ST/ Astronomers make rare exoplanet discovery, and a giant leap in detecting Earth-like bodies

Paradigm

Published in

Paradigm

34 min readJan 19, 2024

Space biweekly vol.90, 4th January — 19th January

TL;DR

Researchers have made the rare discovery of a small, cold exoplanet and its massive outer companion — shedding light on the formation of planets like Earth.
Astronomers have discovered a planet closer and younger than any other Earth-sized world yet identified. It’s a remarkably hot world whose proximity to our own planet and to a star like our sun mark it as a unique opportunity to study how planets evolve.
Researchers have taken the first steps toward finding liquid solvents that may someday help extract critical building materials from lunar and Martian-rock dust, an important piece in making long-term space travel possible. Using machine learning and computational modeling, researchers have found about half a dozen good candidates for solvents that can extract materials on the moon and Mars usable in 3D printing. The powerful solvents, called ionic liquids, are salts that are in a liquid state.
A team of astronomers has unraveled the enigmatic atmosphere of the exoplanet HAT-P-18 b, shedding light on its intriguing blend of gases, clouds, and even the effects of its star’s activity.
Astronomers have detected a three-ringed structure in the nursery of planets in the inner planet-forming disk of a young star. This configuration suggests two Jupiter-mass planets are forming in the gaps between the rings. The detailed analysis is consistent with abundant solid iron grains complementing the dust composition. As a result, the disk likely harbors metals and minerals akin to those in the Solar System’s terrestrial planets. It offers a glimpse into conditions resembling the early Solar System over four billion years ago during the formation of rocky planets such as Mercury, Venus, and Earth.
Neptune is fondly known for being a rich blue and Uranus green — but a new study has revealed that the two ice giants are actually far closer in color than typically thought. The correct shades of the planets have now been confirmed.
Analysis of organic compounds — called polycyclic aromatic hydrocarbons (PAHs) — extracted from the Ryugu asteroid and Murchison meteorite has found that certain PAHs likely formed in the cold areas of space between stars rather than in hot regions near stars as was previously thought. The findings open new possibilities for studying life beyond Earth and the chemistry of objects in space.
Astrophysicists outline the links between atmospheric oxygen and the potential rise of advanced technology on distant planets.
Astronomers believe they may have found the origin of the universe’s giant odd radio circles: they are shells formed by outflowing galactic winds, possibly from massive exploding stars known as supernovae.
Analysis of iron meteorites from the earliest years of the solar system indicate that the planetary ‘seeds’ that ultimately formed Earth contained water.
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

The SOPHIE search for northern extrasolar planets

by N. Heidari, I. Boisse, N. C. Hara, T. G. Wilson, et al in Astronomy & Astrophysics

Astronomers have made the rare discovery of a small, cold exoplanet and its massive outer companion — shedding light on the formation of planets like Earth.

The findings include a planet with radius and mass between that of the Earth and Neptune, with a potential orbit around its host star of 146 days. The star system also contains an outer, large companion, 100 times the mass of Jupiter.

This is a rare discovery, with exoplanets smaller and lighter than Neptune and Uranus being notoriously hard to detect, with only a few being identified to this day. Such rare systems are particularly interesting to better understand planetary formation and evolution; they are thought to be a key step for the detection of Earth-like planets around stars.

The new planetary system is discovered around the star HD88986. This star has a similar temperature to the Sun with a slightly larger radius and is bright enough to be seen by keen observers at dark sky sites across the UK, such as Bannau Brycheiniog National Park (Brecon Beacons). This study is led by Neda Heidari, an Iranian postdoctoral fellow at the Institut d’astrophysique de Paris (IAP). In the UK, Thomas Wilson, a senior research fellow at the University of Warwick, co-led the analysis of satellite data including searching for new planets. The team also includes researchers at 29 other institutes from nine countries including Switzerland, Chile, and the USA.

Periodogram of RVs and activity indicators of HD 88986. From top to bottom: HIRES and HIRES+ S-index, SOPHIE+ S-index, bisector, RVs, and residuals of RVs after Keplerian fit on the 146.1 d. The vertical red line illustrates the planet candidates on 146.1 d, which have no corresponding peak in activity indicators. The vertical gray strip marks the estimated rotational period of the star.

The planetary system includes a cold planet smaller than Neptune, a so-called sub-Neptune, HD88986b. This planet has the longest orbital period (146 days) among known exoplanets smaller than Neptune or Uranus with precise mass measurements.

Neda Heidari, IAP, explained: “Most of the planets we’ve discovered and measured for their mass and radius have short orbits, typically less than 40 days. To provide a comparison with our solar system, even Mercury, the closest planet to the Sun, takes 88 days to complete its orbit. This lack of detection for planets with longer orbits raises challenges in understanding how planets form and evolve in other systems and even in our solar system. HD88986b, with its orbital period of 146 days, potentially has the longest known orbit among the population of small planets with precise measurements.”

HD88986b was detected using the SOPHIE — a high-precision spectrograph (a machine that analyses wavelengths of light from exoplanets) at the Haute-Provence Observatory, France. SOPHIE detects and characterises exoplanets using the ‘radial-velocity method’; measuring tiny motion variations of the star induced by planets orbiting it.

