Category Archives: Planetary Science

Solving Solar Puzzle Could Help Save Earth From Planet-wide Blackouts (Planetary Science)

New solar modelling could help predict space weather

Could solar storms knock out the global internet? Yes, but we don’t know when or how it could happen. Mathematician Dr Geoffrey Vasil has proposed a new understanding of the Sun’s convection zone to help.

Lead author of the study Dr Geoffrey Vasil.
Lead author of the study Dr Geoffrey Vasil. Photo: Louise Cooper

Scientists at the University of Sydney and in the USA have solved a long-standing mystery about the Sun that could help astronomers predict space weather and help us prepare for potentially devastating geomagnetic storms if they were to hit Earth.

The Sun’s internal magnetic field is directly responsible for space weather – streams of high-energy particles from the Sun that can be triggered by solar flares, sunspots or coronal mass ejections that produce geomagnetic storms. Yet it is unclear how these happen and it has been impossible to predict when these events will occur.

Now, a new study led by Dr Geoffrey Vasil from the School of Mathematics & Statistics at the University of Sydney could provide a strong theoretical framework to help improve our understanding of the Sun’s internal magnetic dynamo that helps drive near-Earth space weather.

The Sun is made up of several distinct regions. The convection zone is one of the most important – a 200,000-kilometre-deep ocean of super-hot rolling, turbulent fluid plasma taking up the outer 30 percent of the star’s diameter.

Existing solar theory suggests the largest swirls and eddies take up the convection zone, imagined as giant circular convection cells as pictured here by NASA (and published below).

However, these cells have never been found, a long-standing problem known as the ‘Convective Conundrum’.

Dr Vasil said there is a reason for this. Rather than circular cells, the flow breaks up into tall spinning cigar-shaped columns ‘just’ 30,000 kilometres across. This, he said, is caused by a much stronger influence of the Sun’s rotation than previously thought.

“You can balance a skinny pencil on its point if you spin it fast enough,” said Dr Vasil, an expert in fluid dynamics. “Skinny cells of solar fluid spinning in the convection zone can behave similarly.”

The findings have been published in the Proceedings of the National Academy of Sciences of the United States of America.

“We don’t know very much about the inside of the Sun, but it is hugely important if we want to understand solar weather that can directly impact Earth,” Dr Vasil said.

“Strong rotation is known to completely change the properties of magnetic dynamos, of which the Sun is one.”

Artist's image of the internal structure of the Sun. NASA
Diagram showing the internal structure of the Sun based on existing theory that assumes circular convection cells near the solar surface. Dr Vasil’s new model suggests thinner, spinning ‘cigar-shaped’ convection cells driving the Sun’s magnetic dynamo. Image: NASA

Dr Vasil and collaborators Professor Keith Julien of the University of Colorado and Dr Nicholas Featherstone at Southwest Research Institute in Boulder, say that this predicted rapid rotation inside the Sun suppresses what otherwise would be larger-scale flows, creating more variegated dynamics for the outer third of the solar depth.

“By properly accounting for rotation, our new model of the Sun fits observed data and could dramatically improve our understanding of the Sun’s electromagnetic behaviour,” said Dr Vasil, who is the lead author of the study.

In the most extreme cases, solar geomagnetic storms can shower the Earth with pulses of radiation capable of frying our sophisticated global electronics and communication infrastructure.

A huge geomagnetic storm of this type hit Earth in 1859, known as the Carrington Event, but this was before our global reliance on electronics. The fledgling telegraph system from Melbourne to New York was affected.

“A similar event today could destroy trillions of dollars’ worth of global infrastructure and take months, if not years, to repair,” Dr Vasil said.

A solar coronal mass ejection in August 2012

A small-scale event in 1989 caused massive blackouts in Canada in what some initially thought might have been a nuclear attack. In 2012 a solar storm similar in scale to the Carrington Event passed by Earth without impacting, missing our orbit around the Sun by just nine days.

“The next solar max is in the middle of this decade, yet we still don’t know enough about the Sun to predict if these cyclical events will produce a dangerous storm,” Dr Vasil said. 

“While a solar storm hitting Earth is very unlikely, like an earthquake, it will eventually happen and we need to be prepared.”

Solar storms emerging from within the Sun can take from several hours to days to reach Earth. Dr Vasil said that better knowledge of the internal dynamism of our home star could help planners avoid disaster if they have enough warning to shut down equipment before a blast of energetic particles does the job instead.

“We cannot explain how sunspots form. Nor can we discern what sunspot groups are most prone to violent rupture. Policymakers need to know how often it might be necessary to endure a days-long emergency shutdown to avoid a severe catastrophe,” he said.

Dr Vasil and his colleagues’ theoretical model will now need to be tested through observation to further improve the modelling of the Sun’s internal processes. To do this, scientists will use a technique known as helioseismology, to listen inside the beating heart of the star.

“We hope our findings will inspire further observation and research into the driving forces of the Sun,” he said.

This could involve the unprecedented launch of polar orbiter observational satellites outside the elliptical plane of the Solar System.

Declaration

Dr Geoffrey Vasil received no additional funding for this paper. Professor Keith Julien acknowledges support from NASA and the US National Science Foundation. Dr Nicholas Featherstone also acknowledges support from NASA.


