Space Physics: The Solar System and Orbits

The Solar System

The solar system consists of the Sun, planets, dwarf planets, moons, asteroids, and comets.
The Sun is located at the centre of the solar system and is a star.
Planets, dwarf planets and their moons, as well as many asteroids and comets, orbit around the Sun.
The eight recognised planets in our solar system are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Dwarf planets, such as Pluto, are smaller bodies that have not cleared their orbital path of other debris.
Comets are icy bodies that develop tails as they approach the Sun.

Orbits

The gravitational pull of the Sun is what keeps planets and other bodies in their orbits.
In the solar system, all planets move in elliptical (oval-shaped) orbits around the Sun following Kepler’s first law of planetary motion.
The closer a planet is to the Sun, the stronger the Sun’s gravitational pull and the faster the planet moves.
Orbital speed varies depending on the distance a planet or object is from the Sun: objects further away from the Sun move more slowly than those closer to it.
Satellites, both natural (like moons) and artificial, also follow elliptical orbits around the planets they orbit.

Gravitational Field Strength

The force of gravity decreases with distance. It is stronger closer to a planet and weaker the further away you are.
This change in gravitational field strength explains why objects weigh less the further they are from the centre of the Earth.

Centripetal Force

When bodies move in circular paths, they constantly change direction, which means that they are accelerating.
This acceleration is caused by a resultant force, known as a centripetal force, which always acts towards the centre of the circle.
In the case of orbits, the centripetal force is provided by gravity.

** Satellites and their uses**

Artificial satellites are human-made objects that orbit Earth or other celestial bodies.
There are two types of artificial satellites: geostationary satellites, which stay above the same point on the Earth’s equator, and low Earth orbit satellites, which orbit closer to the Earth and travel around it very quickly.
Uses for these satellites include communications, weather forecasting, observing the Earth’s climate, and scientific research.
The time periods and paths of satellites depend on their height above the Earth. The higher the satellite is above the Earth, the longer its orbital period.

Space Travel

Missions such as those conducted by NASA’s Apollo programme have allowed astronauts to land on the moon and return safely to Earth.
Modern space exploration includes unmanned missions to Mars, the use of space telescopes and the international space station.
The challenges of such exploration include surviving in a vacuum and dealing with extreme temperatures, managing power supplies, taking off and landing, and the long durations of space travel.