Unraveling the mysteries of fog in complex terrain

With Heber Valley study, U researchers shed new light on how fog forms in mountainous areas, providing insights for improving forecasts for a weather phenomenon that poses serious travel hazards

Peer-Reviewed Publication

UNIVERSITY OF UTAH

 

IMAGE: 

IN THE WINTER OF 2022, UNIVERSITY OF UTAH RESEARCHERS OPERATED THIS WEATHER STATION NEAR UTAH'S DEER CREEK RESERVOIR IN THE HEBER VALLEY WHERE THEY INSTALLED A TROVE OF METEOROLOGICAL INSTRUMENTATION FOR AN INTENSIVE STUDY OF FOG FORMATION. 

view more 

CREDIT: ZHAOXIA PU, UNIVERSITY OF UTAH

Of the world’s various weather phenomena, fog is perhaps the most mysterious, forming and dissipating near the ground with fluctuations in air temperature and humidity interacting with the terrain itself.

While fog presents a major hazard to transportation safety, meteorologists have yet to figure out how to forecast it with the precision they have achieved for precipitation, wind and other stormy events.

This is because the physical processes resulting in fog formation are extremely complex, according to Zhaoxia Pu, a professor of atmospheric sciences at the University of Utah.

“Our understanding is limited. In order to accurately forecast fog we should better understand the process that controls fog formation,” said Pu, who led a fog study focusing on a northern Utah valley.

Now, in a recent paper published by the American Meteorological Society, Pu and her colleagues have reported their findings from the Cold Fog Amongst Complex Terrain (CFACT) project, conceived to investigate the life cycle of cold fog in mountain valleys.

Also working on the project, funded by a $1.17 million grant from the National Science Foundation, were several other members of the U Department of Atmospheric Sciences, including Gannet Hallar and Sebastian Hoch, along with Eric Pardyjak of the Department of Mechanical Engineering, a group of scientists from the National Center for Atmospheric Research (NCAR), and Dr. Ismail Gultepe from Ontario Tech University, Canada.

Because it reduces visibility, fog poses serious hazards to the traveling public. For example, fog is the second leading cause of aircraft accidents after high winds. It leads to automobile crashes and disrupts ferry operations.

Between 1995 and 2004 in the United States, 13,720 have died in fog-related accidents.

Improving fog forecasting would make traveling more safe, Pu said.

Today, most forecasting uses a computer model known as Numerical Weather Prediction (NWP), which processes massive meteorological observations with computer models to output predictions for precipitation, temperature, and all sorts of other elements of the weather. However the current computer model doesn’t work well for fog, and Pu’s team hopes that improvements can be made using the masses of data they gathered over seven weeks in the winter of 2022 at several sites in the Heber Valley.

“Fog involves a lot of physics processes so it requires a computer model that can better represent all these processes,” Pu said. “Because fog is clouds near the ground, it requires a high-resolution model to resolve it, so we need models at a very fine scale, which are computationally very expensive. The current models (relatively coarser in resolution) are not capable of resolving the fog processes, and we need to improve the models for better fog prediction.”

Located bout 50 miles southeast of Salt Lake City, Heber Valley is nestled behind the Wasatch Mountains and framed by two major reservoirs on the Provo River.

This scenic basin is a typical mountain valley, hemmed by Mt. Timpanogos and other high peaks, with the reservoirs serving as a moisture source.  The seven-week study window covered the time of year when Heber Valley is the foggiest.

Valley fog is a perfect example of how topography and atmospheric processes converge to create a distinctive weather phenomenon.

The ground is cooling overnight while denser, cooler air drops from mountain tops collecting in the valleys, in a phenomenon known as “cold air drainage.” Cooled by the ground, the dropping air temperature can approach the dew point, and if there is sufficient moisture in the air, fog begins to form, becoming the most dense around sunrise when surface temperatures are lowest.

Winter nights create favorable conditions for different forms of fog, such as cold-air pool fog, ephemeral mountain valley fog and radiative ice fog.

The Heber Valley project homed in on cold-air fog which forms in freezing temperatures below zero degrees Celsius, according to Pu. However by observing how these varying kinds of fog form and dissipate, the researchers are continuing to learn about the meteorological conditions and physical processes governing the formation of fog.