Reference: Geoffrey M. Vasil, Keith Julien, Nicholas A. Featherstone. Rotation suppresses giant-scale solar convection. Proceedings of the National Academy of Sciences, 2021; 118 (31): e2022518118 DOI: 10.1073/pnas.2022518118


Provided by University of Sydney

What Lies Beneath The Far Side of the Moon? (Planetary Science)

Researchers have discovered multiple layers of soil that lie directly beneath an area on the far side of the Moon’s surface, overturning an existing theory of a single deep layer in the same area.

A new technique for processing lunar radar data has allowed scientists to see what lies beneath the surface of the Moon in the clearest ever detail.

In a study led by the University of Aberdeen, a team of researchers discovered multiple layers of soil that lie directly beneath an area on the far side of the Moon’s surface, overturning an existing theory of a single deep layer in the same area.

The area studied was the landing site of the Chang’E-4 spacecraft mission – the first to the far side of the Moon.

Analysis of radar data captured by the mission’s rover, Yutu-2, had suggested the existence of a single soil layer in the Moon’s regolith (subsurface).  However, the data did not indicate the existence of different layers of soil, which were transparent to electromagnetic waves due to the smooth boundaries between them.

By developing a new method of processing the data captured by Yutu-2, which uses the shape of radar signatures of buried rocks and boulders to infer the properties of surrounding lunar soil and detect previously unseen layers with smooth boundaries, scientists were able to detect four distinct layers of soil, stacked to a depth of 12 metres.

Dr Iraklis Giannakis, from the University of Aberdeen’s School of Geosciences, led the research in collaboration with counterparts from the University of Edinburgh, Northumbria University and Chinese University of Geosciences Wuhan.  The results have been published in the journal Geophysical Research Letters.

Dr Giannakis said: “The novel radar processing method that we have developed has allowed us to study the radar data from the Chang’E-4 landing site in much greater detail.

This will be of great importance in terms of increasing our understanding of planetary soils, as we can now see what lies beneath the surface in more detail than ever before”

Dr Iraklis Giannakis

“By doing so, we have discovered that, rather than a homogenous 12 metre deep regolith whose material source was thought to be a nearby crater called Finsen, there is a more complicated structure where the first 12 metres consist of four distinct layers that were previously unseen using conventional radar processing.”

Dr Giannakis said that the development of a new method of interpreting lunar radar data is a significant development in planetary exploration.

He said: “We are experiencing the new golden era of space exploration with numerous successful planetary missions and many more planned for the future.

“Tianwen-1 and Perseverance are two successful Mars missions that include radar in their scientific payloads, as well as the Chang’E-3, E-4, E-5 and the planned Chang’E-7 mission.

“The methodology we have developed can be used to infer the properties of the subsurface using radar and detect previously unseen layered structures within the first 10-20 meters of planetary soils.  

“This will be of great importance in terms of increasing our understanding of planetary soils, as we can now see what lies beneath the surface in more detail than ever before.”


Reference: Giannakis, I., Zhou, F., Warren, C., & Giannopoulos, A. (2021). Inferring the Shallow Layered Structure at the Chang’E-4 Landing Site: A Novel Interpretation Approach Using Lunar Penetrating Radar. Geophysical Research Letters, 48, e2021GL092866. https://doi.org/10.1029/2021GL092866


Provided by University of Aberdeen

Lunar Samples Solve Mystery Of the Moon’s Supposed Magnetic Shield (Planetary Science)

Rochester geophysicists’ latest findings will inform the next generation of moon exploration.

In 2024, a new age of space exploration will begin when NASA sends astronauts to the moon as part of their Artemis mission, a follow-up to the Apollo missions of the 1960s and 1970s.

Some of the biggest questions that scientists hope to explore include determining what resources are found in the moon’s soil and how those resources might be used to sustain life.

In a paper published in the journal Science Advances, researchers at the University of Rochester, leading a team of colleagues at seven other institutions, report their findings on a major factor that influences the types of resources that may be found on the moon: whether or not the moon has had a long-lived magnetic shield at any point in its 4.53 billion-year history.

The presence or absence of a shield matters because magnetic shields protect astronomical bodies from harmful solar radiation. And the team’s findings contradict some longstanding assumptions.

“This is a new paradigm for the lunar magnetic field,” says first author John Tarduno, the William R. Kenan, Jr., Professor of Geophysics in the Department of Earth and Environmental Sciences and dean of research for Arts, Sciences & Engineering at Rochester.

Did the moon ever have a magnetic shield?

For years, Tarduno has been a leader in the field of paleomagnetism, studying the development of Earth’s magnetic shield as a means to understanding planetary evolution and environmental change.

Earth’s magnetic shield originates deep within the planet’s core. There, swirling liquid iron generates electric currents, driving a phenomenon called the geodynamo, which produces the shield. The magnetic shield is invisible, but researchers have long recognized that it is vital for life on Earth’s surface because it protects our planet from solar wind—streams of radiation from the sun.

But has Earth’s moon ever had a magnetic shield?“This is a new paradigm for the lunar magnetic field.”

