The Idiot’s Guide to Everything: Mercury

Posted on November 6, 2011



The closest planet to our sun in the solar system, Mercury is something of an unknown, even in this time of great knowledge and technology. It is very much a secretive world, with little known about this small planet. It is incredibly difficult to see even with the best telescopes, as it stays so close to the sun constantly. Not even the great Hubble telescope can look directly at Mercury! As it is so close to the sun, to look directly at Mercury would cause irreparable damage to the Hubble telescope, rendering it useless for observing Mercury. It is possible to see Mercury with the naked eye however, all be it rarely and with great difficulty. Even to this day, half of the planet has never been seen, but this could change soon as the MESSENGER probe became the first probe to enter orbit around Mercury in 2011.

Mercury is a very small planet, in fact ever since Pluto was downgraded to a dwarf planet Mercury has taken its place as the smallest in our solar system. It isn’t that much bigger than our very own moon. It has a diameter of 4880km, which is one third that of Earth’s. Like the other planet between Earth and the sun, Venus, it has no natural satellites. It’s size is not the only thing it shares with the moon, as it also has a landscape entirely dominated by craters, although Mercury’s craters are much shallower than those found on the moon. These craters were most likely formed by large meteorites hitting Mercury in the past, the most famous of which is the Caloris Basin, discovered in 1974 and covering an area bigger than France. Sacre bleu! The Caloris Basin was formed when a 100km wide asteroid hit the planet and sent shock waves throughout. This led to the hilly terrain we find on Mercury today. Mercury has a huge iron core which makes up 75% of its diameter. The core also makes up 42% of its volume. In comparison, the core of the Earth makes up only 17% of its volume. This huge iron core is then followed by silicate material in the crust and mantle, making up the remaining 30%. It has a maximum temperature of a whopping 450 degrees Celsius. Hot.

Interestingly, despite being so close to the sun Mercury is actually the darkest planet in the entire solar system. It reflects only 11% of the sunlight that hits it. It is also home to some of the coldest temperatures around, with its cold poles reaching up to -183 degrees Celsius. These crater filled poles are almost constantly in shadow, and one particular train of scientific thought believes there may be ice here.

Mercury also has the most eccentric orbit of all the planets. It has an elliptical orbit, which means that it rotates in a sort of oval type shape, and its distance from the sun varies constantly. At its closest, Mercury can be found 28.6million miles from the sun, whilst at its farthest point this stretches to 45.4million miles. It is the fastest of all the planets, taking juts 88 earth days to Orbit the sun. Originally, scientists believed that its rotational period was also around 88 days, meaning that one side of Mercury would have been covered in constant darkness. This was proved wrong in 1964, when it was found that Mercury rotated on its axis every 58 days. This is around two thirds of its orbit time, which means it rotates on its axis three times every two years.

Whilst Mercury has an atmosphere that is barely worth mentioning and its very existence is constantly questioned by scientists, it is also the only solid planet other than Earth to have a magnetic field. However, it is unknown where this comes from, and finding out is one of the main aims of the MESSENGER mission. Mercury also has a similar high mean density to Earth and indeed Venus. The fact that Mercury is so much smaller than these two however means that this is made up of large proportions of heavy elements, as mentioned with the 70% iron above.

Unlike some of the planets at the larger end of the spectrum, human knowledge of Mercury goes back centuries and centuries. The ancient Greeks and Romans both made mention of it, referring to it as both Apollo and Hermes. The modern name for the planet comes after the Roman god of trade, Mercury. Galileo made the first modern observations of Mercury in 1610, This was followed by the discovery by Giovanni Zupus that Mercury circled the sun. The first map of the planet was made between 1881 and 1889 by Schiaparelli, and it wasn’t until as late as 1968 that the first photograph of Mercury was taken, by Surveyor 7. Until MESSENGER this year, only one probe had ever visited Mercury, this being Mariner 10 between 1974 and 1975. With the arrival of MESSENGER this year, there is hope that more can be ascertained about the secretive world of Mercury.

Has there ever been life on Mercury? The simple answer to this is, well, no. Mercury is just far too close to the sun and too extreme for life to flourish. Strangely enough however, Mercury does possess the three signposts that we look for with regards to life as we know it. There is oxygen and methane in its incredibly thin atmosphere, and water in the form of ice at its poles. So why no life? Well, firstly, the oxygen levels are far too low to support life as we know it today. Also, whilst there may be water in the form of ice, there certainly is no liquid water to be found on Mercury. Finally, the temperatures on the planet make any claim of life completely unreasonable. If an astronaut were to visit Mercury, its fair to say he would not be coming back. Life on earth may be tough sometimes, but given the choice between Burley Park, Leeds and Mercury, I think I’ll stay in Yorkshire thank you very much.