Astronomers uncover methane emission on a cold brown dwarf

Using new observations from the James Webb Space Telescope (JWST), astronomers have discovered methane emission on a brown dwarf, an unexpected finding for such a cold and isolated world. Published in the journal Nature, the findings suggest that this brown dwarf might generate aurorae similar to those seen on our own planet as well as on Jupiter and Saturn.

More massive than planets but lighter than stars, brown dwarfs are ubiquitous in our solar neighborhood, with thousands identified. Last year, Jackie Faherty, a senior research scientist and senior education manager at the American Museum of Natural History, led a team of researchers who were awarded time on JWST to investigate 12 brown dwarfs. Among those was CWISEP J193518.59-154620.3 (or W1935 for short) -- a cold brown dwarf 47 light years away that was co-discovered by Backyard Worlds: Planet 9 citizen science volunteer Dan Caselden and the NASA CatWISE team. W1935 is a cold brown dwarf with a surface temperature of about 400° Fahrenheit, or about the temperature at which you'd bake chocolate chip cookies. The mass for W1935 isn't well known but it likely ranges between 6-35 times the mass of Jupiter.

After looking at a number of brown dwarfs observed with JWST, Faherty's team noticed that W1935 looked similar but with one striking exception: it was emitting methane, something that's never been seen before on a brown dwarf.

"Methane gas is expected in giant planets and brown dwarfs but we usually see it absorbing light, not glowing," said Faherty, the lead author of the study. "We were confused about what we were seeing at first but ultimately that transformed into pure excitement at the discovery."

Computer modeling yielded another surprise: the brown dwarf likely has a temperature inversion, a phenomenon in which the atmosphere gets warmer with increasing altitude. Temperature inversions can easily happen to planets orbiting stars, but W1935 is isolated, with no obvious external heat source.

"We were pleasantly shocked when the model clearly predicted a temperature inversion," said co-author Ben Burningham from the University of Hertfordshire. "But we also had to figure out where that extra upper atmosphere heat was coming from."

To investigate, the researchers turned to our solar system. In particular, they looked at studies of Jupiter and Saturn, which both show methane emission and have temperature inversions. The likely cause for this feature on solar system giants is aurorae, therefore, the research team surmised that they had uncovered that same phenomenon on W1935.

Planetary scientists know that one of the major drivers of aurorae on Jupiter and Saturn are high-energy particles from the Sun that interact with the planets' magnetic fields and atmospheres, heating the upper layers. This is also the reason for the aurorae that we see on Earth, commonly referred to as the Northern or Southern Lights since they are most extraordinary near the poles. But with no host star for W1935, a solar wind cannot contribute to the explanation.

There is an enticing additional reason for the aurora in our solar system. Both Jupiter and Saturn have active moons that occasionally eject material into space, interact with the planets, and enhance the auroral footprint on those worlds. Jupiter's moon Io is the most volcanically active world in the solar system, spewing lava fountains dozens of miles high, and Saturn's moon Enceleadus ejects water vapor from its geysers that simultaneously freezes and boils when it hits space. More observations are needed, but the researchers speculate that one explanation for the aurora on W1935 might be an active, yet-to-be discovered moon.

"Every time an astronomer points JWST at an object, there's a chance of a new mind-blowing discovery," said Faherty. "Methane emission was not on my radar when we started this project but now that we know it can be there and the explanation for it so enticing I am constantly on the look-out for it. That's part of how science moves forward."

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Surprising methane discovery in Yukon glaciers: 'Much more widespread than we thought'

Global melting is prying the lid off methane stocks, the extent of which we do not know. A young researcher from University of Copenhagen has discovered high concentrations of the powerful greenhouse gas in meltwater from three Canadian mountain glaciers, where it was not thought to exist -- adding new unknowns to the understanding of methane emissions from Earth's glaciated regions

The helicopter's rotor blades spin as its skillful pilot performs aerial acrobatics between the steep Yukon mountain sides where PhD student Sarah Elise Sapper is leading her first field expedition deep into the heart of the mountains of northwestern Canada. From the helicopter windows, her eyes fall on the jagged edge of the Donjek glacier: meltwater swirls out from beneath the ice like a whirlpool.

Soon after landing, it becomes apparent that Sarah has stumbled upon an unusual find on the first attempt. Seconds after starting up her portable methane analyzer it is clear that the air is enriched with methane and the culprit is soon found. Collecting a sample of meltwater, she measures concentrations of methane that far exceed expectations.

"We expected to find low values in the meltwater because it is believed that glacial methane emissions require larger ice masses such as vast ice sheets. But the result was quite the opposite. We measured concentrations up to 250 times higher than those in our atmosphere," explains Sarah Elise Sapper of the University of Copenhagen's Department of Geosciences and Natural Resource Management.

The field party lifted off and continued to two more mountain glaciers, Kluane and Dusty. And after measuring the methane in the meltwater of each of those two glaciers, the preliminary finding turned out to be more than an anomaly. Here too, measurements showed high methane concentrations. Somewhere beneath the ice, there are previously unknown sources of the gas.

Demonstrates possibility of widespread methane emissions

"The finding is surprising and raises several important questions within this area of research," says Associate Professor Jesper Riis Christiansen of the Department of Geosciences and Natural Resource Management.

Christiansen, the research article's co-author, believes that the finding demonstrates the possibility of methane being present beneath many of the world's glaciers, ones that have thus far been written off.

"When we suddenly see that even mountain glaciers, which are small in comparison with an ice sheet, are able to form and emit methane, it expands our basic understanding of carbon cycling in extreme environments on the planet. The formation and release of methane under ice is more comprehensive and much more widespread than we thought," he says.

Until now, the prevailing view has been that methane in meltwater could only be found in oxygen- free environments under large masses of ice like the Greenland Ice Sheet.

The researchers assume that the production of methane is biological and happens when an organic carbon source -- e.g., deposits from prehistoric marine organisms, soils, peat or forests -- is decomposed by microorganisms in the absence of oxygen, such as we know from wetlands. As such, it is surprising that the mountain glaciers emit methane.

"The meltwater from the surface of glaciers is oxygen-rich when it travels to the bottom of the ice. So we found it quite surprising that all this oxygen is used up somewhere along the way, so that oxygen-free environments form underneath these mountain glaciers. And even more surprising that it happens to such a degree, that microbes start producing methane and we can observe these high methane concentrations in the water flowing out at the glacier edges" states Sarah Elise Sapper.

"Sarah's findings change our basic understanding and send us back to the drawing board in relation to some of the key mechanisms at play," adds Jesper Riis Christiansen.

An uncertain role for the climate of the future

According to the researchers, the findings in Canada do not immediately spur an increased concern in relation to their effect on climate change. However that conclusion may be temporary.

"Methane plays a major role in warming our planet. The challenge with methane is that it is a super-potent greenhouse gas and increasing emissions will accelerate climate warming. From a global perspective, we can measure how much is emitted into the atmosphere and, roughly speaking, where the methane comes from, using the isotopes found in the atmospheric methane. And for now, the contribution of methane from ice-covered regions on our planet, including ice sheets and glaciers, isn't increasing," explains Jesper Riis Christiansen.

However, he emphasizes that the measurements cannot distinguish between methane from glaciated regions and methane from wetlands. Therefore, the numbers could be deceiving. And, the effect of melting remains unknown.

Jesper Riis Christiansen believes that the findings demand vigilance.

"The three sites Sarah measured were randomly selected due to the availability of a research station and helicopter, yet methane was found in all three. In itself, that is a good reason to better understand the area. There's too much that we don't know, and the melting glaciers expose unknown environments that have remained hidden for thousands of years. In reality, no one knows how emissions will behave," says Jesper Riis Christiansen.

He hopes that a better understanding of methane behaviour beneath glaciers will also help researchers better understand the mechanisms at play when wetlands release methane, and thereby contribute to the development of solutions to remove methane from the atmosphere through oxidation -- e.g., through the use of certain soil types.

A subglacial black box

The actual sources and locations of subglacial methane production actually remain somewhat of a mystery, hidden beneath ice masses of all sizes. Indeed, this methane can only be measured as the meltwater emerges from beneath the ice. And because it originates from large areas below the ice masses, this makes it difficult to access exactly where the production happens.

It is known to not originate from the ice itself, as concentrations both in the ice and meltwater atop it are lower than what is measured at the glacier edge. As such, the researchers believe that the methane must derive from a source beneath the ice. And the best theory, as mentioned, is that it is formed by microbes in oxygen-free pockets and then carried out with meltwater.

But this indirect knowledge of the source leaves a great deal of uncertainty about how much methane is hidden beneath the ice.

"It's a big black box under the ice -- and you could say that the meltwater is prying the lid off it. We do not know whether methane emissions from glacial areas will increase in the future with increased melting, or whether the 'lid' has already been opened to such a degree that the methane beneath the ice is actually being washed out with the meltwater," says Sarah Elise Sapper.

