"Milky Way Galaxy is Dominated Two Types of Alien Worlds" --Rocky Earth-Like Planets and Gas-Enshrouded Mini-Neptunes19 Jun 2017, 18:51 UTC
New research from Caltech shows that our galaxy has a strong preference for two types of planets: rocky planets up to 1.75 times the size of Earth, and gas-enshrouded mini-Neptune worlds, which are from 2 to 3.5 times the size of Earth (or somewhat smaller than Neptune). Our galaxy rarely makes planets with sizes in between these two groups.
Since the mid-1990s, when the first planet around another sun-like star was discovered, astronomers have been amassing what is now a large collection of exoplanets—nearly 3,500 have been confirmed so far. In a new Caltech-led study, researchers have classified these planets in much the same way that biologists identify new animal species and have learned that the majority of exoplanets found to date fall into two distinct size groups: rocky Earth-like planets and larger mini-Neptunes. The team used data from NASA's Kepler mission and the W. M. Keck Observatory.
This sketch illustrates a family tree of exoplanets. (NASA/Kepler/Caltech , T. Pyle)
"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," says Andrew Howard, professor of astronomy at Caltech and ...