NASA has announced another set of discoveries from its Kepler space telescope mission meant to hunt the universe for potentially life-supporting worlds: 10 new, potentially Earth-like worlds.

Data gathered from the Kepler probe, while primarily concerned about prospects of alien life, is also intended to help scientists in planet classification. From this new set of findings, planets are effectively divided into two distinct varieties.

Two Planet Groups In Focus

In total, Kepler has identified 4,034 potential exoplanets. Out of those planetary candidates, 2,335 have been confirmed as exoplanets while 50 have been designated as potentially life-supporting entries.

Among the potentially habitable ones is Kepler object of interest (KOI)-7711, deemed a likely Earth-analogue because of its similar size and distance from its own star. Interest has been drummed up over this possible Earth cousin, but more has to be known about the said planet.

Now, a study led by a team from the California Institute of Technology noted that most exoplanets found so far are close in size either to Earth or Neptune. It remains puzzling, though, how such a gap between the two planetary sizes exists.

Their analysis reflected two groups that planets in this galaxy fall into: rocky planets that are up to 1.75 times Earth’s size, and gaseous Neptune-like ones from 2 to 3.5 times the size of Earth. Neptune is about four times Earth’s size.

The team sought to classify the planets akin to how biologists group animal species.

"This is a major new division in the family tree of planets, analogous to discovering that mammals and lizards are distinct branches on the tree of life," said principal investigator and professor Andrew Howard in their statement.

Why The Gap Between The 2 Groups’ Planetary Sizes?

The work was based on Kepler data along with the W.M. Keck Observatory, which hunts planets via its High Resolution Echelle Spectrometer (HIRES) on the Keck I telescope. With the recent data, the researchers measured the sizes of the 2,000 planets with four times the precision previously achieved.

But why is it that in the solar system, there is hardly any planet with a size that’s neither that of Earth nor Neptune?

The reason behind the gap remains unclear, but there are two likely explanations. First, nature is believed to be fond of making plenty of planets roughly Earth’s size. Some of these worlds, for reasons not yet fully within grasp, end up getting enough gas to “jump the gap" and turn into gaseous mini-Neptunes.

"A little bit of hydrogen and helium gas goes a very long way,” explained Howard. “So, if a planet acquires only 1 percent of hydrogen and helium in mass, that's enough to jump the gap.”

The second possible explanation involves planets losing gas. By acquiring just a little bit of gas, or the amount necessary to position it in the gap, the gas can be burned off once exposed to radiation emitted by the host star.

It’s not likely for planets to have the right gas amount to inhabit the gap, while those that have enough can see their thin atmosphere blown off, added Howard.

The team is now planning to delve on heavy elements found in every planet, seeking to find out more about the composition of those promising other-worlds and improve predictions about the planets’ formation.

That's it for the Kepler, at least as far as its primary mission is concerned. Their Monday conference was hailed the end of an era, 23 years since scientists William Borucki and David Koch first dreamt of a telescope that could capture the "stellar dimmings" needed to spot planets, as Sky and Telescope reported.

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