University of Washington scientists build virtual lifeless Earth for exoplanet research

Researchers at the University of Washington created a virtual Earth without life and published the model Sept. 18 in The Planetary Science Journal, establishing a baseline for distinguishing habitable exoplanets from inhabited ones.

The study is titled “A Whole-planet Model of the Earth without Life for Terrestrial Exoplanet Studies.” The work came out of University of Washington research meant to prepare scientists for observations by future telescopes such as the Habitable Worlds Observatory.

More than 6,000 planets beyond our solar system are now cataloged, and Earth remains the only known inhabited world. Researchers want to identify atmospheres that can only be explained by life’s influence, but Earth is the only template they have.

Astrobiologists consider surface liquid water backed by a heat-trapping atmosphere the main factor in judging whether a planet can host life as we know it. This definition appears early in the discussion of why astronomers focus on Earth-like atmospheres in the hunt for life. Teams are examining the atmospheres of leading exoplanet candidates for compounds that could be produced by life. Scientists need to identify which atmospheric conditions can be explained without life so they can recognize atmospheres that can only be explained by life’s influence.

Samantha Gilbert-Janizek carried out the work while a doctoral student in astronomy at the University of Washington and now holds a postdoctoral fellowship at UC Riverside. Rory Barnes, an associate professor of astronomy at the University of Washington, led the lab that constructed an earlier model of Earth’s core, mantle, crust and stellar radiation without a surface or atmosphere. She extended that earlier framework by incorporating surface and atmosphere to complete the picture of chemical cycles. Gilbert-Janizek stands as the lead scientist for the abiotic Earth model presented in the journal article.

The model covers 5 billion years, beginning with Earth’s formation 4.5 billion years ago and extending roughly 500 million years beyond the present. The coupled interior-atmosphere evolution model of a lifeless Earth runs from 50 Myr to 5 Gyr; Myr means millions of years and Gyr means billions. That span lets the model track how geochemical systems change without biology across most of planetary history, and its results include observable traits such as surface temperature, albedo and atmospheric water and carbon dioxide. Researchers call the model a first step toward dividing inhabited worlds from merely habitable ones.

The model follows chemical exchange among the core, mantle, crust, surface and atmosphere. It purposely leaves out biological influence so researchers can observe the atmospheric conditions that geology alone creates. The simulation accurately forecast 19 planetary properties, among them heat flow through the mantle.

At 4.5 Gyr, the model aligns with 19 key preindustrial Earth observations within estimated uncertainty. The comparison covers atmospheric carbon dioxide and water vapor, surface temperature and how much light the planet reflects, ocean mass, upper-mantle temperature and upper-mantle heat flow. These factors that are not biological shape a planet’s atmosphere and must be considered when reading exoplanet data.

The group created synthetic Habitable Worlds Observatory reflected-light spectra from 0.2 to 2.0 micrometers for the real Earth and the lifeless Earth after 4.5 Gyr, with line absorptions for carbon dioxide, water, oxygen, ozone and methane. Habitable Worlds Observatory is expected to look at Earth-like planets around Sun-like stars through reflected-light spectroscopy. “This model can help us see how habitable but non-living planets might mimic living planets,” lead author Gilbert-Janizek said.

The model starts up after Earth’s magma ocean solidified, an event that set the atmosphere’s initial composition based on conditions once most of the mantle had solidified. This startup step is one of the assumptions built into the model. The authors assumed plate tectonics operated throughout Earth’s history starting in the middle Hadean, even though other ideas say it began in the Archaean, and this assumption is widely believed and matches the available evidence. They also made assumptions about atmospheric pressure, Earth’s geodynamo strength and hydrogen leaving the atmosphere, and these assumptions are normal in science and explained up front.

Researchers can enter basic details of a rocky exoplanet into the model and run it to see whether the observed atmosphere can be reproduced without life. If the model cannot match the atmosphere, the planet becomes more interesting and draws closer study. This process offers a method to flag atmospheres that might need a biological explanation. Scientists are studying the atmospheres of top exoplanet candidates for compounds that could come from life.

The authors hope the model serves as a plug-and-play tool where researchers enter albedo and atmospheric carbon dioxide to check whether recreating observations indicates an exoplanet is uninhabited. The writers suggest this after describing the model’s added surface and atmosphere parts and before listing the study’s assumptions.

On Earth, plants and animals emit steady streams of oxygen and methane, and these gases destroy each other when they mix, leading an alien astronomer to conclude life is replenishing both. This case demonstrates how living processes can create atmospheric disequilibrium that is hard to account for through nonliving means. The comparison gives researchers a concrete case of how living chemistry can alter a planet’s air.

The model predicts a planet can keep habitable conditions for a long stretch without life, and this matters because false positives challenge the Habitable Worlds Observatory. This forecast helps researchers judge whether an observed atmosphere might be abiotic instead of biological.

The Habitable Worlds Observatory will move exoplanet science from finding potentially habitable worlds to finding atmospheres that show signs of life. Planned telescopes such as the Habitable Worlds Observatory will hunt for signs of life on rocky planets around Sun-like stars using reflected-light spectroscopy, a technique that studies light bouncing off a planet.

Earth is the only known inhabited planet in the universe, and geological evidence shows liquid-water oceans made it habitable for most of its 4.54 Gyr history. Since Earth is the only inhabited world we know, it serves as the template guiding the search for biospheres elsewhere.

The first 6,000 exoplanet discoveries came as bulk finds, while the search is turning more toward Earth-like planets. This observation links the growing need for tools like the new model to the changing nature of exoplanet discovery. The upcoming Habitable Worlds Observatory, if it gets built, brings the shift toward targeting Earth-like planets into sharper focus.

NASA funded the research. Gilbert-Janizek says the improved model can also help guide the design of future telescopes built to study distant planets, including the proposed Habitable Worlds Observatory.

The paper’s DOI is 10.3847/psj/ae9d79. “Realizing the ambitious goals of a telescope like the Habitable Worlds Observatory requires decades of work across many generations of scientists,” Gilbert-Janizek said. The citation lists The Planetary Science Journal, 2026 and the DOI after describing the study and its authors.