Astronomers developed new classifications of exoplanets with the help of the W.M. Keck Observatory atop Mauna Kea.
The Caltech-led study found the majority of planets discovered in other solar systems to fall into two distinct groups: rocky planets that are up to 1.75 times the size of Earth and what scientists labeled mini-Neptunes.
The latter are gas-enshrouded planets that are 2 to 3.5 times the size of Earth but somewhat smaller than Neptune.
The research focused on planets found by the Kepler space telescope, which identified more than 2,300 planets orbiting other stars.
The scientists then used the Keck telescopes to measure the planets with more precision.
“Before, sorting the planets by size was like trying to sort grains of sand with your naked eye,” lead author Benjamin Fulton said in a press release. “Getting the spectra from Keck Observatory is like going out and grabbing a magnifying glass. We could see details that we couldn’t before.”
Kepler identifies exoplanets by looking for dips in starlight caused as they pass in front of their stars.
The research shows there are few planets between these two classifications. While the cause of the gap is not clear, one idea is nature likes to make a lot of planets about the size of Earth and that some acquire enough gas to “jump the gap” and become gaseous mini-Neptunes, a Keck press release said.
Another possible reason is that planets that fall into that gap typically have that additional gas burned off when exposed to their star’s radiation.
It’s also unclear why our solar system doesn’t have any of these mini-Neptunes that are common elsewhere. That will be the focus of additional research, scientists note.