1Astro 102/1041Lecture #15:• Mercury:•General properties.•Surface characteristics.•Interior and evolution.• Reading:– Chapter 7.1, 9.3, 10.3.Astro 102/1042The Main PointMercury is a small, atmospherelessterrestrial planet with a large metallic core and evidence for a complex geologic history.Astro 102/1043Basic Properties of Mercury•Average Distance from Sun: 58,000,000 km (0.39 AU).•But:Orbital eccentricity = 0.206.•So:Distance varies from 46,000,000 to 70,000,000 km.•Orbital period: 88 days.•Period of Spin around axis: 58.65 days (2/3 orbit period!)•Mass = 3.3x1023kg = 0.055 ME.•Radius = 2440 km = 0.38 RE.•Density = 5.4 g/cm3 (recall that Earth ~5.5 g/cm3).•Surface Gravity = 3.7 m/sec2 (38% of Earth's).•Surface Temperatures: -185°C (night), +430°C (day) [!]•Surface superficially lunar, but important differences.Astro 102/1044Observing Mercury in the Sky•Mercury is the innermost planet.•It never gets more than ~28° from the Sun.•Hard to see!– Twilight.– Haze/Smog.– Starlike.
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