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Extraterrestrial liquid water in the Solar System is likely uncommon, although it has been hypothesized to exist in some of its moons, and to have formerly existed on Mars and Venus.[2][3] Extrasolar liquid water has not yet been confirmed to exist. The following list contains candidates that meet the following criteria:
- Confirmed object of Earth mass or greater[a] orbiting within a circumstellar habitable zone (CHZ)
- May not be a star
- Has been studied for more than a year
- Confirmed surface with strong evidence for it being either solid or liquid
- Water vapour detected in its atmosphere
- Gravitational, radio or differentation models predict a wet stratum
Most known extrasolar planetary systems appear to have very different compositions from the Solar System, though there is sampling bias arising from the detection methods.
The goal of current searches is to find Earth-sized planets in the habitable zone of their planetary systems (also called the Goldilocks zone).[4] Planets with oceans could include Earth-sized moons of giant planets, though it remains speculative whether such 'moons' really exist. The Kepler telescope might be sensitive enough to detect them.[5] But there is evidence that rocky planets hosting water may be commonplace throughout the Milky Way.[6]
In June 2020, NASA scientists reported that it is likely that exoplanets with oceans may be common in the Milky Way galaxy, based on mathematical modeling studies.[7]
- ^ "Hubble traces faint signatures of water in exoplanet atmospheres (artist's illustration)". ESA/Hubble Press Release. Retrieved 5 December 2013.
- ^ "Mars Probably Once Had A Huge Ocean". Sciencedaily.com. 2007-06-13. Retrieved 2012-01-22.
- ^ Owen, (2007), news.nationalgeographic.com/news/2007/11/071128-venus-earth_2.html Archived 2016-05-11 at the Wayback Machine
- ^ "Habitable planets may be common". Newscientist.com. Retrieved 2012-01-22.
- ^ "The hunt for habitable exomoons". Astronomynow.com. 2009-09-04. Retrieved 2012-01-22.
- ^ "Water, water everywhere". Astronomynow.com. Retrieved 2012-01-22.
- ^ Shekhtman, Lonnie; et al. (18 June 2020). "Are Planets with Oceans Common in the Galaxy? It's Likely, NASA Scientists Find". NASA. Retrieved 20 June 2020.
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