The Circumplanetary Family
The term “natural satellite” most commonly refers to a body such as the Moon orbiting a planet, but it also applies to bodies orbiting minor planets (P 11), dwarf planets (P 9), and Kuiper belt objects (P 21). As of 2018, 187 satellites are known to orbit the planets of our Solar System, as well as over 300 that orbit minor planets and four that orbit dwarf planets. 12 new satellites of Jupiter were announced in 2018 alone, giving it a grand total of 79 (for now!). 58 satellites orbiting Kuiper belt objects have been discovered thus far, including the six largest of those distant denizens. Planetary satellites in our Solar System range in size from several thousand miles in diameter (including our Moon, the four Galilean moons of Jupiter, Saturn’s Titan, and Neptune’s Triton) to 10 miles for the two moons of Mars, and even smaller for some satellites embedded in planetary rings (P 7).