For the CFACT study, the NCAR and U team set up two major data-collecting stations, one near Deer Creek Reservoir and another a few miles up the Provo River. These are low spots in the valley, about 5,450 feet above sea level, that see the densest fog. These sites were equipped with 100-foot towers to support an array of instruments that captured various meteorological data associated with humidity, wind, visibility, temperature, even snow depths, and soil moisture. The recordings were made from both in situ and remote-sensing platforms.

Additionally, the team recorded a lesser array of data points at nine satellite sites.

During the seven-week CFACT field campaign, nine intensive observation periods (IOPs), each conducted over 24-hour periods, yielded a dataset that included high-frequency radiosonde profiles, tethered balloon profiles, remotely sensed thermodynamic and wind profiles, surface meteorological observations and microphysical and aerosol measurements.

Besides fog IOPs, the variety of non-fog IOPs provided valuable observations for understanding near-surface inversion, ice crystal formation, moisture advection and transportation, and stable boundary layers over complex terrain, all of which are essential factors related to fog formation. Comprehensive studies are ongoing for an improved understanding of cold fog over complex terrain.

The study appeared Nov. 15 in the Bulletin of the American Meteorological Society. U researchers involved with the study included Zhaoxia Pu, Sebastian Hoch, A. Gannet Hallar, Rebecca Beal, Geraldo Carrillo-Cardenas, Xin Li and Maria Garcia of the Department of Atmospheric Sciences and Eric Pardyjak and Alexei Perelet of the Department of Mechanical Engineering.

Heber Valley in northern Utah was the site of an intensive study by the University of Utah into the formation of fog in complex terrain.

CREDIT

University of Utah

Heber Valley in northern Utah was the site of an intensive study by the University of Utah into the formation of fog in complex terrain.

CREDIT

Zhaoxia Pu, University of Utah

---

JOURNAL

Bulletin of the American Meteorological Society

DOI

10.1175/BAMS-D-22-0030.1 

METHOD OF RESEARCH

Observational study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Cold Fog Amongst Complex Terrain

 

 

 

In coastal communities, sea level rise may leave some isolated

Study exposes social, racial vulnerabilities caused by global warming

Peer-Reviewed Publication

OHIO STATE UNIVERSITY

'

COLUMBUS, Ohio – Amid the threat of dramatic sea level rise, coastal communities face unprecedented dangers, but a new study reveals that as flooding intensifies, disadvantaged populations will be the ones to experience some of the most severe burdens of climate change.

While accelerating sea level rise will result in widespread intermittent flooding and long-term inundation in many coastal communities, the paper, recently published in Nature Communications, showed that when these levels increase above 4 feet, minority populations will be disproportionately at risk of isolation.

Rising sea levels could lead to isolation by disrupting transportation networks and roads, meaning that those affected lose access to essential locations such as critical emergency services and schools. 

The study further exposed that renters and older adults face a greater risk of isolation, highlighting the growing connection between historical drivers of existing social inequality and the groups that incur the most risk of climate change.

According to Kelsea Best, lead author of the study and an assistant professor of civil, environmental and geodetic engineering at The Ohio State University, the first step in better characterizing these threats is changing how researchers assess community risk, as most studies measure this by exclusively determining impacts via direct flooding. But concentrating on this sole measurement neglects more complex aftereffects of sea level rise, such as isolation, and reinforces inequality in coastal areas, Best said. 

“We need to re-conceptualize how we measure who is burdened by sea level rise because there are so many ways that people might be burdened before their home is flooded,“ she said. 

Current reports estimate that around 20 million coastal residents in the U.S. will be affected by rising sea levels by 2030, but the paper notes that this number doesn’t include the whole impact global warming will have on certain communities and demographics. 

Notably, because people need access to essential places like grocery stores, public schools, hospitals and fire stations, Best and her colleagues argue that an inability to reach these places impacts individuals just as negatively as if they were living in inundated homes themselves, and should be documented as such. 

Most importantly, their results expose one of the main reasons for these vast differences in risk: A group’s risk of isolation is intimately entwined with specific road networks and where vital services are located in relation to where affected individuals reside. 