These observations revealed the planet and allowed the team to estimate its mass to approximately 17 times that of the Earth. Complementary observations obtained with NASA’s space telescope Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency’s (ESA) space telescope CHaracterising ExOPlanet Satellite (CHEOPS) indicate that the planet probably “transits” in front of it host star. This occurs when its orbit passes on the line of sight between the Earth and the star, partially occulting the star — causing a decrease in its brightness that can be observed and quantified.

Amplitude (red) and phase (green) of a 146.1 d signal as a function of time for different sizes of time windows. Solid lines correspond to estimate and shaded areas to ± 1 σ uncertainties. Denoting by *Tobs* the total time span of observations, a) and b) are obtained with windows of size *Tobs*/3 = 1234.2 d and *Tobs*/9 = 411.42 d, respectively.

These observations by both satellites allowed the team to directly estimate the diameter of the planet as about twice that of the Earth. The findings of the study rely on more than 25 years of observations, also including data from ESA’s Gaia satellite and the Keck Telescope in Hawaii.

Moreover, with an atmosphere temperature of only 190 Celsius degrees, HD88986b provides a rare opportunity for studying the composition of the so-called “cold” atmospheres, as most of the detected atmospheres for exoplanets are above 1,000 Celsius degrees.

Due to the wide orbit of the sub-Neptune HD88986b (as large as 60% of the Earth-Sun distance), HD88986b probably underwent rare interactions with other planets that may exist in the planetary system, and weak loss of mass from the strong ultraviolet radiation of the central star. It may therefore have retained its original chemical composition, allowing scientists to explore the possible scenarios for the formation and evolution of this planetary system.

Thomas Wilson, Department of Physics, University of Warwick, said: “HD88986b is essentially a scaled-down Neptune, between the orbits of Mercury and Venus. It becomes one of the best studied small, cold exoplanets paving the way for studying its atmosphere to understand the similarity to our own planet Earth. It also orbits a star with a similar temperature to the Sun making it a precursor to the Earth-like planets to be found by the PLATO space telescope, in which Warwick plays a leading role.”

The astronomers also revealed a second, outer companion around the central star. This exoplanet is particularly massive (more than 100 times the mass of Jupiter), and its orbit has a period of several tens of years. Further observations are needed to understand its nature and better determine its properties.

TESS Hunt for Young and Maturing Exoplanets (THYME). XI. An Earth-sized Planet Orbiting a Nearby, Solar-like Host in the 400 Myr Ursa Major Moving Group

by Benjamin K. Capistrant, Melinda Soares-Furtado, et al in The Astronomical Journal

A team of astronomers has discovered a planet closer and younger than any other Earth-sized world yet identified. It’s a remarkably hot world whose proximity to our own planet and to a star like our sun mark it as a unique opportunity to study how planets evolve.

Melinda Soares-Furtado, a NASA Hubble Fellow at the University of Wisconsin-Madison who will begin work as an astronomy professor at the university in the fall, and recent UW-Madison graduate Benjamin Capistrant, now a graduate student at the University of Florida, co-led the study with co-authors from around the world.

“It’s a useful planet because it may be like an early Earth,” says Soares-Furtado.

Here is what scientists know about the planet:

The planet is known as HD 63433d and it’s the third planet found in orbit around a star called HD 63433.
HD 63433d is so close to its star, it completes a trip all the way around every 4.2 days.
“Even though it’s really close-orbiting, we can use follow-up data to search for evidence of outgassing and atmospheric loss that could be important constraints on how terrestrial worlds evolve,” Soares-Furtado says. “But that’s where the similarities end — and end dramatically.”
Based on its orbit, the astronomers are relatively certain HD 63433d is tidally locked, which means one side is perpetually facing its star.
That side can reach a brutal 2,300 degrees Fahrenheit and may flow with lava, while the opposite side is forever dark.

The top panel shows the unflattened TESS light curve of HD 63433. The middle panel shows the flattened light curve with our three best-fit transit models for planets b, c, and d, as determined by our edmcmc outputs. The colors of these models correspond to each of the three planets as shown in the bottom panels, which depict the phase-folded light curves for each HD 63433 planet with binned data (red points) plotted over our best-fit models.

What you should know about the planet’s star:

HD 63433 is roughly the same size and star type as our sun, but (at about 400 million years old) it’s not even one-tenth our sun’s age.
The star is about 73 light years away from our own sun and part of the group of stars moving together that make up the constellation Ursa Major, which includes the Big Dipper.
“On a dark night in Madison,” Soares-Furtado says, “you could see [HD 63433] through a good pair of binoculars.”

The study’s authors are collaborating on a planet-hunting project called THYME. In 2020, they used data from NASA’s Transiting Exoplanet Survey Satellite to identify two mini-Neptune-sized planets orbiting HD 63433. Since then, TESS took four more looks at the star, compiling enough data for the researchers to detect HD 63433d crossing between the star and the satellite.

The researchers, including UW-Madison study co-authors graduate student Andrew C. Nine, undergraduate Alyssa Jankowski and Juliette Becker, a UW-Madison astronomy professor, think there is plenty to learn from HD 63433d. The planet is uniquely situated for further study. Its peppy young star is visible from both the Northern and Southern hemispheres, increasing the number of instruments, like the South African Large Telescope or WIYN Observatory in Arizona (both of which UW-Madison helped design and build) that can be trained on the system. And the star is orders of magnitude closer than many Soares-Furtado has studied, possibly affording opportunities to develop new methods to study gasses escaping from the planet’s interior or measure its magnetic field.

