Currently, Earth is the only known planet (or moon) to have consistent, stable bodies of liquid water on its surface. In our solar system, Earth orbits around the sun in an area called the habitable zone. The temperature, along with an ample amount of atmospheric pressure within this zone, allows water to be liquid for long periods of time.
Evidence points to water on other planets in our solar system. In 2015, NASA confirmed that liquid water flows intermittently on present-day Mars. Also in 2015, scientists used data from NASA's Cassini mission to discover that a global ocean lies beneath the icy crust of Saturn's moon Enceladus. Scientists believe that Jupiter's moon Europa has a subsurface ocean as well.
Finding liquid water beyond our solar system may indicate the existence of extraterrestrial life. Using data collected by NASA's Kepler spacecraft and the W.M. Keck Observatory, scientists have determined that 22 percent of solar-type stars in our galaxy have Earth-sized planets in their habitable zone and could host life. Some of these planets are a mere 12 light years away and can be seen with the naked eye in the night's sky.
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NASA Hubble Space Telescope recently spotted what may be plumes of water vapor spouting from a possible subsurface ocean on Europa.