The solar system consists of the Sun and objects that orbit it, including 8 planets, dwarf planets like Pluto, moons, comets, and asteroids. Planets orbit the Sun in nearly circular orbits at different distances, causing their years to range from 88 days for Mercury to 164 years for Neptune. Comets and asteroids also orbit the Sun but have more elliptical orbits. The Moon is Earth's natural satellite, while artificial satellites orbit Earth for uses like communication, navigation, weather monitoring, and spying.

1. YEAR 10 GEOGRAPHY
SPACE
19. THE SOLAR SYSTEM

2. The solar system consists of:
• a star - the Sun
• planets and dwarf planets in orbit around the Sun
• satellite moons in orbit around most of the planets
• comets and asteroids in orbit around the Sun
There are eight planets, including the Earth, and smaller
dwarf planets, such as Pluto, Ceres and Eris.

3. The solar system (showing from left to right from the Sun):
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune

4. The Sun's gravity keeps the planets, dwarf planets, comets
and asteroids in orbit.
The gravity of a planet keeps its own satellites in orbit.

5. The planets take different amounts of time to go around the
Sun.
A single orbit is called the planet's year, and the further out a
planet is the longer its year takes.
The orbits of the planets in the solar system are almost
circular – with the Sun near the centre.
Many diagrams - including the next slides - show the orbits
very squashed from top to bottom.
This is to give a sense of perspective or to fit the diagram to a
page in a book.

6. The orbits of the eight planets

7. Comets are balls of ice and dust in orbit around the Sun.
The orbits of comets are different from those of planets - they
are elliptical.
A comet's orbit takes it very close to the Sun and then far
away again. The time to complete an orbit varies - some
comets take a few years, while others take millions of years to
complete an orbit.
Comets are often visible from Earth when they get close to the
Sun, because the Sun's heat vaporises material from their
surface, and this vapour forms a tail which always points
away from the Sun.

8. Comets have a range of
different orbital periods
and all leave a trail of
debris behind them

9. Types of orbit around Earth

10. Asteroids are comprised of rock and metal, and are smaller
than planets.
Most of them are found in an 'asteroid belt', in orbit around
the Sun between Mars and Jupiter.
The minor planet Ceres is found here, too.
Asteroids can crash into each other.
When they do, they may break apart and their orbit may
change.

11. A meteor hurtling towards Earth and burning up as it hits the atmosphere

12. The orbits of some asteroids cross the Earth's orbit.
At various times during the Earth's history, asteroids have hit
the Earth.
When this happened, a tremendous amount of energy was
released, throwing up billions of tonnes of dust.
This huge dust cloud blocked heat and light from the Sun,
making the Earth very cold.
It is thought that this drop in temperature contributed to the
extinction of dinosaurs.
Scientists worry that an asteroid could still hit the Earth and
cause a global catastrophe.

13. A satellite is anything that orbits a celestial body (star, planet,
moon etc). Both natural and artificial satellites exist.
The Moon is the Earth’s natural satellite.
Scientists believe that it was formed when a Mars-sized planet
collided with the early Earth, throwing some of the crust into
orbit.
However the Moon was formed, it is locked into the Earth’s
gravitation field and circles our planet once every 27.5 days.
Many other moons are the natural satellites for other planets
in our solar system and beyond.

14. Most of the 178 known natural satellites are irregular moons, while only 19 are large enough to be round.
Ganymede, followed by Titan, Callisto, Io and Earth's Moon are the largest natural satellites in the Solar System

15. These have been placed into orbit by man.
Among other jobs, artificial satellites orbiting the Earth are
used for:
• telecommunications (transmitting information between
distant parts of the Earth)
• satellite navigation systems (‘satnav’)
• spying on other countries
• weather forecasts

16. Communications satellites occupy a geostationary orbit.
They are in orbit above the equator at just the right distance
so that it takes them one day to complete an orbit.
As a result, they always appear in the same position when
seen from the ground.
This is why satellite television dishes can be bolted into
position and do not need to move.
Earth observation and monitoring satellites occupy polar
orbits, passing over the North and South poles, and crossing
the equator twice during each orbit.
The Earth spins beneath the satellite as it moves, so the
satellite can scan the whole surface of the Earth.

17. The further a planet is from the sun:
• the slower it moves
• the more time it takes to complete an orbit
For example, Mercury, the closest planet to the Sun, takes just
88 Earth days to complete an orbit.
But Neptune, the furthest out, takes 164 Earth years to
complete an orbit.