natural satellite

History

The first to describe satellite orbits in detail was Johannes Kepler in the early 17th century. Galileo Galilei discovered Jupiter's four largest moons in 1610.

How it works

A satellite is held by the planet's gravity and moves by inertia (the tendency to maintain velocity). The balance of these two forces creates a stable orbit — like a stone thrown horizontally from a mountain, which falls but constantly misses the Earth.

History

The first to describe satellite orbits in detail was Johannes Kepler in the early 17th century. Galileo Galilei discovered Jupiter's four largest moons in 1610.

How it works

A satellite is held by the planet's gravity and moves by inertia (the tendency to maintain velocity). The balance of these two forces creates a stable orbit — like a stone thrown horizontally from a mountain, which falls but constantly misses the Earth.

History

The first observations of planetary satellites were made by Galileo Galilei in 1610, when he discovered the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. Around the same time, Johannes Kepler formulated laws describing the motion of planets and their satellites. Modern research includes the search for exomoons around distant stars and the study of subsurface oceans on Europa and Enceladus through missions like Europa Clipper.

How it works

A satellite is held in orbit by the planet's gravitational pull according to Newton's law of universal gravitation. The centrifugal force of inertia balances the attraction, creating an elliptical orbit according to Kepler's laws. Tidal forces, caused by the gravity gradient, slow rotation, leading to tidal locking (one side always faces the planet). The same mechanism causes tidal heating of the interior, fueling activity on Io and Enceladus.

Open problems & fun facts

The origin of Earth's Moon is still debated: the giant impact model has discrepancies with isotopic composition.; How do satellite systems form around giant planets?; Do habitable subsurface oceans exist on icy moons?

💡 In the Pluto-Charon system, the center of mass lies outside Pluto, making them a binary planetary system.