Methane and CO2 are different greenhouse gases

The half-life of methane in the atmosphere is 12 years.

CO2 has a much longer half-life, at roughly 1000 years.

On the other hand, methane is about 25 times more powerful as a greenhouse gas on a 100-year basis and a far more serious threat to global climate in the shorter term.

Due to greenhouse gas-driven climate change, researchers around the world are working to develop ways to capture or store CO2.

Similarly, solutions are being devised to limit the emission of -- or increase the oxidation of -- methane. Doing so requires more knowledge about how methane is formed.

Facts: Carbon circulation of methane and CO2

Biological traces from animal and plant material in the subsoil consist of carbon.

Within these environments, microorganisms have developed an ability to convert carbon into energy in a process where methane is created as a byproduct in the absence of oxygen (e.g. in beneath ice sheets or in wetlands).

However, if the methane is released into an oxygen-rich environment, it can effectively be oxidized and converted into CO2 by microbes. Wetlands play an important role in this process.

Once, in the atmosphere, methane reacts with other chemicals (hydroxyl radicals) which keep the concentrations down.

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Evidence of geothermal activity within icy dwarf planets

A team co-led by Southwest Research Institute found evidence for hydrothermal or metamorphic activity within the icy dwarf planets Eris and Makemake, located in the Kuiper Belt. Methane detected on their surfaces has the tell-tale signs of warm or even hot geochemistry in their rocky cores, which is markedly different than the signature of methane from a comet.

"We see some interesting signs of hot times in cool places," said SwRI's Dr. Christopher Glein, an expert in planetary geochemistry and lead author of a paper about this discovery.

The Kuiper Belt is a vast donut-shaped region of icy bodies beyond the orbit of Neptune at the edge of the solar system.

Eris and Makemake are comparable in size to Pluto and its moon Charon.

These bodies likely formed early in the history of our solar system, about 4.5 billion years ago.

Far from the heat of our Sun, KBOs were believed to be cold, dead objects.

Newly published work from JWST studies made the first observations of isotopic molecules on the surfaces of Eris and Makemake.

These so-called isotopologues are molecules that contain atoms having a different number of neutrons.

They provide data that are useful in understanding planetary evolution.

The JWST team measured the composition of the dwarf planets' surfaces, particularly the deuterium (heavy hydrogen, D) to hydrogen (H) ratio in methane.

Deuterium is believed to have formed in the Big Bang, and hydrogen is the most abundant nucleus in the universe.

The D/H ratio on a planetary body yields information about the origin, geologic history and formation pathways of compounds containing hydrogen.

"The moderate D/H ratio we observed with JWST belies the presence of primordial methane on an ancient surface. Primordial methane would have a much higher D/H ratio," Glein said.

"Instead, the D/H ratio points to geochemical origins for methane produced in the deep interior. The D/H ratio is like a window. We can use it in a sense to peer into the subsurface. Our data suggest elevated temperatures in the rocky cores of these worlds so that methane can be cooked up. Molecular nitrogen (N2) could be produced as well, and we see it on Eris. Hot cores could also point to potential sources of liquid water beneath their icy surfaces."

Over the past two decades, scientists have learned that icy worlds can be much more internally evolved than once believed.

Evidence for subsurface oceans has been found at several icy moons such as Saturn's moon Enceladus and Jupiter's moon Europa.

Liquid water is one of the key ingredients in determining potential planetary habitability.

The possibility of water oceans inside Eris and Makemake is something that scientists are going to study in the years ahead.

If either of them is habitable, then it would become the most distant world in the solar system that could possibly support life.

Finding chemical indicators of internally driven processes takes them a step in this direction.

"If Eris and Makemake hosted, or perhaps could still host warm, or even hot, geochemistry in their rocky cores, cryovolcanic processes could then deliver methane to the surfaces of these planets, perhaps in geologically recent times," said Dr. Will Grundy, an astronomer at Lowell Observatory, one of Glein's co-authors and lead author of a companion paper.

"We found a carbon isotope ratio (13C/12C) that suggests relatively recent resurfacing."

This work is part of a paradigm shift in planetary science. It is increasingly being recognized that cold, icy worlds may be warm at heart.

Models developed for this study additionally point to the formation of geothermal gases on Saturn's moon Titan, which also has abundant methane.

Furthermore, the inference of unexpected activity on Eris and Makemake underscores the importance of internal processes in shaping what we see on large KBOs and is consistent with findings at Pluto.

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Rising sea levels could lead to more methane emitted from wetlands

As sea levels rise due to global warming, ecosystems are being altered. One small silver lining, scientists believed, was that the tidal wetlands found in estuaries might produce less methane -- a potent greenhouse gas -- as the increasing influx of seawater makes these habitats less hospitable to methane-producing microbes.

However, research from biologists at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley indicates that these assumptions aren't always true. After examining the microbial, chemical, and geological features of 11 wetland zones, the team found that a wetland region exposed to a slight amount of seawater was emitting surprisingly high levels of methane -- far more than any of the freshwater sites.

Their results, now published in mSystems, indicate that the factors governing how much greenhouse gas is stored or emitted in natural landscapes are more complex and difficult to predict than we thought.

"We looked at how many methanogens, the organisms that make methane, are present in soils at these sites and it wasn't really well correlated with the amount of methane observed," said senior author Susannah Tringe, director of Berkeley Lab's Environmental Genomics & Systems Biology Division. "And even if you look at the amount of methanotrophs, organisms that eat methane, in combination with methanogens, that doesn't seem to fully explain it."

Tringe and her colleagues took soil samples from the 11 sites and used high-throughput sequencing to analyze DNA from organisms found in the samples, including bacteria, viruses, and fungi. They examined what genes were present in the sequences and mapped them to known functions -- for example, identifying genes known to be involved in metabolizing nitrogen or genes from bacteria that use sulfate during respiration. Then they worked to model how the genetic information they found, combined with chemical factors in the soil and water, could result in the methane emissions they observed.

Across most of the sites, which ranged from freshwater to full seawater salinities, the amount of methane emitted was inversely related to the amount of salt water that was flowing in and mingling with the river water. But at one site, which had been restored in 2010 from a seasonal grassy pasture for livestock grazing back to its original wetland habitat, the team saw high methane emissions despite the moderate amount of salt water.

Seawater contains more sulfate (an ion with sulfur and oxygen) than freshwater, leading to the assumption that increased influx of seawater in these environments would lead to less methane production as the methanogens that use CO2 to make cellular energy are outcompeted by the bacteria that use sulfate instead.

"Ultimately, we found that there were significant influences from other bacterial groups like the ones that break down carbon and even organisms that are better known as nitrogen cyclers, and we couldn't readily explain the methane emissions by something as simple as, for example, how much sulfate is available or how many methanogens are there," said Tringe.

Another concept in ecology is that restoring habitats to their native state can boost carbon storage, improve water quality, and increase wildlife populations. In recent decades, wetlands have been increasingly recognized as critical ecosystems for these environmental services, leading to widespread efforts to restore ecosystems by removing barriers, pollution, and non-native organisms.

Modeling work by co-author Dennis D. Baldocchi, Executive Associate Dean and professor of Biometeorology at UC Berkeley, suggests that although the restored wetland is adding greenhouse gas to the atmosphere currently, the ecosystem will stabilize and begin to serve as a net carbon sink within 100 to 150 years. This may not be the timeline that stakeholders were hoping for when they restored the area with the goal of carbon sequestration.

"We want to know if these systems will act as long-term carbon sinks," said Baldocchi. "And these microbiological investigations can help refine our models and predictions."

Tringe noted that other labs have observed increased methane production from wetland soils with increased salinity. Scientists from Duke University took soil core samples from a coastal freshwater wetland and exposed them to artificial seawater, and artificial seawater lacking sulfate. In both cases, methane production went up. Tringe's lab recently collaborated with Marcelo Ardón of North Carolina State University to analyze the microbial communities in those soils.

"There was this expectation that sulfate would be the most important thing. And in those studies, not only did salt water stimulate methane production, which again is kind of counter to the dogma that sulfate is important, it happened whether you had sulfate there or not; in fact the sulfate didn't have a big effect on the methane emissions," said Tringe. "So I think these experimental manipulations are reconfirming the story that there's more nuanced effects of seawater intrusion than just a sulfate addition, and also more nuanced factors behind ecosystem restoration."

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NASA's Webb finds signs of possible aurorae on isolated brown dwarf

Astronomers using NASA's James Webb Space Telescope have found a brown dwarf (an object more massive than Jupiter but smaller than a star) with infrared emission from methane, likely due to energy in its upper atmosphere. This is an unexpected discovery because the brown dwarf, W1935, is cold and lacks a host star; therefore, there is no obvious source for the upper atmosphere energy. The team speculates that the methane emission may be due to processes generating aurorae.

