ST/ Rocky planets can form in extreme environments

Paradigm

Published in

Paradigm

33 min readDec 7, 2023

Space biweekly vol.89, 21st November — 7th December

TL;DR

Astronomers have provided the first observation of water and other molecules in the highly irradiated inner, rocky-planet-forming regions of a disk in one of the most extreme environments in our galaxy. These results suggest that the conditions for terrestrial planet formation can occur in a possible broader range of environments than previously thought.
Micrometeorites originating from icy celestial bodies in the outer Solar System may be responsible for transporting nitrogen to the near-Earth region in the early days of our solar system.
Cutting-edge computer simulations combined with theoretical calculations are helping astronomers better understand the origin of some of the universe’s most energetic and mysterious light shows — gamma-ray bursts, or GRBs. The new unified model confirms that some long-lasting GRBs are created in the aftermath of cosmic mergers that spawn an infant black hole surrounded by a giant disk of natal material.
The discovery of a planet that is far too massive for its sun is calling into question what was previously understood about the formation of planets and their solar systems.
The universe is expanding. How fast it does so is described by the so-called Hubble-Lemaitre constant. But there is a dispute about how big this constant actually is: Different measurement methods provide contradictory values. This so-called ‘Hubble tension’ poses a puzzle for cosmologists. Researchers are now proposing a new solution: Using an alternative theory of gravity, the discrepancy in the measured values can be easily explained — the Hubble tension disappears.
Astronomers have found a key new system of six transiting planets orbiting a bright star in a harmonic rhythm. This rare property enabled the team to determine the planetary orbits which initially appeared as an unsolvable riddle.
In a remarkable discovery, astronomers have found a disc around a young star in the Large Magellanic Cloud, a galaxy neighboring ours. It’s the first time such a disc, identical to those forming planets in our own Milky Way, has ever been found outside our galaxy. The new observations reveal a massive young star, growing and accreting matter from its surroundings and forming a rotating disc.
Asteroid Phaethon, which is five kilometers in diameter, has been puzzling researchers for a long time. A comet-like tail is visible for a few days when the asteroid passes closest to the Sun during its orbit. However, the tails of comets are usually formed by vaporizing ice and carbon dioxide, which cannot explain this tail. The tail should be visible at Jupiter’s distance from the Sun.
Wondering whether whether Dark Matter particles actually are produced inside a jet of standard model particles, led researchers to explore a new detector signature known as semi-visible jets, which scientists never looked at before.
Scientists have simulated conditions that allow hazy skies to form in water-rich exoplanets, a crucial step in determining how haziness muddles important telescope observations for the search of habitable worlds beyond the solar system.
And more!

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

Space industry news

Latest research

XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Protoplanetary Disk

by María Claudia Ramírez-Tannus, Arjan Bik, Lars Cuijpers, et al in The Astrophysical Journal Letters

An international team of astronomers has used NASA’s James Webb Space Telescope to provide the first observation of water and other molecules in the highly irradiated inner, rocky-planet-forming regions of a disk in one of the most extreme environments in our galaxy. These results suggest that the conditions for terrestrial planet formation can occur in a possible broader range of environments than previously thought.

These are the first results from the eXtreme Ultraviolet Environments (XUE) James Webb Space Telescope program, which focuses on the characterization of planet-forming disks (vast, spinning clouds of gas, dust, and chunks of rock where planets form and evolve) in massive star-forming regions. These regions are likely representative of the environment in which most planetary systems formed. Understanding the impact of environment on planet formation is important for scientists to gain insights into the diversity of the different types of exoplanets.

The XUE program targets a total of 15 disks in three areas of the Lobster Nebula (also known as NGC 6357), a large emission nebula roughly 5,500 light-years away from Earth in the constellation Scorpius. The Lobster Nebula is one of the youngest and closest massive star-formation complexes, and is host to some of the most massive stars in our galaxy. Massive stars are hotter, and therefore emit more ultraviolet (UV) radiation. This can disperse the gas, making the expected disk lifetime as short as a million years. Thanks to Webb, astronomers can now study the effect of UV radiation on the inner rocky-planet forming regions of protoplanetary disks around stars like our Sun.

This spectrum shows data from the protoplanetary disk termed XUE 1, which is located in the star cluster Pismis 24. The inner disk around XUE 1 revealed signatures of water (highlighted here in blue), as well as acetylene (C2H2, green), hydrogen cyanide (HCN, brown), and carbon dioxide (CO2, red). As indicated, some of the emission detected was weaker than some of the predicted models, which might imply a small outer disk radius. NASA, ESA, CSA, M. Ramírez-Tannus (Max Planck Institute for Astronomy), J. Olmsted (STScI)

Continuum-subtracted MIRI spectrum of XUE 1 (black) with the best-fit slab models. Molecules are shown with colors, and the purple shaded area shows the total model spectrum.

“Webb is the only telescope with the spatial resolution and sensitivity to study planet-forming disks in massive star-forming regions,” said team lead María Claudia Ramírez-Tannus of the Max Planck Institute for Astronomy in Germany.

