Edward Schwieterman

Using Earth’s history to inform the search for life on exoplanets

Anonymous — Tue, 08 Dec 2020 16:26:50 +0000

Using Earth’s history to inform the search for life on exoplanets Anonymous (not verified) Tue, 12/08/2020 - 08:26 More News Jules Bernstein | UCR News December 08, 2020

UC Riverside is leading one of the NASA Astrobiology Program’s eight new research teams tackling questions about the evolution and origins of life on Earth and the possibility of life beyond our solar system.

The teams comprise the inaugural class of NASA’s Interdisciplinary Consortia for Astrobiology Research program. The UCR-led team is motivated by the fundamental question of how to detect planets that could host life and remain habitable despite tremendous change over time, which requires hunting for biological gases in the atmospheres of planets light years beyond our solar system.

This image shows an Earth-like "exomoon" orbiting a gas giant planet in a star's habitable zone. (NASA/JPL-Caltech)

“To achieve this goal, our research focuses on the many diverse chapters of Earth’s history — or alternative Earths — that span billions of years and offer critical templates for examining exoplanets far beyond our solar system,” said UCR biogeochemist Timothy Lyons, the project leader.

Because of their immense distance from us, humans will likely never visit those planets, at least not soon, Lyons said. However, in the near future, scientists will be able to analyze the compositions of these planets’ atmospheres, looking for gases like oxygen and methane that could come from life.

Earth has undergone dramatic changes over the last 4.5 billion years, with major transitions occurring in plate tectonics, climate, ocean chemistry, the structure of our ecosystems, and composition of our atmosphere.

“These changes represent an opportunity,” Lyons said. “The different periods of Earth’s evolutionary history provide glimpses of many, largely alien worlds, some of which may be analogs for habitable planetary states that are very different from conditions on modern Earth.”

Exciting new research frontiers for Lyons’ team include studies of Earth’s first 500 million years, as well as predictions about our planet and its life billions of years in the future.

Studying biosignature gases in Earth’s past will allow the team to design telescopes and refine interpretative models for potential traces of life in distant exoplanet atmospheres, noted Georgia Tech biogeochemist Christopher Reinhard.

Once the researchers understand how Earth and its star — the sun — changed together to maintain liquid oceans teeming with life over billions of years, the team can predict how other planetary systems might also have developed and maintained life and better understand how to search for it.

“Such a ‘mission to early Earth’ must include broad interdisciplinary within the team, impactful synergy within and across the Research Coordination Networks, or RCNs, of the NASA Astrobiology Program, and a commitment to deliverables that will help steer NASA science for decades to come,” said UCR astrobiologist Edward Schwieterman.

Success in this mission will require biological, chemical, geological, oceanographic, and astronomical expertise. Yale University biogeochemist Noah Planavsky said, “our team brings all that to the table.” Accordingly, the diverse expertise within the team includes astronomers, planetary scientists, geologists, geophysicists, oceanographers, biogeochemists, and geobiologists.

The team will collect ancient rock samples and modern sediments from around the world spanning billions of years and use the data they generate to drive wide-ranging computational models for Earth’s ancient and future oceans and atmospheres.

“The models will allow the team to evaluate whether different periods in Earth’s history were characterized by gases that would have been detectable from a distant vantage as products of life, much the way oxygen fingerprints life on our planet today,” said Purdue University Earth and exoplanetary scientist Stephanie Olson.

This work requires a multipronged view of the Earth as a complex system that has varied dramatically over time. Yet despite all the change, Earth has remained persistently habitable, with liquid water oceans teeming with life.

How Earth became and remained habitable and whether its life would have been detectable to a distant observer are the questions that will ultimately define and refine the search for life on exoplanets.

“In short,” said Lyons, “the exciting goal of our team is to provide a new and more holistic view of Earth’s evolutionary history in order to help guide NASA’s mission-specific search for life on distant worlds.”

