Recently NASA announced an astounding discovery: The Kepler missions confirmed the first exoplanet orbiting in the habitable zone of a sun-like G-types star. The newly discovered planet Kepler-22b is a little more than double the size of Earth, and it is located 600 light years away. [1] That is a long way to go, but either way, this discovery is a milestone for the Kepler mission and the search for Earthlike planets.
Kepler space observatory launched in 2009 on a mission to scan an area of the Milky Way galaxy between Cygnus and Lyra in search for Earthlike life supporting planets located in habitable zones. [2] The telescope uses the transit method to detect if a planet passes in front of a star and blocks its light for a very short time. So far 2326 possible planet candidates circling over 1000 stars have been detected by Kepler. Of these, 207 have the size of Earth, 680 are much bigger than our planet, 1181 have the size of Neptune , 203 of Jupiter, and 55 are even larger than Jupiter. But more importantly, 48 of them are confirmed to orbit in habitable zones. [3]
Potential life habitats should be abundant in water and carbon, as well as other elements necessary in organic compounds, such as nitrogen. For the water to stay in liquid form, pressure should not be less than 610Pa. Temperature is also crucial: carbon based life can develop in environments with a temperature up to 160°C and down to several tens of degrees bellow 0°C. Habitats can exist either at the surface or below. [4] All these conditions create the so-called habitable zones. The habitable zone is the range of distances from a star within which water occupies large territories and remains in liquid form on the surface of a planet. [5] It is however not enough for a planet to be in the habitable zone to develop life. Volatiles are needed to form an atmosphere. The planet has to have sufficient mass so that the atmosphere could provide pressure for water to stay liquid; it has to be geologically active; its atmosphere should not leak into space. [6]
Some of the planets discovered by Kepler live in a binary system, orbiting two stars (Kepler-16b), some are much larger than Earth (Kepler-11), or much smaller and rocky (Kepler-10b); others live in complex solar systems with more planets (Kepler-18b, c, and d), yet others seem to be almost identical twins of our planet (Kepler-22b). [7] Kepler may be able to confirm that Earth is not that unique after all.
The latest discovery, Kepler-22b has a revolution period of 290 days, it is 2.4 times larger than Earth, and has a temperature of approximately 22°C. [8] It is yet to be discovered if the planet is gaseous or rocky, what is its mass, and if it has an atmosphere or magnetosphere. Since our technology is far from even studying in depth such a planet, let alone to visit it even by robotic missions, the promise of such discoveries is more in terms of revealing that Earthlike planets could have formed in other solar system and therefore could harbor life.
Notes:
[1] Phillips, Tony. Kepler Confirms First Planet in Habitable Zone of Sun-like Star. NASA Science News. http://science.nasa.gov/science-news/science-at-nasa/2011/05dec_firstplanet/ (accessed December 12, 2011), para. 1
[2] Ames Research Center
[3] Phillips, Tony. Kepler Confirms First Planet in Habitable Zone of Sun-like Star. NASA Science News. http://science.nasa.gov/science-news/science-at-nasa/2011/05dec_firstplanet/ (accessed December 12, 2011), para. 9
[4] Jones, Barrie William. Life in the Solar System and Beyond. Chichester : Praxis Publishing, 2004, 78.
[5] Ibid, 79.
[6] Ibid, 80.
[7] Ames Research Center
[8] Phillips, Tony. Kepler Confirms First Planet in Habitable Zone of Sun-like Star. NASA Science News. http://science.nasa.gov/science-news/science-at-nasa/2011/05dec_firstplanet/ (accessed December 12, 2011), para. 4.
References
Jones, Barrie William. Life in the Solar System and Beyond. Chichester : Praxis Publishing, 2004
Phillips, Tony. Kepler Confirms First Planet in Habitable Zone of Sun-like Star. NASA Science News. http://science.nasa.gov/science-news/science-at-nasa/2011/05dec_firstplanet/ (accessed December 12, 2011).
Image source: NASA/Ames/JPL-Caltech, http://www.nasa.gov/images/content/607691main_Kepler22bArtwork_946-710.jpg
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