a Planemo is a starless planet, and a Uni of Toronto researcher (Ray Jayawardhana) was surprised to find a pair of twin Planemos, explaining that “[The system’s] mere existence is a surprise, & its origin & fate a bit of a mystery.”
They appear to have been forged from a contracting gas cloud (like stars) but are much too small to ever be real stars. The researchers are reluctant to call them “planets” because of the implication that planets orbit around stars — which these don’t.
A question not obviously asked in the ESO-based study was “how far does this go?” — for example, how close can a Planemo-like system come to being star-like? Presumably, that’ll be in next year’s grants.