Over three quarters of the possible planets discovered by NASA's Kepler spacecraft are between the size of Earth and Neptune (which is about four times larger).
This planet size-range seems to be the majority of the universe, but are mysteriously scarce in our own Milky Way, a NASA news release reported.
Recent observations have confirmed these planets are planets of the size originally determined, but researchers are unsure what the objects are made out of or how they were formed.
Researchers also found five rock-based planets that are between 10 and 80 percent larger than Earth. The objects orbit their parent stars in only a few days, making them much too hot to support life.
The researchers looked at the planet's mass (which turned out to be similar to lead) by looking at the reflex wobble of their host star. The higher the mass of the planet the greater gravitational tug on the star, which is what causes the wobble.
"This marvelous avalanche of information about the mini-Neptune planets is telling us about their core-envelope structure, not unlike a peach with its pit and fruit," Geoff Marcy, professor of astronomy at University of California, Berkeley, said. "We now face daunting questions about how these enigmas formed and why our solar system is devoid of the most populous residents in the galaxy."
By calculating the mass researchers could determine if a number of planets were rocky, gaseous, or a mixture of the two compositions. The team worked to determine the chemical composition of theses "strange, but ubiquitous planets." They found "mini-Neptunes" are rocky at the core and composed of "hydrogen, helium and hydrogen-rich molecules in the envelope," the news release reported.
"The ground-based observation research validates 38 new planets, six of which are non-transiting planets only seen in the Doppler data," the news release reported
"Kepler's primary objective is to determine the prevalence of planets of varying sizes and orbits. Of particular interest to the search for life is the prevalence of Earth-sized planets in the habitable zone," Natalie Batalha, Kepler mission scientist at NASA's Ames Research Center in Moffett Field, Calif. said. "But the question in the back of our minds is: are all planets the size of Earth rocky? Might some be scaled-down versions of icy Neptunes or steamy water worlds? What fraction are recognizable as kin of our rocky, terrestrial globe?"
Doppler and TTV data suggests planets with less than 1.5 the radius of Earth tend to be made of "silicates, iron, nickel and magnesium that are found in the terrestrial planets here in the solar system" the news release reported.
