(ORDO NEWS) — The detection of oxygen in an exoplanet’s atmosphere could indicate the existence of life.
On Earth, photosynthetic organisms take in carbon dioxide, sunlight, and water and produce sugars and starches for energy.
Oxygen is a by-product of this process, so if we can find oxygen elsewhere, it will cause a stir.
But the researchers also insist that the oxygen in the exoplanet’s atmosphere indicates the presence of life. This is evidence of life only if we can rule out other pathways for oxygen production.
But scientists cannot rule them out.
The earth is saturated with oxygen. It makes up 46 percent of the earth’s crust and about the same percentage of the mantle, and the atmosphere is about 20 percent oxygen.
The presence of oxygen is associated with the Great Oxygenation Event (GEO), which occurred about two billion years ago.
Ancient cyanobacteria developed pigments that absorb sunlight and use it for photosynthesis.
Oxygen is a waste product of photosynthesis, and life has had several billion years to store oxygen in the atmosphere, mantle, and crust.
So if scientists find oxygen in an exoplanet’s atmosphere, it’s a strong indication that life may be at work. Simple life can boil in the planet’s oceans, absorbing sunlight and releasing oxygen.
But a new study has identified a source of oxygen that is independent of life.
The research paper “Abiotic Production of Molecular Oxygen – The Ion Pathway from Sulfur Dioxide” was published in the journal Science Advances. The lead author is Mons Wallner, PhD student in physics at the University of Gothenburg in Sweden.
Researchers have discovered an abiotic source of oxygen originating from sulfur dioxide. Sulfur is not uncommon in celestial bodies, and because volcanoes produce sulfur and pump it out into the atmosphere, terrestrial volcanic exoplanets can contain oxygen in their atmospheres. And life doesn’t have to be involved.
Instead, the star’s high-energy radiation can ionize the sulfur dioxide molecule. The formula for sulfur dioxide is SO 2 , and when it ionizes, the molecule rearranges itself. This becomes a “double positively charged system”.
It then has a linear shape with both oxygen atoms adjacent to each other and sulfur atoms at the other end. This is called wandering because the oxygen atoms are free to drift in random orbits until they form new compounds.
“In double ionization, two bound electrons in a molecule are ejected, which can lead to a change in the angle between the atoms in the molecule,” lead author Wollner said in a press release.
“Alternatively, which is decisive in this case, wandering can occur, that is, the atoms change places, and the molecule takes on a completely new shape.”
But the constituent molecules may not be converted to SO 2 again. Instead, the sulfur can decay, leaving a simple positively charged oxygen molecule.
Then the positive charge can be neutralized by attracting an electron from another molecule. Molecular oxygen (O 2 ) remains and is vital to life on Earth.
This path to oxygen could explain some of the oxygen we find elsewhere. Io, Ganymede, and Europa contain oxygen in the atmosphere, and a vagrant may be the cause.
Io is a volcanic place – the most volcanic world in the solar system, so life there is excluded. Ganymede and Europa have underground oceans, so they could potentially be home to life.
But this life cannot create an oxygen atmosphere, like earthly life. Another explanation is required to explain the presence of oxygen on these satellites.
According to the researchers, this oxygen pathway could also occur on Earth.
“We also suggest in our paper that this happens naturally on Earth,” said Raimund Feifel, co-author of the paper reporting the results.
This ionic oxygen generation pathway could work for other molecules as well, and that’s up next for researchers. They want to know if other molecules, such as carbon diselenide, undergo double ionization.
“We want to see if this also happens then, or if it was just a lucky coincidence with sulfur dioxide,” Feifel said.
Other researchers have dealt with abiotic sources of O 2 . A 2014 article provides evidence for the formation of molecular oxygen from CO 2 when exposed to high-energy UV radiation.
In a 2015 paper, Japanese researchers showed that near ultraviolet light can produce O2 on exoplanets when interacting with water using Titania (titanium dioxide) as a catalyst.
These results help explain why there was little oxygen in the Earth’s atmosphere prior to the GOE. . Because oxygen is so reactive, there must be a source of replenishment and these pathways may be responsible.
The James Webb Space Telescope is part of the background for this study. Studying exoplanet atmospheres is one of the telescope’s scientific goals, and with its powerful infrared instruments, it is poised to reveal the chemical makeup of exoplanet atmospheres.
If he detects oxygen, there will be a commotion. But as this study shows, there is more to oxygen than life.
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