Habitable planets

Six planets the size of the Earth have been discovered in the habitable zones of stars. The mission of NASA's Kepler discovered his first planets the size of the Earth candidates to life, that is located in the habitable zone of the star, a region where liquid water can exist on the surface of a planet. Five of these planets are about the size of Earth and orbits are in the habitable zone of stars cooler than our sun. These candidates for life are the subject of observation and monitoring to verify their real lives. Kepler confirmed the observation of six planets around a sun-like star. This is the largest group of transiting planets observed around a single star outside our solar system.
"In one generation we went from alien planets, the pillars of science fiction to reality and has allowed Kepler science fiction turns into reality today," said NASA Administrator Charles Bolden.
Several hundred new planets have been identified in the data from the Kepler Mission Science, published Tuesday, February 1, 2011. Among the 1235 candidates identified by Kepler planets in early 2011, 68 are about the size of the Earth, 288 are super-Earth, 662 are about the size of Neptune, 165 are about the size of Jupiter and 19 are larger than Jupiter. 54 new planets in the habitable zone 5 which, in size of the Earth. The 49 remaining candidates in the habitable zone, are super-Earths, 2 times the size of the Earth at a height greater than that of Jupiter. These conclusions are based on the results of observations made between May 12 and September 17, 2009, over 156,000 stars in the Kepler field of view.

This covers only about 1/400 of the sky.
"This large number of planets discovered, in a short time and a tiny fraction of the sky, shows that there must be countless planets orbiting Sun-like stars in our galaxy."
Said William Borucki of Ames Research Center of NASA in Moffett Field, California.
"We went from zero to 68 planets the size of the Earth and from zero to 54 candidates in the habitable zone, some of which may have moons and liquid water."
The results of Kepler were published in February in the journal Nature. Six planets are orbiting Kepler 11, a star very similar to the sun being at about 2,000 light-years away in the constellation Cygnus.
This discovery, due to the data of exoplanet hunter NASA's Kepler, Kepler's is 11, the system Exoplanetary the most comprehensive to date. 6 inner planets are mixtures of rock and gas, which may include water. The rock materials are the mass of the planets, while the gas occupies most of their volume.
The Kepler space telescope, looking for signatures of planets by measuring the slight decrease in the brightness of stars caused by planets passing in front of the star (mini eclipse). This is called a transit.
Transits of planets in the habitable zone of stars like the Sun, occurring about once a year and it takes three transits to check it, so it takes 3 years of observation for planets the size of Earth.
The scientific team also uses Kepler, ground-based telescopes and the Spitzer Space Telescope to observe planetary candidates.

Habitable zone

The circumstellar habitable zone or ecosphere is a theoretical sphere surrounding a star where the temperature on the surface of planets in orbit, allow the appearance of liquid water. Liquid water is vital, because of its role in biochemical reactions. It has properties that are a catalyst for the production of chemicals necessary for life.
Frank Drake calculated the distance of this area in its equation of 1961. This equation takes into account the size, the brightness of the star and the luminosity of the sun.
A star that has 25% of the luminosity of the Sun will have a habitable zone centered at about 0.50 AU. A star that has twice the brightness of the sun, will have a habitable zone centered at 1.41 AU.
A habitable zone (ZH) does not mean that it contains within it life, but there is a possibility depending on many other factors, that a terrestrial planet hosts life.
For example, Earth is home life, but the Moon, located in the same area, is sterile.
The planet candidate in the development of life, must be massive enough to prevent water from escaping. In addition, the space area is not a fixed area, it changes according to the temperature of the star, such as during their evolution the stars becoming brighter and more hot, the habitable area s logically away from the star. A planet will therefore remain as long as possible in this area, to develop all the molecules necessary for life form.
To determine the habitability of a planet, we must not look all conditions met our Earth, or no other planet in the universe might be harboring life, each planet is unique. Only the condition of having liquid water seems necessary, it is considered an essential element for a viable ecosystem because it helps tremendously transporting materials necessary for biochemical activity.

Water is a perfect item to dissolve the materials it stores very well the chemical elements.
So life may be present outside the habitable zone, just that there is liquid water on the surface or depth of a terrestrial planet, a source of energy and chemicals whose life needs to build its materials.
Astrobiologists believe that life forms may exist on other objects in our solar system like Europa, a Galilean moon of Jupiter at 500 million km from Earth. Europe is a covered ice ball the size of our Moon and has a sea of tens of km deep, liquid held by the energy of Jupiter's tidal forces. The friction caused by this stretching causes sufficient heat to maintain liquid water below the frozen surface.
The search for Exoplanets began in 1990.