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Exoplanet found to have a water-cycle

10-1-2019

Mason Bennett, S&T Editor

Ever since the discovery of the first exoplanet (a planet that orbits a solar system other than our own) in the 1990s, astronomers have made steady progress towards finding and probing planets located in the habitable zone of their stars, where conditions can lead to the formation of liquid water and eventually life. The Kepler satellite mission—which has discovered most known exoplanets to date—so far suggests that 5 to 20 percent of planets are located in the habitable zone of their stars. However, despite this large amount of habitable planets, properly analyzing the living conditions and atmospheric properties on any of these planets has been extremely difficult and the process remained elusive—up until recently.

Reports from the Kepler satellite detected the presence of water vapour and potentially even liquid water clouds in the atmosphere on a planet discovered in 2016 named K2-18b. This exoplanet is about nine times larger than Earth and is in fact found in the habitable zone of the star it orbits. The star it orbits is smaller and cooler than our Sun, but due to K2-18b's close proximity to its star, the planet receives almost the same total amount of energy from its star as our Earth receives from the Sun. There are more similarities between this exoplanet and Earth as well. Astronomers believe that that K2-18b may potentially have a water cycle, allowing water to condense into clouds and liquid water rain to fall. This observation was made by combining eight transit observations (the exact moment when an exoplanet passes in front of the star it orbits) taken by the Hubble Space Telescope.

Unfortunately, no life has been discovered as of yet on K2-18b. Scientists believe that the thick gaseous envelope of surrounding the exoplanet is most likely preventing life from existing on its surface. However, this recent discovery of a potential active water cycle shows that even these planets of relatively low mass—which are therefore more difficult to study—can be explored using astronomical instruments developed in recent years. This significantly opens opportunities for astrologists going forward, as there are multiple exoplanets orbiting foreign stars that have been overlooked due to our lack of this technology. Now, by studying these planets which are in the habitable zone of their star and have the right conditions for liquid water, astronomers are one step closer to directly detecting signs of life beyond our Solar System.

This discovery of a potential active water cycle on planet K2-18b is by far the largest step taken yet towards humanities ultimate goal of finding life on other planets, ultimately proving that our experience as living beings is not a unique one. Finally, thanks to these observations and a fully developed climate model of this planet, researchers have shown that water vapour can in fact condense into liquid water. This is a first not only for space exploration enthusiasts, but for the future of man-kind.