February 27, 2013 – First “Habitable Zone” Planet Discovered: The diagram above compares our own solar system to Kepler-22, a star system containing the first “habitable zone” planet discovered by astronomers. The habitable zone is the “sweet spot” around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth.
Kepler-22’s star is a bit smaller than our sun, so its habitable zone is slightly closer in. The diagram shows an artist’s rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Kepler-22b has a yearly orbit of 289 days. The planet is the smallest known to orbit in the middle of the habitable zone of a sun-like star. It’s about 2.4 times the size of Earth.
Astronomers have discovered more than 1,000 new planet candidates, nearly doubling the previously known count. Ten of these candidates are near-Earth-size and orbit in the habitable zone of their host star.
The newly confirmed planet, Kepler-22b, is the smallest yet found to orbit in the middle of the habitable zone of a star similar to our sun. Its discovery is a step closer to finding Earth-like planets.
Previous research hinted at the existence of near-Earth-size planets in habitable zones, but clear confirmation proved elusive. Two other small planets orbiting stars smaller and cooler than our sun recently were confirmed on the very edges of the habitable zone, with orbits more closely resembling those of Venus and Mars. The Kepler-22b discovery is a major milestone on the road to finding Earth’s twin.
Planets are discovered by measuring dips in the brightness of more than 150,000 stars to search for planets that cross in front, or “transit,” the stars. At least three transits are necessary to verify a signal as a planet.
Kepler-22b is located 600 light-years away. While the planet is larger than Earth, its orbit of 290 days around a sun-like star resembles that of our world. The planet’s host star belongs to the same class as our sun, called G-type, although it is slightly smaller and cooler.
Of the 54 habitable zone planet candidates reported in February 2013, Kepler-22b is the first to be confirmed. This milestone will be published in The Astrophysical Journal.
More than 1,000 new planet candidates have been discovered. Since the last “New Planet” catalog was released in February, the number of planet candidates has increased by 89 percent and now totals 2,326. Of these, 207 are approximately Earth-size, 680 are super Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter.
The findings show a dramatic increase in the numbers of smaller-size planet candidates.
Having had more time to observe three transits of planets with longer orbital periods, the new data suggest that planets one to four times the size of Earth may be abundant in the galaxy.
The tremendous growth in the number of Earth-size candidates tells us that we’re honing in on those that are not only Earth-size, but also are potentially habitable by humans.
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