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Early Earth as exoplanet: NASA highlights Virtual Planetary Laboratory research

Posted February 17, 2017

Recently published research from the University of Washington’s Virtual Planetary Laboratory (VPL) using ancient Earth as a stand-in for hypothetically habitable exoplanets has been highlighted by NASA in a feature article.

When haze built up in the atmosphere of Archean Earth, billions of years ago, the young planet might have looked like this artist’s interpretation – a pale orange dot. A team of astronomers including members of the UW’s Virtual Planetary Laboratory thinks the haze was self-limiting, cooling the surface by about 36 degrees Fahrenheit – not enough to cause runaway glaciation. The team’s modeling suggests that atmospheric haze might be helpful for identifying Earthlike exoplanets that could be habitable. Image credit: NASA’s Goddard Space Flight Center/Francis Reddy

Lead author on the research is Giada Arney, who was a UW 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 Astrophysical Journal; the other was published in November 2016 in Astrobiology.

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 the sun was about 20 percent fainter then.

UW 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: “Pale Orange Dot”: Early Earth’s haze may give clue to habitability elsewhere in space.”

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 UW astronomy professor Victoria Meadows, who is principal investigator for the VPL. Benjamin Charnay, a former UW doctoral student now at the Paris-Meudon Observatory, was co-author on one of the two papers, as was Guadalupe Tovar, a UW 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.”

Source: University of Washington

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