Mercury - Overview Distance 36 million miles (0.39 AU) CLOSEST Planet to Sun Orbital Period 88 days FASTEST Planet Rotation Period 59 days SLOW rotation** Radius 2440 km (0.38 R⊕) SMALLEST Planet (no Pluto) 23 Mass 3.3 x 10 kg (0.055 M⊕) LEAST MASSIVE Density 5.4 g/cm3 DENSEST (exc Earth) Atmosphere Essentially none Surface T 800 F (day), -290 F (night) LARGEST TEMP DIFF. **Nearly Synchronous! Mercury - Overview Distance 36 million miles (0.39 AU) CLOSEST Planet to Sun Orbital Period 88 days FASTEST Planet Rotation Period 59 days SLOW rotation Radius 2440 km (0.38 R⊕) SMALLEST Planet (no Pluto) 23 Mass 3.3 x 10 kg (0.055 M⊕) LEAST MASSIVE Density 5.4 g/cm3 DENSEST (exc Earth) Atmosphere Essentially none Surface T 800 F (day), -290 F (night) LARGEST TEMP DIFF. Obliquity 0 degrees seasons? Observing Mercury • Hardest Naked Eye Planet WHY? Mariner 10: Venus/Mercury flyby (1974) 1974: no evidence for recent geologic activity Mercury cooled off? Mercury - Spacecraft data Mariner 10: Venus/Mercury flyby (1974) Measured Mass Calculated HIGH density (5.4g/cm3) WHY?? LARGE iron core! Mercury - Spacecraft data Mariner 10: Venus/Mercury flyby (1974) Small Magnetic Field (1% Earth)! WHY?? Mercury - Spacecraft data Messenger: Mercury Orbiter (2004-) Flybys: 2/1/08, 10/6/08, 9/29/09 Mercury Orbit: March 18, 2011 Inner Core Molten! Surface Features Messenger Terrain Craters/Rayed Craters Impact Basins Planitiae (Plains) South Pole Current Geologic Activity? Surface Features Rays & Bright Craters Different Rock Composition? Surface Features Rupes & Lobate Scarps • Compression Folds/Cliffs • Large (>100 km!) • Mercury contracted quickly from cooling (R<20km) Why? • Closed off volcanic vents Surface Features NEW! Double Ring Basin! Caloris Basin Largest feature on Mercury HUGE (960 km) Impact Basin with WEIRD TERRAIN opposite 3.8-3.9 bil. yrs old WEIRD TERRAIN Mercury - A History ➡Formation close to Sun •sunlight/wind 6.25x more intense... no atmosphere •tidal forces/slow rotation... small magnetic field •HOT ➡Heavy Bombardment ➡Volcanism ➡Planet Cooled (Small!) Venus - Overview “Planet from Hell!” Distance 67 million miles (0.72 AU) 2nd planet from Sun Orbital Period 225 days Rotation Period 243 days Orbits slow & retrograde** Radius 6052 km (0.95 Earth) EARTHLIKE Mass 4.9 x 1024 kg (0.81 Earth) EARTHLIKE Density 5.2 g/cm3 Surface T 860 F HOT HOT HOT Atmosphere 96.5 % Carbon Dioxide Densest of ALL Obliquity 177 degrees seasons? **No Strong Magnetic Field Venus - Early Observations •Galileo - 1610/1611 •Phases of Venus Venus from Earth •Brightest object besides Sun & Moon •why? What time of day is Venus observable? Venus - Radar Mapping RAdio Detection And Ranging Use RADAR to Map surface of Venus! Venus - Earth’s Evil Twin Atmosphere of sulfuric acid & carbon dioxide (96.5% CO2!) Venus - Spacecraft data Magellan (1990-1994) - Orbiter, radar mapping Smooth Surface & Few Craters: Evidence for recent geologic activity INFER core/mantle/Crust (similar to Earth) THICK Lithosphere (HOT) Venusian Surface Features Mountains & Terrae •2 “Continents” •Afrodite Terra •Ishtar Terra Venusian Surface Features Impact Craters Golubkina Crater •not many (~1000) •NO small craters (<3 km) Why Not? •thick atmosphere 30 km •young surface Mead Crater Alcott Crater 63 km 280 km Venusian Surface Features Volcanoes Sif Mons >1600 major volcanoes! 167 larger than 100km! Why so big? Maat Mons Venusian Surface Features Rampant Volcanism - Pancake domes - Coronae 30 km - Lava Channels Mead Crater Effect?? Volcanic Outgassing & Atmosphere Formation - ON VENUS a) Trapped gases released during volcanic activity: – H2O, CO2 , N2 , H2S, SO2 b) Solar UV breaks up some molecules, -light elements escape - O/O2 forms ozone layer, protects from UV TOO c) H2O condenses to form liquid water - rain! HOT! d) Water combines with CO2 to create carbonate rocks (e.g. limestone)X Venus: RUNAWAY Greenhouse Effect •H2O/CO2 are greenhouse gases (absorb IR radiation) T ↑ → water boils, vapor absorbs IR → T ↑ → no water to absorb CO2, CO2 absorbs IR → T ↑ etc. (until insanely hot!).