Astronomers aim to characterize the physical properties and chemical composition of the rocky-planet-forming regions of disks in the Lobster Nebula using the Medium Resolution Spectrometer on Webb’s Mid-Infrared Instrument (MIRI). This first result focuses on the protoplanetary disk termed XUE 1, which is located in the star cluster Pismis 24.

“Only the MIRI wavelength range and spectral resolution allow us to probe the molecular inventory and physical conditions of the warm gas and dust where rocky planets form,” added team member Arjan Bik of Stockholm University in Sweden.

Due to its location near several massive stars in NGC 6357, scientists expect XUE 1 to have been constantly exposed to high amounts of ultraviolet radiation throughout its life. However, in this extreme environment the team still detected a range of molecules that are the building blocks for rocky planets.

Left: HST/ACS F850LP band image of the target position for XUE 1. The three point-like objects are marked by green circles with radii of 01. The cyan circle on A1 marks the position of the Gaia DR3 source 5976051168205228416. The magenta circle (05 radius) marks the position of the Chandra X-ray source. A grid of J2000 coordinates is shown. Right: MIRI F560W image (log intensity scale) of the target position for XUE 1. The white box marks the observed field of view with MRS. The optical positions of the three point-like objects A1, A2, and B are marked by green circles with radii of 01.

“We find that the inner disk around XUE 1 is remarkably similar to those in nearby star-forming regions,” said team member Rens Waters of Radboud University in the Netherlands. “We’ve detected water and other molecules like carbon monoxide, carbon dioxide, hydrogen cyanide, and acetylene. However, the emission found was weaker than some models predicted. This might imply a small outer disk radius.”

“We were surprised and excited because this is the first time that these molecules have been detected under these extreme conditions,” added Lars Cuijpers of Radboud University. The team also found small, partially crystalline silicate dust at the disk’s surface. This is considered to be the building blocks of rocky planets.

These results are good news for rocky planet formation, as the science team finds that the conditions in the inner disk resemble those found in the well-studied disks located in nearby star-forming regions, where only low-mass stars form. This suggests that rocky planets can form in a much broader range of environments than previously believed.

The team notes that the remaining observations from the XUE program are crucial to establish the commonality of these conditions.

“XUE 1 shows us that the conditions to form rocky planets are there, so the next step is to check how common that is,” said Ramírez-Tannus. “We will observe other disks in the same region to determine the frequency with which these conditions can be observed.”

Influx of nitrogen-rich material from the outer Solar System indicated by iron nitride in Ryugu sample

by Toru Matsumoto, Takaaki Noguchi, Akira Miyake, et al in Nature Astronomy

Micrometeorites originating from icy celestial bodies in the outer Solar System may be responsible for transporting nitrogen to the near-Earth region in the early days of our solar system. That discovery was published by an international team of researchers, including University of Hawai’i at Manoa scientists, led by Kyoto University.

Nitrogen compounds, such as ammonium salts, are abundant in material born in regions far from the sun, but evidence of their transport to Earth’s orbital region had been poorly understood.

“Our recent findings suggests the possibility that a greater amount of nitrogen compounds than previously recognized was transported near Earth, potentially serving as building blocks for life on our planet,” says Hope Ishii, study co-author and affiliate faculty at the Hawai’i Institute of Geophysics and Planetology in the UH Manoa School of Ocean and Earth Science and Technology (SOEST).

Like all asteroids, Ryugu is a small, rocky object that orbits the sun. The Japan Aerospace Exploration Agency’s Hayabusa2 spacecraft explored Ryugu and brought material from its surface back to Earth in 2020. This intriguing asteroid is rich in carbon and has undergone significant space weathering caused by micrometeorite collisions and exposure to charged ions streaming from the sun.

TEM and STEM analysis of modified framboidal magnetite in a Ryugu grain.

In this study, the scientists aimed to discover clues about the materials arriving near Earth’s orbit, where Ryugu is currently located, by examining the evidence of space weathering in Ryugu samples. Using an electron microscope, they found that the surface of the Ryugu samples are covered with tiny minerals composed of iron and nitrogen (iron nitride: Fe4N).

“We proposed that tiny meteorites, called micrometeorites, containing ammonia compounds were delivered from icy celestial bodies and collided with Ryugu,” said Toru Matsumoto, lead author of the study and assistant professor at Kyoto University. “The micrometeorite collisions trigger chemical reactions on magnetite and lead to the formation of the iron nitride.”

The iron nitride was observed on the surface of magnetite, which consists of iron and oxygen atoms. When magnetite is exposed to the space environment, oxygen atoms are lost from the surface by the irradiation of hydrogen ions from the sun (solar wind) and by heating through micrometeorite impact. These processes form metallic iron on the very surface of the magnetite, which readily reacts with ammonia, creating ideal conditions for synthesis of iron nitride.

