FILE PHOTO: An artist's concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun in this NASA image released on July 23, 2015. The planet, which is about 60 percent bigger than Earth, is located about 1,400 light years away in the constellation Cygnus. NASA/Ames/JPL-Caltech/T. Pyle/Handout via Reuters/File PhotoATTENTION EDITORS - FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. IT IS DISTRIBUTED, EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS.