The scientist who discovered in 1610 that Jupiter has four large moons was:

In January 1610, the Italian scientist Galileo Galilei used his improved telescope to observe Jupiter and discovered four moons orbiting it. These moons, Io, Europa, Ganymede and Callisto, are now called the Galilean moons.

The discovery:

• Galileo first saw them on 7 January 1610 as small "stars" in a line near Jupiter.
• Over several nights he noticed that they changed positions and moved with Jupiter, so he concluded that they were orbiting the planet.
• He published his findings in March 1610 in a short book called "Sidereus Nuncius" (The Starry Messenger).
• He named them the "Medicean Stars" in honour of the Medici family of Florence.
• The present names were suggested by the German astronomer Simon Marius, who claimed to have seen the moons at about the same time.

Why the discovery was important:

• It was the first time objects were seen orbiting a body other than the Earth.
• It showed that not everything in the universe revolves around the Earth.
• This supported the Sun-centred (heliocentric) model of Nicolaus Copernicus.

Galileo's other discoveries with the telescope:

• Mountains and craters on the Moon.
• The phases of Venus, which showed that Venus orbits the Sun.
• Sunspots on the Sun.
• That the Milky Way is made up of countless stars.

Conflict with the Church:

• Galileo's support for the heliocentric model led to his trial by the Roman Inquisition in 1633.
• He was forced to recant and spent the rest of his life under house arrest.

About the Galilean moons:

• Io is the most volcanically active body in the solar system.
• Europa has an icy surface with a likely ocean beneath it.
• Callisto is one of the most heavily cratered bodies known.

Why not the other options?

• ✗Johannes Kepler gave the three laws of planetary motion.
• ✗Tycho Brahe made precise naked-eye observations of the planets.
• ✗William Herschel discovered Uranus in 1781.