Gravity in the solar system

Gravity

Gravity is a force that attracts objects towards each other. The more mass an object has, the greater its force of gravity:

  • gravity forces between the Earth and the Moon keep the Moon in orbit around the Earth
  • gravity forces between the Sun and the Earth keep the Earth in orbit around the Sun

The different effects of gravity on Earth compared to Jupiter or Pluto

Space objectg, gravitational field strength (N/kg)
The Sun (star)293.0
Mercury3.7
Venus8.8
Earth9.8
Moon (satellite)1.7
Mars 3.7
Ceres (dwarf planet)0.27
Jupiter 24.7
Saturn10.5
Uranus9.0
Neptune11.7
Pluto (dwarf planet)0.49

Even on the surface of the Earth, there are local variations in the value of g (gravity). These variations are due to latitude (the Earth isn't a perfect sphere; it buldges in the middle), altitude and the local geological structure of the region.

At 1000km above Earth's surface gravity reduces as the distance from Earth's centre is greater and

The feeling of weightlessness

Weight caused by gravity is not always obvious. Astronauts on the International Space Station appear to be weightless. However, they are still orbiting the Earth and are within its gravitational field, so they still have weight. They seem to be weightless because both they and the space station are constantly falling towards the Earth.

Professor Brian Cox explores the feeling of weightlessness that is caused by freefall