It is believed that Mercury was heavy bombarded by comets and asteroids during and shortly after its formation 4. It is believed that Mercury was volcanically active during this period. Basins such as the Caloris Basin were filled with magma, producing smooth plains similar to the lunar marias found on the Moon.
The largest known crater is Caloris Basin, with a diameter of 1, km or miles. About 15 impact basins have been identified on Mercury, with more to be revealed. Two geologically distinct plains regions on Mercury have been identified. These crater plains appear to have obliterated many earlier craters. Unlike lunar maria, the smooth plains of Mercury have the same albedo as the older inter-crater plains.
Other factors indicate that this shrinking and geological activity may be present to this day. The volcanic system on Mercury is quite complex, though its exact age is hard to pinpoint but it is speculated to be billions of years old. Temperatures on the surface of Mercury are both hot and cold. These changes in temperature are the most drastic in the entire Solar System.
Mercury is a terrestrial planet having three main layers: a core, mantle and crust. The iron core has slowly cooled and contracted for about 4. It is believed that if the effects of the gravitational compression were to be factored out from both Mercury and Earth, Mercury would take the first place as the densest. This density also indicates that its core is huge and rich in iron.
It is too small and hot for its gravity to retain any significant atmosphere over long periods of time. Thus Mercury does not have an atmosphere, but it does have a thin exosphere.
The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below K, far lower than the global average. Water ice strongly reflects radar, and observations by the meter Goldstone Solar System Radar and the VLA in the early s revealed that there are patches of high radar reflection near the poles.
Although ice was not the only possible cause of these reflective regions, astronomers think it was the most likely. Even if it is small and has a slow day-long rotation, Mercury has a significant and apparently global magnetic field. It has been estimated that this magnetic field has 1. It is speculated that the magnetic field is generated by a dynamo effect, similar to the magnetic field of Earth. The Rembrandt Basin displays a "wheel and spoke" pattern on its central floor that has never been seen on any other planet or moon.
Rembrandt Size Comparison The km mile wide Rembrandt basin is large enough to cover the northeastern United States. The surface of Mercury has landforms that indicate its crust may have contracted.
They are long, sinuous cliffs called lobate scarps. These scarps appear to be the surface expression of thrust faults, where the crust is broken along an inclined plane and pushed upward. What caused Mercury's crust to shrink? As the interior of the planet cooled it contracted. Gravity then forced the crust to adjust to a smaller interior. Another large lobate scarp on Mercury is Discovery Rupes. Rupes is Latin for cliff.
Discovery is about kilometers miles long and up to 1. Notice that the walls and floors of two impact craters have been deformed by the thrust fault that formed the scarp. How do we know how high Discovery Rupes is? The results of this study should motivate more research on the factors that control the evolution of landscapes on these and possibly other airless bodies. Cook, T. Published on 26 June Marchi's research suggests that widespread volcanic activity on Mercury during its early years as a planet is to blame for the artificially young surface.
One reason for this could be that when the solar system was pelted with asteroids early in its history, Mercury's thin crust was punctured by space rocks, Marchi said. The impacts may have caused increased volcanism on the planet, effectively resurfacing the entire planet a short time after Mercury formed.
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