They identified these disparities in risk by overlaying OpenStreetMap (OSM) road network data with National Oceanographic and Atmospheric Administration (NOAA) mean higher high water (MHHW) scenarios. These projections were then combined with recent census data to estimate the percentage of a population that would be left out or missed in estimates of who would be impacted by sea level rise if researchers only counted those who suffered direct inundation. 

“If we take a one-size-fits-all approach, or a seemingly ‘neutral’ approach to understanding who gets access to safe, affordable housing and community in a world with climate change, then we’re really just exacerbating these inequities and it’s not good enough,” said Best. “We have to deliberately seek to provide access to adaptation resources to groups of people who have historically been left out and therefore have fewer resources to respond in the first place.”

The researchers showed that Hispanic populations are often overrepresented in the total citizenry for being at risk of isolation beginning at 4 feet of sea level rise, and Black populations are overrepresented after 6 feet. Alternatively, white populations are underrepresented after 5 feet of sea level rise. 

But to determine when these disparities will begin to develop, Best’s team compared two long-term sea level rise scenarios: an intermediate scenario in which global sea level rise increased by a meter by 2100, and a high scenario in which that number increased to 2 meters by the same year. 

Alarmingly, the study found strong evidence that these isolation effects would set in by 2120 in the intermediate scenario and as early as 2090 in the high scenario. “This timeline matters from a planning and adaptation perspective,” said Best. “Part of why we included the temporal piece is to say this issue would not be as much of a problem if we had urgent, aggressive mitigation. 

“The effects of climate change are going to be further reaching and more cascading than might be directly obvious, and those effects are not going to be felt equitably,” said Best. “So we need to be thinking about those populations most at risk from the beginning and develop policies to support them.” 

The work was supported by the Clark Distinguished Chair Endowment (given to study co-author Deb. A. Neimeier of the University of Maryland) and the National Science Foundation. Other co-authors were Qian He from Rowan University, Allison C. Reilly from the University of Maryland, and Mitchell Anderson and Tom Logan from the University of Canterbury. 

#

Contact: Kelsea Best, Best.309.osu.edu

Written by: Tatyana Woodall, Woodall.52@osu.edu

---

JOURNAL

Nature Communications

DOI

10.1038/s41467-023-43835-6 

ARTICLE TITLE

Demographics and risk of isolation due to sea level rise in the United States

SPACE

FASHI releases the largest extragalactic HI catalog with FAST

Peer-Reviewed Publication

SCIENCE CHINA PRESS

 

IMAGE: 

THE PROMOTIONAL IMAGE SHOWS THE PROJECT ABOUT THE FIVE-HUNDRED-METER APERTURE SPHERICAL RADIO TELESCOPE (FAST) ALL SKY HI SURVEY (FASHI). AS THE IMAGE ILLUSTRATES, THE POWERFUL FAST TELESCOPE IS OBSERVING DISTANT GALAXIES, RECORDING THEIR HI EMISSION, AND REVEALING THE DETAILED PHYSICAL PROPERTIES OF THE GALAXIES.

view more 

CREDIT: ©SCIENCE CHINA PRESS

The FAST All Sky HI survey (FASHI) was designed to cover the entire sky observable by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), spanning approximately 22000 square degrees of declination between -14 deg and +66 deg, and in the frequency range of 1050-1450 MHz, with the expectation of eventually detecting more than 100000 HI sources. Between August 2020 and June 2023, FASHI had covered more than 7600 square degrees, which is approximately 35% of the total sky observable by FAST. FASHI team has detected a total of 41741 extragalactic HI sources in the frequency range 1305.5-1419.5 MHz. When completed, FASHI team will provide the largest extragalactic HI catalog and an objective view of HI content and large-scale structure in the local universe.

Lister Staveley-Smith, a professor at the University of Western Australia and a peer reviewer of the paper, called their work: “That’s an impressive milestone. That’s is an extremely important contribution to astronomical research, particularly in the field of galaxy evolution.”

Hélène Courtois, a professor at the University of Lyon 1, called their work: “The paper is a fantastic news for projects like Cosmic Flows!! I didn’t know that the FASHI survey was already going so strongly since 3 years!! The quality of the spectra that are shown is exquisite, the completeness of the sample is amazing and showing the excellent sensitivity of the instrument. The area surveyed in just 3 years gives high hopes that the full sky that can be accessed by the FAST will be covered in a record of time! The paper was a total surprise to me , and reading page after page of the article was just like being a child unwrapping slowly and with delight a Christmas gift.”

