Unit 16: Astronomy and Space Science
LEARNING AIM A: To understand the fundamental aspects of the Solar System
The sun and its family
What is the solar system?
A solar system by definition is, the collection of eight planets and their moons that
orbit around the sun. The solar system consists of the Sun, and the eight planets,
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune; dwarf planets
such as Pluto and dozens of moons and millions of asteroids, comets and
meteoroids (Barnett, 2019).
Terrestrial Planets
The inner planets, also known as the terrestrial planets, are mercury, Venus, Earth and
Mars. These planets are dense, with a rocky terrain and mainly made of iron. They have
few moons which are kept in orbit by the gravitational pull of the sun. The first Planet,
closest to the sun is Mercury.
Mercury - Their composition, Prominent moons, Origin, Rings, Characteristics
Mercury is the smallest planet and is closest to the sun. It was formed around 4.5 billion
years ago and it has a radius of 2439.7km. Even though it is closest to the sun, it has a
distance of about 36 million miles. However, it has the hottest surface due to its closest
proximity to the sun, with temperatures of 4.30 degrees Celsius during the day and
these temperatures can drop to –180 degrees at night due to the planet not having an
atmosphere than can retain heat. Due to the rocky and catered surface of the planet, it
is highly unlikely that any form of life could survive on this planet. In addition to this, its
orbit is not spherical, it is more like an ‘egg shape’ , so mercury has an AU of 2.9 from
the sun to 4.3 AU from the sun. Mercury spins very slowly on its axis and has a rotation
completion time of 59 earth days. When the planet is closest to the sun, it does not have
a sunrise or a sunset like most of the other planets, this is because the morning sun is
, believed to rise briefly and rise again on other parts of the
surface. This then happens in reverse during sunset.
Therefore, one full day on mercury is 176 on earth. The axis
is only at 2 degrees, which means the planet is upright and
doesn’t experience seasons like many other planets.
Mercury has an exosphere (instead of an atmosphere) which
is composed of: Oxygen Sodium Helium Hydrogen and
Potassium.
It was created by atoms which blasted off the surface due to solar wind and caused
micrometeoroid impacts. It is the second densest planet in the solar system and 85% of
the planets radius is a metallic core, evidence showing that it is mostly liquid. In contrast
to this, the outer shell of mercury is 400km is cratered rock and if we were to stand on
this surface it would be a lot brighter than the earth and the sun would appear three
times as large.
Venus Their composition, Prominent moons, Origin, Rings, Characteristics
The second terrestrial planet closest to the sun is
Venus. Venus was formed 4.5 billion years ago, it spins
very slowly and interestingly in the opposite direction to
other planets. It is a very similar size and density to
earth as it has a radius of 6052km, and is often called
earth’s twin (NASA, 2019). However, despite the similar
density and size, the conditions of Venus are different than on earth. For instance,
Venus has the hottest surface in the solar system. This is due to the thick atmosphere
being 97% carbon dioxide, which causes the greenhouse effect, where the surface
reached 500 degrees Celsius, which is hot enough to melt lead. However, due to the
different layers, which present themselves as different temperatures. The layer in which
the clouds are is around the same temperature as earths surface. Venus, as mentioned
before, is the one of only planet to rotate east to west instead of west to east. Uranus is
, also known to do this. It completes a full rotation in 243 earth days, which is the longest
day of any planet in the solar system.
On Venus, one day and night cycle is 117 earth days as it rotates in the opposite
direction of its orbital revolution in the sun. The orbital shape of Venus is also almost
perfectly circular, unlike most planets tat have oval shaped orbitals. Venus also has an
axis tilt of 3 degrees so it spins upright, Therefore it cannot experience seasons. The
structure of the planet is much like earths: an iron core, approximately 3200km of
radius, mantle made of hot rock and a surface that is a thin crust of rock hat moves as
Venus’ mantle shifts to create volcanoes.
From space, Venus appears white as it is covered in a layer of clouds made from
sulfuric acid. At the surface the planet’s rocks vary in shades of grey which look orange
on the surface due to the filtering of sunlight. It has many features such as mountains,
valleys, and thousands of volcanoes. Humans couldn’t survive on Venus due to the high
temperatures and extreme pressure.
Earth - Their composition, Prominent moons, Origin, Rings, Characteristics
The third closest terrestrial planet to the sun is Earth.
Scientists call Earths orbit position “Goldilocks” as it is “just
right” conditions for life to survive. It is the only known
planet in space that we know of that supports life, with its
20 degrees surface, life can grow and produce In these
conditions. Scientists believe that when planets were first
formed by the gravitational pull upon rock, there was no
water on earth. They believe that water arrived when the comets filled with liquid
bombarded the earth and left the water that we have today. Earth is the biggest
terrestrial planet and the fifth biggest overall. It has a radius of 6371km and is exactly
1AU from the sun (NASA Science, 2019). so the light takes around eight minutes to
reach our planet, Earth takes 365.25 days to complete one trip around the sun. Earth
has an axis of rotation of 23.4 degrees. This tilt allows the Earth to experience seasons;
