Lecture15 - Lecture#15 Mercury General properties Surface...

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1 Astro 102/104 1 Lecture #15: • Mercury: General properties. Surface characteristics. Interior and evolution. • Reading: – Chapter 7.1, 9.3, 10.3. Astro 102/104 2 The Main Point Mercury is a small, atmosphereless terrestrial planet with a large metallic core and evidence for a complex geologic history. Astro 102/104 3 Basic 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 = 3.3x10 23 kg = 0.055 M E . Radius = 2440 km = 0.38 R E . Density = 5.4 g/cm 3 (recall that Earth ~5.5 g/cm 3 ). Surface Gravity = 3.7 m/sec 2 (38% of Earth's). Surface Temperatures: -185°C (night), +430°C (day) [!] Surface superficially lunar, but important differences. Astro 102/104 4 Observing 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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