The RCNs are the new face of astrobiology at NASA, following 20 years of exciting research under the umbrella of the NASA Astrobiology Institute, which supported the UCR-led team previously.

The $4.6 million new award from NASA will span five years and includes team members from Georgia Tech, Yale University, Purdue University, UCLA, NASA Ames Research Center and collaborators from around the world.

Tim Lyons and Edward Schwieterman contributed significantly to this story.

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UCR team among scientists developing guidebook for finding life beyond earth

Anonymous — Fri, 04 Sep 2020 00:41:56 +0000

UCR team among scientists developing guidebook for finding life beyond earth Anonymous (not verified) Thu, 09/03/2020 - 17:41 More News Sarah Nightingale | UCR News June 25, 2018

If you’re looking for a manual on the hunt for alien life, you’re in luck.

Some of the leading experts in the field, including a UC Riverside team of researchers, have written a major series of review papers on the past, present, and future of the search for life on other planets. Published in Astrobiology, the papers represent two years of work by the Nexus for Exoplanet Systems Science(NExSS), a NASA-coordinated research network dedicated to the study of planetary habitability, and by NASA’s Astrobiology Institute.

Scientists have identified more than 3,500 planets around other stars (called exoplanets) and many more will be discovered in the coming decades. Some of these are rocky, Earth-sized planets that are in the habitable zones of their stars, meaning it’s neither too hot nor too cold for liquid water — and possibly life — to exist.

The five papers will serve as a reference for scientists searching for signs of life, called biosignatures, in the data they collect from future telescope observations.

“In less than 30 years, we’ve gone from not knowing whether planets existed outside our solar system to being able to pinpoint potentially habitable planets and collect data that will enable us to look for the signatures of life,” said Edward Schwieterman, a postdoctoral researcher in UCR’s Department of Earth Sciences and lead author on the first paper in the series. “These advances offer unprecedented opportunities to answer the age-old question, ‘are we alone?’, but at the same time demand that we move forward with great care by developing robust models that allow us to seek and identify life with a high degree of certainty.”

Schwieterman’s paper reviews three types of biosignatures that astrobiologists have previously proposed as markers for life on other planets, all of which must be remotely detected since exoplanets orbit distant stars that we cannot reach in person. The markers include:

Fingerprints of life. (NASA/Aaron Gronstal)

Gaseous biosignatures — byproducts of life that can be detected in the atmosphere, such as oxygen produced by photosynthesis, as on Earth.
Surface biosignatures — life-induced changes in the absorption and reflection of light on the surface of a planet, such as the red-edge caused when plants absorb red light during photosynthesis but reflect infrared light that is not used.
Temporal biosignatures — time-dependent fluctuations in gaseous or surface biosignatures, such as biologically modulated changes in the Earth’s atmosphere that occur during different seasons.

Schwieterman is part of UCR’s NASA-funded Alternative Earths Astrobiology Center, an interdisciplinary group that is developing a “search engine” for life on other worlds by delving into our own planet’s dynamic, 4.5-billion-year history. Though dramatically different in terms of atmospheric composition and climate, the different chapters of Earth’s history have one thing in common: oceans teeming with a remarkable diversity of simple and complex life.

“We are using Earth to guide our search for life on other planets because it is the only known example we have,” said Timothy Lyons, a distinguished professor of biogeochemistry and director of the Alternative Earths Astrobiology Center. “But Earth actually offers us a great diversity of possibilities. Rather than being constrained to a study of present-day life, we use geological and geochemical analyses to examine the billions of years that life survived, evolved, and thrived on Earth under conditions that are very different than today’s, hence the concept of ‘alternative Earths.’”

UCR's Edward Schwieterman.

Edward Schwieterman, a postdoctoral researcher in UCR’s Department of Earth Sciences.