A Unified Picture of Short and Long Gamma-Ray Bursts from Compact Binary Mergers

by Ore Gottlieb, Brian D. Metzger, Eliot Quataert, Danat Issa, Tia Martineau, Francois Foucart, Matthew D. Duez, Lawrence E. Kidder, Harald P. Pfeiffer, Mark A. Scheel in The Astrophysical Journal Letters

Cutting-edge computer simulations combined with theoretical calculations are helping astronomers better understand the origin of some of the universe’s most energetic and mysterious light shows — gamma-ray bursts, or GRBs. The new unified model confirms that some long-lasting GRBs are created in the aftermath of cosmic mergers that spawn an infant black hole surrounded by a giant disk of natal material.

Astronomers previously thought that black holes that generate long GRBs typically form when massive stars collapse. However, the new model shows that they can also arise when two dense objects merge, such as a pair of neutron stars — the dense, dead remnants of massive stars — or a black hole and a neutron star. The findings explain recently observed long GRBs that astronomers couldn’t link to collapsing stars.

“Our findings, which connect observations with underlying physics, have unified many unresolved mysteries in the field of gamma-ray bursts,” says Ore Gottlieb, lead author on the new study and a research fellow at the Flatiron Institute’s Center for Computational Astrophysics (CCA) in New York City. “For the first time, we can look at GRB observations and know what happened before the black hole formed.”

GRBs are some of the brightest and most violent events in the cosmos. Since their first detection in 1967, GRBs have dazzled and puzzled astronomers. Even decades later, the exact mechanisms that generate the powerful blasts of gamma rays remain uncertain. Over the years, astronomers have noticed two distinct populations of GRBs — ones lasting less than a second and others that linger for 10 seconds or more. Researchers eventually determined that short GRBs originate from jets launched after the merger of two compact objects and that long GRBs can occur when jets are launched during the collapse of massive rotating stars. But in the past year, two unusual long GRB observations suggested that collapsing behemoths weren’t the only things causing long GRBs.

The jet power evolution of postmerger accretion disks for varying levels of magnetic flux ranging from non-MAD to MAD. Dark gray lines show the postmerger mass accretion rate evolution (right vertical axis) obtained for four BH–NS merger simulations (Gottlieb et al. 2023a) and the five BNS merger simulations presented here, all of which generate massive disks, Md ≈ 0.1 M⊙

Gottlieb and his colleagues ran state-of-the-art simulations to test how mergers of massive compact objects can spark GRBs. The new simulations took months to run and were conducted in part on one of the Flatiron Institute’s supercomputers. The new simulations start when the two compact objects are in a close orbit and follow the jets until they are far from the merger site. This approach allows the researchers to make fewer assumptions about the physics involved. By combining the simulations with constraints from astronomical data, the scientists constructed a unified model for the GRB origins.

The researchers determined that the unusual GRBs are generated in the aftermath of a merger between two compact objects. After merging, the objects create a black hole surrounded by a large accretion disk — a rapidly-rotating doughnut of magnetically charged leftover material — that can pump out long GRBs. This information from the simulation helps astronomers understand not only the objects creating these GRBs but also what came before them.

“If we see a long GRB like the ones observed in 2022, we now know that it’s coming from a black hole with a massive disk,” Gottlieb says. “And knowing there is a massive disk, we now can figure out the ratio of the masses of the two parental objects because their mass ratio is related to the properties of the disk. For example, the merger of unequal-mass neutron stars will inevitably produce a long-duration GRB.”

The scientists hope to use the unified model to identify what objects create short GRBs. Those bursts, the model suggests, could be caused by black holes with smaller accretion disks, or they might come from an object called a hypermassive neutron star, which is an unstable form of the star that quickly collapses to form a black hole, but not before it pulses out short GRBs. The scientists hope that with more observations of GRBs, they can further refine their simulation to determine all GRB origins. Though GRB sightings remain relatively rare, astronomers aim to capture many more when the Vera C. Rubin Observatory starts observing in early 2025.

“As we get more observations of GRBs at different pulse durations, we’ll be better able to probe the central engines powering these extreme events,” Gottlieb says.

A Neptune-mass exoplanet in close orbit around a very low-mass star challenges formation models

by Guðmundur Stefánsson, Suvrath Mahadevan, Yamila Miguel, et al in Science

The discovery of a planet that is far too massive for its sun is calling into question what was previously understood about the formation of planets and their solar systems, according to Penn State researchers.

In a paper, researchers report the discovery of a planet more than 13 times as massive as Earth orbiting the “ultracool” star LHS 3154, which itself is nine times less massive than the sun. The mass ratio of the newly found planet with its host star is more than 100 times higher than that of Earth and the sun.

The finding reveals the most massive known planet in a close orbit around an ultracool dwarf star, the least massive and coldest stars in the universe. The discovery goes against what current theories would predict for planet formation around small stars and marks the first time a planet with such high mass has been spotted orbiting such a low-mass star.

“This discovery really drives home the point of just how little we know about the universe,” said Suvrath Mahadevan, the Verne M. Willaman Professor of Astronomy and Astrophysics at Penn State and co-author on the paper. “We wouldn’t expect a planet this heavy around such a low-mass star to exist.”

He explained that stars are formed from large clouds of gas and dust. After the star is formed, the gas and dust remain as disks of material orbiting the newborn star, which can eventually develop into planets.

