Juno spacecraft measures oxygen production on Jupiter's moon, Europa

NASA's Juno spacecraft has directly measured charged oxygen and hydrogen molecules from the atmosphere of one of Jupiter's largest moons, Europa. According to a new study co-authored by SwRI scientists and led by Princeton University, these observations provide key constraints on the potential oxygenation of its subsurface ocean.

"These findings have direct implications on the potential habitability of Europa," said Juno Principal Investigator Dr. Scott Bolton of SwRI, a co-author of the study.

"This study provides the first direct in-situ measurement of water components existing in Europa's atmosphere, giving us a narrow range that could support habitability."

In 2022, Juno completed a flyby of Europa, coming as close as 352 kilometers to the moon.

The SwRI-developed Jovian Auroral Distributions Experiment (JADE) instrument aboard Juno detected significant amounts of charged molecular oxygen and hydrogen lost from the atmosphere.

"For the first time, we've been able to definitively detect hydrogen and oxygen with in-situ measurements and further confirm that Europa's atmosphere is made primarily of hydrogen and oxygen molecules," said SwRI Staff Scientist and co-author Dr. Robert Ebert.

The source of these molecules is thought to be water ice on Europa's surface.

Jupiter's rampant radiation breaks H2O's molecular bonds, leaving behind oxygen and hydrogen.

The heavier oxygen molecules remain more constrained to the surface, or near-surface atmosphere, while the lighter-weight hydrogen predominately escapes into the atmosphere and beyond.

Oxygen produced in the ice is either lost from the atmosphere and/or sequestered in the surface.

Oxygen retained in Europa's ice may work its way to its subsurface ocean as a possible source of metabolic energy.

"Europa's ice shell absorbs radiation, protecting the ocean underneath. This absorption also produces oxygen within the ice, so in a way, the ice shell acts as Europa's lung, providing a potential oxygen source for the ocean." said Princeton University Research Scholar Dr. Jamey Szalay, the study's lead author.

"We put narrow constraints on the total oxygen production at Europa currently at around 12 kg per second. Before Juno, previous estimates ranged from a few kg per second to over 1,000 kg per second. The findings unambiguously demonstrate oxygen is continuously produced in the surface, just a good bit lower than we expected."

"We designed JADE to measure the charged particles that create Jupiter's auroras," said SwRI Staff Scientist and co-author Dr. Frederic Allegrini.

"Flybys of Europa were not part of the primary Juno mission. JADE was designed to work in a high-radiation environment but not necessarily Europa's environment, which is constantly bombarded with high levels of radiation. Nonetheless, the instrument performed beautifully."

The new measurements contribute to a greater understanding of Europa and its environment, open the door for newer, more precise models.

The study's new estimation of how much oxygen is produced within Europa's surface, for instance, could inform future research related to its subsurface ocean and potential habitability.

As these observations provide the first charged particle composition measurements within Europa's vicinity, they provide an important new window into the moons' complex interaction with its environment.

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Unlocking the secrets of a 'Hot Saturn' and its spotted star

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

Their findings, published last month in the journal Monthly Notices of the Royal Astronomical Society, paint a complete picture of the HAT-P-18 b's atmosphere while exploring the great challenge of distinguishing its atmospheric signals from the activity of its star.

HAT-P-18 b is located over 500 light-years away with a mass similar to Saturn's but a size closer to that the larger planet Jupiter. As a result, the exoplanet has a "puffed-up" atmosphere that is especially ideal for analysis.

Passing over a spotted star

Observations from the JWST were taken while the HAT-P-18 b was passing in front of its Sun-like star. This moment is called a transit and is crucial to detect and further characterise an exoplanet from hundreds of light-years away with surprising precision.

Astronomers don't observe light that is being emitted directly by the distant planet. Rather, they study how the central star's light is being blocked and affected by the planet orbiting it, and so must try to disentangle signals caused by the presence of the planet from those caused by the star's own properties.

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

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

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

"We found that accounting for stellar contamination implies the existence of spots and clouds instead of haze and recovers a water vapour abundance of almost an order of magnitude lower," said lead author Marylou Fournier-Tondreau.