“This is our solar backyard, and that’s kind of exciting,” Soares-Furtado says. “What sort of information can a star this close, with such a crowded system around it, give away? How will it help us as we move on to look for planets among the maybe 100 other, similar stars in this young group it’s part of?”

Toward Metal Extraction from Regolith: Theoretical Investigation of the Solvation Structure and Dynamics of Metal Ions in Ionic Liquids

by Azmain F. Islam, Soumik Banerjee in The Journal of Physical Chemistry B

Researchers have taken the first steps toward finding liquid solvents that may someday help extract critical building materials from lunar and Martian-rock dust, an important piece in making long-term space travel possible.

Using machine learning and computational modeling, Washington State University researchers have found about half a dozen good candidates for solvents that can extract materials on the moon and Mars usable in 3D printing. The work is led by Soumik Banerjee, associate professor in WSU’s School of Mechanical and Materials Engineering.

The powerful solvents, called ionic liquids, are salts that are in a liquid state.

“The machine learning work brought us down from the 20,000-foot to the 1,000-foot level,” Banerjee said. “We were able to down select a lot of ionic liquids very quickly, and then we could also scientifically understand the most important factors that determine whether a solvent is able to dissolve the material or not.”

As part of its Artemis mission, NASA, which funded Banerjee’s work, wants to send humans back to the moon and then to deeper space to Mars and beyond. But to make such long-term missions possible, astronauts will have to use the materials and resources in those extraterrestrial environments, using 3D printing to make structures, tools, or parts from essential elements extracted from lunar or Martian soil.

“In situ resource utilization is a big deal over the next couple of decades for NASA,” said Banerjee. “Otherwise, we would need a terribly high payload of materials to carry from Earth.”

Acquiring those building materials must be done in an environmentally friendly and energy efficient way. The method to mine the elements also can’t use water, which isn’t available on the moon. Ionic liquids, which Banerjee’s group has been studying for more than a decade for use in batteries, could be the answer.

Testing each ionic liquid candidate in a lab is expensive and time consuming, however, so the researchers used machine learning and modeling at the level of atoms to narrow down from hundreds of thousands of candidates. They looked for those that might digest lunar and Martian materials, extract important elements such as aluminum, magnesium, and iron, regenerate themselves, and perhaps produce oxygen or water as a byproduct to help provide life-support. Identifying superior qualities that the solvents will need, the researchers were able to find about half a dozen very strong candidates.

Important factors for success included the size of the molecular ions that make up the salts, its surface charge density, which is the charge per unit area of the ions, and the mobility of the ions in the liquids.

Near-Infrared Transmission Spectroscopy of HAT-P-18 b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST

by Marylou Fournier-Tondreau, Ryan J MacDonald, et al in Monthly Notices of the Royal Astronomical Society

Led by researchers from Université de Montréal’s Trottier Institute for Research on Exoplanets (iREx), a team of astronomers has harnessed the power of the revolutionary James Webb Space Webb Telescope (JWST) to study the “hot Saturn” exoplanet HAT-P-18 b.

Their findings paint a complete picture of the HAT-P-18 b’s atmosphere while exploring the great challenge of distinguishing its atmospheric signals from the activity of its star. HAT-P-18 b is located over 500 light-years away with a mass similar to Saturn’s but a size closer to that the larger planet Jupiter. As a result, the exoplanet has a “puffed-up” atmosphere that is especially ideal for analysis.

Observations from the JWST were taken while the HAT-P-18 b was passing in front of its Sun-like star. This moment is called a transit and is crucial to detect and further characterise an exoplanet from hundreds of light-years away with surprising precision. Astronomers don’t observe light that is being emitted directly by the distant planet. Rather, they study how the central star’s light is being blocked and affected by the planet orbiting it, and so must try to disentangle signals caused by the presence of the planet from those caused by the star’s own properties.

Just like our Sun, stars do not have uniform surfaces. They can have dark star spots and bright regions, which can create signals that mimic a planet’s atmospheric attributes. A recent study of the exoplanet TRAPPIST-1 b and its star TRAPPIST-1 led by UdeM doctoral student Olivia Lim witnessed an eruption, or flare, on the surface of the star, which affected observations.

In the case of planet HAT-P-18 b, Webb caught the exoplanet right as it was passing over a dark spot on its star, HAT-P-18. This is called a spot-crossing event, and its effect was evident in the data collected for the new study. The iREx team also reported the presence of numerous other star spots on HAT-P-18’s surface which were not blocked out by the exoplanet.

To accurately determine the exoplanet’s atmospheric composition, the researchers had to simultaneously model the planet’s atmosphere as well as its star’s peculiarities. In their study, they point out that such consideration will be crucial in treating future exoplanet observations via the Webb to fully harness their potential.

“We found that accounting for stellar contamination implies the existence of spots and clouds instead of haze and recovers a water vapour abundance of almost an order of magnitude lower,” said lead author Marylou Fournier-Tondreau.
“So considering the system’s host star makes a big difference,” added Fournier-Tondreau, who did the work as a master’s student at iREx and is now pursuing a Ph.D. at the University of Oxford.
“It’s actually the first time that we clearly disentangle the signature of hazes versus starspots, thanks to Canada’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) instrument, which provides wider wavelength coverage extending into the visible light domain.”