Schwieterman’s review outlines the complexities of searching for life on planets that are too far away to visit, including phenomena called false positives and false negatives. “The search for life using biosignatures is not as simple as looking for a single molecule or compound. Atmospheric oxygen, for example, could be a sign of life, but there are many nonbiological ways that oxygen gas could be produced on an exoplanet. Conversely, it is possible that life could exist in the absence of oxygen gas, similar to early life on Earth or portions of the oceans today,” Schwieterman said. “This is one reason temporal biosignatures, which are based on dynamic phenomena such as atmospheric seasonality, might be more robust biosignatures in some circumstances.”

More research on the ways nature can fool scientists into thinking a lifeless planet is alive or vice versa is described in the second paper in the series. The third and fourth papers propose novel investigations that would expand our conception of biosignatures to myriad habitable planets that are radically different from past or present Earth. The final article discusses how the search for life through biosignatures is incorporated into telescope and mission design.

In addition to Schwieterman and Lyons, Stephanie Olson, a graduate student in Earth Sciences, contributed to this research. The team, together with Christopher Reinhard, an assistant professor at Georgia Institute of Technology and a member of UCR-led Alternative Earths Astrobiology team, contributed to several other papers in the series.

“Together, these papers highlight UCR’s contributions to the understanding of exoplanet biosignatures and the implications for instrument design going forward,” Schwieterman said.

“These articles will provide an entry point for people from disparate fields interested in how they too might contribute to the search for life outside our solar system.”

UCR’s Alternative Earths team is funded by the NASA Astrobiology Institute. Read a NASA news releaseabout this research.

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Carbon monoxide detectors could warn of extraterrestrial life

Anonymous — Fri, 04 Sep 2020 00:34:43 +0000

Carbon monoxide detectors could warn of extraterrestrial life Anonymous (not verified) Thu, 09/03/2020 - 17:34 More News Sarah Simpson | UCR News March 18, 2019

Carbon monoxide detectors in our homes warn of a dangerous buildup of that colorless, odorless gas we normally associate with death. Astronomers, too, have generally assumed that a build-up of carbon monoxide in a planet’s atmosphere would be a sure sign of lifelessness. Now, a UC Riverside-led research team is arguing the opposite: celestial carbon monoxide detectors may actually alert us to a distant world teeming with simple life forms.

Edward Schwieterman, a postdoctoral researcher in UCR’s Department of Earth Sciences.

“With the launch of the James Webb Space Telescope two years from now, astronomers will be able to analyze the atmospheres of some rocky exoplanets,” said Edward Schwieterman, the study’s lead author and a NASA Postdoctoral Program fellow in UCR’s Department of Earth Sciences. “It would be a shame to overlook an inhabited world because we did not consider all the possibilities.”

In a study published today in The Astrophysical Journal, Schwieterman’s team used computer models of chemistry in the biosphere and atmosphere to identify two intriguing scenarios in which carbon monoxide readily accumulates in the atmospheres of living planets.

In the first scenario, the team found answers in our own planet’s deep past. On the modern, oxygen-rich Earth, carbon monoxide cannot accumulate because the gas is quickly destroyed by chemical reactions in the atmosphere. But three billion years ago, the world was a very different place. The oceans were already teeming with microbial life, but the atmosphere was nearly devoid of oxygen and the sun was much dimmer.

The team’s models reveal that this ancient version of inhabited Earth could maintain carbon monoxide levels of roughly 100 parts per million (ppm)—several orders of magnitude greater the parts-per-billion traces of the gas in the atmosphere today.

“That means we could expect high carbon monoxide abundances in the atmospheres of inhabited but oxygen-poor exoplanets orbiting stars like our own sun,” said Timothy Lyons, one of the study’s co-authors, a professor of biogeochemistry in UCR’s Department of Earth Science, and director of the UCR Alternative Earths Astrobiology Center. “This is a perfect example of our team’s mission to use the Earth’s past as a guide in the search for life elsewhere in the universe.”

