The Kepler spacecraft was launched from the United States on March 6, 2009 into space to find other planets and more specifically other earthlike worlds that could have liquid water on their surface and potentially harbor life. According to the NASA website and various articles, Kepler has discovered hundreds of planets, some of them might be habitable.
Gliese 581g: Gliese 581g, or Zarmina as the planet is colloquially known, orbits a red dwarf star 20 light years away every 36.5 days. This planet has a minimum mass of 3.1 Earth masses and has a radius 1.3 times that of Earth. It is the sixth planet in its planetary system and orbits right in the middle of its star’s habitable zone.The “habitable zone” around the star is a zone where liquid water could exist on the planet’s surface given that it has an atmosphere.
Gliese 581g, however, faces a significant problem with being habitable; red dwarfs are small, dim stars that put out a lot less energy than our own yellow dwarf star. This means that Gliese 581g orbits very close to its star, so close that it will probably become tidally locked to its star. Tidal locking is when one face of the planet always faces it’s star. Just as only one face of the moon always faces us. So one half of the planet will be boiling hot while the other side will be freezing cold. However, if Gliese 581g has a dense atmosphere, heat from the hot side will travel on strong convection currents to the cold side and might help moderate these extreme temperatures. This would mean there would be constant hurricane-force winds across the planet however, the planet could still be habitable. Red dwarves are also ‘flare stars’ which mean that they regularly and randomly undergo extreme changes in energy output with extreme discharges of high energy waves like x rays and gamma rays. The good news is that red dwarfs are common, in fact red dwarves outnumber yellow dwarves (like our sun) nearly ten to one. Red dwarves are extremely long lived, so long lived that no red dwarf has died since the universe first came into being 13.7 billion years ago. It is thought that red dwarves could live for trillions of years. If life can live on planets orbiting red dwarves than life might be more common than we previously thought.
Gliese 667Cc:Gliese 667C is a red dwarf star in a triple star system 22.7 light years away. Gliese 667Cc only orbits the third star in the system, Gliese 667C. This planet is 4.39 Earth’s mass with a radius 1.79 times that of Earth. Gliese 667C has 7 planets, 3 of which lie in the habitable zone.
Kepler 62b:Kepler 62b orbits a yellow dwarf like our own sun 600 light years away. This planet is 7.92 Earth masses and has a radius 2.35 times that of Earth. The average temperature could be 295 kelvin or 22 degrees Celsius depending on density and content of a potential atmosphere. This planet is most likely an ocean world with a very thick and dense atmosphere. It might have a gaseous outer shell, or it could be a tiny gas world, like a mini jupiter.
HD85512b:HD85512 is an orange dwarf 36 light years away. HD85512b has a mass of 3.6 Earth masses and a radius 1.4 times that of earth. HD85512b orbits its star every 54.13 days and might be tidally locked. The average temperature, given the likelihood for an atmosphere, might be around 298 kelvin or 25 degrees Celsius.
Orange dwarves, or k-type stars, are main sequence stars similar to our sun but cooler. Stars are ranked from O, B, A, F, G, K, M. O being extremely bright and short lived, while M-type stars are red dwarfs. K-type stars are intermediaries between G type main sequence stars like our sun and red dwarves. K-type stars are of special interest to planet hunters looking for habitable planets because orange dwarves are stable main sequence stars for 15 to 30 billion years as opposed to our sun’s life span which is only 10 billion years. They are also 3 to 4 times more abundant than yellow dwarves. Planets orbiting a k-type star in the habitable zone are far enough away that they will not become tidally locked, making k-type stars perfect for planets that could harbor life forms.
Kepler 62f:Kepler 62 has 5 planets orbiting it, with 2 others being in the habitable zone. Kepler 62 is a k-type star 1200 light years away. Kepler 62f is a super earth (rocky world larger than earth) with a mass of 2.57 earth masses and a radius 1.41 times that of earth. This planet orbits its star in the outer fringes of the habitable zone and might have vast areas of frozen water. If it isn’t completely frozen over, scientists estimate the average temperature with an Earth like atmosphere to be 208K or -64 degrees Celsius. This planet is the fifth in the system.
Kepler 62e:Kepler 62e is the fourth planet in the Kepler 62 system and lies in the hotter edge of the habitable zone. This planet is larger with 3.57 earth masses and a radius 1.61 times that of earth. Kepler 62e orbits its star every 122 days. Its gravity would be 1.39 times that of earths or 13.59 m/s^2. Both kepler 62e and 62f are approximately 7 billion years. Kepler 62e is the most Earth like planet discovered so far. Scientists can even guess at climate, both these worlds are probably covered in an expansive ocean. Kepler 62e will most likely be very warm with tropical climates extending all the way up to the poles, while kepler 62f will probably be covered in ice.
Scientists hope to find more habitable planets in the future and perhaps, not too far away, we’ll find Earth’s twin.