"Like a double-stuffed Oreo of planetary proportions, the star LHS 1903 boasts two rocky exoplanets sandwiching two gaseous ones.
From the star outward, the lineup — rocky-gaseous-gaseous-rocky — defies models that predict rocky planets appearing close in and gaseous ones further out.
The configuration hints at a history of violence in the system,
potentially refining our understanding of planetary formation, researchers report February 12 in Science.
(OR---The configuration hints that this is unique because it was DESIGNED that way)
“Bad stuff does happen in young planetary systems,” says Andrew Cameron. “This one has the look of something that’s been turned inside out.”
LHS 1903 is a red dwarf star located roughly 116 light-years away and is about half as massive as the sun. Its four companions all orbit in less than 30 days, making for a compact system whose worlds range from around 1.4 to 2.5 times our planet’s radius, straddling the boundary between super-Earths and mini-Neptunes.
Planets are thought to form from the dusty disks surrounding young stars. (MAYBE---you "thought" wrong) Rocky planets typically grow closer in, where intense starlight can strip away their atmospheres. Gas is more prevalent in the outer disk, spawning giants like Jupiter that often retain thick envelopes.
“LHS 1903 follows that pattern beautifully for the first three planets,” Cameron says. “Then, something weird happened to the fourth planet.”
Based on its density, LHS 1903’s fourth planet appears to be rocky, whereas the two planets starward from it seem to be wrapped in gaseous envelopes. It would be like finding a world resembling Venus out past the orbit of Neptune.
The fourth planet may have ("may have"---so you are just GUESSING? OR---it may have been made that way for a REASON you have not figured out yet) grown up late, “just as the system ran out of gas,” Cameron says."
ScienceNews
