https://phys.org/news/2020-12-planet-lot-methane-atmosphere-life.html
If a planet has a lot of methane in its atmosphere, life is the most likely cause:
The ultra-powerful James Webb Space Telescope will launch soon. Once it's deployed and in position at the Earth-Sun Lagrange Point 2, it'll begin work. One of its jobs is to examine the atmospheres of exoplanets and look for biosignatures. It should be simple, right? Just scan the atmosphere until you find oxygen, then close your laptop and head to the pub: Fanfare, confetti, Nobel prize.
Of course, Universe Today readers know it's more complicated than that. Much more complicated.
In fact, the presence of oxygen is not necessarily reliable. It's methane that can send a stronger signal indicating the presence of life.
Oxygen might seem like the obvious thing to look for in a planet's atmosphere when searching for signs of life, but that's not the case. Its presence or lack thereof is not a reliable indicator. Earth's history makes that clear.
Modern Earth's atmosphere contains about 21% oxygen, and we know that most of it comes from organisms in the planet's oceans. But there's a hitch: Once cyanobacteria on ancient Earth started producing oxygen as a byproduct of photosynthesis, it still took an awfully long time before the atmosphere became oxygenated, possibly a billion years.
What if we examined an exoplanet, found no oxygen, then moved on, not realizing that there was life down there, at the beginning of oxygenating that world? What if we were a billion years too early, and life hasn't oxygenated the exoplanet's atmosphere yet? Rocky planets have many oxygen sinks, and biologically produced oxygen wouldn't be found free in the atmosphere until those sinks were becoming saturated.
more at link:
the paper:
https://iopscience.iop.org/article/10.3847/PSJ/abb99e
Abundant Atmospheric Methane from Volcanism on Terrestrial Planets Is Unlikely and Strengthens the Case for Methane as a Biosignature:
Abstract:
The disequilibrium combination of abundant methane and carbon dioxide has been proposed as a promising exoplanet biosignature that is readily detectable with upcoming telescopes such as the James Webb Space Telescope. However, few studies have explored the possibility of nonbiological CH4 and CO2 and related contextual clues. Here we investigate whether magmatic volcanic outgassing on terrestrial planets can produce atmospheric CH4 and CO2 with a thermodynamic model. Our model suggests that volcanoes are unlikely to produce CH4 fluxes comparable to biological fluxes. Improbable cases where volcanoes produce biological amounts of CH4 also produce ample carbon monoxide. We show, using a photochemical model, that high abiotic CH4 abundances produced by volcanoes would be accompanied by high CO abundances, which could be a detectable false-positive diagnostic. Overall, when considering known mechanisms for generating abiotic CH4 on terrestrial planets, we conclude that observations of atmospheric CH4 with CO2 are difficult to explain without the presence of biology when the CH4 abundance implies a surface flux comparable to modern Earth's biological CH4 flux. A small or negligible CO abundance strengthens the CH4+CO2 biosignature because life readily consumes atmospheric CO, while reducing volcanic gases likely cause CO to build up in a planet's atmosphere. Furthermore, the difficulty of volcanically generated CH4-rich atmospheres suitable for an origin of life may favor alternatives such as impact-induced reducing atmospheres.
If a planet has a lot of methane in its atmosphere, life is the most likely cause:
The ultra-powerful James Webb Space Telescope will launch soon. Once it's deployed and in position at the Earth-Sun Lagrange Point 2, it'll begin work. One of its jobs is to examine the atmospheres of exoplanets and look for biosignatures. It should be simple, right? Just scan the atmosphere until you find oxygen, then close your laptop and head to the pub: Fanfare, confetti, Nobel prize.
Of course, Universe Today readers know it's more complicated than that. Much more complicated.
In fact, the presence of oxygen is not necessarily reliable. It's methane that can send a stronger signal indicating the presence of life.
Oxygen might seem like the obvious thing to look for in a planet's atmosphere when searching for signs of life, but that's not the case. Its presence or lack thereof is not a reliable indicator. Earth's history makes that clear.
Modern Earth's atmosphere contains about 21% oxygen, and we know that most of it comes from organisms in the planet's oceans. But there's a hitch: Once cyanobacteria on ancient Earth started producing oxygen as a byproduct of photosynthesis, it still took an awfully long time before the atmosphere became oxygenated, possibly a billion years.
What if we examined an exoplanet, found no oxygen, then moved on, not realizing that there was life down there, at the beginning of oxygenating that world? What if we were a billion years too early, and life hasn't oxygenated the exoplanet's atmosphere yet? Rocky planets have many oxygen sinks, and biologically produced oxygen wouldn't be found free in the atmosphere until those sinks were becoming saturated.
more at link:
the paper:
https://iopscience.iop.org/article/10.3847/PSJ/abb99e
Abundant Atmospheric Methane from Volcanism on Terrestrial Planets Is Unlikely and Strengthens the Case for Methane as a Biosignature:
Abstract:
The disequilibrium combination of abundant methane and carbon dioxide has been proposed as a promising exoplanet biosignature that is readily detectable with upcoming telescopes such as the James Webb Space Telescope. However, few studies have explored the possibility of nonbiological CH4 and CO2 and related contextual clues. Here we investigate whether magmatic volcanic outgassing on terrestrial planets can produce atmospheric CH4 and CO2 with a thermodynamic model. Our model suggests that volcanoes are unlikely to produce CH4 fluxes comparable to biological fluxes. Improbable cases where volcanoes produce biological amounts of CH4 also produce ample carbon monoxide. We show, using a photochemical model, that high abiotic CH4 abundances produced by volcanoes would be accompanied by high CO abundances, which could be a detectable false-positive diagnostic. Overall, when considering known mechanisms for generating abiotic CH4 on terrestrial planets, we conclude that observations of atmospheric CH4 with CO2 are difficult to explain without the presence of biology when the CH4 abundance implies a surface flux comparable to modern Earth's biological CH4 flux. A small or negligible CO abundance strengthens the CH4+CO2 biosignature because life readily consumes atmospheric CO, while reducing volcanic gases likely cause CO to build up in a planet's atmosphere. Furthermore, the difficulty of volcanically generated CH4-rich atmospheres suitable for an origin of life may favor alternatives such as impact-induced reducing atmospheres.
