Scientists Warn of “Oxygen False Positives” in Search for Signs of Alien Life on Other Planets

Oxygen in the environment might not be a completely dependable ‘biosignature,’ however there are methods to differentiate incorrect positives from indications of life, researchers state.

In the look for life on other worlds, the existence of oxygen in a world’s environment is one prospective indication of biological activity that may be identified by future telescopes. A brand-new research study, nevertheless, explains numerous situations in which a lifeless rocky world around a sun-like star might progress to have oxygen in its environment.

The brand-new findings, released on April 13, 2021, in AGU Advances, highlight the requirement for next-generation telescopes that can defining planetary environments and looking for numerous lines of proof for life in addition to identifying oxygen.

“This is useful because it shows there are ways to get oxygen in the atmosphere without life, but there are other observations you can make to help distinguish these false positives from the real deal,” stated very first author Joshua Krissansen-Totton, a Sagan Fellow in the Department of Astronomy and Astrophysics at UC Santa Cruz. “For each scenario, we try to say what your telescope would need to be able to do to distinguish this from biological oxygen.”

In the coming years, maybe by the late 2030s, astronomers intend to have a telescope efficient in taking images and spectra of possibly Earth-like worlds around sun-like stars. Coauthor Jonathan Fortney, teacher of astronomy and astrophysics and director of UCSC’s Other Worlds Laboratory, stated the concept would be to target worlds comparable enough to Earth that life may have emerged on them and identify their environments.

“There has a been a lot of discussion about whether detection of oxygen is ‘enough’ of a sign of life,” he stated. “This work really argues for needing to know the context of your detection. What other molecules are found in addition to oxygen, or not found, and what does that tell you about the planet’s evolution?”

This indicates astronomers will desire a telescope that is delicate to a broad series of wavelengths in order to find various kinds of particles in a world’s environment.

The scientists based their findings on a comprehensive, end-to-end computational design of the development of rocky worlds, beginning with their molten origins and extending through billions of years of cooling and geochemical biking. By differing the preliminary stock of unpredictable aspects in their design worlds, the scientists got a remarkably wide variety of results.

Oxygen can begin to develop in a world’s environment when high-energy ultraviolet light divides water particles in the upper environment into hydrogen and oxygen. The light-weight hydrogen preferentially gets away into area, leaving the oxygen behind. Other procedures can eliminate oxygen from the environment. Carbon monoxide and hydrogen launched by outgassing from molten rock, for instance, will respond with oxygen, and weathering of rock likewise mops up oxygen. These are simply a few of the procedures the scientists included into their design of the geochemical development of a rocky world.

“If you run the model for Earth, with what we think was the initial inventory of volatiles, you reliably get the same outcome every time–without life you don’t get oxygen in the atmosphere,” Krissansen-Totton stated. “But we also found multiple scenarios where you can get oxygen without life.”

For example, a world that is otherwise like Earth however begins with more water will wind up with really deep oceans, putting enormous pressure on the crust. This successfully closes down geological activity, consisting of all of the procedures such as melting or weathering of rocks that would eliminate oxygen from the environment.

In the opposite case, where the world begins with a fairly percentage of water, the lava surface area of the at first molten world can freeze rapidly while the water stays in the environment. This “steam atmosphere” puts adequate water in the upper environment to enable build-up of oxygen as the water separates and hydrogen gets away.

“The typical sequence is that the magma surface solidifies simultaneously with water condensing out into oceans on the surface,” Krissansen-Totton stated. “On Earth, once water condensed on the surface, escape rates were low. But if you retain a steam atmosphere after the molten surface has solidified, there’s a window of about a million years when oxygen can build up because there are high water concentrations in the upper atmosphere and no molten surface to consume the oxygen produced by hydrogen escape.”

A 3rd situation that can cause oxygen in the environment includes a world that is otherwise like Earth however begins with a greater ratio of co2 to water. This results in a runaway greenhouse impact, making it too hot for water to ever condense out of the environment onto the surface area of the world.

“In this Venus-like situation, all the volatiles start in the environment and couple of are left in the mantle to be outgassed and mop up oxygen,” Krissansen-Totton stated.

He kept in mind that previous research studies have actually concentrated on climatic procedures, whereas the design utilized in this research study checks out the geochemical and thermal development of the world’s mantle and crust, in addition to the interactions in between the crust and environment.

“It’s not computationally intensive, but there are a lot of moving parts and interconnected processes,” he stated.

Reference: “Oxygen False Positives on Habitable Zone Planets Around Sun‐Like Stars” by Joshua Krissansen‐Totton, Jonathan J. Fortney, Francis Nimmo and Nicholas Wogan, 13 April 2021, AGU Advances.
DOI: 10.1029/2020AV000294

In addition to Krissansen-Totton and Fortney, the coauthors consist of Francis Nimmo, teacher of Earth and planetary sciences at UC Santa Cruz, and Nicholas Wogan at the University of Washington, Seattle. This research study was supported by NASA.