“The planet-forming disk around the low-mass star LHS 3154 is not expected to have enough solid mass to make this planet,” Mahadevan said. “But it’s out there, so now we need to reexamine our understanding of how planets and stars form.”

An artistic rendering of the mass comparison of LHS 3154 system and our own Earth and Sun. Credit: Penn State / Penn State. Creative Commons

The researchers spotted the oversized planet, named LHS 3154b, using an astronomical spectrograph built at Penn State by a team of scientists led by Mahadevan. The instrument, called the Habitable Zone Planet Finder or HPF, was designed to detect planets orbiting the coolest stars outside our solar system with the potential for having liquid water — a key ingredient for life — on their surfaces. While such planets are very difficult to detect around stars like our sun, the low temperature of ultracool stars means that planets capable of having liquid water on their surface are much closer to their star relative to Earth and the sun. This shorter distance between these planets and their stars, combined with the low mass of the ultracool stars, results in a detectable signal announcing the presence of the planet, Mahadevan explained.

“Think about it like the star is a campfire. The more the fire cools down, the closer you’ll need to get to that fire to stay warm,” Mahadevan said. “The same is true for planets. If the star is colder, then a planet will need to be closer to that star if it is going to be warm enough to contain liquid water. If a planet has a close enough orbit to its ultracool star, we can detect it by seeing a very subtle change in the color of the star’s spectra or light as it is tugged on by an orbiting planet.”

Located at the Hobby-Eberly Telescope at the McDonald Observatory in Texas, the HPF provides some of the highest precision measurements to date of such infrared signals from nearby stars.

“Making the discovery with HPF was extra special, as it is a new instrument that we designed, developed and built from the ground-up for the purpose of looking at the uncharted planet population around the lowest mass stars,” said Guðmundur Stefánsson, NASA Sagan Fellow in Astrophysics at Princeton University and lead author on the paper, who helped develop HPF and worked on the study as a graduate student at Penn State. “Now we are reaping the rewards, learning new and unexpected aspects of this exciting population of planets orbiting some of the most nearby stars.”

The instrument has already yielded critical information in the discovery and confirmation of new planets, Stefánsson explained, but the discovery of the planet LHS 3154b exceeded all expectations.

“Based on current survey work with the HPF and other instruments, an object like the one we discovered is likely extremely rare, so detecting it has been really exciting,” said Megan Delamer, astronomy graduate student at Penn State and co-author on the paper. “Our current theories of planet formation have trouble accounting for what we’re seeing.”

In the case of the massive planet discovered orbiting the star LHS 3154, the heavy planetary core inferred by the team’s measurements would require a larger amount of solid material in the planet-forming disk than current models would predict, Delamer explained. The finding also raises questions about prior understandings of the formation of stars, as the dust-mass and dust-to-gas ratio of the disk surrounding stars like LHS 3154 — when they were young and newly formed — would need to be 10 times higher than what was observed in order to form a planet as massive as the one the team discovered.

“What we have discovered provides an extreme test case for all existing planet formation theories,” Mahadevan said. “This is exactly what we built HPF to do, to discover how the most common stars in our galaxy form planets — and to find those planets.”

A simultaneous solution to the Hubble tension and observed bulk flow within 250 h−1 Mpc

by Sergij Mazurenko, Indranil Banik, Pavel Kroupa, Moritz Haslbauer in Monthly Notices of the Royal Astronomical Society

The universe is expanding. How fast it does so is described by the so-called Hubble-Lemaitre constant. But there is a dispute about how big this constant actually is: Different measurement methods provide contradictory values. This so-called “Hubble tension” poses a puzzle for cosmologists. Researchers from the Universities of Bonn and St. Andrews are now proposing a new solution: Using an alternative theory of gravity, the discrepancy in the measured values can be easily explained — the Hubble tension disappears.

The expansion of the universe causes the galaxies to move away from each other. The speed at which they do this is proportional to the distance between them. For instance, if galaxy A is twice as far away from Earth as galaxy B, its distance from us also grows twice as fast. The US astronomer Edwin Hubble was one of the first to recognize this connection.

In order to calculate how fast two galaxies are moving away from each other, it is therefore necessary to know how far apart they are. However, this also requires a constant by which this distance must be multiplied. This is the so-called Hubble-Lemaitre constant, a fundamental parameter in cosmology. Its value can be determined, for example, by looking at the very distant regions of the universe. This gives a speed of almost 244,000 kilometers per hour per megaparsec distance (one megaparsec is just over three million light years).

“But you can also look at celestial bodies that are much closer to us — so-called category 1a supernovae, which are a certain type of exploding star,” explains Prof. Dr. Pavel Kroupa from the Helmholtz Institute of Radiation and Nuclear Physics at the University of Bonn. It is possible to determine the distance of a 1a supernova to Earth very precisely. We also know that shining objects change color when they move away from us — and the faster they move, the stronger the change. This is similar to an ambulance, whose siren sounds deeper as it moves away from us.

If we now calculate the speed of the 1a supernovae from their color shift and correlate this with their distance, we arrive at a different value for the Hubble-Lemaitre constant — namely just under 264,000 kilometers per hour per megaparsec distance. “The universe therefore appears to be expanding faster in our vicinity — that is, up to a distance of around three billion light years — than in its entirety,” says Kroupa. “And that shouldn’t really be the case.”

