Giant Planets Spin Faster Than 'Failed Stars' — A Surprising Mass-Spin Reversal
Keck Observatory's KPIC instrument measured the spin of giant gas planets and brown dwarfs ('failed stars') using spectroscopy. In the HR 8799 system, the brown dwarf — more than three times heavier — rotates about six times slower than its lighter planetary neighbor. The likely culprit: a newborn planet's magnetic field braking against its birth disk, offering a new way to tell planets and stars apart.