UW researchers build lifeless virtual Earth to guide exoplanet searches

University of Washington researchers created a digital Earth that leaves out biology, aiming to set a planetary baseline for studying exoplanet atmospheres, in work that appeared in The Planetary Science Journal on Sept. 18.

The catalog of worlds beyond our solar system now includes more than 6,000 planets, and scientists are studying the air of the most promising known worlds for chemicals that life could produce. Astronomers hope to find clear evidence of life in the atmosphere of a distant planet. Astrobiologists give priority to Earth-like atmospheres that retain enough heat for liquid surface water because scientists view liquid water as the key factor for life as we know it, with heat retention and atmospheric chemistry defining habitability in this framing and liquid water serving as the central marker for potential biology on distant worlds. The aim is to distinguish habitable planets from inhabited ones by finding atmospheric conditions that biology alone can explain, which is the research goal of finding atmospheres that geology alone cannot explain and would point toward biological influence.

Samantha Gilbert-Janizek led the work while a doctoral student in astronomy at the University of Washington and now works as a postdoctoral fellow at UC Riverside. Rory Barnes, an associate professor of astronomy at the University of Washington, is the senior author, and his lab created the earlier model.

The older code treated the planet’s interior and incoming starlight but omitted the boundary layers where gases accumulate.

The model ran for 5 billion years, starting at Earth’s formation 4.5 billion years ago and extending about 500 million years ahead. That run time stretches from planetary formation to the distant future, letting scientists track long-term geochemical change without biology. The software tracked chemicals as they moved between the core, mantle, crust, atmosphere and surface over time, linking interior reservoirs to the surface and air to capture how volatiles and heat move across geological history. The researchers purposely excluded the effect of life on Earth’s geochemical systems, removing biology to create a lifeless reference that astronomers can use to compare with actual exoplanet observations.

The model matched 19 observed planetary properties, including the movement of heat through the mantle. Matching these observed Earth properties shows the code represents real planetary physics and chemistry. Once calibrated to Earth, the model can forecast how atmospheres change on any rocky planet, allowing researchers to change basic planetary inputs to simulate other rocky worlds and test possible atmospheric histories.

Differences between a real observed atmosphere and the lifeless model can help identify possible evidence of life. When geology alone fails to reproduce detected chemistry, the planet rises in priority for biological study. The simulation acts as a filter: matching worlds are lower priority, while mismatches warrant closer inspection.

Heat and gases from a planet’s interior and from its star are nonbiological forces that shape its atmosphere, because stellar irradiation and internal heat drive atmospheric chemistry without biology, so scientists must model both to avoid mistaking geology for biology. Scientists can enter basic details about a rocky exoplanet into the model and check whether geology by itself matches its observed atmosphere. The model can lower the chance of mistaking geological activity for signs of alien life.

If the simulation fails to match an observed atmosphere, the planet could become a more interesting target for investigation. Interactions among a planet’s interior, surface and air can create gases that resemble biological byproducts, meaning geological processes alone can produce life-linked gases. Some atmospheres may hold gases associated with life even when geological exchanges among the interior, surface and atmosphere produced them.

Plants and animals on Earth release steady flows of oxygen and methane into the air. Biology continually replaces these gases, which would otherwise vanish through chemical reactions, since oxygen and methane react with each other and disappear when they meet, so their coexistence implies an active source is maintaining both supplies. An alien astronomer looking at Earth might suspect something alive is replacing both gases.

The simultaneous presence of reactive gases in Earth’s air could look like evidence of life to distant observers. Finding a potentially habitable planet does not prove that life exists there, which is why a lifeless Earth model serves as a comparison baseline.

Gilbert-Janizek said the model shows that planets without life can still appear habitable, explaining that the tool estimates the likelihood that an observed exoplanet atmosphere indicates surface biology. She also said the tool helps determine the probability that an observed exoplanet atmosphere points to life on the surface, connecting simulation output directly to the interpretation of future telescope spectra from distant worlds.

Barnes said Gilbert-Janizek finished an Earth model that at the same time matches properties of the core, mantle, surface and atmosphere following more than a decade of work. He described the result as a calibration milestone that improves confidence in future exoplanet simulations. Barnes said the calibration means scientists can trust future simulations of exoplanets to be accurate.

Gilbert-Janizek said the model can help inform the design of future telescopes such as the proposed Habitable Worlds Observatory. She said achieving the goals of a telescope like the Habitable Worlds Observatory will take decades of work by many generations of scientists, framing the research as part of a long, multi-generational effort to answer whether humanity is alone in the universe. NASA’s proposed Habitable Worlds Observatory aims to study potentially habitable planets orbiting other stars.

Other University of Washington co-authors are Jessica Birky, now a postdoctoral researcher at the University of Oklahoma, and Rodolfo Garcia, now a high school teacher in the Seattle area. Both are former University of Washington astronomy doctoral students who contributed to the paper. NASA paid for the research, and UW News and Mirage News identify NASA as the project’s funding source. The full list of co-authors appears with the study, and UW News and Mirage News note that the complete author roster appears in the published paper.

Interesting Engineering reports that the paper does not point to an inhabited exoplanet or detect life beyond Earth, stressing that the paper offers an interpretive tool rather than a discovery of biology beyond Earth. The article’s DOI is 10.3847/psj/ae9d79, and Phys.org provides the digital object identifier for the September 2026 Planetary Science Journal article, which uses a lifeless Earth simulation as a reference point for studying terrestrial exoplanets. The paper is titled “A Whole-planet Model of the Earth without Life for Terrestrial Exoplanet Studies” and appeared in The Planetary Science Journal in 2026.