Which astronomer first observed the four largest moons of Jupiter in 1610?

Which astronomer first observed the four largest moons of Jupiter in 1610? Galileo Galilei made the landmark telescopic observations.

Using an improved refracting telescope, Galileo began recording strange points of light near Jupiter on 7 January 1610. At first he thought they were fixed stars, but their positions changed from night to night. By 15 January, he concluded that the objects were orbiting Jupiter rather than Earth. The four moons are now called Io, Europa, Ganymede, and Callisto.

Galileo published the discovery in Sidereus Nuncius, or The Starry Messenger, in March 1610. The observation showed that not every celestial body revolved around Earth, challenging the geocentric model associated with Ptolemaic astronomy and strengthening the case for a Sun-centred cosmos.

Simon Marius independently observed the moons at nearly the same time and supplied the mythological names later adopted, but Galileo’s earlier publication made him the canonical discoverer in most histories. A related surprise is that Ganymede, the largest of the four, is larger in diameter than Mercury.