The work was recently published in the journal SCIENCE CHINA Physics, Mechanics and Astronomy. Researchers from Guizhou University, the National Astronomical Observatories under the Chinese Academy of Sciences, and Peking University in China contributed to the study.

  

FASHI sky distribution of the currently released 41741 H I sources (in blue dots) in the galactic hemispheres, showing the coarseness of the limits imposed by practical and scheduling constraints. For comparison, ALFALFA α100 (Haynes et al., 2018) and HIPASS galaxies (Koribalski et al., 2004; Meyer et al., 2004; Wong et al., 2006) are also shown with red and green points, respectively. The two black dashed lines indicate the position of the of the galactic plane at galactic latitude b = ±10deg.

CREDIT

©Science China Press

See the article and download the catalog:

The FAST all sky HI survey (FASHI): The first release of catalog

https://zcp521.github.io/fashi

https://fast.bao.ac.cn/cms/article/271/

https://ui.adsabs.harvard.edu/abs/2023arXiv231206097Z

http://engine.scichina.com/doi/10.1007/s11433-023-2219-7

---

JOURNAL

Science China Physics Mechanics and Astronomy

DOI

10.1007/s11433-023-2219-7 

ARTICLE PUBLICATION DATE

Sodium’s high-pressure transformation can tell us about the interiors of stars, planets

Scientists reveal how the element’s electrons chemically bond when under pressures like those found below Earth’s crust

Peer-Reviewed Publication

UNIVERSITY AT BUFFALO

Travel deep enough below Earth’s surface or inside the center of the Sun, and matter changes on an atomic level. 

The mounting pressure within stars and planets can cause metals to become nonconducting insulators. Sodium has been shown to transform from a shiny, gray-colored metal into a transparent, glass-like insulator when squeezed hard enough. 

Now, a University at Buffalo-led study has revealed the chemical bonding behind this particular high-pressure phenomenon.

While it’s been theorized that high pressure essentially squeezes sodium’s electrons out into the spaces between atoms, researchers’ quantum chemical calculations show that these electrons still very much belong to the surrounding atoms and are chemically bonded to each other.

“We’re answering a very simple question of why sodium becomes an insulator, but predicting how other elements and chemical compounds behave at very high pressures will potentially give insight into bigger-picture questions,” says Eva Zurek, Ph.D., professor of chemistry in the UB College of Arts and Sciences and co-author of the study, which was published in Angewandte Chemie, a journal of the German Chemical Society. “What’s the interior of a star like? How are planets’ magnetic fields generated, if indeed any exist? And how do stars and planets evolve? This type of research moves us closer to answering these questions.”

The study confirms and builds upon the theoretical predictions of the late renowned physicist Neil Ashcroft, whose memory the study is dedicated to.

It was once thought that materials always become metallic under high pressure — like the metallic hydrogen theorized to make up Jupiter’s core — but Ashcroft and Jeffrey Neaton’s seminal paper two decades ago found some materials, like sodium, can actually become insulators or semiconductors when squeezed. They theorized that sodium’s core electrons, thought to be inert, would interact with each other and the outer valence electrons when under extreme pressure. 

“Our work now goes beyond the physics picture painted by Ashcroft and Neaton, connecting it with chemical concepts of bonding,” says the UB-led study’s lead author, Stefano Racioppi, Ph.D., a postdoctoral researcher in the UB Department of Chemistry. 

Pressures found below Earth’s crust can be difficult to replicate in a lab, so using supercomputers in UB’s Center for Computational Research, the team ran calculations on how electrons behave in sodium atoms when under high pressure. 

The electrons become trapped within the interspatial regions between atoms, known as an electride state. This causes sodium’s physical transformation from shiny metal to transparent insulator, as free-flowing electrons absorb and retransmit light but trapped electrons simply allow the light to pass through. 

However, researchers’ calculations showed for the first time that the emergence of the electride state can be explained through chemical bonding.