After modelling the exoplanet and the star in the HAT-P-18 system, the iREx astronomers performed a meticulous dissection of HAT-P-18 b’s atmospheric composition. By inspecting the light that filters through the exoplanet’s atmosphere as it transits its host star, the researchers discerned the presence of water vapour (H2O) and carbon dioxide (CO2).

The researchers also detected the possible presence of sodium and observed strong signs of a cloud deck in HAT-P-18 b’s atmosphere, which appears to be muting the signals of many of the molecules found within it. They also concluded that the star’s surface was covered by many dark spots that can significantly influence the interpretation of the data.

An earlier analysis of the same JWST data led by a team at Johns Hopkins University had also revealed a clear detection of water and CO2, but also reported the detection of small particles at high-altitudes called hazes and found hints of methane (CH4). The iREx astronomers paint a different picture.

The CH4 detection was not confirmed, and the water abundance they determined was 10 times lower than previously found. They also found that the previous study’s detection of hazes could instead be caused by star spots on the star’s surface, highlighting the importance of considering the star in the analysis.

Mid-infrared evidence for iron-rich dust in the multi-ringed inner disk of HD 144432

by J. Varga, L. B. F. M. Waters, M. Hogerheijde, R. van Boekel, et al in Astronomy & Astrophysics

The origin of Earth and the Solar System inspires scientists and the public alike. By studying the present state of our home planet and other objects in the Solar System, researchers have developed a detailed picture of the conditions when they evolved from a disk made of dust and gas surrounding the infant sun some 4.5 billion years ago.

With the breathtaking progress made in star and planet formation research aiming at far-away celestial objects, we can now investigate the conditions in environments around young stars and compare them to the ones derived for the early Solar System. Using the European Southern Observatory’s (ESO) Very Large Telescope Interferometer (VLTI), an international team of researchers led by József Varga from the Konkoly Observatory in Budapest, Hungary, did just that. They observed the planet-forming disk of the young star HD 144432, approximately 500 light-years away.

“When studying the dust distribution in the disk’s innermost region, we detected for the first time a complex structure in which dust piles up in three concentric rings in such an environment,” says Roy van Boekel. He is a scientist at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany and a co-author of the underlying research article to appear in the journal Astronomy & Astrophysics. “That region corresponds to the zone where the rocky planets formed in the Solar System,” van Boekel adds. Compared to the Solar System, the first ring around HD 144432 lies within Mercury’s orbit, and the second is close to Mars’s trajectory. Moreover, the third ring roughly corresponds to Jupiter’s orbit.

Up to now, astronomers have found such configurations predominantly on larger scales corresponding to the realms beyond where Saturn circles the Sun. Ring systems in the disks around young stars generally point to planets forming within the gaps as they accumulate dust and gas on their way. However, HD 144432 is the first example of such a complex ring system so close to its host star. It occurs in a zone rich in dust, the building block of rocky planets like Earth. Assuming the rings indicate the presence of two planets forming within the gaps, the astronomers estimated their masses to resemble roughly that of Jupiter.

The astronomers determined the dust composition across the disk up to a separation from the central star that corresponds to the distance of Jupiter from the Sun. What they found is very familiar to scientists studying Earth and the rocky planets in the Solar System: various silicates (metal-silicon-oxygen compounds) and other minerals present in Earth’s crust and mantle, and possibly metallic iron as is present in Mercury’s and Earth’s cores. If confirmed, this study would be the first to have discovered iron in a planet-forming disk.

“Astronomers have thus far explained the observations of dusty disks with a mixture of carbon and silicate dust, materials that we see almost everywhere in the Universe,” van Boekel explains. However, from a chemical perspective an iron and silicate mixture is more plausible for the hot, inner disk regions. And indeed, the chemical model that Varga, the main author of the underlying research article, applied to the data yields better-fitting results when introducing iron instead of carbon.

Furthermore, the dust observed in the HD 144432 disk can be as hot as 1800 Kelvin (approx. 1500 degrees Celsius) at the inner edge and as moderate as 300 Kelvin (approx. 25 degrees Celsius) farther out. Minerals and iron melt and recondense, often as crystals, in the hot regions near the star. In turn, carbon grains would not survive the heat and instead be present as carbon monoxide or carbon dioxide gas. However, carbon may still be a significant constituent of the solid particles in the cold outer disk, which the observations carried out for this study cannot trace.

Iron-rich and carbon-poor dust would also fit nicely with the conditions in the Solar System. Mercury and Earth are iron-rich planets, while the Earth contains relatively little carbon.

“We think that the HD 144432 disk may be very similar to the early Solar System that provided lots of iron to the rocky planets we know today,” says van Boekel. “Our study may pose as another example showing that the composition of our Solar System may be quite typical.”

This illustration is a sketch of the HD 144432 disk as observed with the VLTI. The data are consistent with a structure of three concentric rings. The gaps between the rings generally indicate large planets are forming by accumulating dust and gas along their orbit around the host star. The silicate minerals are primarily present as crystals in the inner hot zone. The VLTI observations cannot constrain the cold outer disk.

