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. The critical point for carbon dioxide is about 88 degrees Fahrenheit (31 degrees Celsius) and about 73 times Earth's atmospheric pressure at sea level. This is about equal in pressure to that found nearly a half-mile (0.8 kilometers) under the ocean's surface. Supercritical carbon dioxide is increasingly used in a variety of applications, such as decaffeinating coffee beans and dry cleaning. Ordinarily, carbon dioxide is not considered a viable solvent to host the chemical reactions for life, but the properties of supercritical fluids can differ quite significantly from the regular versions of those fluids — for instance, while regular water is not acid, supercritical water is acidic. Given how substantially different supercritical carbon dioxide is from regular carbon dioxide in terms of physical and chemical properties, scientists explored whether it could be suitable for life. Full story via Space.com.
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