While the moon has no magnetic shield now, there has been debate over whether or not the moon may have had a prolonged magnetic shield at some point in its history.

“Since the Apollo missions, there has been this idea that the moon had a magnetic field that was as strong or even stronger than Earth’s magnetic field at around 3.7 billion years ago,” Tarduno says.

The belief that the moon had a magnetic shield was based on an initial dataset from the 1970s that included analyses of samples collected during the Apollo missions. The analyses showed that the samples had magnetization, which researchers believed was caused by the presence of a geodynamo.

But a couple of factors have since given researchers pause.

“The core of the moon is really small and it would be hard to actually drive that kind of magnetic field,” Tarduno explains. “Plus, the previous measurements that record a high magnetic field were not conducted using heating experiments. They used other techniques that may not accurately record the magnetic field.”

When lunar samples meet lasers

Inset image shows close-up detail of lunar glass subsample in the quartz square tubing and being analyzed by a magnetometer.
A subsample of lunar glass is placed in 2-by-2 millimeter fused quartz square tubing (inset) then analyzed using the lab’s superconducting quantum interference device (SQUID) magnetometer. The results provide information about the moon’s soil—and may help inform a new wave of lunar experiments. (University of Rochester photos / J. Adam Fenster)

Tarduno and his colleagues tested glass samples gathered on previous Apollo missions, but used CO2 lasers to heat the lunar samples for a short amount of time, a method that allowed them to avoid altering the samples. They then used highly sensitive superconducting magnetometers to more accurately measure the samples’ magnetic signals.

“One of the issues with lunar samples has been that the magnetic carriers in them are quite susceptible to alteration,” Tarduno says. “By heating with a laser, there is no evidence of alteration in our measurements, so we can avoid the problems people may have had in the past.”

The researchers determined that the magnetization in the samples could be the result of impacts from objects such as meteorites or comets—not the result of magnetization from the presence of a magnetic shield. Other samples they analyzed had the potential to show strong magnetization in the presence of a magnetic field, but didn’t show any magnetization, further indicating that the moon has never had a prolonged magnetic shield.

“If there had been a magnetic field on the moon, the samples we studied should all have acquired magnetization, but they haven’t,” Tarduno says. “That’s pretty conclusive that the moon didn’t have a long-lasting dynamo field.”

Lack of magnetic shield means an abundance of elements

Astronaut collects lunar samples with a parked lunar roving vehicle in the background.
The belief that the moon had a magnetic shield was based on an initial dataset from the 1970s that included analyses of lunar samples collected during the Apollo missions. (Photo credit: Flickr/NASA Johnson)

Without the protection of a magnetic shield, the moon was susceptible to solar wind, which may have caused a variety of volatiles—chemical elements and compounds that can be easily evaporated—to become implanted in the lunar soil. These volatiles may include carbon, hydrogen, water, and helium 3, an isotope of helium that is not present in abundance on Earth.

“Our data indicates we should be looking at the high end of estimates of helium 3 because a lack of magnetic shield means more solar wind reaches the lunar surface, resulting in much deeper reservoirs of helium 3 than people thought previously,” Tarduno says.

The research may help inform a new wave of lunar experiments based on data that will be gathered by the Artemis mission. Data from samples gathered during the mission will allow scientists and engineers to study the presence of volatiles and better determine if these materials can be extracted for human use. Helium 3, for instance, is currently used in medical imaging and cryogenics and is a possible future fuel source.

A lack of magnetic shielding also means that ancient lunar soils may hold records of past solar wind emissions. Analyzing cores of soil samples could therefore provide scientists with a better understanding of the evolution of the sun.

“With the background provided by our research, scientists can more properly think about the next set of lunar experiments to perform,” Tarduno says. “These experiments may focus on current lunar resources and how we could use them and also on the historical record of what is trapped in the lunar soil.”

Featured image: The lunar glass samples tested by Rochester scientists were gathered during NASA’s 1972 Apollo 16 mission. (University of Rochester photo / J. Adam Fenster)


Reference: John A. Tarduno et al, Absence of a long-lived lunar paleomagnetosphere, Science Advances (2021). DOI: 10.1126/sciadv.abi7647


Provided by University of Rochester

New ESO Observations Show Rocky Exoplanet Has Just Half the Mass of Venus (Planetary Science)

A team of astronomers have used the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile to shed new light on planets around a nearby star, L 98-59, that resemble those in the inner Solar System. Amongst the findings are a planet with half the mass of Venus — the lightest exoplanet ever to be measured using the radial velocity technique — an ocean world, and a possible planet in the habitable zone.“The planet in the habitable zone may have an atmosphere that could protect and support life,”says María Rosa Zapatero Osorio, an astronomer at the Centre for Astrobiology in Madrid, Spain, and one of the authors of the study published today in Astronomy & Astrophysics.

The results are an important step in the quest to find life on Earth-sized planets outside the Solar System. The detection of biosignatures on an exoplanet depends on the ability to study its atmosphere, but current telescopes are not large enough to achieve the resolution needed to do this for small, rocky planets. The newly studied planetary system, called L 98-59 after its star, is an attractive target for future observations of exoplanet atmospheres. Its orbits a star only 35 light-years away and has now been found to host rocky planets, like Earth or Venus, which are close enough to the star to be warm.