Retrieving the results was only possible with exceptionally high-resolution observations, as provided by the VLTI. By combining the four VLT 8.2-metre telescopes at ESO’s Paranal Observatory, they can resolve details as if astronomers would employ a telescope with a primary mirror of 200 metres in diameter. Varga, van Boekel and their collaborators obtained data using three instruments to achieve a broad wavelength coverage ranging from 1.6 to 13 micrometres, representing infrared light.

MPIA provided vital technological elements to two devices, GRAVITY and the Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE). One of MATISSE’s primary purposes is to investigate the rocky planet-forming zones of disks around young stars. “By looking at the inner regions of protoplanetary disks around stars, we aim to explore the origin of the various minerals contained in the disk — minerals that later will form the solid components of planets like the Earth,” says Thomas Henning, MPIA director and co-PI of the MATISSE instrument.

However, producing images with an interferometer like the ones we are used to obtaining from single telescopes is not straightforward and very time-consuming. A more efficient use of precious observing time to decipher the object structure is to compare the sparse data to models of potential target configurations. In the case of the HD 144432 disk, a three-ringed structure represents the data best.

Besides the Solar System, HD 144432 appears to provide another example of planets forming in an iron-rich environment. However, the astronomers will not stop there. “We still have a few promising candidates waiting for the VLTI to take a closer look at,” van Boekel points out. In earlier observations, the team discovered a number of disks around young stars that indicate configurations worth revisiting. However, they will reveal their detailed structure and chemistry using the latest VLTI instrumentation. Eventually, the astronomers may be able to clarify whether planets commonly form in iron-rich dusty disks close to their parent stars.

Modelling the seasonal cycle of Uranus’s colour and magnitude, and comparison with Neptune

by Patrick G J Irwin, Jack Dobinson, Arjuna James, Nicholas A Teanby, Amy A Simon, Leigh N Fletcher, Michael T Roman, Glenn S Orton, Michael H Wong, Daniel Toledo, Santiago Pérez-Hoyos, Julie Beck in Monthly Notices of the Royal Astronomical Society

Neptune is fondly known for being a rich blue and Uranus green — but a new study has revealed that the two ice giants are actually far closer in colour than typically thought.

The correct shades of the planets have been confirmed with the help of research led by Professor Patrick Irwin from the University of Oxford. He and his team found that both worlds are in fact a similar shade of greenish blue, despite the commonly-held belief that Neptune is a deep azure and Uranus has a pale cyan appearance.

Astronomers have long known that most modern images of the two planets do not accurately reflect their true colours. The misconception arose because images captured of both planets during the 20th century — including by NASA’s Voyager 2 mission, the only spacecraft to fly past these worlds — recorded images in separate colours. The single-colour images were later recombined to create composite colour images, which were not always accurately balanced to achieve a “true” colour image, and — particularly in the case of Neptune — were often made “too blue.” In addition, the early Neptune images from Voyager 2 were strongly contrast enhanced to better reveal the clouds, bands, and winds that shape our modern perspective of Neptune.

Professor Irwin said: “Although the familiar Voyager 2 images of Uranus were published in a form closer to ‘true’ colour, those of Neptune were, in fact, stretched and enhanced, and therefore made artificially too blue.” “Even though the artificially-saturated colour was known at the time amongst planetary scientists — and the images were released with captions explaining it — that distinction had become lost over time.”
“Applying our model to the original data, we have been able to reconstitute the most accurate representation yet of the colour of both Neptune and Uranus.”

Top panel: Disc-averaged radiance spectra of Uranus and Neptune, compared to the spectrum of a perfectly reflecting Lambertian surface at the same solar distance (i.e. ‘Sun’). Bottom panels compare the same three spectra (normalized) as viewed through a long-slit spectrometer to demonstrate the efficacy of the colour-rendering procedure described in this paper.

In the new study, the researchers used data from Hubble Space Telescope’s Space Telescope Imaging Spectrograph (STIS) and the Multi Unit Spectroscopic Explorer (MUSE) on the European Southern Observatory’s Very Large Telescope. In both instruments, each pixel is a continuous spectrum of colours. This means that STIS and MUSE observations can be unambiguously processed to determine the true apparent colour of Uranus and Neptune.

The researchers used these data to re-balance the composite colour images recorded by the Voyager 2 camera, and also by the Hubble Space Telescope’s Wide Field Camera 3 (WFC3). This revealed that Uranus and Neptune are actually a rather similar shade of greenish blue. The main difference is that Neptune has a slight hint of additional blue, which the model reveals to be due to a thinner haze layer on that planet.

The study also provides an answer to the long-standing mystery of why Uranus’s colour changes slightly during its 84-year orbit of the Sun. The authors came to their conclusion after first comparing images of the ice giant to measurements of its brightness, which were recorded by the Lowell Observatory in Arizona from 1950–2016 at blue and green wavelengths. These measurements showed that Uranus appears a little greener at its solstices (i.e. summer and winter), when one of the planet’s poles is pointed towards our star. But during its equinoxes — when the Sun is over the equator — it has a somewhat bluer tinge.

Part of the reason for this was known to be because Uranus has a highly unusual spin. It effectively spins almost on its side during its orbit, meaning that during the planet’s solstices either its north or south pole points almost directly towards the Sun and Earth. This is important, the authors said, because any changes to the reflectivity of the polar regions would therefore have a big impact on Uranus’s overall brightness when viewed from our planet. What astronomers were less clear about is how or why this reflectivity differs. This led the researchers to develop a model which compared the spectra of Uranus’s polar regions to its equatorial regions.

