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Methane in the plumes of Saturn's moon Enceladus: Possible signs of life? – Phys.org

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This artist’s impression depicts NASA’s Cassini spacecraft flying through a plume of presumed water erupting from the surface of Saturn’s moon Enceladus. Credit: NASA

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 , the Cassini spacecraft detected a relatively high concentration of certain molecules associated with on the bottom of Earth’s oceans, specifically dihydrogen, 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 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.

Methane in the plumes of Saturn's moon Enceladus: Possible signs of life?
This cutaway view of Saturn’s moon Enceladus is an artist’s rendering that depicts possible hydrothermal activity that may be taking place on and under the seafloor of the moon’s subsurface ocean, based on results from NASA’s Cassini mission. Credit: NASA/JPL-Caltech

“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.”

According to the authors, a very promising advance of the paper lies in its methodology, as it is not limited to specific systems such as interior oceans of icy moons and paves the way to deal with chemical data from planets outside the solar system as they become available in the coming decades.


Explore further

Researchers study methane-rich plumes from Saturn’s icy moon Enceladus


More information:
Antonin Affholder et al, Bayesian analysis of Enceladus’s plume data to assess methanogenesis, Nature Astronomy (2021). DOI: 10.1038/s41550-021-01372-6

Citation:
Methane in the plumes of Saturn’s moon Enceladus: Possible signs of life? (2021, July 7)
retrieved 7 July 2021
from https://phys.org/news/2021-07-methane-plumes-saturn-moon-enceladus.html

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Hot and dry: SPIRou reveals the atmosphere of hot Jupiter Tau Boötis b – News | Institute for Research on Exoplanets

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Measuring the composition of the atmosphere of the hot Jupiter Tau Boötis b more precisely than ever, an iREx-led team of astronomers provides a better understanding of giant exoplanets.

Artistic rendition of the exoplanet Tau Boötis b and its host star, Tau Boötis. Credit : ESO/L. Calçada.

Using the SPIRou spectropolarimeter on the Canada-France-Hawaii Telescope in Hawaii, a team led by Stefan Pelletier, a PhD student at Université de Montréal’s Institute for Research on Exoplanets (iREx), studied the atmosphere of the gas giant exoplanet Tau Boötis b, a scorching hot world that takes a mere three days to orbit its host star. 

Their detailed analysis, presented in a paper published today in the Astronomical Journal, shows that the atmosphere of the gaseous planet contains carbon monoxide, as expected, but surprisingly no water, a molecule that was thought to be prevalent and should have been easily detectable with SPIRou. 

Tau Boötis b is a planet that is 6.24 times more massive than Jupiter and eight times closer to its parent star than Mercury is to the Sun. Located only 51 light-years from Earth and 40 per cent more massive than the Sun, its star, Tau Boötis, is one of the brightest known planet-bearing stars, and is visible to the naked eye in the Boötes constellation.

Tau Boötis b was one of the first exoplanets ever discovered, in 1996, thanks to the radial velocity method, which detects the slight back-and-forth motion of a star generated by the gravitational tug of its planet. Its atmosphere had been studied a handful of times before, but never with an instrument as powerful as SPIRou to reveal  its molecular content. 

Searching for water 

Assuming Tau Boötis b formed in a protoplanetary disk with a composition similar to that of our Solar System, models show that water vapour should be present in large quantities in its atmosphere. It should thus have been easy to detect with an instrument such as SPIRou.

“We expected a strong detection of water, with maybe a little carbon monoxide,” explained Pelletier. “We were, however, surprised to find the opposite: carbon monoxide, but no water.”

The team worked hard to make sure the results could not be attributed to problems with the instrument or the analysis of the data.

“Once we convinced ourselves the content of water was indeed much lower than expected on Tau Boötis b, we were able to start searching for formation mechanisms that could explain this,” said Pelletier.

Studying hot Jupiters to better understand Jupiter and Saturn

“Hot Jupiters like Tau Boötis b offer an unprecedented opportunity to probe giant planet formation”, said co-author Björn Benneke, an astrophysics professor and  Pelletier’s PhD supervisor at UdeM. “The composition of the planet gives clues as to where and how this giant planet formed.”

The key to revealing the formation location and mechanism of giant planets is imprinted in their molecular atmospheric composition. The extreme temperature of hot Jupiters allows most molecules in their atmospheres to be in gaseous form, and therefore detectable with current instruments. Astronomers can thus precisely measure the content of their atmospheres.