These findings are being presented at the 243rd meeting of the American Astronomical Society in New Orleans.

To help explain the mystery of the infrared emission from methane, the team turned to our solar system. Methane in emission is a common feature in gas giants like Jupiter and Saturn. The upper-atmosphere heating that powers this emission is linked to aurorae.

On Earth, aurorae are created when energetic particles blown into space from the Sun are captured by Earth's magnetic field. They cascade down into our atmosphere along magnetic field lines near Earth's poles, colliding with gas molecules and creating eerie, dancing curtains of light. Jupiter and Saturn have similar auroral processes that involve interacting with the solar wind, but they also get auroral contributions from nearby active moons like Io (for Jupiter) and Enceladus (for Saturn).

For isolated brown dwarfs like W1935, the absence of a stellar wind to contribute to the auroral process and explain the extra energy in the upper atmosphere required for the methane emission is a mystery. The team surmises that either unaccounted internal processes like the atmospheric phenomena of Jupiter and Saturn, or external interactions with either interstellar plasma or a nearby active moon, may help account for the emission.

A Detective Story

The aurorae's discovery played out like a detective story. A team led by Jackie Faherty, an astronomer at the American Museum of Natural History in New York, was awarded time with the Webb telescope to investigate 12 cold brown dwarfs. Among those were W1935 -- an object that was discovered by citizen scientist Dan Caselden, who worked with the Backyard Worlds zooniverse project -- and W2220, an object that was discovered using NASA's Wide Field Infrared Survey Explorer. Webb revealed in exquisite detail that W1935 and W2220 appeared to be near clones of each other in composition. They also shared similar brightness, temperatures, and spectral features of water, ammonia, carbon monoxide, and carbon dioxide. The striking exception was that W1935 showed emission from methane, as opposed to the anticipated absorption feature that was observed toward W2220. This was seen at a distinct infrared wavelength to which Webb is uniquely sensitive.

"We expected to see methane because methane is all over these brown dwarfs. But instead of absorbing light, we saw just the opposite: The methane was glowing. My first thought was, what the heck? Why is methane emission coming out of this object?" said Faherty.

The team used computer models to infer what might be behind the emission. The modeling work showed that W2220 had an expected distribution of energy throughout the atmosphere, getting cooler with increasing altitude. W1935, on the other hand, had a surprising result. The best model favored a temperature inversion, where the atmosphere got warmer with increasing altitude. "This temperature inversion is really puzzling," said Ben Burningham, a co-author from the University of Hertfordshire in England and lead modeler on the work. "We have seen this kind of phenomenon in planets with a nearby star that can heat the stratosphere, but seeing it in an object with no obvious external heat source is wild."

Clues from our Solar System

For clues, the team looked in our own backyard, to the planets of our solar system. The gas giant planets can serve as proxies for what is seen going on more than 40 light-years away in the atmosphere of W1935.

The team realized that temperature inversions are prominent in planets like Jupiter and Saturn. There is still ongoing work to understand the causes of their stratospheric heating, but leading theories for the solar system involve external heating by aurorae and internal energy transport from deeper in the atmosphere (with the former a leading explanation).

Brown Dwarf Aurora Candidates in Context

This is not the first time an aurora has been used to explain a brown dwarf observation. Astronomers have detected radio emission coming from several warmer brown dwarfs and invoked aurorae as the most likely explanation. Searches were conducted with ground-based telescopes like the Keck Observatory for infrared signatures from these radio-emitting brown dwarfs to further characterize the phenomenon, but were inconclusive.

W1935 is the first auroral candidate outside the solar system with the signature of methane emission. It's also the coldest auroral candidate outside our solar system, with an effective temperature of about 400 degrees Fahrenheit (200 degrees Celsius), about 600 degrees Fahrenheit warmer than Jupiter.

In our solar system the solar wind is a primary contributor to auroral processes, with active moons like Io and Enceladus playing a role for planets like Jupiter and Saturn, respectively. W1935 lacks a companion star entirely, so a stellar wind cannot contribute to the phenomenon. It is yet to be seen whether an active moon might play a role in the methane emission on W1935.

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Climate change shown to cause methane to be released from the deep ocean

New research has shown that fire-ice -- frozen methane which is trapped as a solid under our oceans -- is vulnerable to melting due to climate change and could be released into the sea.

An international team of researchers led by Newcastle University found that as frozen methane and ice melts, methane -- a potent greenhouse gas -- is released and moves from the deepest parts of the continental slope to the edge of the underwater shelf.

They even discovered a pocket which had moved 25 miles (40 kilometres).

Publishing in the journal Nature Geoscience, the researchers say this means that much more methane could potentially be vulnerable and released into the atmosphere as a result of climate warming.

Methane hydrate

Methane hydrate, also known as fire-ice, is an ice-like structure found buried in the ocean floor that contains methane.

Vast amounts of methane are stored as marine methane under oceans.

It thaws when the oceans warm, releasing methane into oceans and the atmosphere -- known as dissociated methane -- contributing to global warming.

The scientists used advanced three-dimensional seismic imaging techniques to examine the portion of the hydrate that dissociated during climatic warming off the coast of Mauritania in Northwest Africa.

They identified a specific case where dissociated methane migrated over 40 kilometres and was released through a field of underwater depressions, known as pockmarks, during past warm periods.

Lead author, Professor Richard Davies, Pro-Vice-Chancellor, Global and Sustainability, Newcastle University, said: "It was a Covid lockdown discovery, I revisited imaging of strata just under the modern seafloor offshore of Mauritania and pretty much stumbled over 23 pockmarks. Our work shows they formed because methane released from hydrate, from the deepest parts of the continental slope vented into the ocean. Scientists had previously thought this hydrate was not vulnerable to climatic warming, but we have shown that some of it is."

Researchers have previously studied how changes in bottom water temperature near continental margins can affect the release of methane from hydrates.

However, these studies mainly focused on areas where only a small portion of global methane hydrates are located.

This is one of only a small number that investigate the release of methane from the base of the hydrate stability zone, which is deeper underwater.

The results show that methane released from the hydrate stability zone travelled a significant distance towards land.

Professor Dr Christian Berndt, Head of the Research Unit Marine Geodynamics, GEOMAR, in Kiel, Germany, added:

"This is an important discovery. So far, research efforts focused on the shallowest parts of the hydrate stability zone, because we thought that only this portion is sensitive to climate variations.

"The new data clearly show that far larger volumes of methane may be liberated from marine hydrates and we really have to get to the bottom of this to understand better the role of hydrates in the climate system."

Methane is the second most abundant anthropogenic greenhouse gas after carbon dioxide (CO2). Figures from the United States Environmental Protection Agency show that methane accounts for about 16% of global greenhouse gas emissions.

The study results can play a key role in helping to predict and address the impact of methane on our changing climate.

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Water world? Methane, carbon dioxide in atmosphere of massive exoplanet

A new investigation with NASA's James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. Webb's discovery adds to recent studies suggesting that K2-18 b could be a Hycean exoplanet, one which has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface.

The first insight into the atmospheric properties of this habitable-zone exoplanet came from observations with NASA's Hubble Space Telescope, which prompted further studies that have since changed our understanding of the system.

K2-18 b orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth in the constellation Leo. Exoplanets such as K2-18 b, which have sizes between those of Earth and Neptune, are unlike anything in our solar system. This lack of equivalent nearby planets means that these 'sub-Neptunes' are poorly understood, and the nature of their atmospheres is a matter of active debate among astronomers.

The suggestion that the sub-Neptune K2-18 b could be a Hycean exoplanet is intriguing, as some astronomers believe that these worlds are promising environments to search for evidence for life on exoplanets.

"Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere," explained Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper announcing these results. "Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations."

The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be a water ocean underneath a hydrogen-rich atmosphere in K2-18 b. These initial Webb observations also provided a possible detection of a molecule called dimethyl sulfide (DMS). On Earth, this is only produced by life. The bulk of the DMS in Earth's atmosphere is emitted from phytoplankton in marine environments.

The inference of DMS is less robust and requires further validation. "Upcoming Webb observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18 b at significant levels," explained Madhusudhan.

While K2-18 b lies in the habitable zone, and is now known to harbor carbon-bearing molecules, this does not necessarily mean that the planet can support life. The planet's large size -- with a radius 2.6 times the radius of Earth -- means that the planet's interior likely contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface. Hycean worlds are predicted to have oceans of water. However, it is also possible that the ocean is too hot to be habitable or be liquid.

"Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy," explained team member Subhajit Sarkar of Cardiff University. "We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere."

Characterizing the atmospheres of exoplanets like K2-18 b -- meaning identifying their gases and physical conditions -- is a very active area in astronomy. However, these planets are outshone -- literally -- by the glare of their much larger parent stars, which makes exploring exoplanet atmospheres particularly challenging.

