The most extraordinary feature on Jupiter is the Great Red Spot, a giant hurricane-like storm that's lasted more than 300 years. At its widest, the Great Red Spot is about twice the size of Earth, and its edge spins counterclockwise around its center at speeds of about 270 to 425 mph (430 to 680 km/h). The color of the storm, which usually varies from brick red to slightly brown, may come from small amounts of sulfur and phosphorus in the ammonia crystals in Jupiter's clouds. The spot has been shrinking for quite some time, although the rate may be slowing in recent years.Jupiter's gargantuan magnetic field is the strongest of all the planets in the solar system at nearly 20,000 times the strength of Earth's. It traps electrically charged particles in an intense belt of electrons and other electrically charged particles that regularly blasts the planet's moons and rings with radiation more than 1,000 times the lethal level for a human, enough to damage even heavily shielded spacecraft, such as NASA's Galileo probe. The magnetosphere of Jupiter swells out some 600,000 to 2 million miles (1 million to 3 million kilometers) toward the sun and tapers to a tail extending more than 600 million miles (1 billion km) behind the massive planet.
Jupiter also spins faster than any other planet, taking a little under 10 hours to complete a turn on its axis, compared with 24 hours for Earth. This rapid spin makes Jupiter bulge at the equator and flatten at the poles.
Jupiter broadcasts radio waves strong enough to detect on Earth. These come in two forms — strong bursts that occur when Io, the closest of Jupiter's large moons, passes through certain regions of Jupiter's magnetic field, and continuous radiation from Jupiter's surface and high-energy particles in its radiation belts.