Q. 19

State the physical c

Answer :

Physical conditions of different planets
(i) Mercury (Budha)1. It is the closest planet to the sun. Its distance from sun is 57 ´ 106 km. Since it is very close to the sun, most of the time it is hidden in the glare of the sun. It can be visible before the sun rise in the east and after the sun set in the west. It appears quite bright and correspondingly it is termed as 'morning star' and 'evening star'. It is termed as star because it appears very bright in the sky. 2. It is of the same size as moon.
3. It revolves round the sun in 88 days and takes 58 days to complete one rotation about its own axis.
4. Life cannot exist on mercury due to lack of atmosphere and extremes of temperature [340° C ↔ ] (-150° C) and it has no protective blanket around it to save it from harmful radiations.5. The surface features of mercury resemble those of moon more than those of the earth.6. It has no moon or satellite of its own.(ii) Venus (Shukra) 1. Its distance from the sun is 108 × 106 km.
2. It completes its orbit round the sun is 225 days.
3. It has almost the same radius, density and mass as that of earth. Thus, it is called twin of earth.
4. It is the brightest planet and appears as a morning and evening star.
5. The surface temperature of venus is about 450° C and it is covered by thick blanket of cloud made up of CO2, H2, O2, N2. No life is possible on this planet because of high temperature, absence of water and sufficient oxygen.
6. It has no moon or satellite of its own.(iii) The Earth (Prithvi) 1. Its distance from the sun is 149 × 106 km.
2. It has plenty of water, oxygen in the atmosphere and is neither too cold nor too hot, making life possible on this planet.
3. It takes days to complete one revolution round the sun and 24 hours to complete one rotation round its axis.
4. It has thick blanket of ozone layer high up in its atmosphere to save life from harmful effects of ultraviolet radiations coming from the sun.
5. It has one satellite called moon.(iv) Mars (Mangal) 1. Its distance is 227 × 106 km from sun.
2. It takes 687 days to complete one revolution round the sun and 24 hours to complete one rotation round its axis.
3. It has slightly reddish appearance.
4. It has two natural satellites or moons named Phobos and Deibos.
5. Unlike Mercury and Venus it can be seen in any part of the night sky.
6. The day temperature varies from 5° C to 15° C and there is no evidence as yet of life on Mars.
7. It has no protective blanket to protect it from harmful solar radiations.(v) Jupiter (Brihaspati or Guru) 1. Its distance from sun is 778 × 106 km.
2. It takes 12 years to complete one revolution round the sun.
3. It is the largest planet and is more massive than the combined mass of other planets of the solar system.
4. It has a dozen satellites or moons. Four of them are quite large and bright and can be seen with a low power telescope.
5. There is a faint ring consisting of extremely small particles around Jupiter.(vi) Saturn (Shani)1. After Jupiter, Saturn is the second biggest planet of the solar system.2. It looks like a large yellow star to the naked eye.3. It possesses well-developed set-of rings around it. These rings consist of particles whose sizes vary from tiny specks to rocks measuring a few kilometers in diameter.4. It is at a distance of 1427 × 106 km from the sun.5. It takes about 29.5 years to complete one revolution round the sun.6. It is said to have 30 satellites or moons.(vii) Uranus (Arun) 1. This is the seventh planet from the sun and is 2870 × 106 km away from sun.
2. It takes 84 years to complete one revolution round the sun.
3. It has 21 satellites or moons.
4. It rotates about its axis from east to west in contrast to other planets which rotate from west to east.
5. Its atmosphere contains hydrogen and methane.(viii) Neptune (Varun) 1. It is the eighth planet in terms of its distance from the sun.
2. It has 8 satellites revolving around it.
3. Its distance from sun is 4505 × 106 km.
4. It takes 165 years to complete one revolution round the sun.  

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