The longer we stay on Earth, the more apparent it becomes that maybe we should have a backup plan should we live long enough to completely dry ‘er up. On our quest to find the perfect place to call Second Home, we’ve come across these incredible exoplanets. Factoring in the Earth Similarity Index or ESI, we’ve compiled the Top 10 Earth-like planets discovered over the past decade.
Also known as Earth 2.0, the discovery of Kepler 452b by the Kepler space telescope was announced in July of 2015. Found 1,400 light-years away from Earth, the super-Earth, which has an ESI of .83, was located in the habitable zone of a G-type star that shares a very similar mass and surface temperature of our Sun. While 452b’s smaller radius indicates it may have a rocky, terrestrial surface, the habitability of the exoplanet remains widely unknown, though it is believed to be subjected to a runaway greenhouse effect. The exoplanet is approximately 60% larger than Earth and has a year that’s only 5% longer than our own, earning it the title of Earth’s Cousin.
Kepler 186f of the Kepler 186 system may only have an ESI of .61, but the 2014 discovery is the first Earth-like exoplanet to have a radius similar to Earth’s - measuring in at about 10% larger. Found 500 light-years from Earth in the Cygnus constellation, 186f has an orbital period of 130 days and only receives 1/3 the energy from its star that Earth receives from the Sun. In terms of livability, 186f is within the habitable zone, but unknown atmospheric factors make how habitable it may be impossible to determine. Like Kepler 442b, 186f has a low obliquity that keeps it from experiencing seasons like Earth. Of the four other planets in the Kepler system, 186f is believed to not be tidally locked like its neighbors and may be the only one far enough away from the Kepler star to sustain water.
Kepler 62 f may only have an ESI of .67, but this super-Earth, discovered at the same time as 62e at about 1,200 light-years away from Earth, poses one of the best scenarios for habitability. Where the exoplanet may fall short in its ability to sustain life is its possible lack of an atmosphere, which would lead to any surface water to be ice. At 1.4 times larger than Earth and with an orbital period of 267 days, life on 62f would be fairly similar to life on Earth – that is, of course, if its atmosphere were similar to that of our own. As of now, much remains unknown about the theoretically habitable planet, including whether or not it’s mostly terrestrial or predominantly covered in water.
A Super-Earth found within the habitable zone of the Kepler 62 star, this exoplanet, which was discovered in 2013, has an ESI of .83 and has some of the imperative qualities of potentially livable planets. On top of being rocky, the planet is also believed to be covered in an extensive amount of water. One factor working against 62 e as a habitable zone is the 20% increase in stellar flux from what we experience on Earth, which can trigger temperatures as high as 170° F or about 77 ° C, and start a detrimental greenhouse effect. In relation to Earth, 62 e is 60% larger and orbits the Kepler 62 star 243 days quicker and receives 20% more sunlight than Earth does.
Wolf 1061 c
At an ESI of .76, Wolf 1061 c is a potentially rocky super-Earth exoplanet discovered in December of 2015, some 14 light-years away from Earth. Orbiting Wolf 1061 at .084 AU, the exoplanet is closer to the inner edge of the habitable zone and is believed to be tidally locked. With one side permanently fixated on its star, the possibility of an extreme difference in temperatures on either side of the planet is incredibly likely. On the warmer side, liquid water may be sustainable, though it’s hypothesized to have an icy equilibrium temperature of -58° F or about -50° C, that could be offset by a thick atmosphere that allows for a transfer of heat away from the side of the planet facing Wolf 1061.
In January of 2015, the newly found Kepler 438b, located 470 light years away, was deemed one of the most “Earth-like” planets ever discovered, making it an incredible candidate for the potential of life. Though it has a potential ESI of .88 and still carries similarities to our home world, research later that year determined that, while still “Earth-like,” 438b may be missing qualities needed for habitation – such as an atmosphere. The planet’s nearby star emits flares 10 times more powerful than the Sun, leading to the possibility of a stripped atmosphere. There’s still hope that Kepler-438b, which is 12% larger and receives 40% more light than Earth, may be usable if it has a magnetic field like our own.
With an ESI of .87, Proxima b may be one of the most Earth-like exoplanets to date, but that doesn’t mean it’s the greatest candidate for habitability. Though it shares many characteristics with Earth and touts a higher ESI, if you haven’t noticed yet, that’s not a guaranteed proponent of habitability. In fact, Proxima b, which is only 4.2 light-years away, is likely uninhabitable due to incredibly high stellar wind pressures. Compared to Earth, Proxima b is thought to be subjected to pressures of more than 2,000 times what we experience. Coupled with the radiation from its host star, it’s possible that the exoplanet would have no atmosphere to sustain life. In October of 2016, researchers at the National Center for Scientific Research in France hypothesized a chance for surface oceans and a thin atmospheric layer, though proof has yet to be discovered.
Launched in 2009, NASA’s Kepler space observatory has succeeded on numerous occasions in its mission to find Earth-sized planets. Announced in January of 2015, alongside the discovery of Kepler-438b, 442b has an ESI of .83 and a radius of 1.34 radians, quite a bit larger than Earth’s radius of .009 radians. While located within the habitable zone and deemed one of the most Earth-like planets in regards to temperature and size, life would be quite a bit different on 442b. For instance, a year would only be 112.3 days long and we’d experience only 70% of the sunlight that we’re used to receiving on Earth. Since the axial tilt is believed to be fairly small, we also shouldn’t expect to enjoy the quarterly change in seasons that we’re accustomed to.
Gliese 667 Cc
Orbiting around the red dwarf star Gliese 667 C some 23 light years away, the exoplanet Gliese 667 Cc is within the habitable zone and has an ESI of .84. In November of 2011, astronomers noticed the super-Earth and started to find similarities to our own planet. The habitability of Gliese 667 Cc depends on where you’re aiming to terraform as the two hemispheres display complete opposite properties. One side is completely shrouded in permanent darkness while the other is constantly facing towards the red dwarf. It’s believed that, between these hemispheres, there is a sliver of space that may experience temperatures suitable for human life. There is, however, a possibility of extreme tidal heating upwards of 300 times that of Earth, calling into question whether, at times, if Gliese 667 Cc may be a little too hot for habitation.
In June of 2014, the High Accuracy Radial Velocity Planet Searcher discovered the potentially habitable exoplanet Kapteyn B. Found to reside in a system estimated at over 11 billion years old, about 7 billion years older than our own solar system, Kapteyn B orbits the red subdwarf star Kapteyn and is 12.8 light-years away from Earth. Kapteyn B has an ESI of .67 and, while found within a habitable zone capable of liquid water, is believed to have a temperature of approximately -91° F or roughly -68° C and, therefore, too cold to sustain water in a liquid form, but with enough C02 in its atmosphere, this may not even be a factor. Working against the argument of habitability is the fact that some researchers, such as Paul Robertson at Penn State University, think Kapteyn B may not even exist and may just be a starspot mimicking a planetary signal.