"So considering the system's host star makes a big difference," added Fournier-Tondreau, who did the work as a master's student at iREx and is now pursuing a Ph.D. at the University of Oxford.

"It's actually the first time that we clearly disentangle the signature of hazes versus starspots, thanks to Canada's NIRISS (Near-Infrared Imager and Slitless Spectrograph) instrument, which provides wider wavelength coverage extending into the visible light domain."

H2O, CO2, and clouds in a scorching atmosphere

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

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

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

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

Could the exoplanet support life? Not likely. While molecules like water, carbon dioxide, and methane can be interpreted as biosignatures, or signs of life, in certain ratios or in combination with other molecules, HAT-P-18 b's scorching temperatures of close to 600 degrees Celsius do not bode well for the planet's habitability.

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New catalyst lowers cost for producing environmentally sustainable hydrogen from water

A plentiful supply of clean energy is lurking in plain sight. It is the hydrogen we can extract from water (H2O) using renewable energy. Scientists are seeking low-cost methods for producing clean hydrogen from water to replace fossil fuels, as part of the quest to combat climate change.

Hydrogen can power vehicles while emitting nothing but water. Hydrogen is also an important chemical for many industrial processes, most notably in steel making and ammonia production. Using cleaner hydrogen is highly desirable in those industries.

A multi-institutional team led by the U.S. Department of Energy's (DOE) Argonne National Laboratory has developed a low-cost catalyst for a process that yields clean hydrogen from water. Other contributors include DOE's Sandia National Laboratories and Lawrence Berkeley National Laboratory, as well as Giner Inc.

"A process called electrolysis produces hydrogen and oxygen from water and has been around for more than a century," said Di-Jia Liu, senior chemist at Argonne. He also holds a joint appointment in the Pritzker School of Molecular Engineering at the University of Chicago.

Proton exchange membrane (PEM) electrolyzers represent a new generation of technology for this process. They can split water into hydrogen and oxygen with higher efficiency at near room temperature. The reduced energy demand makes them an ideal choice for producing clean hydrogen by using renewable but intermittent sources, such as solar and wind.

This electrolyzer runs with separate catalysts for each of its electrodes (cathode and anode). The cathode catalyst yields hydrogen, while the anode catalyst forms oxygen. A problem is that the anode catalyst uses iridium, which has a current market price of around $5,000 per ounce. The lack of supply and high cost of iridium pose a major barrier for widespread adoption of PEM electrolyzers.

The main ingredient in the new catalyst is cobalt, which is substantially cheaper than iridium. "We sought to develop a low-cost anode catalyst in a PEM electrolyzer that generates hydrogen at high throughput while consuming minimal energy," Liu said. "By using the cobalt-based catalyst prepared by our method, one could remove the main bottleneck of cost to producing clean hydrogen in an electrolyzer."

Giner Inc., a leading research and development company working toward commercialization of electrolyzers and fuel cells, evaluated the new catalyst using its PEM electrolyzer test stations under industrial operating conditions. The performance and durability far exceeded that of competitors' catalysts.

Important to further advancing the catalyst performance is understanding the reaction mechanism at the atomic scale under electrolyzer operating conditions. The team deciphered critical structural changes that occur in the catalyst under operating conditions by using X-ray analyses at the Advanced Photon Source (APS) at Argonne. They also identified key catalyst features using electron microscopy at Sandia Labs and at Argonne's Center for Nanoscale Materials (CNM). The APS and CNM are both DOE Office of Science user facilities.

"We imaged the atomic structure on the surface of the new catalyst at various stages of preparation," said Jianguo Wen, an Argonne materials scientist.

In addition, computational modeling at Berkeley Lab revealed important insights into the catalyst's durability under reaction conditions.

The team's achievement is a step forward in DOE's Hydrogen Energy Earthshot initiative, which mimics the U.S. space program's "Moon Shot" of the 1960s. Its ambitious goal is to lower the cost for green hydrogen production to one dollar per kilogram in a decade. Production of green hydrogen at that cost could reshape the nation's economy. Applications include the electric grid, manufacturing, transportation and residential and commercial heating.

"More generally, our results establish a promising path forward in replacing catalysts made from expensive precious metals with elements that are much less expensive and more abundant," Liu noted.

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