page_title: Kepler-69c
section_title: Proposed habitability
hierarchical_section_title: Kepler-69c / Proposed habitability
caption_attribution_description: English: This artist's concept shows a Super Venus planet on the left, and a Super Earth on the right. Researchers use a concept known as the habitable zone to distinguish between these two types of planets, which exist beyond our solar system. Super Venuses and Super Earths are similar to Venus and Earth, respectively, but larger in mass. Similar to our solar system's worlds, a Super Venus would most likely be a dry, toxic wasteland while a Super Earth might host oceans. The habitable zone is the region around a star where liquid water -- an essential ingredient for life as we know it -- can pool on the surface. Earth lies within the habitable zone around our star. A recent study looked at the planet Kepler-69c, discovered by NASA's Kepler mission and originally thought to lie in its star's habitable zone. The planet is 1.7 times the size of Earth and lies 2,700 light-years away. The analysis showed that this planet lies just outside the inner edge of the zone, making it more of a Super Venus than a Super Earth. That means the planet is not a tropical paradise, but more likely scorching hot, with volcanic eruptions. The search for planets as small as Earth, situated in the habitable zones of stars like our sun, is ongoing.
context_page_description: Kepler-69c is a confirmed super-Earth extrasolar planet, likely rocky, orbiting the Sun-like star Kepler-69, the outermost of two such planets discovered by NASA's Kepler spacecraft. It is located about 2,430 light-years from Earth.
context_section_description: The exoplanet, along with the exoplanets Kepler-62e and Kepler-62f, were announced in the media as being located within the star's "habitable zone", a region where liquid water could exist on the surface of the planet. It was described as being one of the most Earth-like planets, in terms of size and temperature yet found and, according to the scientists, a "prime candidate to host alien life".
  Due to uncertainties in the stellar parameters, the error bars on the value of the incident flux on this planet are quite large, at 1.91+0.43
  −0.56 times the level of Earth. Using the nominal parameters, the planet is too close to the star to be habitable, though the uncertainties allow for the possibility that it may actually lie in the innermost region of the habitable zone, however even with the lowest error bar measurement, a stellar flux of 1.35 S⊕ would still be high enough to boil away any oceans. A more recent analysis has shown that the planet is likely more analogous to Venus, which is known to be one of the most inhospitable places to life in the Solar System, and thus highly unlikely to be habitable to such organisms.
  The planet would be inhospitable because of a runaway greenhouse effect on its surface. Any oceans on its surface would've boiled away due to the high stellar flux, and as this occurred, the temperature would've risen to around 322 K (49 °C; 120 °F). The water vapor would've accumulated in the atmosphere to the point where the surface temperature would rise to around 500 K (227 °C; 440 °F) as the planet would've been overwhelmed by water vapor (it is a powerful greenhouse gas). Little amounts of carbon dioxide would've been present, as Kepler-69c was probably an ocean planet (with little to no landmasses) very shortly after its star was born into the main sequence, before the stellar flux increased to its estimated present value. The surface pressure would've also increased to around 100 times Earth's surface pressure (100 kilopascals, 100 atm.) because of the amount of water vapor in the atmosphere.
caption: Artist's conception of a comparison between a Venus-like and Earth-like planet. Based on recent research, Kepler-69c is more likely a super-Venus, analogous to Venus but more massive, and completely uninhabitable.
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