Inner Planets of Solar System

Planets

• In 2006 International astronomical Union (IAU) has given a standard definition of a planet. Moreover this definition has also become a measuring scale to decide whether a celestial body qualifies as a planet or not. According to it a celestial body is defined as a planet when it:
  • Orbits around the Sun.
  • Has mass enough to assume nearly round shape.
  • Should not encroach others orbit. 
• Hence according to the above situation till 8 planets qualifies to be planet.
• These are terrestrial planets Mercury, Venus, Earth, mars and gas giants Jupiter, Saturn, Uranus, and Neptune.

Mercury

• Mercury is the smallest among all the planets in the Solar System.
• It orbits around the Sun in 88 days which is shortest among all the planets of the solar system. This fact is because Mercury is very near to the Sun and hence its orbital circumference is small.
• In Roman the messenger to the gods are called Mercury.
• Its tilt on its axis is i.e., about 1/30 degree which is smallest among all the 8 planets.
• Mariner 10 and MESSENGER are two satellites who have surveyed mercury.
• It is very near to sun due to which it does not holds atmosphere due to gravitational pull of the sun. Hence in absence of atmosphere and water no life exists on Mercury.

Venus

• In Roman goddess of love and beauty is called as Venus. Its orbit is nearly circular with an eccentricity of less than 1%, which is unique among all the 8 planets. Venus' orbit is the nearly circular which is unique among all the 8 planets of solar system
• Mass, density and radius are nearly equal to the Earth. Due to this it is called as Earth’s twin.
• Its atmosphere contains 96 % of CO2. Its atmosphere is densest among all the 4 terrestrial or inner planet.
• It is the brightest Planet of the Solar system and is the second-brightest natural object in the night sky after the Moon.
• Venus is having a unique characteristic among all the planets as the rotational period of Venus (243 days) is longer then the revolution period (225 days ).
• One of the most striking characteristic of Venus is that it revolves around the Sun from East to West whereas other planets revolve around the Sun from West to East. Uranus also revolve around the Sun from East to West like Venus. Due to this odd fact Sun on the Venus and Uranus rises in the west and sets to the east.
• Since, Venus is seen with naked eye in the East in the morning and in the west in the evening, it is called Morning Star as well as Evening Star.
• It’s one side is always facing the Sun and its surface temperature is always 450 degree Celsius.
• It does not possess any satellite.
• Venus was visited by the spacecraft Mariner-2 in 1962. This was the first time that any aircraft had visited to the Venus.

Earth

• If we count planet wise it is the third planet from the Sun. It is the only planet which harbours life.
• Density of the Earth is highest in solar system.
• It is largest among the four terrestrial planet of the solar system.
• Earth revolves around the sun in about 365.26 days.
• Earth's rotates on its axis and its axis is tilted 23½ degree from the perpendicular and 66 ½ degree from the plane of elliptic.
• This tilted axis of rotation of Earth is the main reason for seasonal variation on Earth.
• Earth is the only planet known where water founds. As the average temperature and air pressure of earth’s atmosphere creates suitable condition to collect water in all three forms on the earth. This condition exists only on earth in the universe.
• Earth is having several features which support life. Atmosphere of earth which contains nitrogen and oxygen and strong magnetic field protects living beings from harmful solar radiation.
• Earth is called blue planet as it looks blue when seen from the space. This blue colour is due to the presence of water on the earth.
• Earth is having only one natural satellite i.e., moon. Moon also revolves around earth in 27.3 days.
• Note:
  • Full moon can be seen only once in about a month’s time.
  • Full moon night other name is Poornima. A fortnight later after Full moon, it is a New moon night or Amavasya.

 Mars

• Mars is the fourth planet from the Sun and the second-smallest (Seventh largest) planet in the Solar System, after Mercury.
• In Roman Mars is the god of war.
• Due to the presence of iron oxide on its surface it looks red hence often it is reffered as red planet.
• Mars is a terrestrial planet with a thin atmosphere mostly consisting of Carbon dioxide.
• There are white patches on its surface, which shrink in summer and expand in winter. Mars changes colour in different season. These white patches, scientist’s guess would be ice which melts in summer and freezes in winter.
• As the atmosphere of Mars doesn’t contain oxygen as well as mars is having no water life is not possible on it. However scientists still in search of finding whether life exists in past?
• Mars is also tilted on its axis by 25^o like Earth, so mars also experiences four seasons as Earth.
• Like Earth, Mars has polar ice caps, although those on Mars are made up mostly of carbon dioxide ice (dry ice), while those on Earth are made up of water ice.
• Mars has two tiny natural satellites, Phobos and Deimos, which are small and irregularly shaped. Scientists think that these satellites may be captured by mars gravity.
• Mars is seen from the earth with the naked eye.
• Mars is called the red planet because of its red appearance due to presence of iron.
• Mars has some of the most highly varied and interesting terrain of any of the terrestrial planets, some of it is quite spectacular:
  1. Olympus Mons: It occupies the position of largest volcano in the Solar system. It also occupies the second largest known mountain in the Solar System.
  2. Tharsis: It is a huge protruding outside structure on the surface of the Earth which is 4000 km across and 10 km high.
  3. Valles Marineris: It occupies the position of the largest canyons in the Solar System.
  4. Hellas Planitia: It lies in the Venus's southern hemisphere and is an impact crater which is 6 km deep and 2000 km in diameter.