Alien life might flourish on an exotic kind of carbon dioxide, researchers say. This "supercritical" carbon dioxide, which has features of both liquids and gases, could be key to extraterrestrial organisms much as water is to biology on Earth.

Most familiar as a greenhouse gas that traps heat, helping warm the planet, carbon dioxide is exhaled by animals and used by plants in photosynthesis. While it can exist as a solid, liquid and gas, past a critical point of combined temperature and pressure, carbon dioxide can enter a "supercritical" state. Such a supercritical fluid has properties of both liquids and gases. For example, it can dissolve materials like a liquid, but flow like a gas.

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