L7_Mercury_28jan08 - Mercury INTRODUCTION Spherical rocky...

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Unformatted text preview: Mercury INTRODUCTION Spherical rocky body, eccentric orbit ( ~ 0.21) Mean Distance from Sun: 57,910,000 km ( 0.387 AU) Radius ~2439 km; Rotation Period: 58.6 Earth days [Resonance 3:2] Orbital Period: 88 Earth days Weak global magnetic field as on earth ~ 0.0035 Gauss (0.01X Earth Magnetic Field) Little seismic activity or heat flow; most internal activity stopped long ago Mercury Physical Parameters Orbital Resonance of Mercury Mercurys 3:2 spin-orbit coupling means that after two orbits, the planet has rotated three times. This peculiar arrangement means that for a hypothetical astronaut on Mercury (black dot) sunrises occur only every 176 days. Mercurys Hot Poles Mercurys hot poles," depicted in red, appear clearly on both the night (left) and day (right) hemispheres in this map of radio emission at 3.6 cm in wavelength. This microwave energy is escaping to space from about 70 cm below the surface. It is a consequence of the much- stronger sunlight that these locations receive when the planet passes through perihelion of its rather eccentric orbit. Spherical Mercury similar to Moon During three flybys in 1974- 75, the Mariner 10 spacecraft recorded 3,500 useful images of the planet. However, due to the repetitive orbital geometry of these encounters, Mercury presented much the same sunlit face each time. Planetary geologist Mark Robinson carefully reconstructed this mosaic and that in Figure 5 from individual frames acquired by the approaching spacecraft. From this perspective, Mercury looks generally similar to the Moon . Spherical Mercury similar to Moon This aspect of Mercury, recorded as Mariner 10 from the planet, shows large tracts of smooth plains, a terrain type that may be due to extensive volcanism or the splashed-out debris from large impacts. Partially visible along the day- night terminator north above center is Caloris basin, a gigantic multiringed impact scar. Mean Density 5.4 g cm-3 (Earth: 5.52 g cm-3 ) Surface Gravity 2.78 m s-2 No earth-like atmosphere Surface exposed to meteoritic bombardment Strong exposure to cosmic rays, solar wind Atmosphere Composition: He~ 42%, Na ~ 42%, O~ 15%, Others ~ 1% Atmospheric Pressure: <0.3 millibars Temperature Range 100 - 700 K (mean ~ 452K) Mercury Geophysics...
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L7_Mercury_28jan08 - Mercury INTRODUCTION Spherical rocky...

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