A rocky planet orbiting Proxima Centauri might sustain liquid water (artist’s depiction). Credit: NASA, ESA, G. Bacon (STSc)

A second scenario is even more favorable for the buildup of carbon monoxide: the photochemistry around red dwarf stars like Proxima Centauri, the star nearest our sun at 4.2 light years away. The team’s models predict that if a planet around such a star were inhabited and rich in oxygen, then we should expect the abundance of carbon monoxide to be extremely high—anywhere from hundreds of ppm to several percent.

“Given the different astrophysical context for these planets, we should not be surprised to find microbial biospheres promoting high levels of carbon monoxide,” Schwieterman said. “However, these would certainly not be good places for human or animal life as we know it on Earth.”

Earth-sized, rocky planets have been discovered orbiting in the habitable zone of Proxima Centauri and other similar stars, meaning they could harbor liquid water, an essential ingredient for life. Such planets are likely targets for further characterization by the James Webb Space Telescope, scheduled for launch in March 2021.

The current study is one component of a broad effort to prepare for these future missions by cataloguing different combinations of atmospheric gases that might be evidence of an inhabited world—so-called biosignature gases. Some gases, such as carbon monoxide, had been proposed previously as ‘antibiosignatures’— evidence that a planet is not inhabited —if remotely detectable at sufficient abundance. But those assumptions only apply in specific cases.

Carbon monoxide features prominently in oxygen-rich atmospheres in the habitable zone of a red dwarf star like Proxima Centauri.

“Although other studies have done exoplanet photochemical modeling that includes carbon monoxide, no one had focused on carbon monoxide on Earth-like exoplanets in such a systematic way,” Schwieterman said. “Now we have a guidebook for determining what levels of carbon monoxide are compatible with a photosynthetic biosphere.”

In addition to Schwieterman and Lyons, the paper’s authors are Christopher Reinhard from the Georgia Institute of Technology; Stephanie Olson, a former UCR graduate student now a postdoctoral fellow at the University of Chicago; Kazumi Ozaki, a former NASA Postdoctoral Program fellow at Georgia Tech now from Toho University in Japan; Chester E. Harman from Columbia University, and Peng K. Hong from Chiba Institute of Technology. This project was funded by the NASA Astrobiology Institute.

(Header photo: Hubble telescope photograph of Proxima Centauri. Credit: ESA/Hubble & NASA)

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New study dramatically narrows the search for advanced life in the universe

Anonymous — Thu, 03 Sep 2020 23:12:12 +0000

New study dramatically narrows the search for advanced life in the universe Anonymous (not verified) Thu, 09/03/2020 - 16:12 More News Jules Bernstein | UCR News June 10, 2019

RIVERSIDE, CA – Scientists may need to rethink their estimates for how many planets outside our solar system could host a rich diversity of life.

In a new study, a UC Riverside–led team discovered that a buildup of toxic gases in the atmospheres of most planets makes them unfit for complex life as we know it.

Traditionally, much of the search for extraterrestrial life has focused on what scientists call the “habitable zone,” defined as the range of distances from a star warm enough that liquid water could exist on a planet’s surface. That description works for basic, single-celled microbes — but not for complex creatures like animals, which include everything from simple sponges to humans.

The team’s work, published today in The Astrophysical Journal, shows that accounting for predicted levels of certain toxic gases narrows the safe zone for complex life by at least half — and in some instances eliminates it altogether.

“This is the first time the physiological limits of life on Earth have been considered to predict the distribution of complex life elsewhere in the universe,” said Timothy Lyons, one of the study’s co-authors, a distinguished professor of biogeochemistry in UCR’s Department of Earth and Planetary Sciences, and director of the Alternative Earths Astrobiology Center, which sponsored the project.

“Imagine a ‘habitable zone for complex life’ defined as a safe zone where it would be plausible to support rich ecosystems like we find on Earth today,” Lyons explained. “Our results indicate that complex ecosystems like ours cannot exist in most regions of the habitable zone as traditionally defined.”

