NASA's Kepler spacecraft has found 219 planet candidates outside the solar system. Of these, 10 appear to have the potential to host life. One of these could be an Earth twin.
KOI 7711.01: Earth's Potential Twin
The extraterrestrial world is only slightly larger than our home planet. The amount of light it receives from its star is also the same as the amount of light Earth receives from the sun. These characteristics make this planet candidate a potential place for living organisms to thrive.
Dubbed KOI 7711.01, the world is 30 percent larger than Earth. It also orbits a sun-like star. The Earth-size planet likewise lies in the region around its host star where it receives just the right amount of heat for liquid water, if it exists, to soak on its surface.
Despite its similarities with Earth, scientists said it may still be too soon to identify KOI 7711.01 as an Earth twin since they have not yet confirmed if it has an atmosphere or liquid water.
"There's a lot we don't know about this planet. It's hard to say whether it's really an Earth twin — we need to know more about its atmosphere, whether there's water on the planet," said Susan Thompson, from SETI Institute in Mountain View, who is also the lead author of the catalog study.
Kepler Space Telescope's Hunt For Earth-Like Worlds
Kepler was launched in March 2009. Its mission is to find out how common planets that are similar to Earth are in the Milky Way galaxy.
"When we search for life outside our solar system we focus on finding planets with characteristics that mimic that of Earth," Elisa Quintana, from SETI Institute, said after Kepler's discovery of the first Earth-size planet. "Finding a habitable zone planet comparable to Earth in size is a major step forward."
The space telescope can gather information about planets and how far they are from their host stars by watching for blips in brightness when these exoplanets cross between their stars and Earth. Over the years, the space observatory has found several candidates for an Earth-like world.
One of these is the exoplanet called Kepler-438b, which was discovered in January 2015. The planet has temperature similar to Earth, is only 12 percent larger than our planet, and receives about 40 percent more light. The world is also within the habitable zone.
Scientists, however, eventually found out that the exoplanet is regularly bombarded by superflares and coronal mass ejections from its star, which suggest it is not a viable place for alien life to thrive.
Kepler has so far found more than 2,300 confirmed planets that orbit a star. The number is more than 80 percent of the total discovered by all of the world's observatories combined. Its latest finds are in a region of the Milky Way, hundreds of thousands of light-years away from Earth in between the stars Vega and Deneb.
The latest mission catalog of planet candidates is from the space telescope's first four years of data.