With the contribution of ESO’s VLT, the team was able to infer that three of the planets may contain water in their interiors or atmospheres. The two planets closest to the star in the L 98-59 system are probably dry, but might have small amounts of water, while up to 30% of the third planet’s mass could be water, making it an ocean world.

Furthermore, the team found “hidden” exoplanets that had not previously been spotted in this planetary system. They discovered a fourth planet and suspect there is a fifth, in a zone at the right distance from the star for liquid water to exist on its surface. “We have hints of the presence of a terrestrial planet in the habitable zone of this system,” explains Olivier Demangeon, a researcher at the Instituto de Astrofísica e Ciências do Espaço, University of Porto in Portugal and lead author of the new study.

The study represents a technical breakthrough, as astronomers were able to determine, using the radial velocity method, that the innermost planet in the system has just half the mass of Venus. This makes it the lightest exoplanet ever measured using this technique, which calculates the wobble of the star caused by the tiny gravitational tug of its orbiting planets.

The team used the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument on ESO’s VLT to study L 98-59. “Without the precision and stability provided by ESPRESSO this measurement would have not been possible,” says Zapatero Osorio. “This is a step forward in our ability to measure the masses of the smallest planets beyond the Solar System.”

The astronomers first spotted three of L 98-59’s planets in 2019, using NASA’s Transiting Exoplanet Survey Satellite (TESS). This satellite relies on a technique called the transit method — where the dip in the light coming from the star caused by a planet passing in front of it is used to infer the properties of the planet — to find the planets and measure their sizes. However, it was only with the addition of radial velocity measurements made with ESPRESSO and its predecessor, the High Accuracy Radial velocity Planet Searcher (HARPS) at the ESO La Silla 3.6-metre telescope, that Demangeon and his team were able to find extra planets and measure the masses and radii of the first three. “If we want to know what a planet is made of, the minimum that we need is its mass and its radius,” Demangeon explains.

The team hopes to continue to study the system with the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST), while ESO’s Extremely Large Telescope (ELT), under construction in the Chilean Atacama Desert and set to start observations in 2027, will also be ideal for studying these planets. “The HIRES instrument on the ELT may have the power to study the atmospheres of some of the planets in the L 98-59 system, thus complementing the JWST from the ground,” says Zapatero Osorio.

“This system announces what is to come,” adds Demangeon. “We, as a society, have been chasing terrestrial planets since the birth of astronomy and now we are finally getting closer and closer to the detection of a terrestrial planet in the habitable zone of its star, of which we could study the atmosphere.”

More information

This research was presented in a paper entitled “A warm terrestrial planet with half the mass of Venus transiting a nearby star” to appear in Astronomy & Astrophysics (doi: 10.1051/0004-6361/202140728).

The team is composed of Olivier D. S. Demangeon (Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Portugal [IA/UPorto], Centro de Astrofísica da Universidade do Porto, Portugal [CAUP] and Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Portugal [FCUP]), M. R. Zapatero Osorio (Centro de Astrobiología, Madrid, Spain [CSIC-INTA]), Y. Alibert (Physics Institute, University of Bern, Switzerland [Bern]), S. C. C. Barros (IA/UPorto, CAUP and FCUP), V. Adibekyan (IA/UPorto, CAUP and FCUP), H. M. Tabernero (IA/UPorto and CAUP), A. Antoniadis-Karnavas (IA/UPorto & FCUP), J. D. Camacho (IA/UPorto & FCUP), A. Suárez Mascareño (Instituto de Astrofísica de Canarias, Tenerife, Spain [IAC] and Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain [ULL]), M. Oshagh (IAC/ULL), G. Micela (INAF – Osservatorio Astronomico di Palermo, Palermo, Italy), S. G. Sousa (IA/UPortol & CAUP), C. Lovis (Observatoire de Genève, Université de Genève, Geneva, Switzerland [UNIGE]), F. A. Pepe (UNIGE), R. Rebolo (IAC/ULL & Consejo Superior de Investigaciones Científicas, Spain), S. Cristiani (INAF – Osservatorio Astronomico di Trieste, Italy [INAF Trieste]), N. C. Santos (IA/UPorto, CAUP and FCUP), R. Allart (Department of Physics and Institute for Research on Exoplanets, Université de Montréal, Canada and UNIGE), C. Allende Prieto (IAC/ULL), D. Bossini (IA/UPorto), F. Bouchy (UNIGE), A. Cabral (Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Portugal [IA/FCUL] and Departamento de Física da Faculdade de Ciências da Universidade de Lisboa, Portugal), M. Damasso (INAF – Osservatorio Astrofisico di Torino, Italy [INAF Torino]), P. Di Marcantonio (INAF Trieste), V. D’Odorico (INAF Trieste & Institute for Fundamental Physics of the Universe, Trieste, Italy [IFPU]), D. Ehrenreich (UNIGE), J. Faria (IA/UPorto, CAUP and FCUP), P. Figueira (European Southern Observatory, Santiago de Chile, Chile [ESO-Chile] and IA/UPorto), R. Génova Santos (IAC/ULL), J. Haldemann (Bern), J. I. González Hernández (IAC/ULL), B. Lavie (UNIGE), J. Lillo-Box (CSIC-INTA), G. Lo Curto (European Southern Observatory, Garching bei München, Germany [ESO]), C. J. A. P. Martins (IA/UPorto and CAUP), D. Mégevand (UNIGE), A. Mehner (ESO-Chile), P. Molaro (INAF Trieste and IFPU), N. J. Nunes (IA/FCUL), E. Pallé (IAC/ULL), L. Pasquini (ESO), E. Poretti (Fundación G. Galilei – INAF Telescopio Nazionale Galileo, La Palma, Spain and INAF – Osservatorio Astronomico di Brera, Italy), A. Sozzetti (INAF Torino), and S. Udry (UNIGE).