Using computer models to study atmospheric climate and photochemistry on a variety of planets, the team first considered carbon dioxide. Any scuba diver knows that too much of this gas in the body can be deadly. But planets too far from their host star require carbon dioxide — a potent greenhouse gas — to maintain temperatures above freezing. Earth included.

“To sustain liquid water at the outer edge of the conventional habitable zone, a planet would need tens of thousands of times more carbon dioxide than Earth has today,” said Edward Schwieterman, the study’s lead author and a NASA Postdoctoral Program fellow working with Lyons. “That’s far beyond the levels known to be toxic to human and animal life on Earth.”

The new study concludes that carbon dioxide toxicity alone restricts simple animal life to no more than half of the traditional habitable zone. For humans and other higher order animals, which are more sensitive, the safe zone shrinks to less than one third of that area.

What is more, no safe zone at all exists for certain stars, including two of the sun’s nearest neighbors, Proxima Centauri and TRAPPIST-1. The type and intensity of ultraviolet radiation that these cooler, dimmer stars emit can lead to high concentrations of carbon monoxide, another deadly gas. Carbon monoxide binds to hemoglobin in animal blood — the compound that transports oxygen through the body. Even small amounts of it can cause the death of body cells due to lack of oxygen.

Carbon monoxide cannot accumulate on Earth because our hotter, brighter sun drives chemical reactions in the atmosphere that destroy it quickly. Although the team concluded recently that microbial biospheres may be able to thrive on a planet with abundant carbon monoxide, Schwieterman emphasized that “these would certainly not be good places for human or animal life as we know it on Earth.”

Scientists have confirmed nearly 4,000 planets orbiting stars other than the sun, but none of them will be possible to visit in person. They are simply too far away. Closest is Proxima Centauri b, which would take 54,400 years for current spacecraft to reach. Using telescopes to detect abundances of certain gases in their atmospheres is one of the only ways to study these so-called exoplanets.

“Our discoveries provide one way to decide which of these myriad planets we should observe in more detail,” said Christopher Reinhard, a former UCR graduate student now an assistant professor at the Georgia Institute of Technology, co-author of this study, and co-leader of the Alternative Earths team. “We could identify otherwise habitable planets with carbon dioxide or carbon monoxide levels that are likely too high to support complex life.”

Findings from the team’s previous work is already informing next-generation space missions such as NASA’s proposed Habitable Exoplanet Observatory. For example, because oxygen is essential to complex life on Earth and can be detected remotely, the team has been studying how common it may be in different planets’ atmospheres.

Other than Earth, no planet in our solar system hosts life that can be characterized from a distance. If life exists elsewhere in the solar system, Schwieterman explained, it is deep below a rocky or icy surface. So, exoplanets may be our best hope for finding habitable worlds more like our own.

“I think showing how rare and special our planet is only enhances the case for protecting it,” Schwieterman said. “As far as we know, Earth is the only planet in the universe that can sustain human life.”

In addition to Schwieterman, Lyons, and Reinhard, the paper’s authors are Stephanie Olson from the University of Chicago and Chester E. Harman from Columbia University. This project was funded by the NASA Astrobiology Institute.

Three planets orbiting TRAPPIST-1 fall within that star’s habitable zone. (Image courtesy of R. Hurt/ NASA/JPL-Caltech/)

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Atmospheric seasons could signal alien life

Anonymous — Thu, 03 Sep 2020 22:43:50 +0000

Atmospheric seasons could signal alien life Anonymous (not verified) Thu, 09/03/2020 - 15:43 More News Sarah Nightingale | UCR News May 09, 2018

Dozens of potentially habitable planets have been discovered outside our solar system, and many more are awaiting detection.

Is anybody — or anything — there?

Satellites monitor how ‘greenness’ changes with Earth’s seasons. (NASA)

The hunt for life in these places, which are impossible to visit in person, will begin with a search for biological products in their atmospheres. These atmospheric fingerprints of life, called biosignatures, will be detected using next-generation telescopes that measure the composition of gases surrounding planets that are light years away.

