WHAT IS A PLANET?
According to the International Astronomical Union (IAU), the official governing body for matters concerning naming astronomical objects, came to a definition of the term “planet.” According to the IAU, a planet is a celestial body that meets the following criteria:
- is in orbit around the Sun,
- has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
- has cleared the neighbourhood around its orbit.
HOW MANY PLANETS ARE THERE IN THE SOLAR SYSTEM?
According to the IAU’s definition for planet above, there are 8 known planets in the Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Did you know?
Pluto is no longer considered a planet under the IAU definition, it is sometimes still mentioned as a dwarf planet.
MERCURY –
Mercury is the closest planet to the Sun and is also the smallest of the eight planets in our solar system. For every 2 orbits of the Sun, which takes around 88 Earth days.
Mercury is the smallest planet in the solar system with a diameter of 4,879 km and is one of five planets that is visible to the naked eye. This planet is named after the messenger of the Roman gods, who is also known as Hermes in Greek mythology.
VENUS –
Venus is the second planet from the Sun and the third brightest object in Earth’s sky after the Sun and Moon. It is sometimes referred to as the sister planet to Earth, because their size and mass are so similar. Venus is also the closest planet to Earth.
EARTH –
Earth is the third planet from the Sun and largest of the terrestrial planets. Surprisingly, while it is only the fifth largest planet in terms of size and mass, it is the densest of all the planets. Earth is the only planet in the solar system not named after a mythological being.
MARS –
Mars is the fourth planet from the Sun and last of the terrestrial planets. Like the rest of the planets in the solar system (except Earth), Mars is named after a mythological figure – the Roman god of war. In addition to its official name, Mars is sometimes called the Red Planet because of the brownish-red color of its surface. Mars is the second smallest planet in the solar system behind Mercury.
JUPITER –
Named after the Roman king of the gods, Jupiter is fitting of its name. With a mass of 1.90 x 1027 kg and a mean diameter of 139,822 km, Jupiter is easily the largest and most massive planet in the Solar System.
SATURN –
Saturn is the sixth planet from the Sun and second largest planet of the Solar System in terms of diameter and mass. If compared, it is easy to see why Saturn and Jupiter have been designated as relatives. From atmospheric composition to rotation, these two planets are extremely similar. Because of these factors, Saturn was named after the father of the god Jupiter in Roman mythology.
URANUS –
Uranus, named after the the father of the Roman god Saturn, is the seventh planet in the Solar System and third of the gas giants. It is the third largest planet by diameter, yet fourth most massive.
NEPTUNE –
Neptune is the eighth planet from the Sun and last of the known planets. While it is the third largest planet with respect to mass, it is only the fourth largest in terms of diameter. Due to its blue colour, Neptune was named after the Roman god of the Sea.
