Recently published research from the 91̽»¨’s (VPL) using ancient Earth as a stand-in for hypothetically habitable exoplanets has been highlighted by NASA in .

Lead author on the research is , who was a 91̽»¨astronomy doctoral student when doing the work and is now with NASA’s Goddard Spaceflight Center in Greenbelt, Maryland. One was published Feb. 8 in the ; the other was published in November 2016 in .

For astronomers looking for signs of life in the atmospheres of exoplanets, NASA’s article says, “the role of atmospheric haze has been hazy.” These researchers looked to the atmosphere of Earth during the Archean Era — a geological era 4 to 2.5 billion years ago — to better understand the role of atmospheric haze and its possible relation to life.

The authors set out best- and worst-case scenarios for haze on a faraway planet. The best case is that such haze could provide “a smorgasbord of carbon-rich, or organic, molecules that could be transformed by chemical reactions into precursor molecules for life” — and the haze might even help block harmful ultraviolet radiation that can break down DNA.

On the downside, however, such haze could get so thick it blocks a significant fraction of the light, leaving the planet beneath much colder. This, they write, could have had “a profound effect” on early Earth because .

91̽»¨News wrote about the research when Arney and others presented findings to the American Astronomical Society’s Division of Planetary Sciences conference in November 2015. Read the article: “.”

Arney has many co-authors on the two papers. UW-related co-authors for both are Edward Schwieterman, now at the University of California, and 91̽»¨astronomy professor , who is principal investigator for the VPL. , a former 91̽»¨doctoral student now at the Paris-Meudon Observatory, was co-author on one of the two papers, as was Guadalupe Tovar, a 91̽»¨undergraduate student in astronomy.

Other co-authors are Shawn Domagal-Goldman, Melissa Trainer and Drake Deming of NASA’s Goddard Center; Mark Claire of the University of St. Andrews in Scotland; Eric Wolf of the University of Colorado, Boulder and Eric Hébrard of the University of Exeter, UK.

Domagal-Goldman, who is also a VPL affiliate, said, “Our modeling suggests that a planet like hazy Archean Earth orbiting a star like the young sun would be cold. But we’re saying it would be cold like the Yukon in winter, not cold like modern-day Mars.”

Arney added, “We like to say that Archean Earth is the most alien planet we have geochemical data for.”

Read the NASA feature story on the two papers: .

The research was funded by the .

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For more information about this research contact Arney at giada.n.arney@nasa.gov or Meadows at vsm@astro.washington.edu.

Is it life, or merely the illusion of life?

Research from the 91̽»¨-based published Feb. 26 in Astrophysical Journal Letters will help astronomers better identify — and thus rule out — “false positives” in the search for life beyond Earth.

Powerful devices such as the , set for launch in 2018, may help astronomers look for life on a handful of faraway worlds by searching for, among other things, evidence of oxygen — a “biosignature” — in their atmospheres. This is done by transit spectroscopy, or studying the spectral features of light visible through a planet’s atmosphere when it transits or passes in front of its host star.

“We wanted to determine if there was something we could observe that gave away these ‘false positive’ cases among exoplanets,” said lead author , a doctoral student in astronomy. “We call them ‘biosignature impostors’ in the .

“The potential discovery of life beyond our solar system is of such a huge magnitude and consequence, we really need to be sure we’ve got it right — that when we interpret the light from these exoplanets we know exactly what we’re looking for, and what could fool us.”

Here on Earth, oxygen is produced almost exclusively by photosynthesis — plants and algae converting the sun’s rays into energy to sustain life. And so Earth’s oxygen biosignature is indeed evidence of life. But that may not be universally true.

from the Virtual Planetary Laboratory has found that some worlds can create oxygen “abiotically,” or by nonliving means. This is more likely in the case of planets orbiting low-mass stars, which are smaller and dimmer than our sun and the most common in the universe.

The first abiotic method they identified results when the star’s ultraviolet light splits apart carbon dioxide (CO₂) molecules, freeing some of the oxygen atoms to form into O_2, the kind of oxygen present in Earth’s atmosphere.

The giveaway that this particular oxygen biosignature might not indicate life came when the researchers, through computer modeling, found that the process produces not only oxygen but also significant and potentially detectable amounts of carbon monoxide. “So if we saw carbon dioxide and carbon monoxide together in the atmosphere of a rocky planet, we would know to be very suspicious that future oxygen detections would mean life,” Schwieterman said.

The team also found an indicator for abiotic oxygen resulting from starlight similarly breaking down atmospheric water, H₂O, allowing hydrogen to escape and leaving vast quantities of oxygen — far more than the Earth has ever had in its atmosphere.

In such cases, Schwieterman said, oxygen molecules collide with each other frequently, producing short-lived pairs of oxygen molecules that become O₄ molecules, with their own unique signature.

“Certain O₄ features are potentially detectable in transit spectroscopy, and many more could be seen in reflected light,” Schwieterman said. “Seeing a large O₄ signature could tip you off that this atmosphere has far too much oxygen to be biologically produced.”

“With these strategies in hand, we can more quickly move on to more promising targets that may have true oxygen biosignatures,” he said.

“It’s one thing to detect a biosignature gas, but another thing to be able to interpret what you are looking at, said , 91̽»¨professor of astronomy and principal investigator of the Virtual Planetary Laboratory. “This research is important because biosignature impostors may be more common for planets orbiting low-mass stars, which will be the first places we look for life outside our solar system in the coming decade.”

Schwieterman’s other 91̽»¨co-authors are astronomy professor and doctoral students and .

Other co-authors are Shawn Domagal-Goldman of the NASA Goddard Space Flight Center in Greenbelt, Maryland; Drake Deming of the University of Maryland; and Chester Harman of Pennsylvania State’s Center for Exoplanets and Habitable Worlds.

The research was funded by the NASA Astrobiology Institute.

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For more information, contact Schwieterman at 321-505-1605 or eschwiet@uw.edu. Follow him on Twitter at @nogreenstars.

Cooperative agreement # NNA13AA93A.