New research shows that dry, desert-like planets outside our solar system are probably poor candidates for life. Scientists estimate there are billions of planets beyond the solar system, and more than 6,000 exoplanets are confirmed. The study focuses on Earth-sized worlds and how much surface water they need to stay habitable.
The authors find an Earth-sized planet needs at least 20 to 50% of the water in Earth’s oceans to maintain a key geologic carbon cycle. In that cycle, carbon dioxide from volcanoes enters the atmosphere, returns to the surface in rain, weathers rocks, and is carried to the deep interior by plate tectonics before coming back through volcanism. Without enough water, carbon builds up, the climate warms, and surface water can evaporate away.
The team used complex simulations and adjusted models for drier conditions. They point to Venus as an example and say future missions to Venus could test the models.
Difficult words
- exoplanet — planet that orbits a star outside our solar systemexoplanets
- habitable — able to support living organisms on the surface
- geologic — related to rocks, Earth's long-term changes and layers
- carbon cycle — process moving carbon between air, land, and interior
- volcanism — movement of magma and gases to the surface
- plate tectonics — movement of large Earth plates on the mantle
- evaporate — change from liquid to gas because of heat
- simulation — computer model that imitates real systems or processessimulations
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Discussion questions
- How important do you think surface water is for life on a planet? Give one or two reasons.
- Do you agree that missions to Venus could help test models about dry planets? Why or why not?
- If scientists find an Earth-sized planet with little water, would you want to study it? Explain briefly.
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