Featured image: This artist’s impression shows L 98-59b, one of the planets in the L 98-59 system 35 light-years away. The system contains four confirmed rocky planets with a potential fifth, the furthest from the star, being unconfirmed. In 2021, astronomers used data from the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO) instrument on ESO’s VLT to measure the mass of L 98-59b, finding it to be half that of Venus. This makes it the lightest planet measured to date using the radial velocity technique. Credit: ESO/M. Kornmesser


Reference: O. D. S. Demangeon et al, Warm terrestrial planet with half the mass of Venus transiting a nearby star, Astronomy & Astrophysics (2021). DOI: 10.1051/0004-6361/202140728


Provided by ESO

Unparalleled Bounty of Oscillating Red Giant Stars Detected (Planetary Science)

An unprecedented collection of pulsating giant red stars has been identified by astronomers at the University of Hawaiʻi Institute for Astronomy (IfA). Using observations from NASA’s Transiting Exoplanet Survey Satellite (TESS), the researchers detected the stars, whose rhythms arise from internal sound waves and provide the opening chords of a symphonic exploration of our galactic neighborhood.

Related UH News story: UH astronomers to uncover the secrets of stars and exoplanets with NASA‘s TESS satellite, April 18, 2018

Since its launch in 2018, TESS has primarily hunted for exoplanets–worlds beyond our solar system. But its sensitive measurements of changing stellar brightness make the telescope ideal for observing stellar oscillations or material within the internal structure of stars. It’s an area of research called asteroseismology.

 “Our initial result, using only a month of stellar measurements from TESS’s first two years, shows that we can determine the masses and sizes of these oscillating giants with high precision that will only improve as TESS goes on,” said Marc Hon, a NASA Hubble Fellow at IfA. “What’s really unparalleled is that TESS’s broad coverage allows us to make these measurements uniformly across almost the entire sky.”

TESS has identified more than 158,000 pulsating red giants. Credit: NASA

This large bounty of oscillating red giants will be used for unprecedented detailed studies using the ground-based telescopes on Maunakea. 

“We have already started follow-up observations of some of the most intriguing oddballs we have uncovered in our large TESS dataset, which will tell us more about their origin,” said Hon. “We have just scratched the surface of the treasure trove of data enabled by TESS.”

 Hon presented the research on Wednesday during the TESS Science Conference, an event held virtually, August 2–6 and supported by the Massachusetts Institute of Technology in Cambridge, where scientists discuss the latest results of the mission. He is the lead author of the study that is accepted for publication in the Astrophysical Journal, with co-authors including fellow IfA colleagues Jamie Tayar and Daniel Huber

Widening opportunities 

Oscillations in the Sun were first observed in the 1960s. But solar-like oscillations in thousands of stars weren’t detected until the French-led Convection, Rotation and Planetary Transits space telescope, which operated from 2006 to 2013. NASA’s Kepler and K2 missions, which surveyed from 2009 to 2018, found tens of thousands of oscillating giants. TESS is expanding access to these oscillations through its observations in space. 

 “With a sample this large, giants that might occur only one percent of the time become pretty numerous,” said Tayar, a Hubble Postdoctoral Fellow at IfA. “Now we can start thinking about finding even rarer stars.”

TESS monitors large swaths of the sky for about a month at a time using its four cameras, covering about 75% of the sky during its two-year primary mission. Each camera captures a full image 24-by-24 degrees (48 times the size of the Moon in our sky) across, every 30 minutes. Since late summer 2020, the cameras have been collecting these images at an even faster rate.

The images are used to generate light curves—graphs of changing brightness—for nearly 24 million stars, each spanning 27 days, the length of time TESS stares at one patch of the sky. To sift through this immense accumulation of measurements, Hon and his colleagues taught a computer how to recognize pulsating giants. The team used machine learning, a form of artificial intelligence that trains computers to make decisions based on general patterns without explicitly programming them.

 To train the system, the team used Kepler light curves for more than 150,000 stars, of which about 20,000 were oscillating red giants. When the neural network finished processing all of the TESS data, it had identified 158,505 pulsating giants.

 The team determined colors and distances for each giant using data from the European Space Agency’s Gaia mission, and plotted the masses of these stars across the sky. A fundamental prediction in galactic astronomy is that younger, higher-mass stars should lie closer to the plane of the galaxy, marked by the high density of stars that create the glow of the Milky Way in the night sky.

