Scientists have several ways and methods of classification of the potential habitability of exoplanets. A key factor in this definition is the semimajor axis of exoplanets (average distance from the planet to its star) inside habitable zone of the star. The inhabited area, in turn, is the space between the star and planet where planets like Earth that may contain water in liquid form on its surface. Without this capability the presence of the life which we know on Earth is impossible.
Of course, scientists check and other characteristics of exoplanets before they announce potentially habitable. For example, the composition of these exoplanets need to be rocky rather than gaseous. In addition, the radius and the mass of the planet should not exceed of 0.5-1.5 and 0.1-5.0 indicators of Land respectively.
Below is a list selected of the Laboratory of planetary studies at the University of Puerto Rico exoplanets most relevant all of these indicators.
Tau Ceti E
Star Tau Ceti is about 12 light years from Earth in the constellation of the whale. So close on an astronomical scale distance allows you to see a star in the night sky even to the naked eye. The content ratio of magnesium to silicon is 1,78 stars, which makes it about 70 percent larger than our Sun.
Tau Ceti E, which is located in the system, is currently the planetary candidate. In other words, scientists have not yet confirmed that this object is an exoplanet. The detected object was in 2012. The sidereal period (the period of a complete revolution of the object around the star) is 168 earth days.
The orbit of Tau Ceti E is located near the inner boundary of the habitable zone of the star, so there is a possibility that its surface may contain liquid water. The average temperature on the planet’s surface is close to 70 degrees Celsius. For comparison, the average Earth temperature is about 15 degrees Celsius. Extremely hot climate Tau Ceti E is making the planet unsuitable for human life, but may be suitable for a content life at an early stage of its development.
Its radius is 1.1-2.0 times greater than the radius of the Earth. Weight approximately 4.3 times the mass of our planet. All scientists noted factors make Tau Ceti E is an appropriate candidate for life in embryonic form. It is possible, when humanity still figure out how far space travel-Tau Ceti E is able to support more advanced forms of life.
Kepler 438b
Exoplanet Kepler 438b refers to the system of stars Kepler 438 and is located in 473 light years from Earth in the constellation Lyra. This star is about 4.4 billion years older than our Sun and belongs to the class of red dwarfs. The low brightness of the star to decrease the radius of its habitable zone.
Exoplanet Kepler 438b is only 12 percent bigger than Earth and has a mass of 0.6 to 4.0 times the mass of our planet. Scientists suggest that this exoplanet is likely rocky and is inside the habitable zone of a star that potentially means the possibility of existence of liquid water.
The radius of Kepler 438b is approximately 1.1 times the radius of the Earth. And although all the other factors point towards its potential habitability, life on this planet will be very difficult for humans, because the average temperature of its surface is 3 degrees Celsius.
Perhaps humans ever adapt to life at such temperatures, however, it will not be easy. Currently the planet is more suitable for the development of early life, rather than for human colonization.
The Gliese 667C E
The star Gliese 667C is a red dwarf and is 22 light years from Earth in the constellation Scorpius. This red dwarf is part of a triple star system that contains two orange dwarf who turn into around each other. Red dwarf, in turn, goes around both stars. It is believed that the age of all the three stars is from 2 to 10 billion years.
The Gliese 667C E is an unconfirmed exoplanet. Year on it lasts 62 earth days, and its radius of about 1.0-1.8 times the radius of the Earth. The Gliese 667C E actually extends the limits of acceptable radius for potentially habitable planets, but the mass of the planet is about 2.7 times greater than the mass of the Earth.
This potential exoplanet is in a comfortable habitable zone where water in liquid form. However, there is a problem. The planet has a synchronous orbit with its star, which means that one side constantly facing the star and, consequently, is very hot, while the other side is constantly rotated from the star and, consequently, very cold. Despite the fact that this factor somewhat limits the potential level of habitability, it does not change the probability that the planet can sustain human life.
Kepler 186f
The star Kepler 186 is located at 561 light year from Earth in the constellation of Cygnus. She is a red dwarf, smaller and cooler than our Sun. These factors, in turn, reduce the radius of the habitable zone of the star.
Year on the exoplanet Kepler 186f is $ 130 earth days. It is in the habitable zone of the star and the size is very similar to Earth. Although scientists have not yet figured out the mass of Kepler 186f, which has a radius just 1.1 times the radius of the Earth.
