NASA’s Alien Planet Hunters Rethink Habitability –“Water and Oxygen Not the Only Factors”




“Planets can be habitable and not have life with any impact,” Arizona State astrophysicist Steve Desch told researchers at a recent workshop in Laramie, Wyoming on "Habitable Worlds" run by The Nexus for Exoplanet System Science, a NASA research network dedicated to the study of planetary habitability.

The search for exoplanets is at a watershed moment in finding life on other worlds, propelled by the discoveries of habitable zone terrestrial planets in both ground and space-based surveys, and the potential for future telescopes such as the James Webb Space Telescope to characterize the atmospheres of some of these rocky planets.


Preparing for such an epic historic moment needs a diverse community of Earth scientists, heliophysicists, planetary scientists, and astrophysicists asking what does it mean to be habitable? What conditions are needed for habitability and how do those conditions arise? What are the indicators of these conditions and their histories? How can we observe these indicators.



Steve Desch observed that astronomers use NASA’s upcoming James Webb Space Telescope to probe the atmosphere of an Earth-mass world for signs of life chase hints of atmospheric oxygen for years—before realizing that they were false positives produced by geological activity instead of living things.

Desch and his fellow attendees argued that the standard definition of habitability—having liquid water on a planet’s surface should not the factor that should guide exoplanet exploration. Instead, the scientists say, the field should focus on the chances of detecting alien life, should it exist. “Planets can be habitable and not have life with any impact,” Desch told researchers at the meeting.

One study presented at the meeting that we posted today on The Daily Galaxy shows how a planet covered in oceans could be starved of phosphorus, a nutrient without which earthly life cannot thrive. Other research concluded that a water-world planet could be geologically dead, lacking any of the planetary processes that nurture life on Earth.

"Research on early Earth's environments increases our chance of success by revealing processes and planetary properties that guide our search for life on nearby exoplanets," says Victoria Meadows, University of Washington astronomy professor and principal investigator for the NASA Astrobiology Institute's Virtual Planetary Laboratory.

The amount of biomass – life – in Earth's ancient oceans may have been limited due to low recycling of the key nutrient phosphorus, according to this new research by the University of Washington and the University of St. Andrews in Scotland. The research also probes the role of volcanism in supporting Earth's early biosphere — and may apply to the search for life on other worlds.

“Habitability is not only about finding the signature of an alien life form taking a deep breath,” said Elizabeth Tasker, an astronomer and exoplanet researcher at the Japan Aerospace Exploration Agency's Institute for Space and Aeronautical Sciences in Sagamihara. It’s also about how a planet’s geology and chemistry interconnect to create a welcoming or hostile environment, complicating the search for extraterrestrial life.

“We have this stereotype that if we have oceans, we have life,” says Tessa Fisher, a microbial ecologist at Arizona State. But her recent work contradicts this idea. Fisher and her colleagues studied what would happen on an “aqua planet” with a surface that is almost or completely covered by enough water to fill Earth’s oceans five times.

“We need to look carefully at picking the right planet,” Tasker says.

Towards the end of the Laramie meeting, attendees voted on whether scientists will find evidence of life on an exoplanet by 2040: 47 said no and 29 said yes. The larger share was willing to bet that life would be found on another world in the 2050s or 2060s.

Image credit: MIT

The Daily Galaxy via NatureScientific AmericanUSRA,  and Early Earth's Ancient Oceans –"A Guide to the Impact of Marine Biospheres on Alien Planets"





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