Exploration of Venus. Venus - Overview. Telescopic observation of Venus Only see cloud layers reflect 76% of incoming sunlight

Transcription

1 Key Concepts: Lecture 14 Exploration of : structure, surface, magnetic field Atmosphere (runaway greenhouse) Use of radar: transparency of atmospheres in radio; Doppler effect Comparison of Terrestrial Planets Telescopic observation of Only see cloud layers reflect 76% of incoming sunlight Visited by ~ 20 spacecraft Mariner 2 - first to visit in 1962 Venera 7 - Soviet Space Craft - first to land on another planet Venera 9 - first photographs of surface Magellan - detailed maps of surface from radar - Overview Second planet from Sun s sister planet similar sizes, masses, densities, cratering & chemical compositions Property Radius 6052 km 6378 km Mass 4.7 x Kg 6.0 x kg Density 5240 kg/m kg/m 3 Escape Speed 10.4 km/sec 11.2 km/sec Atmosphere Carbon dioxide, Nitrogen Nitrogen, Oxygen Orbit and Rotation Orbit of around Sun most circular orbit of all planets 225 days for 1 complete orbit Rotation of Retrograde - in opposite direction of most other planets and most satellites in solar system Very slow: 243 days for 1 full rotation (siderial day); 117 days for solar day.

2 Structure of Interior structure similar to similar mass, size & density Metallic core somewhat lower density than somewhat smaller core than Large rocky mantle Rocky crust Magnetic Field Very, very weak magnetic field - Why? rotates much more slowly (243 times) than internal dynamo weaker weaker magnetic field - 10,000 times weaker than! Interaction with solar wind differs from solar wind runs right into upper atmosphere of carries off some of the atmosphere Surface of Varied Terrain mountains high plateaus canyons ridges craters Overall relatively flat compared to Only 10% of surface above 10 km Radar to map surface Atmospheres are quite transparent in the radio wave band.

3 and measure rotation rates Uses Doppler effect: waves are compressed if emitting object is moving towards us; expanded if moving away from us. Surface of - Volcanoes and Lava Domes Volcanoes occur in complex groups Lava Domes Shield volcanoes relatively flat often having a collapsed central volcanic crater at summit Surface of Surface of - Impact Craters Few craters Several upland plateaus, resembling continents Low-land lava plains Some volcanoes, maybe active, as revealed by variable gas emissions in atmosphere Relatively few impact craters young surface overall No small craters Radar map: small meteoroids burn up in dense atmosphere Craters come in bunches large meteoroids that reach surface break up in atmosphere

4 Atmosphere of Constituents: 96% carbon dioxide 3.5% nitrogen water, sulfuric acid clouds, hydrochloric acid Variability may indicate volcanic eruptions Fast winds in upper atmosphere, almost no wind at surface Greenhouse Effect on ~76% of sunlight reflected by clouds & never reaches surface Yet surface temperature extremely high! Surface temperature high due to strong greenhouse effect No oceans or life to remove CO 2 Temperature & Pressure Temperature increases as you get closer to the surface surface temperature ~800 K Pressure increases as you get closer to the surface 90 times greater than s surface pressure! Questions about Why is its rotation retrograde? Perhaps due to giant impact. Why did atmosphere evolve so differently than the s? Probably because conditions never arose for large amounts of liquid water oceans (too hot initially, or not enough supplied by comets).

5 Summary: Terrestrial Planets Evolution of Terrestrial Planets: atmospheres Mercury Mars Mercury All terrestrial planets are differentiated Larger planets take longer to cool and still have active mantles (plate tectonics on, active volcanoes on & ) and liquid cores Mars Tsurface ~ 623K (day) ~ 100K (night) Volcanic activity creates secondary atmosphere Gravity holds atmosphere. Light atoms escape most easily. Higher temperatures allow heavier atoms to escape Water and life remove CO 2 and life creates O 2 Tsurface ~ 750K Tsurface ~ 300K Tsurface ~ 218K Evolution of Terrestrial Planets: interiors Evolutionary Stage of Terrestrial Planets Mars Mercury Moon Planet accretes from planetesimals Solid crust forms. Heavy infall of planetesimals -> cratering Major cratering ends. Mare-type basins flood with lava. Surface tectonically active. Volcanoes, plate motions or other mantle motions. Mantle solidifies. Tectonic activity ends on surface. Interior cold. All tectonic activity stops. Small planets cool fastest and go through this planetary evolution faster