“In our Solar System, Jupiter and Saturn are really cold,” said Benneke. “Some molecules such as water are frozen and hidden deep in their atmospheres; thus, we have a very poor knowledge of their abundance. Studying hot Jupiters provides a way to better understand our own giant planets. The low amount of water on Tau Boötis b could mean that our own Jupiter is also drier than we had previously thought.” 



SPIRou: a unique instrument

Tau Boötis b is one of the first planets studied with the new SPIRou instrument since it was recently put into service at the Canada-France-Hawaii Telescope. This instrument was developed by researchers from several scientific institutions including UdeM.

“This spectropolarimeter can analyze the planet’s thermal light — the light emitted by the planet itself — in an unprecedentedly large range of colours, and with a resolution that allows for the identification of many molecules at once: water, carbon monoxide, methane, etc.” said co-author and iREx researcher Neil Cook, an expert on the SPIRou instrument. 

The team spent 20 hours observing the exoplanet with SPIRou between April 2019 and June 2020.

“We measured the abundance of all major molecules that contain either carbon or oxygen,” said Pelletier. “Since they are the two most abundant elements in the universe, after hydrogen and helium, that gives us a very complete picture of the content of the atmosphere.” 

Like most planets, Tau Boötis b does not pass in front of its star as it orbits around it, from Earth’s point of view. However, the study of exoplanet atmospheres has mostly been limited to “transiting” planets – those that cause periodic dips in the light of their star when they obscure part of their light.

“It is the first time that we get such precise measurements on the atmospheric composition of a non-transiting exoplanet,” said PhD student Caroline Piaulet, a co-author of the study.

“This work opens the door to studying in detail the atmospheres of a large number of exoplanets, even those that do not transit their star.” 

A composition similar to Jupiter

Through their analysis, Pelletier and his colleagues were able to conclude that Tau Boötis b’s atmospheric composition has roughly five times as much carbon as that found in the Sun, quantities similar to that measured for Jupiter. 

This may be a suggest that hot Jupiters could form much further from their host star, at distances that are similar to the giant planets in our Solar System, and have simply experienced a different evolution, which included a migration towards the star. 

“According to what we found for Tau Boötis b, it would seem that, at least composition-wise, hot Jupiters may not be so different from our own Solar System giant planets after all,” concluded Pelletier.

About this study 

Where is the water? Jupiter-like C/H ratio but strong H2O depletion found on Tau Boötis b using SPIRou,” by Stefan Pelletier et al., was published July 28th, 2021 in the Astronomical Journal. 

In addition to Stefan Pelletier, Björn Benneke, Neil Cook and Caroline Piaulet, the team includes Institute for research on exoplanets (iREx) members Antoine Darveau-Bernier, Anne Boucher, Louis-Philippe Coulombe, Étienne Artigau, David Lafrenière, Simon Delisle, Romain Allart, René Doyon, Charles Cadieux and Thomas Vandal, all based at Université de Montréal, and seven other co-authors from France, the United States, Portugal and Brazil. 

Funding was provided by the the Technologies for Exo-Planetary Science (TEPS) CREATE program, the Fonds de recherche du Québec – Nature et technologies (FRQNT), the Natural Sciences and Engineering Research Council of Canada (NSERC), the Trottier Family Foundation and the French National Research Agency (ANR).

Media Contacts 

Marie-Eve Naud
EPO Coordinator, Institute for Research on Exoplanets
Université de Montréal, Montréal, Canada
514-279-3222, marie-eve.naud@umontreal.ca

Scientific Contacts 

Stefan Pelletier (lead author)
Ph.D. Candidate, Institute for Research on Exoplanets
Université de Montréal, Montréal, Canada
stefan.pelletier@umontreal.ca  

Björn Benneke (co-author)
Professor, Institute for Research on Exoplanets
Université de Montréal, Montréal, Canada
514-578-2716, bjorn.benneke@umontreal.ca  

Additional links 

Scientific article (Astronomical Journal, open source version on arXiv.org)
Université de Montréal press release
Canada-France-Hawaii press release

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Scientists capture most-detailed radio image of Andromeda galaxy to date – UBC News

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‘Disk of galaxy’ identified as region where new stars are born

Scientists have published a new, detailed radio image of the Andromeda galaxy – the Milky Way’s sister galaxy – which will allow them to identify and study the regions of Andromeda where new stars are born.

Sofia Fatigoni

The study – which is the first to create a radio image of Andromeda at the microwave frequency of 6.6 GHz – was led by University of British Columbia physicist Sofia Fatigoni, with colleagues at Sapienza University of Rome and the Italian National Institute of Astrophysics. It was published online in Astronomy and Astrophysics.