The planet is on the outer boundary of the habitable zone of a star, making the average temperature on its surface is 0 degrees Celsius. Exoplanet was actually on the edge of the possibilities for human settlement, if not for one thing. Its dense atmosphere contains a lot of carbon dioxide.
Kepler 62f
The star Kepler 62 is located in the constellation Lyra, approximately 1200 light years from Earth. This star has a mass and a radius that is approximately 0.69 times and 0.63 times more than our Sun.
Exoplanet Kepler 62f, a year which lasts about 268 days, was discovered in 2013. Its mass is comparable with mass of Jupiter. She only 0.11 times the mass of our gas giant and 318 times the mass of Earth. The radius of Kepler 62f is about 1.4 times the radius of the Earth. The planet is in the habitable zone of a star, which makes possible the presence on its surface of water in liquid form.
The average temperature here is -30 degree Celsius, making the world very cold for humans. Nevertheless, all gathered about this planet facts speak in favor of Kepler 62f as a suitable candidate for colonization.
Captain B
Red dwarf Kapteyn is 13 light years from Earth in the constellation of the Painter. This star has a mass of about 0.28 times more and with a radius of 0.29 times that of the Sun. Age star Captain is estimated in 8 billion years.
The star was named after who discovered it in the 19th-century Dutch astronomer of Jacobus Cornelius Captain. This star is moving relative to the Sun with very high spatial velocity. Its high apparent magnitude (brightness) is visible even to Amateur telescopes.
Captain B is still unproven exoplanet. Year on it lasts 48 earth hours. Its radius is unknown. However, its mass is five times greater than the mass of the Earth. On the planet may contain liquid water. Even incomplete information about the planet and its star doing Captain B a potential candidate for future colonization.
Wolf 1061c
The star wolf 1061 is a red dwarf and is located at 14 light years away in the constellation Ophiuchus. She is the 35th among the closest to the Earth stars. Its mass is about 0.25 times the mass of the Sun. The fact that the whole system is wrapped around a red dwarf star, making the radius of the habitable zone of this star is smaller compared to the brighter stars.
Exoplanet wolf 1061c, is likely to be rocky and is located in a zone where surface temperature suitable for maintaining water in liquid form. The gravity of the planet is about 1.8 times larger than the earth. The planet has a synchronous rotation with its star. In other words, one side always facing the star, while the other she turned around, making one side very hot and the other very cold.
This difference of extreme temperatures hardly make the planet a potential candidate for colonization. However, life can be maintained at the border of the two temperature zones. However, the environment here can hardly be called comfortable.
The Gliese 667C F
In the system of the star Gliese 667C, in addition to the Gliese 667C E is another an object waiting for confirmation of belonging to the exoplanets. It is about the Gliese 667C F. It was discovered in 2013 and is 24 light years from Earth. A year on Gliese 667C F lasts 39 earth days. The mass of the planet is about 2.7 times greater than the mass of the Earth. The radius of the planet equal to 1.5 the radius of our planet. All known facts about the planet make it a good candidate for the title of potentially habitable exoplanets.
Kepler 442b
The age of the star Kepler 442 is about 3 billion years. Its mass and radius of 0.61 times and 0.60 times the mass and radius of the Sun respectively. Is Kepler 442 1100 light years from Earth in the constellation Lyra.
The presence of Kepler 442b exoplanets in this system was discovered in 2015. The shadow of the planet reduced the brightness of its stars, an orange dwarf, when that was watched by the astronomers. Scientists have found that a year on Kepler 442b lasts about 112 terrestrial days. The radius of the exoplanet at 1.34 times the radius of the Earth. Most likely, Kepler 442b refers to the type of rocky planets in the system, where the surfaces of the planets may be present and maintaining water in liquid form. Among all found by February 2016 exoplanets Kepler 442b is considered by scientists as the most similar to Earth.
The Gliese 667C C
The exoplanet Gliese 667C C is also drawn around the red dwarf Gliese 667C. Its orbital period is about 28 earth days. The mass of the planet is approximately 0.01 times the mass of Jupiter. Scientists have not been able to figure out what kind of a planet is gaseous or rocky.
However, the Gliese 667C C is located in the habitable zone, where planets can support water in liquid form. Therefore, most likely, it is a rocky planet, and therefore, when the combination of all known factors, it will one day be able to live the mankind.
Based on this collection, many exoplanets ever really can become a new haven for humanity. But, of course, only after we invent a means of interstellar travel.