It’s a tricky business, since biosignatures based on single measurements of atmospheric gases could be misleading. To complement these markers, and thanks to funding from the NASA Astrobiology Institute, scientists at the University of California, Riverside’s Alternative Earths Astrobiology Center are developing the first quantitative framework for dynamic biosignatures based on seasonal changes in the Earth’s atmosphere.

Titled “Atmospheric Seasonality As An Exoplanet Biosignature,” a paper describing the research was published today in The Astrophysical Journal Letters. The lead author is Stephanie Olson, a graduate student in UCR’s Department of Earth Sciences.

As Earth orbits the sun, its tilted axis means different regions receive more rays at different times of the year. The most visible signs of this phenomenon are changes in the weather and length of the days, but atmospheric composition is also impacted. For example, in the Northern Hemisphere, which contains most of the world’s vegetation, plant growth in summer results in noticeably lower levels of carbon dioxide in the atmosphere. The reverse is true for oxygen.

“Atmospheric seasonality is a promising biosignature because it is biologically modulated on Earth and is likely to occur on other inhabited worlds,” Olson said. “Inferring life based on seasonality wouldn’t require a detailed understanding of alien biochemistry because it arises as a biological response to seasonal changes in the environment, rather than as a consequence of a specific biological activity that might be unique to the Earth.” Further, extremely elliptical orbits rather than axis tilt could yield seasonality on extrasolar planets, or exoplanets, expanding the range of possible targets.

In the paper, the researchers identify the opportunities and pitfalls associated with characterizing the seasonal formation and destruction of oxygen, carbon dioxide, methane, and their detection using an imaging technique called spectroscopy. They also modeled fluctuations of atmospheric oxygen on a life-bearing planet with low oxygen content, like that of Earth billions of years ago. They found that ozone (O₃), which is produced in the atmosphere through reactions involving oxygen gas (O₂) produced by life, would be a more easily measurable marker for the seasonal variability in oxygen than O₂itself on weakly oxygenated planets.

“It’s really important that we accurately model these kinds of scenarios now, so the space and ground-based telescopes of the future can be designed to identify the most promising biosignatures,” said Edward Schwieterman, a NASA Postdoctoral Program fellow at UCR. “In the case of ozone, we would need telescopes to include ultraviolet capabilities to easily detect it.”

Schwieterman said the challenge in searching for life is the ambiguity of data collected from so far away. False positives — nonbiological processes that masquerade as life — and false negatives — life on a planet that produces few or no biosignatures — are both major concerns.

“Both oxygen and methane are promising biosignatures, but there are ways they can be produced without life,” Schwieterman said.

Olson said observing seasonal changes in oxygen or methane would be more informative.

“A potentially powerful way to assess exoplanets for inhabitation would be to observe their atmospheres throughout their orbits to see if we can detect changes in these biosignature gases over the course of a year,” she said. “In some circumstances, such changes would be difficult to explain without life and may even allow us to make progress towards characterizing, rather than simply recognizing, life on an exoplanet.”

Timothy Lyons, a professor of biogeochemistry in UCR’s Department of Earth Science and director of the Alternative Earths Astrobiology Center, said this work advances the fundamental approach to searching for life on very distant planets.

“We are particularly excited about the prospect of characterizing oxygen fluctuations at the low levels we would expect to find on an early version of Earth,” Lyons said. “Seasonal variations as revealed by ozone would be most readily detectable on a planet like Earth was billions of years ago, when most life was still microscopic and ocean dwelling.”

In addition to Olson, Schwieterman, and Lyons, the paper’s authors are Andy Ridgwell and Stephen Kane from UC Riverside, Christopher Reinhard from the Georgia Institute of Technology, and Victoria Meadows from the University of Washington. The work is funded by the NASA Astrobiology Institute and the National Science Foundation (NSF) Frontiers in Earth System Dynamics (FESD).

