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Updated June 01, 2013
On December 6, 2011, NASA confirmed the discovery of the first planet located in the "habitable zone", its star. The kepler-22b exoplanet is in a region where liquid water could exist on the surface of a planet.
Kepler-22b, is the smallest of the planets found in the middle of the habitable zone of a star like our Sun.
The small planet about 2.4 times the radius of the Earth. Scientists do not yet know whether Kepler-22b has an essentially rocky composition, entirely gas or liquid, but its discovery is a step in the search for planets similar to Earth.
Kepler had already discovered more than 1 000 new planetary candidates.
Ten of these candidates have a size similar to that of the Earth and its orbit is in the habitable zone of their host star. Candidates require special monitoring to ensure that they are terrestrial planets.
Two other small planets orbiting stars smaller and cooler than our Sun, have recently been confirmed on the edge of a habitable zone, with orbits more like those of Venus and Mars.
"This is an important step on the path that will allow us to find an Earth twin," said Douglas Hudgins, Kepler program scientist at NASA.
"The results of Kepler continue to demonstrate the importance of NASA's science missions, which aim to address some of the biggest questions about our place in the Universe."
Since March 6, 2009, the date of its launch, the Kepler telescope looks for exoplanets by measuring occultation luminosity of more than 150,000 stars in the Milky Way, rather than in regions of the constellations of Cygnus and Lyra. This monster of Technology NASA sees large, since it is equipped with a photometer to measure the brightness of tens of thousands of stars simultaneously, to increase the chances of discovery by the transit method.
nota: A transit occurs each time the planet passes between its star and the observer, at that time, the planet obscures some of the light from the star, producing a detectable periodic dimming. Kepler needs at least three transits to check a signal such as a planet.
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Image: This image compares the artist's kepler-22 solar system with our own solar system. The two stars have comparable sizes. The exoplanet Kepler-22b is ideally placed in an orbit, it is in the habitable zone of its star.
Luck has smiled
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"Luck has smiled for the detection of this planet," said William Borucki, principal investigator at NASA (Ames Research Center at Moffett Field, California), he led the team that discovered Kepler-22b.
"The first transit was captured just three days after giving the probe operation. We have seen the third transit during the 2010 holiday season."
The Kepler science team uses ground-based telescopes and the Spitzer Space Telescope to observe the planet candidates found that the probe.
The star field that Kepler observes in the constellation Cygnus and Lyra, can be seen from ground-based observatories. Kepler-22b is located 600 light-years. Although this planet is larger than the Earth's orbit, 290 days around a star like the sun, like ours.
The host star of kepler-22b belongs to the same class as our Sun, G-type, although it is slightly smaller and cooler. The Kepler team at its inaugural conference of the 5 to 9 December 2011, announced 1,094 new discoveries of planets candidates. Since the last catalog was issued in February, the number of candidates identified by Kepler increased by 89% and now stands at 2326.
Of these, 207 are about the size of the Earth, 680 are super Earths, 1181 are about the size of Neptune, 203 are Jupiter-sized and 55 are larger than Jupiter. Since Kepler observes the many planets in orbit around their sun, it seems that the planets, one to four times the size of the Earth are abundant in the galaxy.
The number of Exoterra i.e. the size of Earth and super Earths candidates has increased by over 200% and 140% since February 2011.
kepler-22b is the first planet that NASA's Kepler mission confirmed as being located in an orbit in the habitable zone of a star. The habitable zone around a star allows water to exist in liquid form, a requirement for life to continue.
The planet kepler-22b is 2.4 times the size of Earth, making it the smallest ever found in an orbit in the middle of a habitable zone of a star like our sun.
Image: Scientists do not yet know if the planet has a predominantly rocky an entirely gaseous or liquid composition. But it is possible that the atmosphere there is this world of clouds, as shown here in this artist's interpretation. Credit: NASA / Ames / JPL-Caltech.