Scientists have created a model of a lifeless Earth to search for life on exoplanets

The search for life beyond Earth requires not only the discovery of planets with suitable conditions, but also an understanding of what natural processes can create similar biological features. The atmosphere of a distant world may contain water and carbon dioxide, but this does not mean that there are living organisms on it. To interpret the observations more accurately, the scientists created a computer model of the Earth, which completely excluded the influence of life. How it will help to search for inhabited worlds and distinguish them from inhabited planets is described in the Izvestia article.

A land without a biosphere

Researchers from the University of Washington have developed a comprehensive computer model of the Earth that describes its evolution without the involvement of living organisms. The work was published in The Planetary Science Journal (PSJ). The model covers the period from 50 million years after the planet's formation to the 5 billion year mark and reproduces 19 key characteristics of the pre-industrial Earth after 4.5 billion years of evolution.

In the calculations, scientists combined the processes occurring in the core, mantle, Earth's crust, on the surface and in the atmosphere. The model takes into account the exchange of chemicals between these parts of the planet, as well as the influence of solar radiation. Among the characteristics that have been reproduced are the content of carbon dioxide and water vapor in the atmosphere, surface temperature, the reflectivity of the planet, the mass of the oceans and the temperature of the upper mantle.

The previously existing model already described the internal structure of the Earth and the influence of stellar radiation, but did not take into account the surface and atmosphere in full. The new work combined these components and allowed us to trace how geological processes affect conditions on the planet's surface.

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When a planet looks like it's alive

One of the main difficulties in the search for extraterrestrial life is to distinguish between inhabited and inhabited worlds. The former have conditions potentially suitable for the existence of organisms, such as liquid water and a suitable temperature. The latter should have signs of biological processes.

At the same time, some characteristics of the atmosphere may arise without the involvement of life. On Earth, for example, geological processes affect the gas content in the atmosphere, and the interaction of the surface and subsurface determines climatic conditions. Therefore, the detection of individual substances on an exoplanet does not in itself prove the existence of organisms there.

What traces does a lifeless planet leave?

The researchers also calculated what the spectrum of reflected light from a lifeless Earth would look like. To do this, they modeled the wavelength range from 0.2 to 2 microns — it is in this area that observations are expected to be carried out using the future Habitable Worlds Observatory (HWO).

The calculations took into account the spectral characteristics of carbon dioxide, water vapor, oxygen, ozone and methane. This is important because some of these substances are considered by astronomers as potential biosignatures — signs that may indicate the existence of living organisms. However, their presence must be assessed in the context of other characteristics of the planet and possible non-biological sources.

The resulting spectrum can become a reference for comparison with observations of real exoplanets. If the atmospheric characteristics of a distant world can be explained by geological and physical processes without the involvement of biology, this will reduce the likelihood that the detected signals are related to life. If the model cannot reproduce the observed pattern, the planet will become a more interesting object for further study.

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The next step is other planets.

Scientists expect to adapt the model to specific exoplanets. To do this, researchers will be able to set the initial parameters of the studied world, including the characteristics of the atmosphere and the reflectivity of the surface, and then check whether the observations can be explained without biological processes.

Such work may be useful in the preparation of the future HWO observatory. The NASA project involves the creation of a space telescope to study Earth-like planets around stars similar to the Sun. One of its tasks will be to search for atmospheric signs that may indicate the existence of life.

However, the model has limitations: It is based on a number of assumptions about the early history of the Earth, including the development of plate tectonics and the composition of the atmosphere. In addition, the successful reproduction of the characteristics of a lifeless planet does not definitively prove the absence of organisms. To search for life, it will be necessary to compare the simulation results with observations and take into account other possible explanations for atmospheric signals.