 “Our map demonstrates for the first time that this is indeed the case across nearly the whole sky,” said Huber. “With the help of Gaia, TESS has now given us tickets to a red giant concert in the sky.”

Featured image: Illustration of red giant stars near and far sweeping across the sky. Credit: NASA


Reference: Marc Hon et al, A ‘Quick Look’ at All-Sky Galactic Archeology with TESS: 158,000 Oscillating Red Giants from the MIT Quick-Look Pipeline, arXiv:2108.01241v1 [astro-ph.SR] arxiv.org/abs/2108.01241


Provided by University of Hawaii at Manoa

New Study Sheds Light On the Mysterious Dimming of Betelgeuse (Planetary Science)

Betelgeuse (α Orionis) is the bright reddish star located in the shoulder of the Orion constellation and can be seen by the naked eye in the night sky.

From October 2019 to March 2020, Betelgeuse demonstrated a mysterious dimming, capturing the attention and imagination of both astronomers and the public. While being a variable star that exhibits periodic and sometimes irregular light change, this dimming is the most significant observed in the last 50 years. It became fainter by more than 2.5 times, which even can be noticed by the naked eye in the night sky. Several scenarios have been put forward by astronomers around the world: pre-phase of supernova explosion, obscuring dust, or changes in the photosphere of the star.

A new study led by Prof. Zhao Gang from National Astronomical Observatories of Chinese Academy of Sciences (NAOC) sheds light on the nature of the mysterious dimming of Betelgeuse. Scientists from Shandong University and the University of Missouri (U.S.) also joined this study.

The study was published in Nature Communications on August 5, 2021.

Betelgeuse is the brightest star in the night sky in the near-infrared wavelength range. This is the most suitable wavelength range for investigating red supergiants like Betelgeuse.

The research team investigated the high-resolution near-infrared spectra of Betelgeuse obtained at Weihai Observatory of Shandong University on January 31, March 19, April 4, and April 6, 2020, covering the dimming and post-dimming phases. “Taking our advantage in spectroscopic analysis, we aim to understand the possible cause of the mysterious dimming of Betelgeuse,” said Prof. Zhao Gang, the corresponding author of this study.

To this end, the team developed a special technique for determining the effective temperatures of red supergiants.

“Our method is based on the measurement of titanium oxide (TiO) and cyanide (CN) molecular lines in stellar spectra. The cooler a star is, the more these molecules can form and survive in its atmosphere and the molecular lines are stronger in the stellar spectrum. In a hotter atmosphere, these molecules dissociate easily and do not survive,” said Dr. Sofya Alexeeva, the first author of this study.

“We have found that at the minimum of its luminosity, the effective temperature of Betelgeuse on January 31, 2020, was 3476 Kelvins. However, after it recovered its brightness, on April 6, 2020, the effective temperature was 3646 Kelvins. The changing of the effective temperature by 170 K is sufficient to explain this mysterious dimming,” said Dr. Sofya Alexeeva.

What could lead to a temperature drop by 170 K? It could be caused by a large dark star-spot on the surface of Betelgeuse. The presence of spots on red supergiants is a well-known phenomenon. These spots are likely a consequence of convective flows or cool convective cells, which are widely believed to be present in such stars.

“Our findings offer insight in to the nature of red supergiant stars, the main contributors to the enrichment of heavy elements in the Universe,” said Prof. Zhao Gang.

Featured image: During the end of 2019 and the beginning of 2020, Betelgeuse (α Orionis) became fainter by more than 2.5 times and this is the most significant dimming observed in the recent decades. Credit: Alena Alexeeva and REN Dayong


Reference: Sofya Alexeeva et al, Spectroscopic evidence for a large spot on the dimming Betelgeuse, Nature Communications (2021). DOI: 10.1038/s41467-021-25018-3


Provided by Chinese Academy of Sciences

Superflares: Less Harmful To Exoplanets Than Previously Thought (Planetary Science)

Superflares, extreme radiation bursts from stars, have been suspected of causing lasting damage to the atmospheres and thus habitability of exoplanets. A newly published study found evidence that they only pose a limited danger to planetary systems, since the radiation bursts do not explode in the direction of the exoplanets.

Using optical observations from the Transiting Exoplanet Survey Satellite (TESS), astronomers at the Leibniz Institute for Astrophysics Potsdam (AIP), in collaboration with scientists in the US and Spain, studied large superflares on young, small stars. These class of stars, also called “red dwarfs,” have a lower temperature and mass than our own Sun.

Many exoplanets have been found around these types of stars. The question is whether these exoplanets are habitable, since red dwarfs are more active than our Sun, and flare much more frequently and intensely. Flares are magnetic explosions in the atmospheres of stars that expel intense electromagnetic radiation into space. Large flares are associated with the emission of energetic particles that can hit exoplanets orbiting the flaring star, and alter or even evaporate the planetary atmospheres.

Ekaterina Ilin, PhD student at AIP, and the team developed a method to locate where on the stars’ surface flares are launched from. “We discovered that extremely large flares are launched from near the poles of red dwarf stars, rather than from their equator, as is typically the case on the Sun,” said Ilin. “Exoplanets that orbit in the same plane as the equator of the star, like the planets in our own solar system, could therefore be largely protected from such superflares, as these are directed upwards or downwards out of the exoplanet system. This could improve the prospects for the habitability of exoplanets around small host stars, which would otherwise be much more endangered by the energetic radiation and particles associated with flares compared to planets in the solar system.”

