木卫四又称为「卡利斯托」（Callisto、英语发音：/kəˈlɪstoʊ/、希腊文：Καλλιστώ），是围绕木星运转的一颗卫星，由伽利略·伽利莱在1610年首次发现。木卫四是太阳系第三大卫星，也是木星第二大卫星，仅次于木卫三。木卫四的直径为水星直径的99%，但是质量只有它的三分之一。该卫星的轨道在四颗伽利略卫星中距离木星最远，约为188万公里。木卫四并不像内层的三颗伽利略卫星（木卫一、木卫二和木卫三）那般处于轨道共振状态，所以并不存在明显的潮汐热效应。 木卫四属于同步自转卫星，永远以同一个面朝向木星。木卫四由于公转轨道较远，表面受到木星磁场的影响小于内层的卫星。

Callisto /kəˈlɪstoʊ/ (Jupiter IV) is the second-largest moon of Jupiter, after Ganymede. It is the third-largest moon in the Solar System and the largest object in the Solar System not to be properly differentiated. Callisto was discovered in 1610 by Galileo Galilei. At 7006482100000000000♠4821 km in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 7009188300000000000♠1883000 km. It is not in an orbital resonance like the three other Galilean satellites—Io, Europa, and Ganymede—and is thus not appreciably tidally heated. Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward; Jupiter appears to stand nearly still in Callisto's sky. It is less affected by Jupiter's magnetosphere than the other inner satellites because of its more remote orbit, located just outside Jupiter's main radiation belt.