Scientists simulate an Earth without life to help hunt for aliens and inhabited worlds

A new computer simulation that depicts Earth, or a rocky planet in general, without life is the latest tool in the quest to discover whether or not we are alone in the universe.Life leaves its mark on a planet, particularly its atmosphere, in the form of a mixture of biochemically created gases. Some are obvious, while others can be produced by both biology and geology, meaning that distinguishing a planet that has life from one that does not, solely based on what gases we can detect in its atmosphere, can be difficult. The key is in knowing which atmospheric conditions can be explained without life.To aid in distinguishing between habitable and inhabited planets, planetary scientist Samantha Gilbert-Janizek of the University of California, Riverside, developed a model that simulates the evolution of a rocky planet without life."The model can help us see how habitable but non-living planets might mimic living planets," Gilbert-Janizek, who was a PhD student at the University of Washington when the research was conducted, said in a statement. Gilbert-Janizek built upon a model previously developed by Washington’s Rory Barnes that simulated the core, mantle, and crust of a planet. This new model pushed the simulation two steps further by incorporating the surface and atmosphere of the planet as well. In all, the model simulates 19 properties of a rocky planet that are not related to life, including the amount of heat a planet receives from its star, the exchange of heat and chemicals from the core to the surface, and the outflow of certain gases from the subsurface.Gilbert-Janizek’s starting point was to simulate the development of Earth had life never arisen here, therefore providing a baseline with which to compare to exoplanets. She ran the simulation from the birth of Earth 4.5 billion years ago to 500 million years into the future. The result was a lifeless world, but one that still had oceans and an atmosphere."When we interpret observations of an exoplanet’s atmosphere, this tool will help us determine the probability that what we observe indicates life on the surface," said Gilbert-Janizek.An illustration shows the landscape of a primordial Earth before life arose as lightning splits the skies (Image credit: Robert Lea (created with Canva))What makes the simulation especially useful is its plug-and-play nature. Researchers can simply apply the bulk properties of whichever planet they are studying to the model, and then just let it run. If the result is a planet with an atmosphere that matches what is detected spectroscopically by the James Webb Space Telescope or, in the future, the various extremely large 30-meter-plus ground-based telescopes or NASA’s planned Habitable Worlds Observatory, then we know that planet probably does not have life as we know it. However, if the simulated planet without life does not match what we observe on the real planet, then it becomes possible that life is present and altering the atmosphere."Dr Gilbert-Janizek’s work represents an exciting step toward understanding where life can exist in the universe,” said Barnes. "After more than a decade of work by many scientists, Dr Gilbert-Janizek has finally completed a model of the Earth that simultaneously reproduces properties of Earth’s core, mantle, surface and atmosphere. That calibration gives us confidence that future simulations of exoplanets will be accurate."While any deviation from what is predicted by the model will not necessarily mean there is definitely life on a planet, it will help pick out those worlds that are worthy of follow-up studies by the next generation of telescopes.Gilbert-Janizek’s model is described in a paper published in The Planetary Science Journal.