1. Which of the planets is nearest the Sun?

Mercury is. Its mean distance from the Sun is 58,000,000 kilometres. The eccentricity of its orbit is large, however, so that at perihelion it is 46,000,000 kilometres, while at aphelion, it is 69,000,000 kilometres from the Sun.

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2. How big is Mercury?

Mercury is the smallest of the planets. Its diameter is 4,900 kilometres. Mercury has 0.06 of the volume of the Earth and 0.15 of the Earth's surface area. Mercury's mass has not been known well because Mercury has no satellites. It has about 1/20 of the mass of the Earth. It would take 6,000,000 Mercurys to make one Sun.

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3. How fast does Mercury travel around the Sun?

Mercury's speed in its orbit is from 36.8 kilometres per second at aphelion - when it is farthest from the Sun - to 56 kilometres per second at perihelion - when it is nearest to the Sun.

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4. Is Mercury's motion about the Sun regular?

Yes. Mercury follows the laws of Johannes Kepler about the motions of all planets: it travels much faster when it is nearer the Sun, than it does when it is in the part of its orbit which lies farther from the Sun.

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5. Does Mercury have any atmosphere?

There is practically no atmosphere on Mercury, but traces of carbon dioxide were observed there.

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6. How far is Venus from the Sun?

The mean distance of Venus from the Sun is 108,000,000 kilometres. The orbit of Venus is so nearly circular that the difference between perihelion and aphelion is about 1.5 million kilometres. Mercury has difference between perihelion and aphelion more than 20 million kilometres. The Earth has difference between perihelion and aphelion about 4,000,000 kilometres.

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7. How big is Venus?

The diameter of Venus is 12,100 kilometres, about 320 kilometres smaller than the diameter of the Earth. In this, Venus is very nearly a twin to the Earth. Its mass is 82% of the mass of the Earth. Its density is 95% of the Earth's density. Its surface gravity is 90% of the surface gravity of the Earth.

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8. How fast does Venus travel around the Sun?

Venus revolves at a speed of 35 kilometres per second. Venus revolves about the Sun in 225 of our days.

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9. Does Venus have an atmosphere?

Yes. Venus has a very dense atmosphere with very white clouds. These clouds cover the planet's surface so that we can't see it. Venus' atmosphere was analysed by the probes. It appeared that it mainly consists of carbon dioxide.

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10. How near to the Earth does Venus come?

Nearer than any other of the planets. When Venus is most directly between the Earth and the Sun, it is less than 40 million kilometres from the Earth. When Venus is far from the Earth, its distance is 260 million kilometres from the Earth.

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