WHAT IS PLANET?
A planet (from Ancient Greek ἀστὴρ πλανήτης (astēr planētēs), meaning "wandering star") is an astronomical object orbiting a star or stellar remnant that
- is massive enough to be rounded by its own gravity,
- is not massive enough to cause thermonuclear fusion, and
- has cleared its neighbouring region of planetesimals.
The term planet is ancient, with ties to history, science, mythology, andreligion. Several planets in the Solar System can be seen by naked eye. These planets were originally seen by many early cultures as divine, or as emissaries of deities. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union (IAU) officially adopted a resolution defining planets within the Solar System. This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit. Although eight of the planetary bodies discovered before 1950 remain "planets" under the modern definition, some celestial bodies, such as Ceres, Pallas, Juno, Vesta (each an object in the Solar asteroid belt), and Pluto (the first trans-Neptunian object discovered), that were once considered planets by the scientific community are no longer viewed as such.
Planets are generally divided into two main types: large low-density gas giants, and smaller rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System. In order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four gas giants, Jupiter, Saturn, Uranus, and Neptune. Six of the planets are orbited by one or more natural satellites.
Earth
¡It differs from the other planets because it has
liquid water on its surface, maintains life, and has active plate movement.
Saturn
¡Well known for its system of three rings
¡The
surface of Saturn looks banded, and has a brown-yellow, butterscotch colour.
¡Saturn’s
rings are probably composed of small particles of ice and rock.
Jupiter
¡The
largest planet in the solar system
¡Jupiter
orbits the Sun once every 12 years.
¡It
rotates very fast in only 10 hours
Venus
¡The
second planet away from the Sun
¡It
is about the same size as the Earth
¡Venus
rotates very slowly
Pluto
¡The
most distant planet from the Sun
¡Pluto
is probably composed of rock.
¡Its
surface and colour are unknown
Mercury
¡The
closest planet to the sun
¡It
rotates slowly, however, only once every 59 days
¡Mercury
is small, about 4850 kilometres ( 3000 miles in diameter)
