Questions About Mercury
- Mercury is the planet closest to the Sun. It is not, however, very close, since it is 36 million miles, or 58 million kilometres away from the Sun!
- The distances of planets from each other and from the Sun are often measured in Astronomical Units, AU. One AU is the average distance between the Earth and the Sun, 93 million miles, or 150 million kilometres. Using this system of measurement, Mercury is 0.39 AU from the Sun.
- Like all the other planets Mercury orbits round the Sun, but its orbit of the Sun lasts for only 88 days. The Earth’s orbit lasts for 365 days and Pluto’s orbit takes 249 YEARS!
- Because Mercury goes round the Sun so quickly, the planet was called after the messenger of the Roman Gods. The messenger Mercury, or Hermes as the Greeks knew him, is usually shown as having wings on his helmet or on his sandals.
- When Mercury orbits the Sun, it travels 36 million miles, or 58 million kilometres in the 88 days of the orbit. It moves at a speed of 48 kilometres a second, or 107,372 miles an hour!
- Unlike the Earth and most other planets Mercury only turns very slowly on its axis, taking 59 days to complete the turn from day to night.
Figure 1. Mercury, showing the craters on the surface.
- Mercury’s sunny side has a temperature rising to 400° Celsius or 750° Fahrenheit. Compare this to a warm summer’s day in London, when the temperature might be 80° Fahrenheit or 26° Celsius.
- Mercury’s dark side, however, is very cold indeed, with the temperature going down to -200° Celsius or -328° Fahrenheit.
- Mercury has no atmosphere around it to protect it from the Sun or to retain any heat when it rotates on its axis.
- Mercury is quite a small planet. Its diameter, the distance right round its middle, is only 3100 miles or 4990 kilometres. The diameter of the Earth is 7926 miles or 12,760 kilometres.
- Mercury’s distance from the Earth is 57 million miles, or 92 million kilometres. Using Astronomical Units Mercury is 0.61 AU from the Earth.
- Mercury has no moons. Moons are satellites that travel with a planet as it orbits the sun. The earth has one moon, Mars has two very small ones, Jupiter, the giant of the planets, has 16!
- The surface of Mercury is covered with craters and completely dry. There is no possibility of life on Mercury.
- The first photographs of the surface of Mercury were taken by the USA Space Agency, NASA. The Mariner 10 spacecraft passed close to the planet in 1974 and 1975 and took very clear photographs.
- NASA’s latest mission to Mercury is called Messenger. The Messenger spacecraft entered Mercury’s orbit in March 2011 and is sending back new pictures of the planet. Messenger is now moving with Mercury round the Sun.
Figure 2. The NASA spacecraft Messenger orbiting round the Sun with Mercury.
- From Messenger we know that Mercury has a large number of very deep and irregular pits. Some of these pits are several miles deep.
- Mercury is one of five planets that can be seen without using a telescope, Mercury, Venus, Mars, Jupiter and Saturn. When you look at the sky at night, the planets do not twinkle in the way that stars do. Mercury is not very easy to see, but it can be seen low in the west just after sunset or in the east just before dawn.
- About once every ten or fifteen years Mercury can be seen crossing the Sun. At this point its orbit has come between the Sun and the Earth. This event is known as a transit. When watching any event near the Sun a proper filter must be used to protect the sight. With this filter Mercury can be seen as a tiny black dot slowly passing across the Sun. You must never try to look directly at the Sun without a filter.