However, there has recently been an observation that could explain this. According to this, the Earth is located in a region of space where there is relatively little matter — comparable to an air bubble in a cake. The density of matter is higher around the bubble. Gravitational forces emanate from this surrounding matter, which pull the galaxies in the bubble towards the edges of the cavity. “That’s why they are moving away from us faster than would actually be expected,” explains Dr. Indranil Banik from St. Andrews University. The deviations could therefore simply be explained by a local “under-density.”

In fact, another research group recently measured the average speed of a large number of galaxies that are 600 million light years away from us. “It was found that these galaxies are moving away from us four times faster than the standard model of cosmology allows,” explains Sergij Mazurenko from Kroupa’s research group, who was involved in the current study.

Bulk flows in spheres of different radii around an observer with a suitable CMB-frame velocity for the Maxwell–Boltzmann, Gaussian, and Exponential density profiles (green, red, and blue curves, respectively).

This is because the standard model does not provide for such under-densities or “bubbles” — they should not actually exist. Instead, matter should be evenly distributed in space. If this were the case, however, it would be difficult to explain which forces propel the galaxies to their high speed.

“The standard model is based on a theory of the nature of gravity put forward by Albert Einstein,” says Kroupa. “However, the gravitational forces may behave differently than Einstein expected.” The working groups from the Universities of Bonn and St. Andrews have used a modified theory of gravity in a computer simulation. This “modified Newtonian dynamics” (abbreviation: MOND) was proposed four decades ago by the Israeli physicist Prof. Dr. Mordehai Milgrom. It is still considered an outsider theory today. “In our calculations, however, MOND does accurately predict the existence of such bubbles,” says Kroupa.

If one were to assume that gravity actually behaves according to Milgrom’s assumptions, the Hubble tension would disappear: There would actually only be one constant for the expansion of the universe, and the observed deviations would be due to irregularities in the distribution of matter.

A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067

by R. Luque, H. P. Osborn, A. Leleu, E. Pallé, A. Bonfanti, O. Barragán, Tet al in Nature

An international collaboration between astronomers using the CHEOPS and TESS space satellites, including NCCR PlanetS members from the University of Bern and the University of Geneva, have found a key new system of six transiting planets orbiting a bright star in a harmonic rhythm. This rare property enabled the team to determine the planetary orbits which initially appeared as an unsolvable riddle.

CHEOPS is a joint mission by ESA and Switzerland, under the leadership of the University of Bern in collaboration with the University of Geneva. Thanks to a collaboration with scientists working with data from NASA’s satellite TESS, the international team could uncover the planetary system orbiting the nearby star HD110067. A very distinctive feature of this system is its chain of resonances: the planets orbit their host star in perfect harmony. Part of the research team are researchers from the University of Bern and the University of Geneva who are also members of the National Center of Competence in Research (NCCR) PlanetS.

The planets in the HD110067 system revolve around the star in a very precise waltz. When the closest planet to the star makes three full revolutions around it, the second one makes exactly two during the same time. This is called a 3:2 resonance. “Amongst the over 5000 exoplanets discovered orbiting other stars than our Sun, resonances are not rare, nor are systems with several planets. What is extremely rare though, is to find systems where the resonances span such a long chain of six planets” points out Dr. Hugh Osborn, CHEOPS fellow at the University of Bern, leader of CHEOPS observation programme involved in the study, and co-author of the publication. This is precisely the case of HD110067 whose planets form a so-called “resonant chain” in successive pairs of 3:2, 3:2, 3:2, 4:3, and 4:3 resonances, resulting in the closest planet completing six orbits while the outer-most planet does one.

Although multiple planets were initially detected thanks to their transits, the exact arrangement of the planets was unclear at first. However, the precise gravitational dance enabled the scientists’ team to solve the puzzle of HD110067. Prof. Adrien Leleu from the University of Geneva, in charge of analysing the orbital resonances, and co-author of the study, explains: “A transit occurs when a planet, from our point of view, passes in front of its host star, blocking a minute fraction of the starlight, creating an apparent dip of its brightness.” From the first observations carried out by NASA’s TESS satellite, it was possible to determine that the two inner planets called ‘b’ and ‘c’ have orbital periods of 9 and 14 days respectively. However, no conclusions could be drawn for the other four detected planets as two were seen to transit once in 2020 and once in 2022 with a large 2-year gap in the data, and the other two transited only once in 2022.

The solution to the puzzle for those four additional planets finally began to emerge thanks to observations with the CHEOPS space telescope. While TESS aims at scanning all of the sky bit by bit to find short-period exoplanets, CHEOPS is a targeted mission, focusing on a single star at a time with exquisite precision. “Our CHEOPS observations enabled us to find that the period of planet ‘d’ is 20.5 days. Also, it ruled out multiple possibilities for the remaining three outer planets, ‘e’, ‘f’ and ‘g’,” reveals Osborn.

Transit duration versus transit depth for all unassigned transits in the TESS data.