The detection of these flares is further evidence that strong and dynamic concentrations of stellar magnetic fields, which can manifest themselves as dark spots and flares, form close to the rotational poles of fast-rotating stars. The existence of such “polar spots” has long been suspected from indirect reconstruction techniques like (Zeeman) Doppler Imaging of stellar surfaces, but has not been detected directly so far. The team achieved this by analysing white-light flares on fast-rotating M dwarf stars that last long enough to have their brightness modulated by being rotated in and out of view on the stellar surface. The authors were able to directly infer the latitude of the flaring region from the shape of the light curve, and also showed that the detection method was not biased towards particular latitudes. “I’m particularly excited that we were finally able to substantiate the existence of polar spots for these fast rotating stars. In the future, this will help us to understand their magnetic field structure better,” adds Katja Poppenhäger, head of the section Stellar Physics and Exoplanets at AIP.

The scientists searched the entire archive of observations obtained by TESS for stars that exhibit large flares by processing the light curves of over 3000 red dwarf stars, totalling over 400 years of cumulative observing time. Among these stars, they found four which were suited for the new method. Their results show that all four flares occurred above ∼55 deg latitude, that is, much closer to the pole than solar flares and spots, which usually occur below 30 deg. This result, even with only four flares, is significant: if flares were spread equally across the stellar surface, the chances of finding four flares in a row at such high latitudes would be about 1:1000. This has implications for models of the magnetic fields of stars and for the habitability of exoplanets that orbit them.

Featured image: Small stars flare actively and expel particles that can alter and evaporate the atmospheres of planets that orbit them. New findings suggest that large superflares prefer to occur at high latitudes, sparing planets that orbit around the stellar equator. Credit: AIP/ J. Fohlmeister


Further information

Original publication

Ekaterina Ilin, Katja Poppenhaeger, Sarah J Schmidt, Silva P Järvinen, Elisabeth R Newton, Julián D Alvarado-Gómez, J Sebastian Pineda, James R A Davenport, Mahmoudreza Oshagh, Ilya Ilyin, Giant white-light flares on fully convective stars occur at high latitudes, Monthly Notices of the Royal Astronomical Society, 2021.

DOI: https://doi.org/10.1093/mnras/stab2159

https://arxiv.org/abs/2108.01917


Provided by AIP

Lucy, Last Stop Before the Asteroids (Planetary Science)

The first of the two missions of NASA’s Discovery Program is almost ready to set out to discover Jupiter’s Trojan asteroids. It will fly over a record number of these fossil remains of the primordial material from which the outer planets formed

Lucy , the first NASA probe designed to explore Jupiter’s Trojan asteroids – a population of ancient small bodies that share the orbit of the gaseous planet – arrived on Friday, July 30 at the agency’s Kennedy Space Center in Florida. The spacecraft is now in a clean room, ready to begin final preparations for launch, scheduled for a 23-day window starting October 16 at Cape Canaveral Space Force Station .

During her twelve-year primary mission, Lucy will explore a record number of asteroids, flying over a main belt asteroid and seven Trojan asteroids (including an asteroid’s mini-moon ). The latter are remnants of the early solar system, now trapped in stable orbits associated with the giant planet, around which they form two “swarms” that precede and follow Jupiter in its path around the Sun, grouped around stable points of gravitational equilibrium known as points by Lagrange .

The probe was flown from Buckley Space Force Base in Aurora, Colorado, aboard a US Air Force C-17 cargo plane. Precisely in Colorado, in the Littleton factories of Lockheed Martin Space , the spacecraft had been designed and assembled.

NASA's Lucy probe arrives in a cargo plane
NASA’s Lucy probe arrives in a cargo plane and is unloaded on the runway of the Launch and Landing Facility at the Kennedy Space Center in Florida on July 30, 2021. Credits: Nasa / Kim Shiflett

Lucy is now ready to begin her latest cycle of pre-launch tests and checks , which include software testing, functional testing of instruments and power supplies, propulsion propellant load testing, telecommunication testing and self-testing of the spacecraft itself. .

“It’s hard to believe we’re finally here after more than seven years of hard work,” says Hal Levison , head of Lucy at the Southwest Research Institute in Boulder, Colorado. «We could not have achieved this without an extremely talented and dedicated team. The time has come to take Lucy into space, so that she can give us back her revolutionary scientific vision on the origin of our planetary system. “

Featured image: The January 2021 test on the deployment of the large circular solar panels of the Lucy mission. Credits: Credit: Lockheed Martin


Provided by INAF

Stars Are Exploding in Dusty Galaxies. We Just Can’t Always See Them (Planetary Science)

Exploding stars generate dramatic light shows. Infrared telescopes like Spitzer can see through the haze and to give a better idea of how often these explosions occur.