The high pressure causes electrons to occupy new orbitals within their respective atoms. These orbitals then overlap with each other to form chemical bonds, causing localized charge concentrations in the interstitial regions.

While previous studies offered an intuitive theory that high pressure squeezed electrons out of atoms, the new calculations found that the electrons are still part of surrounding atoms.

“We realized that these are not just isolated electrons that decided to leave the atoms. Instead, the electrons are shared between the atoms in a chemical bond,” Racioppi says. “They're quite special.”

Other contributors include Malcolm McMahon and Christian Storm from the University of Edinburgh’s School of Physics and Astronomy and Center for Science at Extreme Conditions.

The work was supported by the Center for Matter at Atomic Pressure, a National Science Foundation center led by the University of Rochester that studies how pressure inside stars and planets can rearrange materials’ atomic structure. 

“Obviously it is difficult to conduct experiments that replicate, say, the conditions within the deep atmospheric layers of Jupiter,” Zurek says, “but we can use calculations, and in some cases, high-tech lasers, to simulate these kinds of conditions.”

---

JOURNAL

Angewandte Chemie

DOI

10.1002/anie.202310802 

METHOD OF RESEARCH

Computational simulation/modeling

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

On the Electride Nature of Na-hP4

Further evidence for quark-matter cores in massive neutron stars

New theoretical analysis places the likelihood of massive neutron stars hiding cores of deconfined quark matter between 80 and 90 percent. The result was reached through massive supercomputer runs utilizing Bayesian statistical inference.

Peer-Reviewed Publication

UNIVERSITY OF HELSINKI

 

IMAGE: 

ARTIST’S IMPRESSION OF THE DIFFERENT LAYERS INSIDE A MASSIVE NEUTRON STAR, WITH THE RED CIRCLE REPRESENTING A SIZABLE QUARK-MATTER CORE.

view more 

CREDIT: JYRKI HOKKANEN, CSC

New theoretical analysis places the likelihood of massive neutron stars hiding cores of deconfined quark matter between 80 and 90 percent. The result was reached through massive supercomputer runs utilizing Bayesian statistical inference.

Neutron-star cores contain matter at the highest densities reached in our present-day Universe, with as much as two solar masses of matter compressed inside a sphere of 25 km in diameter. These astrophysical objects can indeed be thought of as giant atomic nuclei, with gravity compressing their cores to densities exceeding those of individual protons and neutrons manyfold.

These densities make neutron stars interesting astrophysical objects from the point of view of particle and nuclear physics. A longstanding open problem concerns whether the immense central pressure of neutron stars can compress protons and neutrons into a new phase of matter, known as cold quark matter. In this exotic state of matter, individual protons and neutrons no longer exist.

”Their constituent quarks and gluons are instead liberated from their typical color confinement and are allowed to move almost freely,” explains Aleksi Vuorinen, professor of theoretical particle physics at the University of Helsinki.

A Strong Phase Transition May Still Ruin the Day

In a new article just published in Nature Communications, a team centred at the University of Helsinki provided a first-ever quantitative estimate for the likelihood of quark-matter cores inside massive neutron stars. They showed that, based on current astrophysical observations, quark matter is almost inevitable in the most massive neutron stars: a quantitative estimate that the team extracted placed the likelihood in the range of 80-90 percent.

The remaining small likelihood for all neutron stars to be composed of only nuclear matter requires the change from nuclear to quark matter to be a strong first-order phase transition, somewhat resembling that of liquid water turning to ice. This kind of rapid change in the properties of neutron-star matter has the potential to destabilize the star in such a way that the formation of even a minuscule quark-matter core would result in the star collapsing into a black hole.

The international collaboration between scientists from Finland, Norway, Germany, and the US was able to further show how the existence of quark-matter cores may one day be either fully confirmed or ruled out. The key is being able to constrain the strength of the phase transition between nuclear and quark matter, expected to be possible once a gravitational-wave signal from the last part of a binary neutron-star merger is one day recorded.

Massive Supercomputer Runs Using Observational Data

A key ingredient in deriving the new results was a set of massive supercomputer calculations utilizing Bayesian inference – a branch of statistical deduction where one infers the likelihoods of different model parameters via direct comparison with observational data. The Bayesian component of the study enabled the researchers to derive new bounds for the properties of neutron-star matter, demonstrating them to approach so-called conformal behavior near the cores of the most massive stable neutron stars.