That is when the team realized that the three inner planets of HD110067 are dancing in a precise 3:2, 3:2 chain of resonances: when the innermost planet revolves nine times around the star, the second revolves six times and the third planet four times.

The team then considered the possibility that the three other planets could also be part of the chain of resonances. “This led to dozens of possibilities for their orbital period,” explains Leleu, “but combining existing observational data from TESS and CHEOPS, with our model of the gravitational interactions between the planets, we could exclude all solutions but one: the 3:2, 3:2, 3:2, 4:3, 4:3 chain.” The scientists could therefore predict that the outer three planets (‘e’, ‘f’ and ‘g’) have orbital periods of 31, 41 days, and 55 days.

This prediction allowed to schedule observations with a variety of ground-based telescopes. Further transits of planet ‘f’ were observed, revealing it was precisely where theory predicted it based on the resonant-chain. Finally, reanalysis of the data from TESS revealed two hidden transits, one from each of planets ‘f’ and ‘g’, exactly at the times expected by the predictions, confirming the periods of the six planets. Additional CHEOPS observations of each planet, and in particular planet ‘e’ are scheduled in the near future.

From the handful of resonant-chain systems found so far, CHEOPS has highly contributed to the understanding of not only HD110067, but also of TOI-178. Another well-known example of a resonant-chain system is the TRAPPIST-1 system which hosts seven rocky planets. However, TRAPPIST-1 is a small and incredibly faint star which makes any additional observations very difficult. HD110067, on the other hand, is more than 50 times brighter than TRAPPIST-1.

“The fact that the planets in the HD110067 system have been detected by the transit method is key. While they pass in front of the star, light also filters through the planetary atmospheres” points out Jo Ann Egger, PhD student at the University of Bern, who computed the composition of the planets using CHEOPS data, and co-author of the study. This property is allowing astronomers to determine the chemical composition and other properties of the atmospheres. Since a lot of light is required, the bright star HD110067 and its orbiting planets are an ideal target for further studies to charachterize the planetary atmospheres. “The sub-Neptune planets of the HD110067 system appear to have low masses, suggesting they may be gas- or water-rich. Future observations, for example with the James Webb Space Telescope (JWST), of these planetary atmospheres could determine whether the planets have rocky or water-rich interior structures,” concludes Egger.

A probable Keplerian disk feeding an optically revealed massive young star

by Anna F. McLeod, Pamela D. Klaassen, Megan Reiter, Jonathan Henshaw, Rolf Kuiper, Adam Ginsburg in Nature

In a remarkable discovery, astronomers have found a disc around a young star in the Large Magellanic Cloud, a galaxy neighbouring ours. It’s the first time such a disc, identical to those forming planets in our own Milky Way, has ever been found outside our galaxy. The new observations reveal a massive young star, growing and accreting matter from its surroundings and forming a rotating disc. The detection was made using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, in which the European Southern Observatory (ESO) is a partner.

“When I first saw evidence for a rotating structure in the ALMA data I could not believe that we had detected the first extragalactic accretion disc, it was a special moment,” says Anna McLeod, an associate professor at Durham University in the UK and lead author of the study published today in Nature. “We know discs are vital to forming stars and planets in our galaxy, and here, for the first time, we’re seeing direct evidence for this in another galaxy.”

This study follows up observations with the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope (VLT), which spotted a jet from a forming star — the system was named HH 1177 — deep inside a gas cloud in the Large Magellanic Cloud. “We discovered a jet being launched from this young massive star, and its presence is a signpost for ongoing disc accretion,” McLeod says. But to confirm that such a disc was indeed present, the team needed to measure the movement of the dense gas around the star.

As matter is pulled towards a growing star, it cannot fall directly onto it; instead, it flattens into a spinning disc around the star. Closer to the centre, the disc rotates faster, and this difference in speed is the smoking gun that shows astronomers an accretion disc is present.

“The frequency of light changes depending on how fast the gas emitting the light is moving towards or away from us,” explains Jonathan Henshaw, a research fellow at Liverpool John Moores University in the UK, and co-author of the study. “This is precisely the same phenomenon that occurs when the pitch of an ambulance siren changes as it passes you and the frequency of the sound goes from higher to lower.”

The detailed frequency measurements from ALMA allowed the authors to distinguish the characteristic spin of a disc, confirming the detection of the first disc around an extragalactic young star.

Massive stars, like the one observed here, form much more quickly and live far shorter lives than low-mass stars like our Sun. In our galaxy, these massive stars are notoriously challenging to observe and are often obscured from view by the dusty material from which they form at the time a disc is shaping around them. However, in the Large Magellanic Cloud, a galaxy 160 000 light-years away, the material from which new stars are being born is fundamentally different from that in the Milky Way. Thanks to the lower dust content, HH 1177 is no longer cloaked in its natal cocoon, offering astronomers an unobstructed, if far away, view of star and planet formation.

Thermal decomposition as the activity driver of near-Earth asteroid (3200) Phaethon

by Eric MacLennan, Mikael Granvik in Nature Astronomy

The asteroid that causes the Geminid shooting star swarm has also puzzled researchers with its comet-like tail. The infrared spectrum of rare meteorites helped to determine the composition of the asteroid.