It found that the polar regions are more reflective at green and red wavelengths than at blue wavelengths, partly because methane, which is red absorbing, is about half as abundant near the poles than the equator. However, this wasn’t enough to fully explain the colour change so the researchers added a new variable to the model in the form of a ‘hood’ of gradually thickening icy haze which has previously been observed over the summer, sunlit pole as the planet moves from equinox to solstice.

Astronomers think this is likely to be made up of methane ice particles. When simulated in the model, the ice particles further increased the reflection at green and red wavelengths at the poles, offering an explanation as to why Uranus is greener at the solstice.

Professor Irwin said: “This is the first study to match a quantitative model to imaging data to explain why the colour of Uranus changes during its orbit.” “In this way, we have demonstrated that Uranus is greener at the solstice due to the polar regions having reduced methane abundance but also an increased thickness of brightly scattering methane ice particles.”

Dr Heidi Hammel, of the Association of Universities for Research in Astronomy (AURA), who has spent decades studying Neptune and Uranus but was not involved in the study, said: “The misperception of Neptune’s colour, as well as the unusual colour changes of Uranus, have bedevilled us for decades. This comprehensive study should finally put both issues to rest.”

The ice giants Uranus and Neptune remain a tantalising destination for future robotic explorers, building on the legacy of Voyager in the 1980s.

Professor Leigh Fletcher, a planetary scientist from the University of Leicester and co-author of the new study, said: “A mission to explore the Uranian system — from its bizarre seasonal atmosphere, to its diverse collection of rings and moons — is a high priority for the space agencies in the decades to come.”

However, even a long-lived planetary explorer, in orbit around Uranus, would only capture a short snapshot of a Uranian year.

“Earth-based studies like this, showing how Uranus’ appearance and colour has changed over the decades in response to the weirdest seasons in the Solar System, will be vital in placing the discoveries of this future mission into their broader context,” Professor Fletcher added.

Polycyclic aromatic hydrocarbons in samples of Ryugu formed in the interstellar medium

by Sarah S. Zeichner, José C. Aponte, Surjyendu Bhattacharjee, et al in Science

Analysis of organic compounds — calledpolycyclic aromatic hydrocarbons (PAHs) — extracted from the Ryugu asteroid and Murchison meteorite has foundthat certainPAHs likely formed in the cold areas of space between stars rather than in hot regions near stars as was previously thought. The findings open new possibilities for studying life beyond Earth and the chemistry of objects in space.

The only Australian members of an international research team, scientists from Curtin’s WA-Organic and Isotope Geochemistry Centre (WA-OIGC) carried out controlled burnings of plants to produce PAHs. ARC Laureate Fellow John Curtin Distinguished Professor Kliti Grice, director of WA-OIGC, said PAHs are organic compounds made up of carbon and hydrogen that are common on Earth but are also found in celestial bodies like asteroids and meteorites.

“We performed controlled burn experiments on Australian plants, which were isotopically compared to PAHs from fragments of the Ryugu asteroid that were returned to Earth by a Japanese spacecraft in 2020, and the Murchison meteorite that landed in Australia in 1969. The bonds between light and heavy carbon isotopes in the PAHs were analysed to reveal the temperature at which they were formed,” Professor Grice said.
“Select PAHs from Ryugu and Murchison were found to have different characteristics: the smaller ones likely in cold outer space, while bigger ones probably formed in warmer environments, like near a star or inside a celestial body.”

Study co-author Dr Alex Holman, also from WA-OIGC, said understanding the isotopic composition of PAHs helps unravel the conditions and environments in which these molecules were created, offering insights into the history and chemistry of celestial bodies like asteroids and meteorites.

“This research gives us valuable insights into how organic compounds form beyond Earth and where they come from in space,” Dr Holman said. “The use of high-tech methods and creative experiments has shown that select PAHs on asteroids can be formed in cold space.”

The oxygen bottleneck for technospheres

by Amedeo Balbi, Adam Frank in Nature Astronomy

In the quest to understand the potential for life beyond Earth, researchers are widening their search to encompass not only biological markers, but also technological ones. While astrobiologists have long recognized the importance of oxygen for life as we know it, oxygen could also be a key to unlocking advanced technology on a planetary scale.

In a new study, Adam Frank, the Helen F. and Fred H. Gowen Professor of Physics and Astronomy at the University of Rochester and the author of The Little Book of Aliens (Harper, 2023), and Amedeo Balbi, an associate professor of astronomy and astrophysics at the University of Roma Tor Vergata, Italy, outline the links between atmospheric oxygen and the potential rise of advanced technology on distant planets.

“We are ready to find signatures of life on alien worlds,” Frank says. “But how do the conditions on a planet tell us about the possibilities for intelligent, technology-producing life?”
“In our paper, we explore whether any atmospheric composition would be compatible with the presence of advanced technology,” Balbi says. “We found that the atmospheric requirements may be quite stringent.”

Frank and Balbi posit that, beyond its necessity for respiration and metabolism in multicellular organisms, oxygen is crucial to developing fire — and fire is a hallmark of a technological civilization. They delve into the concept of “technospheres,” expansive realms of advanced technology that emit telltale signs — called “technosignatures” — of extraterrestrial intelligence.

On Earth, the development of technology demanded easy access to open-air combustion — the process at the heart of fire, in which something is burned by combining a fuel and an oxidant, usually oxygen.

