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Astronomy: Mercury
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Mercury is the closest planet to our Sun. It's one hundred times closer to the Sun than Pluto and difficult to study because of the Sun's brightness. It can only be observed during the twilight hours. This rocky planet looks very much like our Moon, and like our Moon it also has no atmosphere or has had one of any significance. The temparature varies from more than 400o C to - 180o C at night. It orbits the Sun in only 88 Earth-days, the quickest of any of our planets. Mercury spins around its axis exactly 3 times during 2 solar orbits. Before probes and spacecrafts visited Mercury, astronomers measured the gravital pull of the planet on Venus and calculated its density. The relatively strong gravity had to mean a heavy density. But to be sure astronomers needed a spacecraft. Swinging to MercuryIn the 1960's spacecrafts had only gone to the Moon, Mars and Venus. Going further implied bigger and more powerful engines, which turned these projects into overcostly missions.But the NASA Jet Propulsion Laboratory used the idea to use the gravital forces of other planets to swing to further planets. In 1973 with Mariner 10 this was brought into practice succesfully (and after that the Voyager missions used this swinging to reach Jupiter and Saturn). Mariner 10 reached Venus in February 1974 and in March 1974 its camera's and instruments focused on Mercury. MeteoritesMariner 10 showed that the planet is just as densly cratered like our Moon. One crater named Caloris Basin has the size of France and the impact caused a giant mountain chain to form on the other side of the planet.Because of Mercury's small size it cooled down quickly when our solar system formed. The planet has an inactive inner state for at least 2-3 billion years. The lack of smoothening by vulcano erosion causes that every meteorite impact stays. Crusted compression has caused cliffs that cut accross the plains and the craters on the surface. Such compression has taken place during the cooling down period of the planet. Interior of the planetMariner 10 confirmed Mercury has a magnetic field. The density of the planet is the biggest compared to our other planets. This implies that 65 to 70 percent of the planet's weight is accounted for by the - partially fluid - iron core.In 2004 and after 30 years a second spacecraft is launched to orbit Mercury, the Messenger (Mercury Surface Space Environment, Geochemistry and Ranging). Related subjects>> Mariner>> Messenger >> Meteorite impacts |
 Mercury, in many ways a look a like of our Moon. < JPG image 480 X 900 pixels > |
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