The team sidestepped this challenge by analyzing light from K2-18 b's parent star as it passed through the exoplanet's atmosphere. K2-18 b is a transiting exoplanet, meaning that we can detect a drop in brightness as it passes across the face of its host star. This is how the exoplanet was first discovered in 2015 with NASA's K2 mission. This means that during transits a tiny fraction of starlight will pass through the exoplanet's atmosphere before reaching telescopes like Webb. The starlight's passage through the exoplanet atmosphere leaves traces that astronomers can piece together to determine the gases of the exoplanet's atmosphere.

"This result was only possible because of the extended wavelength range and unprecedented sensitivity of Webb, which enabled robust detection of spectral features with just two transits," said Madhusudhan. "For comparison, one transit observation with Webb provided comparable precision to eight observations with Hubble conducted over a few years and in a relatively narrow wavelength range."

"These results are the product of just two observations of K2-18 b, with many more on the way," explained team member Savvas Constantinou of the University of Cambridge. "This means our work here is but an early demonstration of what Webb can observe in habitable-zone exoplanets."

The team's results were accepted for publication in The Astrophysical Journal Letters.

The team now intends to conduct follow-up research with the telescope's MIRI (Mid-Infrared Instrument) spectrograph that they hope will further validate their findings and provide new insights into the environmental conditions on K2-18 b.

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Beaver activity in the Arctic increases emission of methane greenhouse gas

The climate-driven advance of beavers into the Arctic tundra is causing the release of more methane -- a greenhouse gas -- into the atmosphere.

Beavers, as everyone knows, like to make dams. Those dams cause flooding, which inundates vegetation and turns Arctic streams and creeks into a series of ponds. Those beaver ponds and surrounding inundated vegetation can be devoid of oxygen and rich with organic sediment, which releases methane as the material decays.

Methane is also released when organics-rich permafrost thaws as the result of heat carried by the spreading water.

A study linking Arctic beavers to an increase in the release of methane was published in July in Environmental Research Letters.

The lead author is Jason Clark, a former postdoctoral fellow at the University of Alaska Fairbanks Geophysical Institute. Research Professor Ken Tape, also of the Geophysical Institute, was Clark's adviser and is a co-author. Other co-authors include Benjamin Jones, a research assistant professor at the UAF Institute of Northern Engineering; and researchers from the National Park Service and NASA's Jet Propulsion Laboratory.

Tape has done extensive research about the northward migration of beavers and their resultant impact on the Arctic environment.

"What we found is that there are lots of methane hotspots right next to ponds and they start to diminish as you go away from the pond," he said.

The new study is the first to link large numbers of new beaver ponds to methane emissions at the landscape scale. It suggests that beaver engineering in the Arctic will at least initially increase methane release.

"We say 'initially' because that's the data we have," Tape said. "What the longer-term implications are, we don't know."

As a greenhouse gas, methane is 25 times more potent than carbon dioxide at trapping heat in Earth's atmosphere.

It accounts for about 20 percent of global greenhouse gas emissions, according to the U.S. Environmental Protection Agency. The agency says human activities have more than doubled atmospheric methane concentrations in the past two centuries.

The new research focused on 166 square miles of the lower Noatak River basin in Northwest Alaska. Data was obtained by airborne hyperspectral imaging through NASA's Arctic-Boreal Vulnerability Experiment program. That program and the National Science Foundation funded the research.

Hyperspectral cameras image an area in hundreds of wavelengths across the electromagnetic spectrum, including many not visible to the human eye. That differs from other cameras, which typically only image in the primary colors of red, green and blue.

The researchers compared the location of methane hot spots to the locations of 118 beaver ponds and to a number of nearby unaffected stream reaches and lakes. They analyzed the area up to approximately 200 feet from the perimeter of each water body and found a "significantly greater" number of methane hot spots around beaver ponds.

"We have these datasets that largely overlap, in space and mostly in time," Tape said. "It's kind of a simple design relying on a new tool."

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Shrinking Arctic glaciers are unearthing a new source of methane

As the Arctic warms, shrinking glaciers are exposing bubbling groundwater springs which could provide an underestimated source of the potent greenhouse gas methane, finds new research published today in Nature Geoscience.

The study, led by researchers from the University of Cambridge and the University Centre in Svalbard, Norway, identified large stocks of methane gas leaking from groundwater springs unveiled by melting glaciers.

The research suggests that these methane emissions will likely increase as Arctic glaciers retreat and more springs are exposed. This, and other methane emissions from melting ice and frozen ground in the Arctic, could exacerbate global warming.

"These springs are a considerable, and potentially growing, source of methane emissions -- one that has been missing from our estimations of the global methane budget until now," said Gabrielle Kleber, lead author of the research who is from Cambridge's Department of Earth Sciences.

Scientists are concerned that additional methane emissions released by the Arctic thaw could ramp-up human-induced global warming. The springs the researchers studied hadn't previously been recognized as a potential source of methane emissions.

Kleber spent nearly three years monitoring the water chemistry of more than a hundred springs across Svalbard, where air temperatures are rising two times faster than the average for the Arctic. She likens Svalbard to the canary in the coal mine of global warming, "Since it is warming faster than the rest of the Arctic, we can get a preview of the potential methane release that could happen at a larger scale across this region."

Professor Andrew Hodson, study co-author from the University Centre in Svalbard said, "Living in Svalbard exposes you to the front-line of Arctic climate change. I can't think of anything more stark than the sight of methane outgassing in the immediate forefield of a retreating glacier."

Previously, research has centred on methane release from thawing permafrost (frozen ground). "While the focus is often on permafrost, this new finding tells us that there are other pathways for methane emissions which could be even more significant in the global methane budget," said study co-author Professor Alexandra Turchyn, also from Cambridge's Department of Earth Sciences.

Hodson added, "Until this work was conducted, we didn't understand the source and pathways of this gas because we were reading about studies from completely different parts of the Arctic where glaciers are absent."

The methane-delivering springs they identified are fed by a plumbing system hidden beneath most glaciers, which taps into large groundwater reserves within the underlying sediments and surrounding bedrock. Once the glaciers melt and retreat, springs appear where this groundwater network punches through to the surface.

The researchers found that methane emissions from glacial groundwater springs across Svalbard could exceed 2,000 tonnes over the course of a year -- which equates to roughly 10% of the methane emissions resulting from Norway's annual oil and gas energy industry.

This source of methane will likely become more significant as more springs are exposed, said Kleber, "If global warming continues unchecked then methane release from glacial groundwater springs will probably become more extensive."

Glacial groundwater springs aren't always easy to recognize, so Kleber trained her eye to pick them out from satellite images. Zooming in on the areas of land exposed by the retreat of 78 glaciers across Svalbard, Kleber looked for tell-tale blue trickles of ice where groundwater had leaked to the surface and frozen. She then travelled to each of these sites by snowmobile to take samples of the groundwater at locations where the ice had blistered due to pressurized water and gas build up.

When Kleber and the team profiled the chemistry of the water feeding these springs, they found that all bar one of the sites studied were highly concentrated with dissolved methane -- meaning that, when the spring water reaches the surface, there is plenty of excess methane that can escape to the atmosphere.

The researchers also identified localized hotspots of methane emissions, which were closely related to the type of rock from which the groundwater emerges. Certain rocks like shale and coal contain natural gases, including methane, produced by the breakdown of organic matter when the rocks formed. This methane can move upwards through fractures in the rock and into the groundwater.

"In Svalbard we are beginning to understand the complex and cascading feedbacks triggered by glacier melt -- it seems likely that there are more outcomes like this which we have yet to uncover," said Kleber.

Read more at Science Daily

Switching to hydrogen fuel could prolong the methane problem

Hydrogen's potential as a clean fuel could be limited by a chemical reaction in the lower atmosphere, according to research from Princeton University and the National Oceanic and Atmospheric Association.

This is because hydrogen gas easily reacts in the atmosphere with the same molecule primarily responsible for breaking down methane, a potent greenhouse gas. If hydrogen emissions exceed a certain threshold, that shared reaction will likely lead to methane accumulating in the atmosphere -- with decades-long climate consequences.

"Hydrogen is theoretically the fuel of the future," said Matteo Bertagni, a postdoctoral researcher at the High Meadows Environmental Institute working on the Carbon Mitigation Initiative. "In practice, though, it poses many environmental and technological concerns that still need to be addressed."

Bertagni is the first author of a research article published in Nature Communications, in which researchers modeled the effect of hydrogen emissions on atmospheric methane. They found that above a certain threshold, even when replacing fossil fuel usage, a leaky hydrogen economy could cause near-term environmental harm by increasing the amount of methane in the atmosphere. The risk for harm is compounded for hydrogen production methods using methane as an input, highlighting the critical need to manage and minimize emissions from hydrogen production.

