TIL: There Are Free-Floating Planets

Image: J. Skowron

Becoming untethered in space is somewhat of a nightmare for astronauts, but it can happen to planets too - when they are ejected from host stars.

But there's less of them than we originally thought, apparently. Free-floating, Jupiter-mass planets no longer bound by gravity may be at least ten times less common than previously suggested, according to a study published this week.

Theories of planet formation predict the existence of a population of free-floating planets that have been ejected from their parent systems. The masses of these planets are predicted to range from less than one Earth-mass to several Earth masses.

A previous analysis using a technique called gravitational microlensing — which allows the study of objects that emit very little or no light — suggested there were almost twice as many free-floating Jupiter-mass planets as main-sequence stars.

The team, led by Przemek Mroz, analysed a much larger sample of over 2,600 microlensing events detected by the Optical Gravitational Lensing Experiment (OGLE-IV) between 2010 and 2015. Their results indicate that there are no more than 0.25 unbound Jupiter-mass planets per main-sequence star.

The researchers also found a few extremely short events that are consistent with the existence of free-floating Earth-mass and super-Earth-mass planets, which can be scattered and ejected much more efficiently. Further research is needed to understand the processes that untether such planets from their host stars, they say.


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