The Gemini telescope has spotted a possible planet around another star… First Picture of Likely Planet around Sun-like Star …though its mass range and orbit are extreme for it to be called a planet. Firstly it masses somewhere between 7 to 12 Jupiter masses (8 being the most likely), so it’s close to the deuterium-burning mass of 13 Jupiters, which some see as the natural line between ‘planet’ and ‘brown-dwarf’. Still it’s not burning deuterium or anything else, so a “planet” is a reasonable box to put it in.
But it’s also 330 AU from its primary (see this table) and that’s rather far out for a planet proper to form. Anthony Whitworth and colleagues have developed a model that quite efficiently makes such objects… Brown dwarf formation by gravitational fragmentation of massive, extended protostellar discs …and also showed, as much as an SPH model can, that nothing much forms via disk-instability closer than 40 AU… Can giant planets form by gravitational fragmentation of discs?
That does seem like a natural division – planets form via core accretion within 40 AU, brown-dwarfs via gravitational instability further out. Except forming planets via core accretion is yet to jump the very important hurdle from dust to planetesimals. After that everything works, but the small details are still recalcitrant to the best efforts of the theorists! Andrew Youdin gives a lecture on the current problems facing theorists like himself… From Dust to Planetesimals