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Scientists develop new method to detect oxygen on exoplanets

Anonymous — Sat, 01 Aug 2020 02:48:19 +0000

Scientists develop new method to detect oxygen on exoplanets Anonymous (not verified) Fri, 07/31/2020 - 19:48 More News Jules Bernstein | UCR News January 06, 2020

Scientists have developed a new method for detecting oxygen in exoplanet atmospheres that may accelerate the search for life.

One possible indication of life, or biosignature, is the presence of oxygen in an exoplanet’s atmosphere. Oxygen is generated by life on Earth when organisms such as plants, algae, and cyanobacteria use photosynthesis to convert sunlight into chemical energy.

UC Riverside helped develop the new technique, which will use NASA’s James Webb Space Telescope to detect a strong signal that oxygen molecules produce when they collide. This signal could help scientists distinguish between living and nonliving planets.

Since exoplanets, which orbit stars other than our sun, are so far away, scientists cannot look for signs of life by visiting these distant worlds. Instead, they must use a cutting-edge telescope like Webb to see what’s inside the atmospheres of exoplanets.

Conceptual image of water-bearing (left) and dry (right) exoplanets with oxygen-rich atmospheres. The red sphere is the M-dwarf star around which the exoplanets orbit. The dry exoplanet is closer to the star, so the star appears larger. (NASA/GSFC/Friedlander-Griswold)

“Before our work, oxygen at similar levels as on Earth was thought to be undetectable with Webb,” said Thomas Fauchez of NASA’s Goddard Space Flight Center and lead author of the study. “This oxygen signal is known since the early 1980s from Earth’s atmospheric studies but has never been studied for exoplanet research.”

UC Riverside astrobiologist Edward Schwieterman originally proposed a similar way of detecting high concentrations of oxygen from nonliving processes and was a member of the team that developed this technique. Their work was published today in the journal Nature Astronomy.

“Oxygen is one of the most exciting molecules to detect because of its link with life, but we don’t know if life is the only cause of oxygen in an atmosphere,” Schwieterman said. “This technique will allow us to find oxygen in planets both living and dead.”

When oxygen molecules collide with each other, they block parts of the infrared light spectrum from being seen by a telescope. By examining patterns in that light, they can determine the composition of the planet’s atmosphere. Schwieterman helped the NASA team calculate how much light would be blocked by these oxygen collisions.

Intriguingly, some researchers propose oxygen can also make an exoplanet appear to host life when it does not, because it can accumulate in a planet’s atmosphere without any life activity at all.

If an exoplanet is too close to its host star or receives too much star light, the atmosphere becomes very warm and saturated with water vapor from evaporating oceans. This water could then be broken down by strong ultraviolet radiation into atomic hydrogen and oxygen. Hydrogen, which is a light atom, escapes to space very easily, leaving the oxygen behind.

Over time, this process may cause entire oceans to be lost while building up a thick oxygen atmosphere — more even, than could be made by life. So, abundant oxygen in an exoplanet’s atmosphere may not necessarily mean abundant life but may instead indicate a history of water loss. Schwieterman cautions that astronomers are not yet sure how widespread this process may be on exoplanets.

“It is important to know whether and how much dead planets generate atmospheric oxygen, so that we can better recognize when a planet is alive or not,” he said.

Schwieterman is a visiting postdoctoral fellow at UCR who will soon start as assistant professor of astrobiology in the Department of Earth and Planetary Sciences.

The research received funding from Goddard’s Sellers Exoplanet Environments Collaboration, which is funded in part by the NASA Planetary Science Division’s Internal Scientist Funding Model. This project has also received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant, the NASA Astrobiology Institute Alternative Earths team, and the NExSS Virtual Planetary Laboratory.

Webb will be the world’s premier space science observatory when it launches in 2021. It will allow scientists to solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.

Bill Steigerwald and Nancy Jones of NASA Goddard Space Flight Center made significant contributions to this article.

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