Whether it’s cooking, forging metals for structures, crafting materials for homes, or harnessing energy through burning fuels, combustion has been the driving force behind industrial societies. Tracing back through Earth’s history, the researchers found that the controlled use of fire and the subsequent metallurgical advancements were only possible when oxygen levels in the atmosphere reached or exceeded 18 percent. This means that only planets with significant oxygen concentrations will be capable of developing advanced technospheres, and, therefore, leaving detectable technosignatures.

The levels of oxygen required to biologically sustain complex life and intelligence are not as high as the levels necessary for technology, so while a species might be able to emerge in a world without oxygen, it will not be able to become a technological species, according to the researchers.

“You might be able to get biology — you might even be able to get intelligent creatures — in a world that doesn’t have oxygen,” Frank says, “but without a ready source of fire, you’re never going to develop higher technology because higher technology requires fuel and melting.”

Enter the “oxygen bottleneck,” a term coined by the researchers to describe the critical threshold that separates worlds capable of fostering technological civilizations from those that fall short. That is, oxygen levels are a bottleneck that impedes the emergence of advanced technology.

“The presence of high degrees of oxygen in the atmosphere is like a bottleneck you have to get through in order to have a technological species,” Frank says. “You can have everything else work out, but if you don’t have oxygen in the atmosphere, you’re not going to have a technological species.”

The research, which addresses a previously unexplored facet in the cosmic pursuit of intelligent life, underscores the need to prioritize planets with high oxygen levels when searching for extraterrestrial technosignatures.

“Targeting planets with high oxygen levels should be prioritized because the presence or absence of high oxygen levels in exoplanet atmospheres could be a major clue in finding potential technosignatures,” Frank says.
“The implications of discovering intelligent, technological life on another planet would be huge,” adds Balbi. “Therefore, we need to be extremely cautious in interpreting possible detections. Our study suggests that we should be skeptical of potential technosignatures from a planet with insufficient atmospheric oxygen.”

Ionized gas extends over 40 kpc in an odd radio circle host galaxy

by Alison L. Coil, Serena Perrotta, David S. N. Rupke, Cassandra Lochhaas, Christy A. Tremonti, Aleks Diamond-Stanic, Drummond Fielding, James E. Geach, Ryan C. Hickox, John Moustakas, Gregory H. Rudnick, Paul Sell, Kelly E. Whalen in Nature

It’s not every day astronomers say, “What is that?” After all, most observed astronomical phenomena are known: stars, planets, black holes and galaxies. But in 2019 the newly completed ASKAP (Australian Square Kilometer Array Pathfinder) telescope picked up something no one had ever seen before: radio wave circles so large they contained entire galaxies in their centers.

As the astrophysics community tried to determine what these circles were, they also wanted to know why the circles were. Now a team led by University of California San Diego Professor of Astronomy and Astrophysics Alison Coil believes they may have found the answer: the circles are shells formed by outflowing galactic winds, possibly from massive exploding stars known as supernovae.

Coil and her collaborators have been studying massive “starburst” galaxies that can drive these ultra-fast outflowing winds. Starburst galaxies have an exceptionally high rate of star formation. When stars die and explode, they expel gas from the star and its surroundings back into interstellar space. If enough stars explode near each other at the same time, the force of these explosions can push the gas out of the galaxy itself into outflowing winds, which can travel at up to 2,000 kilometers/second.

“These galaxies are really interesting,” said Coil, who is also chair of the Department of Astronomy and Astrophysics. “They occur when two big galaxies collide. The merger pushes all the gas into a very small region, which causes an intense burst of star formation. Massive stars burn out quickly and when they die, they expel their gas as outflowing winds.”

Comparison of ORC4 radio continuum and [O II] line luminosity to radio AGN.

Technological developments allowed ASKAP to scan large portions of the sky at very faint limits which made odd radio circles (ORCs) detectable for the first time in 2019. The ORCs were enormous — hundreds of kiloparsecs across, where a kiloparsec is equal to 3,260 light years (for reference, the Milky Way galaxy is about 30 kiloparsecs across). Multiple theories were proposed to explain the origin of ORCs, including planetary nebulae and black hole mergers, but radio data alone could not discriminate between the theories.

Coil and her collaborators were intrigued and thought it was possible the radio rings were a development from the later stages of the starburst galaxies they had been studying. They began looking into ORC 4 — the first ORC discovered that is observable from the Northern Hemisphere. Up until then, ORCs had only been observed through their radio emissions, without any optical data.

Coil’s team used an integral field spectrograph at the W.M. Keck Observatory on Maunakea, Hawaii, to look at ORC 4, which revealed a tremendous amount of highly luminous, heated, compressed gas — far more than is seen in the average galaxy. With more questions than answers, the team got down to detective work. Using optical and infrared imaging data, they determined the stars inside ORC 4 galaxy were around 6 billion years old.

“There was a burst of star formation in this galaxy, but it ended roughly a billion years ago,” stated Coil.

Cassandra Lochhaas, a postdoctoral fellow at the Harvard & Smithsonian Center for Astrophysics specializing in the theoretical side of galactic winds and a co-author on the paper, ran a suite of numerical computer simulations to replicate the size and properties of the large-scale radio ring, including the large amount of shocked, cool gas in the central galaxy. Her simulations showed outflowing galactic winds blowing for 200 million years before they shut off.

