Close-In Planets Act as “Bouncers” to Create Rogue Worlds

Rogue planets sound like rare travelers amongst the stars, freed from the gravitational constraints of a host system, left to forever wander the interstellar void. But modern models suggest these Free Floating Planets (FFPs) as they are technically known, are actually very common – nineteen times more common than planets beyond the “snow line”, which is the distance from the central star where it becomes cold enough that hydrogen compounds like water, ammonia, and methane can condense into ice. But why are FFPs so common? What forces them out of the stellar systems where they form? A new paper from Xiaochen Zheng of the Beijing Planetarium and his co-authors, available in pre-print in arXiv, offers a plausible explanation – planetary “bouncers”.