Dr. Joonas Nättilä, one of the lead authors of the paper, describes the work as an interdisciplinary effort that required expertise from astrophysics, particle and nuclear physics, as well as computer science. He is about to start as an Associate Professor at the University of Helsinki in May 2024.

”It is fascinating to concretely see how each new neutron-star observation enables us to deduce the properties of neutron-star matter with increasing precision.”

Joonas Hirvonen, a PhD student working under the guidance of Nättilä and Vuorinen, on the other hand emphasizes the importance of high-performance computing:

”We had to use millions of CPU hours of supercomputer time to be able to compare our theoretical predictions to observations and to constrain the likelihood of quark-matter cores. We are extremely grateful to the Finnish supercomputer center CSC for providing us with all the resources we needed!”

Original publication: Annala, E., Gorda, T., Hirvonen, J. et al. Strongly interacting matter exhibits deconfined behavior in massive neutron stars. Nat Commun 14, 8451 (2023). https://doi.org/10.1038/s41467-023-44051-y

Artist’s impression of the different layers inside a massive neutron star, with the red circle representing a sizable quark-matter core.

CREDIT

Jyrki Hokkanen, CSC

JOURNAL

Nature Communications

DOI

10.1038/s41467-023-44051-y 

METHOD OF RESEARCH

Computational simulation/modeling

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Strongly interacting matter exhibits deconfined behavior in massive neutron stars

ARTICLE PUBLICATION DATE

29-Dec-2023

A carbon-lite atmosphere could be a sign of water and life on other terrestrial planets, MIT study finds.

A low carbon abundance in planetary atmospheres, which the James Webb Space Telescope can detect, could be a signature of habitability.

Peer-Reviewed Publication

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

Scientists at MIT, the University of Birmingham, and elsewhere say that astronomers’ best chance of finding liquid water, and even life on other planets, is to look for the absence, rather than the presence, of a chemical feature in their atmospheres. 

The researchers propose that if a terrestrial planet has substantially less carbon dioxide in its atmosphere compared to other planets in the same system, it could be a sign of liquid water — and possibly life — on that planet’s surface. 

What’s more, this new signature is within the sights of NASA’s James Webb Space Telescope (JWST). While scientists have proposed other signs of habitability, those features are challenging if not impossible to measure with current technologies. The team says this new signature, of relatively depleted carbon dioxide, is the only sign of habitability that is detectable now.

“The Holy Grail in exoplanet science is to look for habitable worlds, and the presence of life, but all the features that have been talked about so far have been beyond the reach of the newest observatories,” says Julien de Wit, assistant professor of planetary sciences at MIT. “Now we have a way to find out if there’s liquid water on another planet. And it’s something we can get to in the next few years.”

The team’s findings will appear in Nature Astronomy. De Wit co-led the study with Amaury Triaud of the University of Birmingham in the UK. Their MIT co-authors include Benjamin Rackham, Prajwal Niraula, Ana Glidden Oliver Jagoutz, Matej Peč, Janusz Petkowski, and Sara Seager, along with Frieder Klein at the Woods Hole Oceanographic Institution (WHOI), Martin Turbet of Ècole Polytechnique in France, and Franck Selsis of the Laboratoire d’astrophysique de Bordeaux.

Beyond a glimmer

Astronomers have so far detected more than 5,200 worlds beyond our solar system. With current telescopes, astronomers can directly measure a planet’s distance to its star and the time it takes it to complete an orbit. Those measurements can help scientists infer whether a planet is within a habitable zone. But there’s been no way to directly confirm whether a planet is indeed habitable, meaning that liquid water exists on its surface. 

Across our own solar system, scientists can detect the presence of liquid oceans by observing “glints” — flashes of sunlight that reflect off liquid surfaces. These glints, or specular reflections, have been observed, for instance, on Saturn’s largest moon, Titan, which helped to confirm the moon’s large lakes. 

Detecting a similar glimmer in far-off planets, however, is out of reach with current technologies. But de Wit and his colleagues realized there’s another habitable feature close to home that could be detectable in distant worlds. 

