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All About the Planet Mercury

By Patrick Omari

Mercury in shadow Mercury is the closest planet to the Sun and the smallest of the rocky terrestrial planets in our solar system. Named after the Roman God of commerce, travel and thievery, the planet is a harsh world of extreme temperatures about which relatively little is known. Mercury orbits the Sun at a distance of 46-70 million km and passes within 77.3 million km of the Earth at its closest pass. It takes the small planet just 88 Earth days to complete an orbit round the Sun and 58 days to complete one rotation, a very slow rotation compared with the other planets, only Venus is slower.

Mercury’s structure is typical of that of a terrestrial planet, containing a core, a mantle and then a rocky outer crust. Mercury is the second densest planet in the Solar System, right behind Earth. Mercury’s core is larger in comparison to the diminutive size of the planet giving it the high density. It is believed that at some point in its history Mercury was struck by a planetesimal, stripping away much of the mantle and crust and leaving the planet with a relatively large core.

The surface of Mercury is unforgiving and harsh. It is quite similar to that of the Moon, pockmarked with craters and the remains of meteorite impacts. With no erosion to wear them down the craters last for millions of years. In sunlight temperatures can reach 450 degrees C and drop as low as -170 degrees C at night. The huge fluctuations are due to Mercury’s distance to the Sun and its lack of a real atmosphere. The gravity on the planet is not strong enough to retain a permanent atmosphere and so much of it is lost to the solar winds. There is evidence of ice on Mercury, despite its extreme heat. There are deep craters at the poles of the planet which never see sunlight and so are permanently cold enough for layers of ice to form.

Mercury in colorExploration of Mercury has been slow compared to the other planets. The planet is the hardest to reach by spacecraft as the speed required is extremely high, given its closeness to the Sun. This is combined with the fact that any spacecraft looking to orbit Mercury would be acted upon by the Sun’s gravity. Probes must use an excessive amount of fuel to brake so as not to overshoot Mercury. Landing on the planet is also tricky because of the lack of atmosphere meaning that parachutes and aerobraking are unlikely options. Mercury is not considered a strong candidate for terraforming and colonisation either because of the extreme temperature fluctuations. Mars and Venus as well as some of the gas giant’s moons are seen as more likely options.

Despite the relative difficulties of sending probes to Mercury there have been some observations made from its orbit. The Mariner 10 probe was the first to arrive in March 29th 1974. Mariner 10 did not orbit Mercury, but the Sun instead and used Venus’s gravity to slingshot a path to Mercury. Mariner 10 would fly by Mercury twice more in 1975, photographing 45 percent of the surface. The mission led to the discovery of the Earth-like magnetic field and the surface details of the planet, showing extensive amounts of meteorite impact. The second mission to Mercury, MESSENGER, is currently en-route and will enter orbit in 2011.

Patrick is an expert Research and Travel consultant. His current interest is in Luton airport parking, Stansted parking and Gatwick hotels.
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