— Ch. 1 · The First Four Moons —
Moons of Jupiter.
~3 min read · Ch. 1 of 5
In March 1610, Galileo Galilei published a book describing four new points of light near Jupiter. He had observed them with his telescope starting in January that same year. These objects orbited the giant planet rather than Earth or the Sun. Simon Marius found them independently one day after Galileo but did not publish until 1614. Marius assigned names to these moons: Io, Europa, Ganymede, and Callisto. Those names remain in use today despite initial resistance from astronomers who preferred numerical designations like Jupiter I through Jupiter IV.
Captured Asteroid Families
Jupiter hosts dozens of small irregular satellites orbiting far from the main cluster. These bodies likely originated as asteroids captured by the planet's gravity long ago. Simulations suggest collisions shattered parent asteroids into fragments sharing similar orbits. The Carme group contains thirty-one members moving retrograde around the gas giant. Their inclinations range between 164.3 and 164.9 degrees while semi-major axes span roughly 23 million kilometers. The Ananke group shows wider orbital spreads with inclinations between 144 and 156 degrees. Most members appear gray suggesting formation from broken-up captured asteroids. Some groups like Pasiphae display color variations from red to grey indicating multiple collision events over time.Digital Eyes on the Sky