NASA’s Kepler Telescope has just returned the final batch of data from its primary mission and it includes 10 new Earth-sized worlds in the habitable zone of their star.

This final catalogue, which includes 219 planet candidates, was part of Kepler’s original four-year mission looking at a portion of the sky known as Cygnus. This long observing time allowed it to find some worlds akin to our own, with similar sizes and orbital periods around their stars.

“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, in a press briefing. “Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth.”

The total count of planet candidates now stands at 4,034 found by Kepler, with 2,335 verified as exoplanets. Of these, about 49 are Earth-sized and in the habitable zone of their stars, 30 of which have been verified. And there may be some more in the data.

Within that list of Earth analogues, perhaps the most intriguing is a world called "7711". This world is about 1.3 times the size of ours, but orbits a similar star in a similar position, so it receives a similar amount of energy. Future telescopes like the James Webb Space Telescope (JWST) could allow us to study worlds like this in more detail.

It was also announced that astronomers have found an intriguing division between two types of planet. They found that rocky Earth-size planets and gaseous planets smaller than Neptune, called mini-Neptunes, have a gap between them. Few to no planets were found to form between 1.5 and 2 Earth radii.

“Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree,” Benjamin Fulton from the University of Hawaii in Manoa, who led this study into planet sizes, said during a press briefing.

With this release of data, Kepler’s primary mission is now effectively over. It is now conducting a second mission, called K2, that involves looking at a region of the sky for shorter periods of time.

While this mission will struggle to find Earth-like worlds (three transits are needed to confirm a planet, so a world with an orbit like ours must be observed for three years), it could help us further understand what sort of planets are in the cosmos.

“You don’t necessarily need to do the transit method to find them [Earth-like worlds],” Susan Thompson, a Kepler research scientist at the SETI Institute in California, told IFLScience during the press briefing. “One of the pathways is finding a planet with a transit survey, whether that’s Kepler [or something else], following up on the ground, and then doing a targeted observation.”

While the Kepler mission is continuing for now, it will be joined soon by the Transiting Exoplanet Survey Satellite (TESS). This will look for planets in orbits of between 27 days and a year, and is planned to launch by June 2018.

With this final batch of data, scientists now hope to hone in on one day possibly finding a world exactly like our own. While we don’t yet know for sure, there looks to be quite a few candidates that deserve further study.

“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?” Thompson added in the briefing.