"We have a lot to learn about the consequences of using hydrogen, so the switch to hydrogen, a seemingly clean fuel, doesn't create new environmental challenges," said Amilcare Porporato, Thomas J. Wu '94 Professor of Civil and Environmental Engineering and the High Meadows Environmental Institute. Porporato is a principal investigator and member of the Leadership Team for the Carbon Mitigation Initiative and is also associated faculty at the Andlinger Center for Energy and the Environment.

The problem boils down to one small, difficult-to-measure molecule known as the hydroxyl radical (OH). Often dubbed "the detergent of the troposphere," OH plays a critical role in eliminating greenhouse gases such as methane and ozone from the atmosphere.

The hydroxyl radical also reacts with hydrogen gas in the atmosphere. And since a limited amount of OH is generated each day, any spike in hydrogen emissions means that more OH would be used to break down hydrogen, leaving less OH available to break down methane. As a consequence, methane would stay longer in the atmosphere, extending its warming impacts.

According to Bertagni, the effects of a hydrogen spike that might occur as government incentives for hydrogen production expand could have decades-long climate consequences for the planet.

"If you emit some hydrogen into the atmosphere now, it will lead to a progressive build-up of methane in the following years," Bertagni said. "Even though hydrogen only has a lifespan of around two years in the atmosphere, you'll still have the methane feedback from that hydrogen in 30 years from now."

In the study, the researchers identified the tipping point at which hydrogen emissions would lead to an increase in atmospheric methane and thereby undermine some of the near-term benefits of hydrogen as a clean fuel. By identifying that threshold, the researchers established targets for managing hydrogen emissions.

"It's imperative that we are proactive in establishing thresholds for hydrogen emissions, so that they can be used to inform the design and implementation of future hydrogen infrastructure," said Porporato.

For hydrogen referred to as green hydrogen, which is produced by splitting water into hydrogen and oxygen using electricity from renewable sources, Bertagni said that the critical threshold for hydrogen emissions sits at around 9%. That means that if more than 9% of the green hydrogen produced leaks into the atmosphere -- whether that be at the point of production, sometime during transport, or anywhere else along the value chain -- atmospheric methane would increase over the next few decades, canceling out some of the climate benefits of switching away from fossil fuels.

And for blue hydrogen, which refers to hydrogen produced via methane reforming with subsequent carbon capture and storage, the threshold for emissions is even lower. Because methane itself is the primary input for the process of methane reforming, blue hydrogen producers have to consider direct methane leakage in addition to hydrogen leakage. For example, the researchers found that even with a methane leakage rate as low as 0.5%, hydrogen leakages would have to be kept under around 4.5% to avoid increasing atmospheric methane concentrations.

"Managing leakage rates of hydrogen and methane will be critical," Bertagni said. "If you have just a small amount of methane leakage and a bit of hydrogen leakage, then the blue hydrogen that you produce really might not be much better than using fossil fuels, at least for the next 20 to 30 years."

The researchers emphasized the importance of the time scale over which the effect of hydrogen on atmospheric methane is considered. Bertagni said that in the long-term (over the course of a century, for instance), the switch to a hydrogen economy would still likely deliver net benefits to the climate, even if methane and hydrogen leakage levels are high enough to cause near-term warming. Eventually, he said, atmospheric gas concentrations would reach a new equilibrium, and the switch to a hydrogen economy would demonstrate its climate benefits. But before that happens, the potential near-term consequences of hydrogen emissions might lead to irreparable environmental and socioeconomic damage.

Thus, if institutions hope to meet mid-century climate goals, Bertagni cautioned that hydrogen and methane leakage to the atmosphere must be held in check as hydrogen infrastructure begins to roll out. And because hydrogen is a small molecule that is notoriously difficult to control and measure, he explained that managing emissions will likely require researchers to develop better methods for tracking hydrogen losses across the value chain.

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A window of opportunity for methane to slip by nature's filters

Warmer oceans can lead to large amounts of methane being released from the seabeds, which may amplify climate warming. A new study develops a method to understand the role of microorganisms in increasing emissions of methane from seabeds.

Vast reservoirs of the potent greenhouse gas methane are stored beneath the sea in a solid ice-like combination with water. This solid is known as methane hydrate. For over three decades, various concerns have been raised that warming the seafloor may cause this methane to be rapidly released, perhaps even reaching the atmosphere where it would cause further climate warming. Happily, this methane hydrate is mostly located beneath the seafloor and under hundreds of meters of seawater. Even if warming melts this methane hydrate and releases methane gas, the natural microbial filters present in the seafloor were expected to destroy most of the methane before it ever reaches the open seawater.

However, there have been some gaps in our knowledge of the relevant seafloor processes. In particular, can seafloor warming be rapid enough that methane hydrate could melt so fast that the released methane would overwhelm and ultimately bypass the natural microbial filters? "The microbial filter layer in the sediment -- we call it the 'sulfate-methane transition', where methane is removed -- is somewhat delicate," explains Assistant Professor Christian Stranne at the Department of Geological Sciences, Stockholm University. "The filter layer takes many years to form and reach peak methane-consuming efficiency. The filter is a living thing, made of microorganisms that consume methane under anaerobic (no-oxygen) conditions. The filter also moves up and down within the sediment, depending on the rate at which methane is reaching it."

In a new study, just published in Communications Earth and Environment, Stranne and colleagues from Stockholm University and Linnaeus University have combined a new model of the biological behaviour and vertical movements of this microbial filter with existing models of seafloor sediments' physical behaviour. The physical parts of the model include processes such as how cracks form and methane can move up thorough the sediment after methane hydrates melt.

Christian Stranne explains: "Imagine that the amount of methane rising through the sediment suddenly increases, as might happen if methane hydrate begins to melt faster. It can take decades for the filter to adjust itself to consume methane at the new rate. Our new study shows that during the time that the filter is not reestablished, substantial methane can leak past the filter, and into the ocean water."

Despite this "window of opportunity," methane from melting hydrates that reaches the seawater faces further methane-destroying processes. These processes make it nearly impossible for substantial methane from methane hydrate melting to reach the atmosphere. However, methods as demonstrated in this study can be applied to other regions where seafloor-released methane is much shallower and is more likely to reach the atmosphere, such as the Arctic continental shelves, according to Christian Stranne.

"Methane hydrates are a massive storehouse of carbon, so it remains important to understand how they interact with ocean changes, and potentially, the atmosphere, over long and, in the case of our study, rather short timescales. We now know that there is indeed a possible process for melting methane hydrates to temporarily bypass what was previously thought to be a strong filter in the sediment," says Christian Stranne.

The warming rate is, however, of great importance: "Our results suggest that if our oceans warm at a pace significantly lower than 1 °C per 100 years, the filter can keep up with the pace and remain highly efficient. Unfortunately, we see higher warming rates than that in some of our oceans."

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Fjords emit as much methane as all the deep oceans globally

During heavy storms, the normally stratified layers of water in ocean fjords get mixed, which leads to oxygenation of the fjord floor. But these storm events also result in a spike in methane emissions from fjords to the atmosphere.

Researchers from the University of Gothenburg have estimated that the total emissions of this climate-warming gas are as great from fjords as from all the deep ocean areas in the world put together.

The world's fjords were created when the inland ice receded, and are a relatively rare natural feature, constituting only 0.13 per cent of all the oceans on Earth. However, according to researchers from the University of Gothenburg, emissions of methane from the surface of fjords are comparable to the emissions of this gas from global deep oceans which account for 84 per cent of the global sea surface area. These results were presented in an article in the science journal Limnology and Oceanography Letters.

"It's been known for some time that many fjords have anoxic environments closest to the bottom and that methane forms in the bottom sediment. Usually, only a small portion of this gas ever reaches the atmosphere because it gets broken down as it ascends through the more oxygen-rich waters closer to the surface. But in our research, we recorded large emissions of methane when the water in the fjord was mixed during storm events, for example," says Stefano Bonaglia, researcher in marine geochemistry at the Department of Marine Sciences at the University of Gothenburg.

Anoxic environments produce methane

Detecting and budgeting methane emissions to the atmosphere is essential to be able to model the future climate. Researchers estimate that methane emissions cause about 30 per cent of the greenhouse effect. The contribution of the oceans to methane emissions is budgeted as significantly smaller than from land areas. But human activity has increased eutrophication in coastal areas, and this has created larger areas of anoxic waters on the sea floor. This is particularly apparent in fjords, and although they constitute only 0.13 per cent of the global sea surface area, they account for about half of all methane emissions to the atmosphere.

"This is because in fjords, carbon-rich sediment is deposited from marine plants and animals as well as from materials entering the fjords from the surrounding land via streams that flow into them. As fjords are relatively protected from ocean currents, the water tends to remain stratified in layers at different temperatures and with different concentrations of salt and oxygen. The layers closest to the fjord floor are anoxic regions where methane gas forms as the material in the sediment decomposes," says Stefano Bonaglia.

