fukuhara said. This work will have a considerable impact on the field of geophysics and may, as a result, “indicate possible research directions for the potential to create the elements required for future space development,” said Fukuhara.