Asteroid Phaethon, which is five kilometers in diameter, has been puzzling researchers for a long time. A comet-like tail is visible for a few days when the asteroid passes closest to the Sun during its orbit.

However, the tails of comets are usually formed by vaporizing ice and carbon dioxide, which cannot explain this tail. The tail should be visible already at Jupiter’s distance from the Sun. When the surface layer of an asteroid breaks up, the detached gravel and dust continue to travel in the same orbit and give birth to a cluster of shooting stars when it encounters the Earth. Phaethon causes the Geminid meteor shower, which also appears in the skies of Finland every year around mid-December. At least according to the prevailing hypothesis because that’s when the Earth crosses the asteroid’s path. Until now, theories about what happens on Phaethon’s surface near the Sun have remained purely hypothetical. What comes off the asteroid? How? The answer to the riddle was found by understanding the composition of Phaethon.

In a recent study published in the journal Nature Astronomy by researchers from the University of Helsinki, the infrared spectrum of Phaethon previously measured by NASA’s Spitzer space telescope is re-analyzed and compared to infrared spectra of meteorites measured in laboratories. The researchers found that Phaethon’s spectrum corresponds exactly to a certain type of meteorite, the so-called CY carbonaceous chondrite. It is a very rare type of meteorite, of which only six specimens are known.

Meteorite principal component analysis results.

Asteroids can also be studied by retrieving samples from space, but meteorites can be studied without expensive space missions. Asteroids Ryugu and Bennu, the targets of recent JAXA and NASA sample-return missions, belong to CI and CM meteorites. All three types of meteorites originate from the birth of the Solar System, and partially resemble each other, but only the CY group shows signs of drying and thermal decomposition due to recent heating. All three groups show signs of a change that occurred during the early evolution of the Solar System, where water combines with other molecules to form phyllosilicate and carbonate minerals. However, CY-type meteorites differ from others due to their high iron sulfide content, which suggests their own origin.

Analysis of Phaethon’s infrared spectrum showed that the asteroid was composed of at least olivine, carbonates, iron sulfides, and oxide minerals. All of these minerals supported the connection to the CY meteorites, especially iron sulfide. The carbonates suggested changes in water content that fit the primitive composition, while the olivine is a product of thermal decomposition of phyllosilicates at extreme temperatures.

In the research, it was possible to show with thermal modeling what temperatures prevail on the surface of the asteroid and when certain minerals break down and release gases. When Phaethon passes close to the Sun, its surface temperature rises to about 800°C. The CY meteorite group fits this well. At similar temperatures, carbonates produce carbon dioxide, phyllosilicates release water vapor and sulfides sulfur gas. According to the study, all the minerals identified on Phaethon appear to correspond to the minerals of CY-type meteorites. The only exceptions were the oxides portlandite and brucite, which were not detected in the meteorites. However, these minerals can form when carbonates are heated and destroyed in the presence of water vapor.

Asteroid composition and temperature explained the formation of gas near the Sun, but do they also explain the dust and gravel forming the Geminid meteors? Did the asteroid have enough pressure to lift dust and rock from the surface of the asteroid? The researchers used experimental data from other studies in conjunction with their thermal models, and, based on them, it was estimated that when the asteroid passes closest to the Sun, gas is released from the mineral structure of the asteroid, which can cause the rock to break down. In addition, the pressure produces by carbon dioxide and water vapor is high enough to lift small dust particles from the surface of the asteroid.

“Sodium emission can explain the weak tail we observe near the Sun, and thermal decomposition can explain how dust and gravel are released from Phaethon,” says the study’s lead author, postdoctoral researcher Eric MacLennan from the University of Helsinki.
“It was great to see how each one of the discovered minerals seemed to fall into place and also explain the behavior of the asteroid,” sums up associate professor Mikael Granvik from the University of Helsinki.

Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS

by G. Aad et al. in Physics Letters B

The existence of Dark Matter is a long-standing puzzle in our universe. Dark Matter makes up about a quarter of our universe, yet it does not interact significantly with ordinary matter. The existence of Dark Matter has been confirmed by a series of astrophysical and cosmological observations, including in the stunning recent pictures from James Webb Space Telescope. However, up to date, no experimental observation of dark matter has been reported. The existence of Dark Matter has been a question that high energy and astrophysicists around the world has been investigating for decades.

“This is the reason we do research in basic science, probing the deepest mysteries of the universe. The Large Hadron Collider at CERN is the largest experiment ever built, and particle collisions creating big-bang like condition can be exploited to look for hints of dark matter,” says Professor Deepak Kar, from the School of Physics at the University of the Witwatersrand in Johannesburg, South Africa.

Working at the ATLAS experiment at CERN, Kar and his former PhD student, Sukanya Sinha (now a postdoctoral researcher at the University of Manchester), has pioneered a new way of searching for Dark Matter.

A diagram illustrating the production of semi-visible jets via a t-channel mediator, Φ, producing a pair of dark quarks, labelled qdark.

