How Giant Planets Kept Their Rapid Spin ⚡ экспресс
Using high-resolution spectroscopy, astronomers measured the rotation speeds of 32 companions—from giant planets to brown dwarfs—and combined the data with literature. The comparison showed: planets (2–7 Jupiter masses) spin faster than brown dwarf companions (10–40 Jupiter masses), with significance up to 4.5σ. It's like figure skaters of different weights: the lighter one spins faster—the planetary disk took away less angular momentum during formation. A sharp mass boundary (mass ratio to star <0.8%) separates the rotation regimes. Also, dwarf companions are slower than isolated ones, and objects of 5–40 M_Jup retain more angular momentum after 10 million years.
Using the Keck telescope and spectroscopy (light analysis that reveals rotation speed), astronomers measured 32 objects: from giant planets to brown dwarfs—bodies heavier than planets but lighter than stars that never ignited.
Giant planets spin almost at the breakup limit: their gaseous cocoon at birth barely braked them, like ice under a spinning top. Brown dwarfs, however, lost spin quickly—their disk acted like sand. What's more, dwarfs bound to stars braked more than solitary ones; planets spin equally regardless of companionship.
Surprise: objects with masses 5–40 Jupiters kept more spin than heavier ones (40–100 Jupiters). It seems that during formation, crossing some threshold triggers strong braking. Jupiter with its 10-hour day is just a modest example: many giant planets spin even faster, teetering on the edge of self-destruction.
🎯 A day on Jupiter lasts only 10 hours—faster than any other planet in the Solar System.