"The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogs - planets with roughly the same size and orbit as Earth", said Mario Perez, Kepler program scientist in the Astrophysics Division of NASA's Science Mission Directorate. It's also the final catalog from the spacecraft's view of the patch of sky in the Cygnus constellation.
NASA explained that nature commonly makes rocky planets up to about 75% bigger than Earth.
"This carefully-measured catalog is the foundation for directly answering one of astronomy's most compelling questions - how many planets like our Earth are in the galaxy?" said Susan Thompson, a Kepler research scientist and lead author of the latest study.
This artist rendering provided by NASA/JPL-Caltech/T. Pyle, taken in 2015, depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of a star that is similar to our sun. Of which, 2335 have been verified as exoplanets. "Intermediate-size planets between these two size groups are relatively rare".
This sharpens the dividing line between potentially habitable planets and those that are inhospitable to life as we know it, the researchers said.
Afghan soldier attacks foreign soldiers, wounding 4
Officials from the government hospital have also confirmed that over 20 civilians have also been wounded in the attack. The soldiers were assisting operations against the Islamic State in the restive eastern province of Afghanistan.
Before Kepler was launched, astronomers had hoped that the frequency of Earth-like planets would be about one percent of the stars.
With the release of this catalog, derived from data publicly available on the NASA Exoplanet Archive, there are now 4,034 planet candidates identified by Kepler. "Maybe Kepler today is telling us indirectly. that we are not alone". Once planets are classified as candidates then they can be studied further to determine whether they are actually viable and confirmed exoplanets.
Seven of the 10 newfound Earth-size planets circle stars that are just like ours, not cool dwarf ones that require a planet be quite close to its star for the right temperature. Scientists with the mission expect that Kepler's K2 mission will continue until sometime in 2018.
With the final catalog of planetary candidates from Kepler's original mission released, NASA will now focus on the "K2" mission, which began in 2014.
Typically, exoplanets fall in one of two categories: super-Earths, which have a radius that is 1.5 times that of the Earth, rocky surfaces, and often little to no atmosphere; and those that are like mini-Neptunes, which re about twice the Earth's radius with thick atmospheres and no rocky surface.
Scientists were even able to estimate the size and density of the planets.