Planets

A planet is an astronomical body moving in an elliptical orbit around a star. Planets are massive and are rounded and spherical in the structure under the influence of their own gravitational force. There are about 8 planets in our solar system.

These planets are divided into two types:

• Terrestrials: Planets like Mercury, Venus, Earth and Mars are terrestrials and are closer to the sun. They are primarily composed of rock and metal.
• Giant planets: They are massive planets and include Jupiter, Saturn, Uranus and Neptune. They are further divided into-
• Gas giants – They are composed mainly of hydrogen and helium and are the most massive of the planets. Jupiter and Saturn are gas giants.
• Ice giants – They are composed of substances with high melting points like water, ammonia and methane. Due to their rocky icy cores, they are called ice giants. They include Uranus and Neptune.

Mercury

Mercury is the smallest and innermost planet in the solar system. It has a rocky body, full of wrinkles and craters. It lies closest to the sun and its surface temperature is around 800 degrees Fahrenheit and is too hot to support human life. Its orbital period is 88 days, which means that a year in Mercury is just about 88 earth days long! The atmosphere of mercury has hydrogen, helium, sodium, oxygen, water vapor, and other gases.

Earth

Earth is the third planet from the sun and the fifth largest in the solar system. The atmosphere of the earth has layers of gases that are conducive to life. It contains 78% nitrogen, 21% oxygen, Argon (0.93%), carbon dioxide (0.04%), and other constituents like neon, helium, hydrogen, methane, water vapor, etc. About 29% of the Earth’s surface is land consisting of continents and islands and the remaining 71% is covered with water (hydrosphere). The earth’s core is rich in molten nickel-iron that generates an extensive magnetic field around it. The mean surface temperature of the earth is approximately 57 degrees Fahrenheit and hence, ideal to support the human life system. The earth’s atmosphere also protects us from the impact of meteors and comets.

Moon is the earth’s natural satellite. The moon’s gravitational force influences ocean tides and lengthening of days on earth.

Closer view of Planet Mars

Jupiter

Jupiter is the largest planet in the solar system.  It is one of the brightest objects visible in the night sky after Moon and Venus.  Jupiter has a faint ring system which is invisible from earth. It has a dynamic weather system due to its quick rotations on its axis. It is the fastest spinning planet in the Solar System. It has a strong magnetic field that is 14 times stronger than Earth.

 Saturn

A gas giant, it is the second largest planet in the solar system. It is the least dense planet and its atmosphere is extremely windy and light. Saturn’s most prominent feature is the ring around it, which mostly consists of ice particles, rock debris and dust. The cloud temperature is about -300 degrees Fahrenheit.       

                  Closer view

Neptune

It is the farthest known planet from the sun. Neptune has huge storms, high wind speed, and temperatures go as low as -353 degrees Fahrenheit. It also appears blue, slightly brighter than Uranus, due to the presence of methane.

The table below gives some properties of the planets:  

Check Point

Fill in the blanks:

1. There are about__________ planets in our solar system.
2. _________ and __________ are examples of terrestrial planets.
3. __________ is the smallest and innermost planet of our solar system.
4. The surface of Mars contains huge __________.
5. __________ is the fifth planet from the sun.
6. _________is the only natural satellite of Earth.
7. The atmosphere of ice giant Uranus appears _________ in colour.
8. The planet _________ takes the maximum time to complete its revolution around the sun.

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