When the wind stopped, a forward-moving shock continued to propel high-temperature gas out of the galaxy and created a radio ring, while a reverse shock sent cooler gas falling back onto the galaxy. The simulation played out over 750 million years — within the ballpark of the estimated one-billion-year stellar age of ORC 4.

“To make this work you need a high-mass outflow rate, meaning it’s ejecting a lot of material very quickly. And the surrounding gas just outside the galaxy has to be low density, otherwise the shock stalls. These are the two key factors,” stated Coil. “It turns out the galaxies we’ve been studying have these high-mass outflow rates. They’re rare, but they do exist. I really do think this points to ORCs originating from some kind of outflowing galactic winds.”

Not only can outflowing winds help astronomers understand ORCs, but ORCs can help astronomers understand outflowing winds as well. “ORCs provide a way for us to ‘see’ the winds through radio data and spectroscopy,” said Coil. “This can help us determine how common these extreme outflowing galactic winds are and what the wind life cycle is. They can also help us learn more about galactic evolution: do all massive galaxies go through an ORC phase? Do spiral galaxies turn elliptical when they are no longer forming stars? I think there is a lot we can learn about ORCs and learn from ORCs.”

Accretion of the earliest inner Solar System planetesimals beyond the water snowline

by Damanveer S. Grewal, Nicole X. Nie, Bidong Zhang, Andre Izidoro, Paul D. Asimow in Nature Astronomy

When our Sun was a young star, 4.56 billion years ago, what is now our solar system was just a disk of rocky dust and gas. Over tens of millions of years, tiny pebbles of dust coalesced, like a snowball rolling larger and larger, to become kilometer-sized “planetesimals” — the building blocks of Earth and the other inner planets.

Researchers have long tried to understand the ancient environments in which these planetesimals formed. For example, water is now abundant on Earth, but has it always been? In other words, did the planetesimals that accreted into our planet contain water?

Now, a new study combines meteorite data with thermodynamic modeling and determines that the earliest inner solar system planetesimals must have formed in the presence of water, challenging current astrophysical models of the early solar system. The research was conducted in the laboratory of Paul Asimow (MS ’93, PhD ‘97), Eleanor and John R. McMillan Professor of Geology and Geochemistry.

Researchers have samples of the earliest years of the solar system in the form of iron meteorites. These meteorites are the remnants of the metallic cores of the earliest planetesimals in our solar system that avoided accretion into a forming planet and instead orbited around the solar system before ultimately falling onto our planet.

The chemical compositions of meteorites such as these can reveal information about the environments in which they formed and answer questions such as whether the building blocks of Earth formed far from our Sun, where cooler temperatures allowed the existence of water ice, or if they instead formed closer to the Sun, where the heat would have evaporated any water and resulted in dry planetesimals.

Minimum water required to explain the FeO contents of the parent bodies of iron meteorites based on the Fe/Ni and Fe/Co ratios of their parent cores.

If the latter is correct, then Earth would have formed dry and gained its water through some other method later in its evolution. Though the meteorites themselves do not contain any water, scientists can infer its long-lost presence by examining its impact on other chemical elements. Water is composed of two hydrogen atoms and one oxygen atom. In the presence of other elements, water will often transfer its oxygen atom away in a process called oxidation. For example, iron metal (Fe) reacts with water (H2O) to form iron oxide (FeO). A sufficient excess of water can drive the process further, producing Fe2O3 and FeO(OH), the ingredients of rust. Mars, for example, is covered in rusty iron oxide, providing strong evidence that the Red Planet once had water.

Damanveer Grewal, a former Caltech postdoctoral scholar and first author of the new study, specializes in using chemical signatures from iron meteorites to gather information about the early solar system. Though any iron oxide from the earliest planetesimals is now long gone, the team could determine how much iron would have been oxidized by examining the metallic nickel, cobalt, and iron contents of these meteorites. These three elements should be present in roughly equal ratios relative to other primitive materials, so if any iron was “missing,” this would imply that the iron had been oxidized.

“Iron meteorites have been somewhat neglected by the planet-formation community, but they constitute rich stores of information about the earliest period of solar system history, once you work out how to read the signals,” says Asimow. “The difference between what we measured in the inner solar system meteorites and what we expected implies an oxygen activity about 10,000 times higher.”

The researchers found that those iron meteorites thought to be derived from the inner solar system had about the same amount of missing iron metal as meteorites derived from the outer solar system. For this to be the case, the planetesimals from both groups of meteorites must have formed in a part of the solar system where water was present, implying that the building blocks of planets accreted water right from the beginning.

The signatures of water in these planetesimals challenge many of the current astrophysical models of the solar system. If planetesimals formed at Earth’s current orbital position, water would have existed only if the inner solar system was much cooler than models currently predict. Alternatively, they may have formed further out, where it was cooler, and migrated in.

“If water was present in the early building blocks of our planet, other important elements like carbon and nitrogen were likely present as well,” says Grewal. “The ingredients for life may have been present in the seeds of rocky planets right from the start.”
“However, the method only detects water that was used up in oxidizing iron,” adds Asimow. “It is not sensitive to excess water that might go on to form the ocean. So, the conclusions of this study are consistent with Earth accretion models that call for late addition of even more water-rich material.”