Agriculture drives eutrophication

The researchers from the University of Gothenburg studied By Fjord near Uddevalla during the period 2009-2021 and conducted field studies to measure methane production in the fjord. By Fjord is hypoxic and affected by eutrophication. The Bäve River flows into the fjord, bringing with it high concentrations of nutrients from agriculture in the region. It was clear that during mixing events in the fjord, emissions of methane to the atmosphere rose. During these events, anoxic water from the bottom is lifted rapidly to the surface, taking the methane with it, which can then be emitted into the atmosphere.

1 million tonnes methane

"The methane emissions were high, and American researchers have seen the same types of events in fjords in Canada. We estimate that emissions from all the world's fjords are of the same magnitude -- around 1 Teragram (Tg) or 1 million tonnes per year -- as the budgeted emissions from global deep oceans. This is because the distance from the bottom to the surface of a fjord is much shorter than in deep oceans. This results in more organic matter being deposited in the sediment, and not enough time for the methane to be broken down on its way up to the surface," says Stefano Bonaglia, and adds that if climate change leads to more extreme weather events, methane emissions may rise, but only up to a certain point.

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Methane from waste should not be wasted: Exploring landfill ecosystems

Each year, humans across the globe produce billions of tons of solid waste. Roughly 70% of this refuse ends up deposited in landfills, where it slowly decays. Yet, what may seem an inert accumulation of useless debris, is in reality, a complex ecosystem, teeming with microbial activity. Vast communities of microorganisms feed on the waste, converting it into byproducts -- primarily carbon dioxide (CO2) and methane.

While most landfill methane is captured and flared away, researchers hope instead to make use of this resource, which can be converted into fuels, electricity or used for heating homes (see below).

In a new study published in the journal Applied and Environmental Microbiology, lead author Mark Reynolds, along with his Arizona State University and Industrial colleagues, explore these microbial communities flourishing in leachate, a liquid percolating through solid waste in a landfill. They find that the composition and behavior of specific microbes found in arid landfills, like those in Arizona, are distinct from similar communities in more subtropical or temperate climates. Microbial composition also differs depending on the age of the landfill deposits.

The project was carried out at the Salt River Landfill located in Scottsdale, near ASU's Tempe campus. The facility receives about 1,600 tons of municipal solid waste daily.

Solid waste: a breakdown

The study explores ecosystem-level microbial composition in leachate. Diverse environmental conditions seemingly affect the microbial niches that are compartmentalized across the landfill's 143 acres.

"I think of a landfill as like a big carbon buffet to these microorganisms," says Reynolds, a researcher in the Biodesign Swette Center for Environmental Biotechnology. "Our trash is mostly paper-heavy and it's really rich in cellulose and hemicellulose. These are readily degradable under anaerobic (oxygen-free) conditions."

The capture and use of gases produced in landfills can help reduce hazards associated with landfill emissions, and prevent methane from escaping into the atmosphere. Further, energy projects associated with the capture and processing of landfill gas can generate revenue and create jobs in the community.

By better understanding the behavior of these methane-producing microorganisms, researchers hope to improve the capture of this vital resource and possibly limit the escape of methane and CO2 -- two potent greenhouse gases and leading contributors to climate change -- into the atmosphere.

"We're diving into ecological theory to try to get to the source of what might be driving the organizational patterns of the methane-producing organisms," Reynolds says. The study's multifaceted analysis indicates that temperature and dissolved solids are the two key parameters governing their abundance and diversification. This is good news, because this data is routinely captured at landfill sites commonly on a monthly basis and can provide accurate diagnostics -- telltale indicators of broad trends in overall methane production.

From garbage to fuel

Municipal solid waste landfills accounted for over 15% of methane emissions in 2019, representing the third largest source of global methane emissions. As the study notes, emissions of methane from landfills amount to the equivalent of a billion tons of CO2, or roughly the greenhouse emissions produced by nearly 22 million cars driven for a year.

Typically, most of the methane released by microorganisms in a landfill is captured as biogas and subsequently flared off, converting it to CO2. Although this method limits the climate-damaging effects of the methane itself, it is a short-term and inadequate solution to the problem of greenhouse gas emission from landfills.

In addition to its adverse effect on the climate, the lost methane represents a missed opportunity to capture this valuable resource. The study estimates that approximately one-fifth of the nation's landfills would be suitable for such capture and processing, if economic and other hurdles can be overcome.

Currently, microorganisms degrading municipal solid waste generate landfill gas consisting of roughly 50% methane and 50% CO2. By understanding the subtle workings of these microorganisms -- particularly, methanogenic Archaea, which are the real workhorses in the methane production cycle -- researchers hope to boost methane output.

The increased methane can be harvested and used to create electricity, carbon neutral fuels or to heat homes. The latter option is particularly attractive as no further processing of the methane would be required. Alternately, modifying microbial communities could potentially be used to limit methane output, where mitigation is desired.

On the hunt for archaea

Landfills provide an ideal setting for the detailed study of Archaea, which are notoriously challenging to culture in the laboratory. Roughly 80% of archaea diversity remains largely unexplored. "Our labs are really interested in the methanogens because the same metabolism they enact in the wetlands, which make them the highest source of methane, or instead the human gastrointestinal tract, they enact in the landfills," Reynolds says.

Because the methanogens are primitive, single-celled organisms, they can equally make use of plant, or food matter, or paper products. While the study found similar methane concentrations at their arid landfill site compared to other landfills, different communities of methanogens are doing the heavy lifting. The study demonstrates that microbial behavior is also dependent on the age of the solid waste deposited. Younger waste is higher in temperature compared with older waste and degrades according to different regimes. The aridity has also been shown to greatly affect solid waste breakdown over time.

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Bacteria generate electricity from methane

Generating power while purifying the environment of greenhouse gases should be achievable using bacteria. In a new publication, microbiologists from Radboud University have demonstrated that it is possible to make methane-consuming bacteria generate power in the lab. The study will be published in Frontiers in Microbiology on April 12.

The bacteria, Candidatus Methanoperedens, use methane to grow and naturally occur in fresh water such as ditches and lakes. In the Netherlands, the bacteria mostly thrive in locations where the surface and groundwater are contaminated with nitrogen, as they require nitrate to break down methane.

The researchers initially wanted to know more about the conversion processes occurring in the microorganism. In addition, they were also curious whether it would be possible to use it to generate power. "This could be very useful for the energy sector," says microbiologist and author Cornelia Welte. "In the current biogas installations, methane is produced by microorganisms and subsequently burnt, which drives a turbine, thus generating power. Less than half of the biogas is converted into power, and this is the maximum achievable capacity. We want to evaluate whether we can do better using microorganisms."

A kind of battery

Fellow microbiologists from Nijmegen have previously shown that it is possible to generate power using anammox bacteria that use ammonium during the process instead of methane. "The process in these bacteria is basically the same," says microbiologist Heleen Ouboter. "We create a kind of battery with two terminals, where one of these is a biological terminal and the other one is a chemical terminal. We grow the bacteria on one of the electrodes, to which the bacteria donate electrons resulting from the conversion of methane."

Through this approach, the researchers managed to convert 31 percent of the methane into electricity, but they aim at higher efficiencies. "We will continue focusing on improving the system," Welte says.

From Science Daily

Methane could be the first detectable indication of life beyond Earth

If life is abundant in the universe, atmospheric methane may be the first sign of life beyond Earth detectable by astronomers. Although nonbiological processes can generate methane, a new study by scientists at UC Santa Cruz establishes a set of circumstances in which a persuasive case could be made for biological activity as the source of methane in a rocky planet's atmosphere.

This is especially noteworthy because methane is one of the few potential signs of life, or "biosignatures," that could be readily detectable with the James Webb Space Telescope, which will begin observations later this year.

"Oxygen is often talked about as one of the best biosignatures, but it's probably going to be hard to detect with JWST," said Maggie Thompson, a graduate student in astronomy and astrophysics at UC Santa Cruz and lead author of the new study.

Despite some prior studies on methane biosignatures, there had not been an up-to-date, dedicated assessment of the planetary conditions needed for methane to be a good biosignature. "We wanted to provide a framework for interpreting observations, so if we see a rocky planet with methane, we know what other observations are needed for it to be a persuasive biosignature," Thompson said.

Published March 28 in Proceedings of the National Academy of Sciences, the study examines a variety of non-biological sources of methane and assesses their potential to maintain a methane-rich atmosphere. These include volcanoes; reactions in settings such as mid-ocean ridges, hydrothermal vents, and tectonic subduction zones; and comet or asteroid impacts.