“An idea came to us, by looking at what’s going on with the terrestrial planets in our own system,” Triaud says. 

Venus, Earth, and Mars share similarities, in that all three are rocky and inhabit a relatively temperate region with respect to the sun. Earth is the only planet among the trio that currently hosts liquid water. And the team noted another obvious distinction: Earth has significantly less carbon dioxide in its atmosphere. 

“We assume that these planets were created in a similar fashion, and if we see one planet with much less carbon now, it must have gone somewhere,” Triaud says. “The only process that could remove that much carbon from an atmosphere is a strong water cycle involving oceans of liquid water.” 

Indeed, the Earth’s oceans have played a major and sustained role in absorbing carbon dioxide. Over hundreds of millions of years, the oceans have taken up a huge amount of carbon dioxide, nearly equal to the amount that persists in Venus’ atmosphere today. This planetary-scale effect has left Earth’s atmosphere significantly depleted of carbon dioxide  compared to its planetary neighbors. 

“On Earth, much of the atmospheric carbon dioxide has been sequestered in seawater and solid rock over geological timescales, which has helped to regulate climate and habitability for billions of years,” says study co-author Frieder Klein.

The team reasoned that if a similar depletion of carbon dioxide were detected in a far-off planet, relative to its neighbors, this would be a reliable signal of liquid oceans and life on its surface.

“After reviewing extensively the literature of many fields from biology, to chemistry, and even carbon sequestration in the context of climate change, we believe that indeed if we detect carbon depletion, it has a good chance of being a strong sign of liquid water and/or life,” de Wit says.

A roadmap to life

In their study, the team lays out a strategy for detecting habitable planets by searching for a signature of depleted carbon dioxide. Such a search would work best for “peas-in-a-pod” systems, in which multiple terrestrial planets, all about the same size, orbit relatively close to each other, similar to our own solar system. The first step the team proposes is to confirm that the planets have atmospheres, by simply looking for the presence of carbon dioxide, which is expected to dominate most planetary atmospheres.

“Carbon dioxide is a very strong absorber in the infrared, and can be easily detected in the atmospheres of exoplanets,” de Wit explains. “A signal of carbon dioxide can then reveal the presence of exoplanet atmospheres.”

Once astronomers determine that multiple planets in a system host atmospheres, they can move on to measure their carbon dioxide content, to see whether one planet has significantly less than the others. If so, the planet is likely habitable, meaning that it hosts significant bodies of liquid water on its surface. 

But habitable conditions doesn’t necessarily mean that a planet is inhabited. To see whether life might actually exist, the team proposes that astronomers look for another feature in a planet’s atmosphere: ozone. 

On Earth, the researchers note that plants and some microbes contribute to drawing carbon dioxide, although not nearly as much as the oceans. Nevertheless, as part of this process, the lifeforms emit oxygen, which reacts with the sun’s photons to transform into ozone — a molecule that is far easier to detect than oxygen itself. 

The researchers say that if a planet’s atmosphere shows signs of both ozone and depleted carbon dioxide, it likely is a habitable, and inhabited world.

“If we see ozone, chances are pretty high that it’s connected to carbon dioxide being consumed by life,” Triaud says. “And if it’s life, it’s glorious life. It would not be just a few bacteria. It would be a planetary-scale biomass that’s able to process a huge amount of carbon, and interact with it.”

The team estimates that NASA’s James Webb Space Telescope would be able to measure carbon dioxide, and possibly ozone, in nearby, multiplanet systems such as TRAPPIST-1 — a seven-planet system that orbits a bright star, just 40 light years from Earth. 

“TRAPPIST-1 is one of only a handful of systems where we could do terrestrial atmospheric studies with JWST,” de Wit says. “Now we have a roadmap for finding habitable planets. If we all work together, paradigm-shifting discoveries could be done within the next few years.”

###

Written by Jennifer Chu, MIT News

---

JOURNAL

Nature Astronomy

DOI

10.1038/s41550-023-02157-9 

ARTICLE TITLE

“Atmospheric carbon depletion as a tracer of water oceans and biomass on temperate terrestrial exoplanets”

Scientists discover new way to identify liquid water on exoplanets

Atmospheric CO2 levels hold the key to finding habitable planets and potentially life itself

Peer-Reviewed Publication

UNIVERSITY OF BIRMINGHAM

Scientists have devised a new way to identify habitable planets and potentially inhabited planets, by comparing the amount of carbon dioxide in their atmosphere, to neighbouring planets.