“There have been plethora of collider searches for Dark Matter over the past few decades so far have focused on weakly interacting massive particles, termed WIMPs,” says Kar. “WIMPS is one class of particles that are hypothesised to explain Dark Matter as they do not absorb or emit light and don’t interact strongly with other particles. However, as no evidence of WIMPS’ has been found so far, we realised that the search for Dark Matter needed a paradigm shift.”

“What we were wondering, was whether Dark Matter particles actually are produced inside a jet of standard model particles,” said Kar.This led to the exploration of a new detector signature known as semi-visible jets, which scientists never looked at before.

High energy collisions of protons often result in production of collimated spray of particles, collected in what is termed as jets, from decay of ordinary quarks or gluons. Semi-visible jets would arise when hypothetical dark quarks decay partially to Standard-Model quarks (known particles) and partially to stable dark hadrons (the “invisible fraction”). Since they are produced in pairs, typically along with additional Standard-Model jets, the imbalance of energy or the missing energy in the detector arises when all the jets are not fully balanced. The direction of the missing energy is often aligned with one of the semi-visible jets.

This makes searches for semi-visible jets very challenging, as this event signature can also arise due to mis-measured jets in the detector. Kar and Sinha’s new way of looking for Dark Matter opens up new directions into looking for the existence of Dark Matter.

“Even though my PhD thesis does not contain a discovery of Dark Matter, it sets the first and rather stringent upper bounds on this production mode, and already inspiring further studies,” says Sinha.

Optical properties of organic haze analogues in water-rich exoplanet atmospheres observable with JWST

by Chao He, Michael Radke, Sarah E. Moran, Sarah M. Hörst, Nikole K. Lewis, Julianne I. Moses, Mark S. Marley, Natasha E. Batalha, Eliza M.-R. Kempton, Caroline V. Morley, Jeff A. Valenti, Véronique Vuitton in Nature Astronomy

Scientists have simulated conditions that allow hazy skies to form in water-rich exoplanets, a crucial step in determining how haziness muddles observations by ground and space telescopes.

The research offers new tools to study the atmospheric chemistry of exoplanets and will help scientists model how water exoplanets form and evolve, findings that could help in the search for life beyond our solar system.

“The big picture is whether there is life outside the solar system, but trying to answer that kind of question requires really detailed modeling of all different types, specifically in planets with lots of water,” said co-author Sarah Hörst, a Johns Hopkins associate professor of Earth and planetary sciences. “This has been a huge challenge because we just don’t have the lab work to do that, so we are trying to use these new lab techniques to get more out of the data that we’re taking in with all these big fancy telescopes.”

Model spectra of a water-rich atmosphere around a GJ 1214 b -like planet with 10 nm haze particles.

Whether a planet’s atmosphere contains hazes or other particles has a marked influence on global temperatures, incoming levels of starlight, and other factors that can hinder or foster biological activity, the researchers said. The team ran the experiments in a custom-designed chamber within Hörst’s lab. They are the first to determine how much haze can form in water planets beyond the solar system, Hörst said. Haze consists of solid particles suspended in gas, and it alters the way light interacts with that gas. Different levels and kinds of haze can affect how the particles spread out through an atmosphere, changing what scientists can detect about distant planets with telescopes.

“Water is the first thing we look for when we’re trying to see if a planet is habitable, and there are already exciting observations of water in exoplanet atmospheres. But our experiments and modeling suggest these planets most likely also contain haze,” said Chao He, a planetary scientist who led the research at Johns Hopkins. “This haze really complicates our observations, as it clouds our view of an exoplanet’s atmospheric chemistry and molecular features.”

Scientists study exoplanets with telescopes that look at how light passes through their atmosphere, spotting how atmospheric gases absorb different hues or wavelengths of that light. Distorted observations can lead to miscalculations of the amounts of important substances in the air, such as water and methane, and the type and levels of particles in the atmosphere. Such misinterpretations can impair scientists’ conclusions about global temperatures, the thickness of an atmosphere, and other planetary conditions, Hörst said.

The team concocted two gas mixtures containing water vapor and other compounds hypothesized to be common in exoplanets. They beamed those concoctions with ultraviolet light to simulate how light from a star would start the chemical reactions that produce haze particles. They then measured how much light the particles absorbed and reflected to understand how they would interact with light in the atmosphere.

The new data matched the chemical signatures of a well-studied exoplanet called GJ 1214 b more accurately than previous research, demonstrating that hazes with different optical properties can lead to misinterpretations of a planet’s atmosphere.

Alien atmospheres can be very different from those in our solar system, Hörst said, adding that there are more than 5,000 confirmed exoplanets with varying atmospheric chemistries. The team is now working to create more lab-made haze “analogs” with gas mixtures that more accurately represent what they see with telescopes.

“People will be able to use that data when they model those atmospheres to try to understand things like what the temperature is like in the atmosphere and the surface of that planet, whether there are clouds, how high they are and what they are made of, or how fast the winds go,” Hörst said. “All those kinds of things can help us really focus our attention on specific planets and make our experiments unique instead of just running generalized tests when trying to understand the big picture.”