Although billions of kilometers distant, Uranus (left) and Neptune (right) sport something a terrestrial airline pilot would appreciate: souped-up jet streams that can clock in at more than 1000 kilometers an hour. The two worlds are twin planets, with nearly identical sizes, masses, and compositions. Each is an "ice giant" dominated by a large core of ice, rock, and iron inside a thick atmosphere of hydrogen and helium, which methane gas tinges green and blue. Both worlds have east-to-west jet streams at their equators and west-to-east jet streams at high latitudes; the winds ferry material through the atmospheres and thereby subtly affect the planets' gravitational fields. Now, as researchers report online today in Nature, those fields reveal that the jet streams extend no farther than 1100 kilometers beneath the cloud tops—just a fraction of each planet's size, because the equatorial diameters of Uranus and Neptune are respectively 51,118 and 49,528 kilometers. Many stars host worlds this large, so the finding may have implications for adventurous pilots skirting through the friendly skies of alien solar systems.
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