You’d think that supernovae – the death throes of massive stars and among the brightest, most powerful explosions in the universe – would be hard to miss. Yet the number of these blasts observed in the distant parts of the universe falls way short of astrophysicists’ predictions.

new study using data from NASA’s recently retired Spitzer Space Telescope reports the detection of five supernovae that, going undetected in optical light, had never been seen before. Spitzer saw the universe in infrared light, which pierces through dust clouds that block optical light – the kind of light our eyes see and that unobscured supernovae radiate most brightly.

Download this free poster from NASA, which commemorates the retired Spitzer Space Telescope. Available in English and Spanish. Credit: NASA/JPL-Caltech

To search for hidden supernovae, the researchers looked at Spitzer observations of 40 dusty galaxies. (In space, dust refers to grain-like particles with a consistency similar to smoke.) Based on the number they found in these galaxies, the study confirms that supernovae do indeed occur as frequently as scientists expect them to. This expectation is based on scientists’ current understanding of how stars evolve. Studies like this are necessary to improve that understanding, by either reinforcing or challenging certain aspects of it.

“These results with Spitzer show that the optical surveys we’ve long relied on for detecting supernovae miss up to half of the stellar explosions happening out there in the universe,” said Ori Fox, a scientist at the Space Telescope Science Institute in Baltimore, Maryland, and lead author of the new study, published in the Monthly Notices of the Royal Astronomical Society. “It’s very good news that the number of supernovae we’re seeing with Spitzer is statistically consistent with theoretical predictions.”

The “supernova discrepancy” – that is, the inconsistency between the number of predicted supernovae and the number observed by optical telescopes – is not an issue in the nearby universe. There, galaxies have slowed their pace of star formation and are generally less dusty. In the more distant reaches of the universe, though, galaxies appear younger, produce stars at higher rates, and tend to have higher amounts of dust. This dust absorbs and scatters optical and ultraviolet light, preventing it from reaching telescopes. So researchers have long reasoned that the missing supernovae must exist and are just unseen.

“Because the local universe has calmed down a bit since its early years of star-making, we see the expected numbers of supernovae with typical optical searches,” said Fox. “The observed supernova-detection percentage goes down, however, as you get farther away and back to cosmic epochs where dustier galaxies dominated.”

Detecting supernovae at these far distances can be challenging. To perform a search for supernovae shrouded within murkier galactic realms but at less extreme distances, Fox’s team selected a local set of 40 dust-choked galaxies, known as luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs, respectively). The dust in LIRGs and ULIRGs absorbs optical light from objects like supernovae but allows infrared light from these same objects to pass through unobstructed for telescopes like Spitzer to detect.

The researchers’ hunch proved correct when the five never-before-seen supernovae came to (infrared) light. “It’s a testament to Spitzer’s discovery potential that the telescope was able to pick up the signal of hidden supernovae from these dusty galaxies,” said Fox.

“It was especially fun for several of our undergraduate students to meaningfully contribute to this exciting research,” added study co-author Alex Filippenko, a professor of astronomy at the University of California, Berkeley. “They helped answer the question, ‘Where have all the supernovae gone?’”

The types of supernovae detected by Spitzer are known as “core-collapse supernovae,” involving giant stars with at least eight times the mass of the Sun. As they grow old and their cores fill with iron, the big stars can no longer produce enough energy to withstand their own gravity, and their cores collapse, suddenly and catastrophically.

The intense pressures and temperatures produced during the rapid cave-in forms new chemical elements via nuclear fusion. The collapsing stars ultimately rebound off their ultra-dense cores, blowing themselves to smithereens and scattering those elements throughout space. Supernovae produce “heavy” elements, such as most metals. Those elements are necessary for building up rocky planets, like Earth, as well as biological beings. Overall, supernova rates serve as an important check on models of star formation and the creation of heavy elements in the universe.

“If you have a handle on how many stars are forming, then you can predict how many stars will explode,” said Fox. “Or, vice versa, if you have a handle on how many stars are exploding, you can predict how many stars are forming. Understanding that relationship is critical for many areas of study in astrophysics.”

Next-generation telescopes, including NASA’s Nancy Grace Roman Space Telescope and the James Webb Space Telescope, will detect infrared light, like Spitzer.

“Our study has shown that star formation models are more consistent with supernova rates than previously thought,” said Fox. “And by revealing these hidden supernovae, Spitzer has set the stage for new kinds of discoveries with the Webb and Roman space telescopes.”

More About the Mission

NASA’s Jet Propulsion Laboratory in Southern California conducted mission operations and managed the Spitzer Space Telescope mission for the agency’s Science Mission Directorate in Washington. Science operations were conducted at the Spitzer Science Center at Caltech in Pasadena. Spacecraft operations were based at Lockheed Martin Space in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.

More information about Spitzer is available at:

https://www.nasa.gov/mission_pages/spitzer/main

Featured image: The image shows galaxy Arp 148, captured by NASA’s Spitzer and Hubble telescopes. Specially processed Spitzer data is shown inside the white circle, revealing infrared light from a supernova hidden by dust. Credit: NASA/JPL-Caltech


Reference: Ori D Fox et al, A Spitzer survey for dust-obscured supernovae, Monthly Notices of the Royal Astronomical Society (2021). DOI: 10.1093/mnras/stab1740


Provided by NASA JPL