An international team of researchers from the University of Birmingham (UK), the Massachusetts Institute of Technology (MIT) (US) and elsewhere, have shown that if a planet has a reduced amount of CO2 in its atmosphere compared to neighbouring planets, it suggests there is liquid water on that planet’s surface. The drop in CO2 levels implies that the carbon dioxide in the atmosphere of the planet is being dissolved into an ocean or sequestrated by a planetary-scale biomass.

The research is published today (28 December 2023) in Nature Astronomy.

Habitability is a theoretical astronomical concept that means that a celestial body is capable of hosting and retaining liquid water on its surface. Planets too close to their star are too hot (such as Venus), those too far, are too cold (like Mars), whereas planets in the ‘habitable zone’ are just right. The habitable zone is sometimes referred to as the Goldilocks zone.

Whilst there has been much effort in identifying planets in the theoretical habitable zones of their stars, until now there was no way of knowing whether they truly have liquid water. While the scientific community has made progress in defining biosignatures, chemical tracers of biological processes, until now there had been no practical method for detecting habitability, the planetary property indicating the presence of liquid water.

The researchers devised a new ‘habitability signature’ with which they can identify whether a planet does indeed have liquid water. Before this, the closest scientists had come to identifying liquid on a planetary surface was to use its glint, how star light reflects off water. However, this signature is far too weak for current observatories to detect whereas the new method can be applied with current facilities.

Amaury Triaud, Professor of Exoplanetology at the University of Birmingham, who co-led the study said: “It is fairly easy to measure the amount of carbon dioxide in a planet’s atmosphere. This is because CO2 is a strong absorber in the infrared, the same property causing the current rise in global temperatures here on Earth. By comparing the amount of CO2 in different planets’ atmospheres, we can use this new habitability signature to identify those planets with oceans, which make them more likely to be able to support life.

“For example, we know that initially, the Earth’s atmosphere used to be mostly CO2, but then the carbon dissolved into the ocean and made the planet able to support life for the last four billion years or so.”

As well as developing a new way to identify habitable planets, the research can be used to reveal more insights into environmental tipping points.

Amaury Triaud continues, “By examining the levels of CO2 in other planets’ atmospheres we can empirically measure habitability and compare it to our theoretical expectations. This helps gather context for the climate crisis we face on Earth to find out at which point the levels of carbon make a planet uninhabitable. For example, Venus and Earth look incredibly similar, but there is a very high level of carbon in Venus’ atmosphere. There may have been a past climatic tipping point that led to Venus becoming uninhabitable.”

The new method is not just a signature for habitability, but it can serve as a biosignature too, since biology captures carbon dioxide as well.

Dr Julien de Wit, Assistant Professor of Planetary Sciences at MIT and co-leader of the study explains: “Life on Earth accounts for 20% of the total amount of captured CO2, with the rest mainly being absorbed by the oceans. On another planet, this number could be much larger. One of the tell-tale signs of carbon consumption by biology, is the emission of oxygen. Oxygen can transform into ozone, and it turns out ozone has a detectable signature right next to CO2. So, observing both carbon dioxide and ozone at once can inform us about habitability, but also about the presence of life on that planet.”

An important element of the new study is that those signatures are detectable with current telescopes. Julien de Wit concludes “Despite much early hopes, most of our colleagues had eventually come to the conclusion that major telescopes like the JWST would not be able to detect life on exoplanets. Our work brings new hope. By leveraging the signature of carbon dioxide, not only can we infer the presence of liquid water on a faraway planet, but it also provides a path to identify life itself.”

The next step for the research team is to detect the atmospheric carbon dioxide compositions of a range of exoplanets and identify which have oceans on their surface, and help prioritise further observations towards those that may support life.

ENDS

---

JOURNAL

Nature Astronomy

DOI

10.1038/s41550-023-02157-9 

SUBJECT OF RESEARCH

Not applicable

ARTICLE PUBLICATION DATE

28-Dec-2023