Since Earth is the only known inhabited planet and we happen to live here, it’s only natural to regard it as the ideal place for life to exist. Announcements about discoveries of potentially habitable exoplanets have dominated the world of astronomy and has blown the minds of astrophysicists and science geeks alike. While most of the claims will take years to research and confirm, there have been some discoveries have been scientifically justifiable. A potentially habitable planet implies a terrestrial body with a sustainable supply of water and conditions similar to that of Earth. The planet must lie in the habitable zone. The habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure and have reasonable atmospheric conditions. There is still a lot to research about these exoplanets, but these 5 planets give astrophysicists and astrobiologists a great place to start.
- Proxima Centauri b
Artist rendition
Proxima Centauri is the closest star to the Earth other than the Sun. The planet Proxima Centauri b has been discovered revolving in the habitable zone around the Proxima Centauri, about 4.25 light years away from the Sun. It was discovered in 2016 by the European Southern Observatory (ESO). Even though Proxima b orbits much closer to its star than Earth orbits the sun, the star Proxima Centauri is a red dwarf, which means it is smaller and cooler than the sun. The exoplanet has a mass 1.3 times that of Earth. After it’s discovery, scientists have speculated if the planet is an “ocean” planet or a “desert” planet. The findings have been inconclusive so far, but it is expected that more researches will be launched very soon.
2. Kepler 186f
Artist rendition of Kepler 186f
Also known as “Earth’s Cousin”, Kepler 186f is one of the five planets that orbit the red dwarf Kepler 186f about 500 light years away from the Earth. It is the first planet with a radius similar to Earth discovered in the habitable zone of a star. The results were presented initially at a conference on March 2014 and the public announcement was made a month later. This planet is only slightly larger than Earth, about 10% more massive. It’s possible that the planet has an atmosphere that can help keep water in liquid form on the surface, a prerequisite for life as it is known on Earth.Although they know the alien world is in its star’s habitable zone, scientists still aren’t sure what the planet’s atmosphere consists of, and they cannot say with certainty that Kepler-186f could support life.
3. Wolf 1061c
Artist rendition
This exoplanet lies in the Ophiuchus galaxy about 13.8 light years away, making it second closest potentially habitable planet after Proxima Centauri b. Wolf 1061c is thought to be a rocky planet like Earth, with a mass 4.3 times of our planet, making it a “Super Earth”. Because it is so close to the star, it is likely to be tidally locked, meaning one side permanently faces the star and the other side permanently faces away. Although this scenario could result in extreme temperature differences on the planet, the terminator line that separates the illuminated side and the dark side could potentially be habitable, as the temperature there could be suitable for liquid water to exist. Additionally, a much larger portion of the planet could also be habitable if it has a thick enough atmosphere to facilitate heat transfer away from the side facing it’s host star.
4. Gliese 667Cc
Artist rendition of Gliese 667 Cc with its’s host star
Gliese 667Cc was discovered in April 2012 by an international group of astronomers working at the European Southern Observatory (ESO). It is a super-Earth, some 3.4 times the mass of Earth, orbiting a red dwarf star, Gliese 667 C. At the time of its discovery, scientists called it the most Earth-like object outside of the Solar System. The exoplanet is approximately 23.6 light years away. It has also been suggested that, since this super-Earth is so close to its star, it is probably tidally locked, rotating only once per revolution and keeping the same face toward its star at all times. It is not known if Gliese 667Cc has an ocean or even what kind of atmosphere it has. Gliese 667 Cc features in the story The Audience by Sean McMullen and also in the Alien vs Predator franchise.
5. Kepler 442b
Kepler 442b compared to Earth
This exoplanet was announced in January 2015, courtesy of the Kepler mission. Kepler-442b is 1,100 light-years away in the constellation Lyra and is about one-third larger than Earth. It’s surface temperature is thought to be -40 C, although it could be more temperate. It is outside of the zone where tidal forces from its host star would be enough to tidally lock it. Despite these properties, the small M-type and K-type stars can pose a threat to life. Because of their high stellar activity at the beginning of their lives, they emit strong solar winds. The duration of this period is inversely linked to the size of the star. However, because of the uncertainty of the age of Kepler-442, it is likely it may have passed this stage, making Kepler-442b potentially more suitable for habitability.
Our planet’s complex mix of minerals and atmospheric gases and landscapes and temperature is perfectly tuned for us. But outside our planet, the universe is not as human friendly as it looked on Star Trek, where aliens were hospitable and many exoplanets were human friendly. While there may be countless planets that are habitable for aliens, Earth is the only planet that’s habitable for us. For now, that is.
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