Two of the five planets orbiting a sun-like star known as Kepler-62 are squarely in what astronomers call the habitable zone - not too hot, not too cold and also possibly producing water, experts stated in the journal Science.
"These two are our greatest candidates that may be habitable," stated William Borucki, Kepler science principal investigator at NASA's Ames Research Center. The two planets are somewhat bigger than ours, and at least a couple of billion years older. The first, 62e, is about 40% bigger than Earth.
It may be warm, perhaps also a waterworld, and might experience flashes of lightning, claimed Borucki.The second, 62f, is about 60% bigger than planet earth, and orbits its star every 267 days, near to Earth's annual trajectory of 365 days.
The planet might have polar caps, significant land masses and liquid water, Borucki stated.
Both are orbiting a seven-billion-year-old star some 1,200 light years from Earth in the constellation Lyra.They are near enough to their star to be warm, yet not as near as to boil the oceans. They are distant enough to maintain the likelihood of water without freezing the seas solid, Borucki explained.
Scientists do not yet know if their surfaces are rocky or watery, or if they have atmospheres that could maintain life.
Yet their area and size suggest they "could possibly be composed of condensable compounds and be solid, either as a dry, rocky super-Earth or one composed of a significant amount of water," said the study.Other research studies have indicated that planets with a radius under 1.6 times that of the Earth, like these two, "have been found to have densities indicative of a rocky composition."Astronomers discovered the planets by observing their star dim when the planets pass in front of it, in what is known as a "transit. These are the most identical objects to Earth that we have discovered yet," stated Justin Crepp, assistant professor of physics at the University of Notre Dame.
Crepp initially saw a dot near Kepler-62 about a year ago, and has investigated the movements of the system for months in order to confirm the discovery.
A third possibly habitable planet, Kepler 69c, is on the "inner edge of what has been considered to be the habitable zone," said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, California.
Nevertheless, that one may be small and hot and more like Venus, the second planet from our sun, said Barclay, whose studies was published Thursday in the Astrophysical Journal."We're not definite yet," he told reporters. Its host star, Kepler 69, is about 2,700 light years from Earth in the constellation Cygnus.
All together, the recent discovery add more seven new planets - four of which are outside the habitable zone - to the tally that Kepler has discovered so far, totaling more than 2,700 candidates and confirmed planets.
In late 2011, NASA confirmed its first-ever planet in a habitable zone outside our solar system - Kepler 22b, revolving around its star some 600 light years away.
However, the bigger size of that exoplanet, at 2.4 times the size of the Earth, has left some skepticism over whether the planet is rocky, gaseous or liquid.Another large planet that Kepler has confirmed in the habitable zone, Kepler 47c, is also much bigger than Earth.Kepler, launched in 2009, is NASA's first objective in search of Earth-like planetsorbiting suns resembling ours.It is equipped with the largest camera ever sent into space in its search for planets as small as Earth, including those orbiting stars in a warm, habitable zone where liquid water could exist on the surface of the planet.
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