The Kepler spacecraft continues to make observations in new patches of sky in its extended mission, searching for planets and studying a variety of interesting astronomical objects, from distant star clusters to objects such as the TRAPPIST-1 system of seven Earth-size planets, closer to home.
Kepler scientist Mario Perez says that means that "we are probably not alone" because four years of data show how common Earth-like planets can be. Understanding how frequent planets like our own will help NASA develop the next telescope that will directly image planets like Earth.
The new Kepler analysis also indicates extra-solar planets form in three general sizes, not two as previously thought. Of those, 10 are potentially rocky and located in the habitable zones of their stars where liquid water might be found.
"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.
Of the new candidates, 10 are near in size to Earth and sit in the habitable zone of their stars-the range of orbits in which liquid water could exist on their surfaces.More news: John Avildsen, director of Rocky and The Karate Kid, dies aged 81
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Since launching in 2009, Kepler has been watching more than 200,000 stars in one part of the sky to determine exoplanet candidates, based on the slight dimming of light emitted by stars when potential planets pass across them.
And, in a statement, Nasa said: "There are now 4,034 planet candidates identified by Kepler".
The first portion of the mission, which lasted roughly four years, ended when the telescope lost two of the reaction wheels that kept its instrumentation stabilized for these careful measurements. In the middle are roughly Neptune-size worlds and at the other end of the scale are smaller Earth-analogues. With the launch of our Transiting Exoplanet Survey Satellite (TESS) and the James Webb Space Telescope (JWST) in 2018, we're going to search for planets nearest the sun and measure the composition of their atmospheres.
Kepler hunts for planets by detecting the minuscule drop in a star's brightness that occurs when a planet crosses in front of it, called a transit. Out of 4,034 exoplanets discovered by different teams working with Kepler Telescope, 2,335 have been confirmed in follow-up observations or reviews conducted later. Each star will be observed for 30 days. For reasons scientists don't yet understand, about half of those planets take on a small amount of hydrogen and helium that dramatically swells their size, allowing them to "jump the gap" and join the population closer to Neptune's size.
The James Webb Space Telescope will be able to look at targets discovered by K2 in some detail, and it will be able to focus on at least 10 exoplanets in great detail.
"I'm looking forward to 2030s", said Courtney Dressing, NASA Sagan Fellow.