The case for methane as a biosignature stems from its instability in the atmosphere. Because photochemical reactions destroy atmospheric methane, it must be steadily replenished to maintain high levels.

"If you detect a lot of methane on a rocky planet, you typically need a massive source to explain that," said coauthor Joshua Krissansen-Totton, a Sagan Fellow at UCSC. "We know biological activity creates large amounts of methane on Earth, and probably did on the early Earth as well because making methane is a fairly easy thing to do metabolically."

Nonbiological sources, however, would not be able to produce that much methane without also generating observable clues to its origins. Outgassing from volcanoes, for example, would add both methane and carbon monoxide to the atmosphere, while biological activity tends to readily consume carbon monoxide. The researchers found that nonbiological processes cannot easily produce habitable planet atmospheres rich in both methane and carbon dioxide and with little to no carbon monoxide.

The study emphasizes the need to consider the full planetary context in evaluating potential biosignatures. The researchers concluded that, for a rocky planet orbiting a sun-like star, atmospheric methane is more likely to be considered a strong indication of life if the atmosphere also has carbon dioxide, methane is more abundant than carbon monoxide, and extremely water-rich planetary compositions can be ruled out.

"One molecule is not going to give you the answer -- you have to take into account the planet's full context," Thompson said. "Methane is one piece of the puzzle, but to determine if there is life on a planet you have to consider its geochemistry, how it's interacting with its star, and the many processes that can affect a planet's atmosphere on geologic timescales."

The study considers a variety of possibilities for "false positives" and provides guidelines for assessing methane biosignatures.

"There are two things that could go wrong -- you could misinterpret something as a biosignature and get a false positive, or you could overlook something that's a real biosignature," Krissansen-Totton said. "With this paper, we wanted to develop a framework to help avoid both of those potential errors with methane."

He added that there is still a lot of work to be done to fully understand any future methane detections. "This study is focused on the most obvious false positives for methane as a biosignature," he said. "The atmospheres of rocky exoplanets are probably going to surprise us, and we will need to be cautious in our interpretations. Future work should try to anticipate and quantify more unusual mechanisms for nonbiological methane production."

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Trees are biggest methane ‘vents’ in wetland areas – even when they’re dry

Most of the methane gas emitted from Amazon wetlands regions is vented into the atmosphere via tree root systems -- with significant emissions occurring even when the ground is not flooded, say researchers at the University of Birmingham.

In a study published in the Royal Society journal, Philosophical Transactions A, the researchers have found evidence that far more methane is emitted by trees growing on floodplains in the Amazon basin than by soil or surface water and this occurs in both wet and dry conditions.

Methane is the second most important greenhouse gas and much of our atmospheric methane comes from wetlands. A great deal of research is being carried on into exactly how much methane is emitted via this route, but models typically assume that the gas is only produced when the ground is completely flooded and underwater.

In wetland areas where there are no trees, methane would typically be consumed by the soil on its way to the surface, but in forested wetland areas, the researchers say the tree roots could be acting as a transport system for the gas, up to the surface where it vents into the atmosphere from the tree trunks.

Methane is able to escape via this route even when it is produced in soil and water that is several meters below ground level.

This would mean that existing models could be significantly underestimating the likely extent of methane emissions in wetland areas such as the Amazon basin.

To test the theory, the team carried out measurements across three plots on the floodplains of three major rivers in the central Amazon basin. The same trees were monitored at each plot at four time points over the year to capture their response changing water levels associated with the annual flood. Methane emissions were measured using a portable greenhouse gas analyser and then calculations were done to scale the findings up across the Amazon basin.

Overall, the team estimate that nearly half of global tropical wetland methane emissions are funnelled out by trees, with the unexpected result that trees are also important for emissions at times when the floodplain water table sits below the surface of the soil.

Lead author, Professor Vincent Gauci, in the School of Geography, Earth and Environmental Sciences at the University of Birmingham (and the Birmingham Institute of Forest Research), says: "Our results show that current global emissions estimates are missing a crucial piece of the picture. We now need to develop models and methods that take into account the significant role played by trees in wetland methane emission."

Read more at Science Daily

Researchers reveal how to turn a global warming liability into a profitable food security solution

Like a mirage on the horizon, an innovative process for converting a potent greenhouse gas into a food security solution has been stalled by economic uncertainty. Now, a first-of-its-kind Stanford University analysis evaluates the market potential of the approach, in which bacteria fed captured methane grow into protein-rich fishmeal. The study, published Nov. 22 in Nature Sustainability, finds production costs involving methane captured from certain sources in the U.S. are lower than the market price for conventional fishmeal. It also highlights feasible cost reductions that could make the approach profitable using other methane sources and capable of meeting all global fishmeal demand.

"Industrial sources in the U.S. are emitting a truly staggering amount of methane, which is uneconomical to capture and use with current applications," said study lead author Sahar El Abbadi, who conducted the research as a graduate student in civil and environmental engineering.

"Our goal is to flip that paradigm, using biotechnology to create a high-value product," added El Abbadi, who is now a lecturer in the Civic, Liberal and Global Education program at Stanford.

Two problems, one solution

Although carbon dioxide is more abundant in the atmosphere, methane's global warming potential is about 85 times as great over a 20-year period and at least 25 times as great a century after its release. Methane also threatens air quality by increasing the concentration of tropospheric ozone, exposure to which causes an estimated 1 million premature deaths annually worldwide due to respiratory illnesses. Methane's relative concentration has grown more than twice as fast as that of carbon dioxide since the beginning of the Industrial Revolution due in great part to human-driven emissions.

A potential solution lies in methane-consuming bacteria called methanotrophs. These bacteria can be grown in a chilled, water-filled bioreactor fed pressurized methane, oxygen and nutrients such as nitrogen, phosphorus and trace metals. The protein-rich biomass that results can be used as fishmeal in aquaculture feed, offsetting demand for fishmeal made from small fish or plant-based feeds that require land, water and fertilizer.

"While some companies are doing this already with pipeline natural gas as feedstock, a preferable feedstock would be methane emitted at large landfills, wastewater treatment plants and oil and gas facilities," said study co-author Craig Criddle, a professor of civil and environmental engineering in Stanford's School of Engineering. "This would result in multiple benefits. including lower levels of a potent greenhouse gas in the atmosphere, more stable ecosystems and positive financial outcomes."

Consumption of seafood, an important global source of protein and micronutrients, has increased more than fourfold since 1960. As a result, wild fish stocks are badly depleted, and fish farms now provide about half of all the animal-sourced seafood we eat. The challenge will only grow as global demand for aquatic animals, plants and algae will likely double by 2050, according to a comprehensive review of the sector led by researchers at Stanford and other institutions.

While methane-fed methanotrophs can provide feed for farmed fish, the economics of the approach have been unclear, even as prices of conventional fishmeal have nearly tripled in real terms since 2000. To clarify the approach's potential to meet demand profitably, the Stanford researchers modeled scenarios in which methane is sourced from relatively large wastewater treatment plants, landfills, and oil and gas facilities, as well as natural gas purchased from the commercial natural gas grid. Their analysis looked at a range of variables, including the cost of electricity and labor availability.

Toward turning a profit

In the scenarios involving methane captured from landfills and oil and gas facilities, the analysis found methanotrophic fishmeal production costs -- $1,546 and $1,531 per ton, respectively -- were lower than the 10-year average market price of $1,600. For the scenario in which methane was captured from wastewater treatment plants, production costs were slightly higher -- $1,645 per ton -- than the average market price of fishmeal. The scenario in which methane was purchased from the commercial grid led to the most expensive fishmeal production costs -- $1,783 per ton -- due to the cost of purchasing natural gas.

For every scenario, electricity was the largest expense, accounting for over 45 percent of total cost on average. In states such as Mississippi and Texas with low electricity prices, production costs came down over 20 percent, making it possible to produce fishmeal from methane for $1,214 per ton, or $386 less per ton than conventional fishmeal production. Electricity costs could be reduced further, the researchers say, by designing reactors that better transfer heat to require less cooling, and switching electric-powered applications to those powered by so-called stranded gas that would otherwise be wasted or unused, which can also reduce reliance on grid electricity for remote locations. In scenarios involving methane from wastewater treatment plants, the wastewater itself could be used to provide nitrogen and phosphorus, as well as cooling.

If efficiencies like these could bring down the production cost for a methanotroph-based fishmeal by 20 percent, the process could profitably supply total global demand for fishmeal with methane captured in the U.S. alone, according to the study. Similarly, the process could replace soybean and animal feeds if further cost reductions were achieved.

"Despite decades of trying, the energy industry has had trouble finding a good use for stranded natural gas," said study co-author Evan David Sherwin, a postdoctoral researcher in energy resources engineering at Stanford. "Once we started looking at the energy and food systems together, it became clear that we could solve at least two longstanding problems at once."

