a total of 7 storms. These polar structures are caused by the turbulence in Jupiter's atmosphere and can be compared with the hexagon at Saturn's north pole. In 2000, an atmospheric feature formed in the southern hemisphere that is similar in appearance to the Great Red Spot, but smaller. This was created when smaller, white oval-shaped storms merged to form a single feature—these three smaller white ovals were formed in 1939–1940. The merged feature was named Oval BA. It has since increased in intensity and changed from white to red, earning it the nickname "Little Red Spot". In April 2017, a "Great Cold Spot" was discovered in Jupiter's thermosphere at its north pole. This feature is across, wide, and cooler than surrounding material. While this spot changes form and intensity over the short term, it has maintained its general position in the atmosphere for more than 15 years. It may be a giant vortex similar to the Great Red Spot, and appears to be quasi-stable like the vortices in Earth's thermosphere. This feature may be formed by interactions between charged particles generated from Io and the strong magnetic field of Jupiter, resulting in a redistribution of heat flow. Magnetosphere Jupiter's magnetic field is the strongest of any planet in the Solar System, with a dipole moment of that is tilted at an angle of 10.31° to the pole of rotation. The surface magnetic field strength varies from up to . This field is thought to be generated by eddy currents—swirling movements of conducting materials—within the liquid, metallic hydrogen core. At about 75 Jupiter radii from the planet, the interaction of the magnetosphere with the solar wind generates a bow shock. Surrounding Jupiter's magnetosphere is a magnetopause, located at the inner edge of a magnetosheath—a region between it and the bow shock. The solar wind interacts with these regions, elongating the magnetosphere on Jupiter's lee side and extending it outward until it nearly reaches the orbit of Saturn. The four largest moons of Jupiter all orbit within the magnetosphere, which protects them from the solar wind. The volcanoes on the moon Io emit large amounts of sulfur dioxide, forming a gas torus along its orbit. The gas is ionized in Jupiter's magnetosphere, producing sulfur and oxygen ions. They, together with hydrogen ions originating from the atmosphere of Jupiter, form a plasma sheet in Jupiter's equatorial plane. The plasma in the sheet