The speed of planets rotating around their axes, or stellar days, is a fundamental characteristic that demonstrates the amazing diversity in our Solar System. This parameter is not random; it depends on a complex interplay of factors, including the planet's formation history, mass, gravitational interactions, and physical state. The gradation of planets by rotation speed allows for the identification of several distinct groups, from swift gas giants to slow, one-sided dwarf planets. Group of swift giants: Jupiter and Saturn The absolute record holders for rotation speed are the gas giants. Despite their colossal size, they exhibit the shortest stellar days. Jupiter, the largest planet in the system, completes one rotation around its axis in just 9 hours 55 minutes. Its equatorial zone rotates slightly faster than the polar regions, indicating differential rotation, characteristic of gas spheres. Such high speed leads to powerful atmospheric phenomena, such as the formation of stable bands and the famous Great Red Spot — a giant storm that has been raging for centuries. Saturn follows with a rotation period of 10 hours 33 minutes. Its less dense structure and the famous system of rings, consisting of billions of ice particles, also feel the impact of this colossal speed, which contributes to the formation of a unique hexagonal structure at the planet's north pole. Ice giants and rocky planets: moderate rotation The next group consists of ice giants and rocky planets, whose days last from several hours to one Earth day. Uranus and Neptune have similar rotation periods of 17 hours 14 minutes and 16 hours 6 minutes, respectively. However, Uranus is unique in its orientation: its axis of rotation is tilted almost 98 degrees relative to the plane of its orbit, so it rotates "on its side". Among the planets in the Earth group, Mars and our planet are closest in rotation speed. Martian days last 24 hours 37 minutes, which allowed them to be called "solae". Earth, with a rot ... Read more