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Titan’s river maps may advise Dragonfly’s 'sedimental' journey

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

The fluvial maps and details of their accuracy were published in the Planetary Science Journal (August 2021.) In addition to the maps, the work examined what could be learned by analyzing Earth's rivers by using degraded radar data -- similar to what Cassini saw.

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

"The channel systems are the heart of Titan's sediment transport pathways," said Alex Hayes, associate professor of astronomy in the College of Arts and Sciences. "They tell you how organic material is routed around Titan's surface, and identifies locations where the material might be concentrated near tectonic or perhaps even cryovolcanic features.

"Further, those materials either can be sent down into Titan's liquid water interior ocean, or alternatively, mixed with liquid water that gets transported up to the surface," Hayes said.

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

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

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

On Earth, fluvial geomorphology is typically studied with topographic data and high-resolution visible images, but that was not available for Titan. Instead, Miller used Earth-based radar images and degraded them to match the Cassini radar images of Titan.

This way, Miller could understand the limits of the Cassini dataset and know which results are robust for analysis using low, roughly 1-kilometer resolution data.

"Although the quality and quantity of Cassini SAR images put significant limits on their utility for investigating river networks," Miller said, "they can still be used to understand Titan's landscape at a fundamental level."

River shapes say a lot. "You can use sort of what the river looks like to try to say some things about the type of material that it's flowing through, or like how steep the surfaces, or just what went on in that region," Miller said. "This is using the rivers as a starting point, to then, ideally, learn more about the planet."

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

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Methane in plumes of Saturn's moon Enceladus: Possible signs of life?

An unknown methane-producing process is likely at work in the hidden ocean beneath the icy shell of Saturn's moon Enceladus, suggests a new study published in Nature Astronomy by scientists at the University of Arizona and Paris Sciences & Lettres University.

Giant water plumes erupting from Enceladus have long fascinated scientists and the public alike, inspiring research and speculation about the vast ocean that is believed to be sandwiched between the moon's rocky core and its icy shell. Flying through the plumes and sampling their chemical makeup, the Cassini spacecraft detected a relatively high concentration of certain molecules associated with hydrothermal vents on the bottom of Earth's oceans, specifically dihydrogen, methane and carbon dioxide. The amount of methane found in the plumes was particularly unexpected.

"We wanted to know: Could Earthlike microbes that 'eat' the dihydrogen and produce methane explain the surprisingly large amount of methane detected by Cassini?" said Regis Ferriere, an associate professor in the University of Arizona Department of Ecology and Evolutionary Biology and one of the study's two lead authors. "Searching for such microbes, known as methanogens, at Enceladus' seafloor would require extremely challenging deep-dive missions that are not in sight for several decades."

Ferriere and his team took a different, easier route: They constructed mathematical models to calculate the probability that different processes, including biological methanogenesis, might explain the Cassini data.

The authors applied new mathematical models that combine geochemistry and microbial ecology to analyze Cassini plume data and model the possible processes that would best explain the observations. They conclude that Cassini's data are consistent either with microbial hydrothermal vent activity, or with processes that don't involve life forms but are different from the ones known to occur on Earth.

On Earth, hydrothermal activity occurs when cold seawater seeps into the ocean floor, circulates through the underlying rock and passes close by a heat source, such as a magma chamber, before spewing out into the water again through hydrothermal vents. On Earth, methane can be produced through hydrothermal activity, but at a slow rate. Most of the production is due to microorganisms that harness the chemical disequilibrium of hydrothermally produced dihydrogen as a source of energy, and produce methane from carbon dioxide in a process called methanogenesis.

The team looked at Enceladus' plume composition as the end result of several chemical and physical processes taking place in the moon's interior. First, the researchers assessed what hydrothermal production of dihydrogen would best fit Cassini's observations, and whether this production could provide enough "food" to sustain a population of Earthlike hydrogenotrophic methanogens. To do that, they developed a model for the population dynamics of a hypothetical hydrogenotrophic methanogen, whose thermal and energetic niche was modeled after known strains from Earth.

The authors then ran the model to see whether a given set of chemical conditions, such as the dihydrogen concentration in the hydrothermal fluid, and temperature would provide a suitable environment for these microbes to grow. They also looked at what effect a hypothetical microbe population would have on its environment -- for example, on the escape rates of dihydrogen and methane in the plume.

"In summary, not only could we evaluate whether Cassini's observations are compatible with an environment habitable for life, but we could also make quantitative predictions about observations to be expected, should methanogenesis actually occur at Enceladus' seafloor," Ferriere explained.

The results suggest that even the highest possible estimate of abiotic methane production -- or methane production without biological aid -- based on known hydrothermal chemistry is far from sufficient to explain the methane concentration measured in the plumes. Adding biological methanogenesis to the mix, however, could produce enough methane to match Cassini's observations.

"Obviously, we are not concluding that life exists in Enceladus' ocean," Ferriere said. "Rather, we wanted to understand how likely it would be that Enceladus' hydrothermal vents could be habitable to Earthlike microorganisms. Very likely, the Cassini data tell us, according to our models.

"And biological methanogenesis appears to be compatible with the data. In other words, we can't discard the 'life hypothesis' as highly improbable. To reject the life hypothesis, we need more data from future missions," he added.

The authors hope their paper provides guidance for studies aimed at better understanding the observations made by Cassini and that it encourages research to elucidate the abiotic processes that could produce enough methane to explain the data.

For example, methane could come from the chemical breakdown of primordial organic matter that may be present in Enceladus' core and that could be partially turned into dihydrogen, methane and carbon dioxide through the hydrothermal process. This hypothesis is very plausible if it turns out that Enceladus formed through the accretion of organic-rich material supplied by comets, Ferriere explained.

"It partly boils down to how probable we believe different hypotheses are to begin with," he said. "For example, if we deem the probability of life in Enceladus to be extremely low, then such alternative abiotic mechanisms become much more likely, even if they are very alien compared to what we know here on Earth."

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The moon controls the release of methane in Arctic Ocean

 It may not be very well known, but the Arctic Ocean leaks enormous amounts of the potent greenhouse gas methane. These leaks have been ongoing for thousands of years but could be intensified by a future warmer ocean. The potential for this gas to escape the ocean, and contribute to the greenhouse gas budget in the atmosphere, is an important mystery that scientists are trying to solve.

The total amount of methane in the atmosphere has increased immensely over the past decades, and while some of the increase can be ascribed to human activity, other sources are not very well constrained.

A recent paper in Nature Communications even implies that the moon has a role to play.

Small pressure changes affect methane release

The moon controls one of the most formidable forces in nature -- the tides that shape our coastlines. Tides, in turn, significantly affect the intensity of methane emissions from the Arctic Ocean seafloor.

"We noticed that gas accumulations, which are in the sediments within a meter from the seafloor, are vulnerable to even slight pressure changes in the water column. Low tide means less of such hydrostatic pressure and higher intensity of methane release. High tide equals high pressure and lower intensity of the release" says co-author of the paper Andreia Plaza Faverola.

"It is the first time that this observation has been made in the Arctic Ocean. It means that slight pressure changes can release significant amounts of methane. This is a game-changer and the highest impact of the study." Says another co-author, Jochen Knies.

New methods reveal unknown release sites

Plaza Faverola points out that the observations were made by placing a tool called a piezometer in the sediments and leaving it there for four days.

It measured the pressure and temperature of the water inside the pores of the sediment. Hourly changes in the measured pressure and temperature revealed the presence of gas close to the seafloor that ascends and descends as the tides change. The measurements were made in an area of the Arctic Ocean where no methane release has previously been observed but where massive gas hydrate concentrations have been sampled.

"This tells us that gas release from the seafloor is more widespread than we can see using traditional sonar surveys. We saw no bubbles or columns of gas in the water. Gas burps that have a periodicity of several hours won't be identified unless there is a permanent monitoring tool in place, such as the piezometer." Says Plaza Faverola

These observations imply that the quantification of present-day gas emissions in the Arctic may be underestimated. High tides, however, seem to influence gas emissions by reducing their height and volume.

"What we found was unexpected and the implications are big. This is a deep-water site. Small changes in pressure can increase the gas emissions but the methane will still stay in the ocean due to the water depth. But what happens in shallower sites? This approach needs to be done in shallow Arctic waters as well, over a longer period. In shallow water, the possibility that methane will reach the atmosphere is greater." Says Knies.

May counteract the temperature effects

High sea-level seems thus to influence gas emissions by potentially reducing their height and volume. The question remains whether sea-level rise due to global warming might partially counterbalance the effect of temperature on submarine methane emissions.

"Earth systems are interconnected in ways that we are still deciphering, and our study reveals one of such interconnections in the Arctic: The moon causes tidal forces, the tides generate pressure changes, and bottom currents that in turn shape the seafloor and impact submarine methane emissions. Fascinating!" says Andreia Plaza Faverola.

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