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Mercury, Venus and Mars [Questions 11-16]

11. How big is Mars?

The diameter of Mars is 6,800 kilometres, a little more than half the diameter of the Earth. Mars has 0.391 of the Earth's surface and 0.15 of its volume. The mass of Mars is 0.11 of the mass of the Earth and 1/3,100,000 of the mass of the Sun.

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12. How far is Mars from the Earth?

That depends upon where Mars is in its orbit and in what part of the Earth's orbit our planet is. The two planets are moving about the Sun in the same direction, but not at the same distance from the Sun and not at the same speed. The mean distance of Mars from the Sun is 228 million kilometres. The Earth's mean distance from the Sun is about 150 million kilometres. But the orbit of Mars is much more eccentric than is that of the Earth.
This means that the difference between perihelion and aphelion with Mars is much greater than with the Earth. With the Earth this difference is 4 million kilometres. While with Mars, it is more than 40 million kilometres. Mars makes one revolution about the Sun in 687 of our days. Hence Mars and the Earth are in opposition only once in 780 days. The Earth makes one revolution in 365 1/4 days. If an opposition occurs when Mars is at aphelion its distance is about 99 million kilometres from the Earth. When an opposition occurs with Mars is at perihelion its distance is about 54 million kilometres from the Earth.

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13. What is the temperature on the surface of Mars?

The Martian temperature is from 20 to 30C at noon at Martian equator. It is -100 C at the same place at night. The temperature at the poles is as low as -120C.

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14. How fast does Mars travel about the Sun?

Mars travels at 24 kilometres per second. Mars makes one revolution about the Sun during 687 of our days.

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15. How long is a day on Mars?

A day on Mars is a little longer than on the Earth. Mars rotates on its axis in 24 hours, 37 minutes, 22.58 seconds.

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16. Does Mars have an atmosphere?

Yes. It is very thin.

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• The Sun
• The Earth
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• Jupiter, Saturn, Uranus, Neptune and Pluto
• Meteors and Comets
• Stars
• The Constellations
• Galaxies
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Related Internet Links
• Astro Kids: Mercury
• NASA: The Planets
   
  
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