Simulated Lifeless Earth Gives Alien Hunters a Baseline for Distant Worlds

Scientists have built a computer model that shows how a rocky planet, including Earth, would evolve if life never appeared on it. According to Space.com, the tool is meant to help astronomers judge whether the gases in a distant planet's atmosphere really signal life or can be explained by non-living processes alone.

The model was developed by planetary scientist Samantha Gilbert-Janizek of the University of California, Riverside, who was a PhD student at the University of Washington when the research was done. It is described in a paper published in The Planetary Science Journal.

Why telling "habitable" from "inhabited" is hard

Life changes a planet's atmosphere through a mixture of gases produced by biochemistry. Some of these are obvious signs, Space.com reported, but others can be produced by both biology and geology. That makes it difficult to say from atmospheric gases alone whether a planet is merely habitable or actually inhabited.

The key, according to the report, is knowing which atmospheric conditions can be explained without life.

How the lifeless-planet model works

Gilbert-Janizek built on an earlier model by Rory Barnes of the University of Washington, which simulated a planet's core, mantle and crust. Her version adds the planet's surface and atmosphere as well.

In all, the model tracks 19 properties of a rocky planet that are unrelated to life. They include the 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 below the surface.

As a first test, Gilbert-Janizek simulated an Earth on which life never arose, creating a baseline for comparison with planets beyond the solar system. The run covered the period from Earth's birth 4.5 billion years ago to 500 million years into the future. The result, Space.com said, was a lifeless world that still had oceans and an atmosphere.

Why it matters for the search for alien life

The model is designed to be plug-and-play. Researchers can enter the bulk properties of a planet they are studying and let the simulation run, Space.com reported. If the simulated lifeless planet has an atmosphere matching what telescopes detect, the real planet probably does not have life as we know it. Instruments named in the report include the James Webb Space Telescope, future ground-based telescopes with mirrors of more than 30 meters, and NASA's planned Habitable Worlds Observatory.

If the simulated planet does not match the observations, life may be present and altering the atmosphere. A mismatch would not prove life exists, the report noted, but it could help single out worlds worth follow-up study by the next generation of telescopes.

Gilbert-Janizek said in a statement that the tool will help estimate the probability that an observed atmosphere indicates life on the surface. She also said it can show how habitable but non-living planets might mimic living ones.

What the researchers say about confidence in the model

Barnes said the work is an exciting step toward understanding where life can exist in the universe. He said that after more than a decade of work by many scientists, the model now reproduces properties of Earth's core, mantle, surface and atmosphere at the same time. In his view, that calibration gives confidence that future simulations of exoplanets will be accurate.

For now, the model is a tool for ranking targets rather than a life detector. It does not identify living worlds itself; it narrows the list of planets that deserve closer observation.

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Around Prague, based on reporting by Space.com