Reach for the Stars

Large spherical celestial bodies that orbit a star and do not emit any light of their own. Based on their size and composition, planets can be divided into two separate groups:

The four terrestrial or Earth-type planets are Mercury, Venus, Earth, Mars. Terrestrial planets are closer to the Sun and therefore their surface temperature is high. They are smaller
in both mass and diameter but their density is high.

The gas giants, also called Jovian planets, are Jupiter, Saturn, Uranus and Neptune. They are larger in both mass and dia-
meter but their density is low. They do not have a solid surface.

In ascending order of their size, the planets are Mercury,
Mars, Venus, Earth, Neptune, Uranus, Saturn, Jupiter.

The terrestrial planets have a metallic (mostly iron) core, surrounded by a silicate mantle. Their solid
surface is characterised by relief features like plains, mountains, canyons, volcanoes etc.

Mercury

Diameter: 4880 km

Mass: 3.302 × 1023 kg (0.0553 MEarth)

Average density: 5.427 g/cm3

Characteristics: It is the smallest planet
of the Solar System.

Venus

Diameter: 12,103.6 km

Mass: 4.868 × 1024 kg (0.8150 MEarth)

Average density: 5.24 g/cm3

Characteristics: The brightest planet
in the night sky.

Mars

Equatorial diameter: 6794 km

Mass: 6.4185 × 1023 kg (0.1074 MEarth)

Average density: 3.94 g/cm3

Characteristics: Due to its red colour, it is called the Red planet. It is assumed that besides the Earth, Mars is the only planet in the Solar System
that could be made habitable for humans.

The Earth

Diameter: 12,742.02 km

Mass: 5.974 × 1024 kg

Average density: 5.514 g/cm3

Characteristics:
Of all the terrestrial planets,
it is the planet with the largest mass
and density.

Gas giants

Their structure from the centre outwards: relatively
small, silicate core, surrounded by a metallic hydrogen
zone, above it a layer of liquid molecular hydrogen,
then an envelope of thick atmosphere with swirling
currents, gigantic cyclones. They have rings
made up of particles of various size,
including rocky and icy moons.

Jupiter

Equatorial diameter: 142,987 km

Mass: 1.8986 × 1027 kg (317.89 MEarth)

Average density: 1.326 g/cm3

Characteristics: It is the largest planet in the Solar System,
with a volume 1,316 times greater than that of the Earth.