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Physics
Differences between the planets

There are two main types of planet in our Solar
System, those in the inner belt and those in the
outer belt. Planets in the inner belt are: Mercury,
Venus, Earth and Mars. These planets have a solid
rocky surface and are much smaller than the outer
belt planets (Jupiter, Saturn, Uranus and Neptune).
textbooks nis edu kz

Satellites of planets A view of the surface of Mars,
taken by NASA’s Curiosity rover
Many planets have natural satellites – smaller objects
that rotate around them. The most widely studied is
the Moon, the satellite of the Earth and our nearest
celestial neighbour. Mercury and Venus do not have
any satellites. Two satellites, Phobos and Deimos,
rotate around Mars. Big planets like Jupiter, Saturn,
Uranus and Neptune have lots of satellites.

Other objects in the Solar System
There are millions of objects of small mass between
the orbits of Mars and Jupiter, known as asteroids. The orbit of asteroids around the Sun
Some of them are as small as a grain of sand and
others are a hundred kilometres in diameter.

Other objects consisting of frozen gas and dust orbit
the Sun along quite stretched paths and sometimes
get very close to it, when frozen gas melts and
huge luminous tails appear. These bodies are called
comets. One of the best known is Halley’s Comet,
which approaches the Sun once every 75 years.

Sometimes Solar System objects heat up in the
A comet above planet Earth
Earth’s atmosphere and burn in the upper layers.
These objects are called meteorites.

ACT Work in groups to make a poster about a chosen
planet of the Solar System. Include important data
about this planet and compare it to the Earth. Then
try to answer this question: could humans ever live
there? How?

A meteorite blazing a trail

OVER TO YOU!

1. List and describe the different celestial objects in our 3. Will Halley’s Comet orbit
Solar System. the Sun forever? Explain
your answer.
2. Explain how the celestial objects are different from each other.
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