“This image will allow us to study the structure of Andromeda and its content in more detail than has ever been possible,” said Fatigoni, a PhD student in the department of physics and astronomy at UBC. “Understanding the nature of physical processes that take place inside Andromeda allows us to understand what happens in our own galaxy more clearly – as if we were looking at ourselves from the outside.”

Prior to this study, no maps capturing such a large region of the sky around the Andromeda Galaxy had ever been made in the microwave band frequencies between one GHz to 22 GHz. In this range, the galaxy’s emission is very faint, making it hard to see its structure. However, it is only in this frequency range that particular features are visible, so having a map at this particular frequency is crucial to understanding which physical processes are happening inside Andromeda.

In order to observe Andromeda at this frequency, the researchers required a single-dish radio telescope with a large effective area. For the study, the scientists turned to the Sardinia Radio Telescope, a 64-metre fully steerable telescope capable of operating at high radio frequencies, located in Italy.

The Sardinia Radio Telescope, located in Sardinia, Italy. Credit: S. Fatigoni et al (2021)

The Sardinia Radio Telescope, located in Sardinia, Italy. Credit: S. Fatigoni et al (2021)

It took 66 hours of observation and consistent data analysis for the researchers to map the galaxy with high sensitivity.

They were then able to estimate the rate of star formation within Andromeda, and produce a detailed map that highlighted the ‘disk of the galaxy,’ as the region where new stars are born.

“By combining this new image with those previously acquired, we have made significant steps forward in clarifying the nature of Andromeda’s microwave emissions and allowing us to distinguish physical processes that occur in different regions of the galaxy,” said Dr. Elia Battistelli, a professor in the department of physics at Sapienza and coordinator of the study.

“In particular, we were able to determine the fraction of emissions due to thermal processes related to the early stations of new star formation, and the fraction of radio signals attributable to non-thermal mechanisms due to cosmic rays that spiral in the magnetic field present in the interstellar medium,” Fatigoni said.

Final image of the Andromeda galaxy after averaging over the whole bandwidth at 6.6 GHz. Credit: S. Fatigoni et al (2021)

Final image of the Andromeda galaxy after averaging over the whole bandwidth at 6.6 GHz. Credit: S. Fatigoni et al (2021)

For the study, the team also developed and implemented software that allowed them to test new algorithms to identify never-before-examined lower emission sources in the field of view around Andromeda at a frequency of 6.6 GHz.

From the resulting map, researchers were able to identify a catalog of about 100 ‘point sources’ including stars, galaxies and other objects in the background of Andromeda.

Interview language(s): English, Italian

Note for reporters: Sofia Fatigoni is based in Rome, Italy and is available for interviews until 3 p.m. PST.

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To help chart the cosmos, Western space researchers turn to crowd sourcing – CBC.ca

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Western University researchers have tapped the help of hundreds of amateur and professional astronomers in an effort to make sure no meteor is unable to slip by the Earth undetected.

To do that, they’re relying on the observations taken from 450 cameras in 30 different countries manned by “enthusiastic amateur astronomers” made up of professional and citizen scientists.

That data is then sent to Western University as part of what’s called the Global Meteor Network (GMN), headed by Denis Vida.

“So we have a lot of enthusiastic amateur astronomers, citizen scientists and also professionals that build, operate and maintain these cameras,” Vida told CBC’s Chris dela Torre during Afternoon Drive. “And every night they inspect the data set and send their data to a central server here at the University of Western Ontario.”

It’s not just about observing meteors – it’s about tracking what’s left of the ones that make it to the earth’s surface too.

“So we also observe a meteorite dropping fireballs,” said Vida. “They’re quite rare over an area of let’s say the country the size of France or Spain. Could only expect two to three of those fireballs a year that drop more than, let’s say, 300 grams of meteorites on the ground.”

“So because these events are very rare, it is important to observe 24/7.”

Vida explained that when one of their cameras spot one of them, they collect the data and find its location so they can retrieve what’s left for analysis – and analysis needs to happen quickly.  

“There are certain things in them, like some radionuclide to decay very quickly, but those can tell us how old the meteorite is, how long it was after it was ejected from the parent asteroid that it fell on the ground,” he said.

Vida explained that what ends up on the ground are just “several kilograms of materials” by the time they reach the earth’s surface. They aren’t hot either. They cool down on their descent.

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