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The Core
The Core
Mercury has a Solid and liquid metal core that makes up at least 42% of the planet and 85% of its volume, which is the largest proportion for terrestrial planets in the solar system. Earth's core only makes up 17% of the planet. Mercury's core is mostly composed of iron, with a solid inner core with a liquid middle core and an outer solid iron sulfide layer.
Layers
Layers
Mercury's composition of layers is far different than Earth's. Mercury has solid iron sulfide at the top of the core, which sets constraints on the temperature and is responsible for Mercury's magnetic field. Similarly, to Earth, Mercury has a rocky mantle and crust, but Mercury's is much smaller proportionally.
Atmosphere
Atmosphere
Composition
Composition
Mercury virtually has no atmosphere. Instead, Mercury has a thin exosphere made of atoms blasted off the surface by the solar wind and meteoroids. This is composed mostly of oxygen, sodium, hydrogen, helium and potassium.
Magnetosphere
Magnetosphere
Mercury has a magnetic field offset relative to the planet's equator. The magnetic field is only 1% the strength of Earth's, and does not protect the planet well from exterior debris. However, this weak magnetosphere interacts with strong solar winds to create massive magnetic tornados.
Hokusai is a rayed impact crater on Mercury, which was discovered in 1991 by ground-based radar observations.
Craters on Mercury
Craters on Mercury
The topography of Mercury's surface suggests that the planet was hit by many meteorites after its formation, resulting in this cratered appearance.
It was once thought to be a shield volcano because of its very different appearance from other impact craters. However, further observations with the Arecibo Observatory between 2000 and 2005 showed that it is an impact crater with an extensive ejecta system. The ejecta system is quite bright in the radar images, which means that it is a young geological structure. The surface of the newly formed impact ejecta is quite rugged and causes strong radio scattering.
Topographic map of Mercury
Topographic map of Mercury
Mercury has two geologically significantly different kinds of plains. Between the craters, gently undulating, hilly plains are the oldest areas visible on Mercury's surface, predating the violent crater topography. These crater-buried plains appear to have obliterated many of the older craters and lack craters under 30 km in diameter, as well as smaller ones. It is unclear whether they originated from volcanoes or impacts, and these cratered plains are roughly evenly distributed across the planet's surface.
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