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Planetary Atmospheres, the Environment and Life (ExCos2Y) Topic 1: Composition of Atmospheres

Planetary Atmospheres, the Environment and Life (ExCos2Y) Topic 1: Composition of Atmospheres. Chris Parkes c.parkes@physics.gla.ac.uk Rm 455 Kelvin Building. Lecture Content. 1. Composition of the Atmospheres of Earth, Mars and Venus 2. Evolution of Earth’s Atmosphere

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Planetary Atmospheres, the Environment and Life (ExCos2Y) Topic 1: Composition of Atmospheres

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  1. Planetary Atmospheres, the Environment and Life (ExCos2Y)Topic 1: Composition of Atmospheres Chris Parkes c.parkes@physics.gla.ac.uk Rm 455Kelvin Building

  2. Lecture Content 1. Composition of the Atmospheres of Earth, Mars and Venus 2. Evolution of Earth’s Atmosphere 3. Structure of Planetary Atmospheres 4. Solar Radiation 5. Atmospheric Convection 6. Wind 7. Water 8. Storm Systems 9. Climate Change 10. Revision Reading: The Cosmic Perspective, chapter on planetary atmospheres by Bennett, Donahue, Schneider, Voit. Publisher: Addison Wesley Atmosphere, Weather and Climate by Barry, Chorley. Publisher: Routledge

  3. Planets of the solar system Orbit the Sun Near Spherical Dominate its orbit IAU Prague (2006) Fit to be a planet ?

  4. Atmospheric Composition: Earth, Mars & Venus Venus Earth Mars

  5. Atmospheric Composition: Earth, Mars & Venus Venus Earth Mars

  6. Comparison of physical quantities: Venus Venus Earth Earth Mars Mars Mass * 0.82 1.00 0.11 Distance from Sun * 0.72 1.00 1.52 Radius * 0.95 1.00 0.53 Gravitational Acc. * 0.90 1.00 0.38 Surface Pressure (atm.) 90.00 1.00 0.01 Surface Temp. (K) 750. 280. 240. Planetary Albedo 0.76 0.39 0.16 Rotation Period (days) 243. 1.00 1.03 Orbital period (years) 0.62 1.00 1.88 * Relative to Earth

  7. Comparison of Atmospheric Composition Equilibrium state: production rate = loss rate Sources & Sinks (in balance) Sensitive dependant on: temperature, pressure, quantity, other gases, etc. Venus Earth Mars Nitrogen 3.5% 78% 2.7% Oxygen <0.001% 21% 0.13% Carbon Dioxide 96.5% 0.035% 95.3% Argon 0.007% 0.93% 1.6% Water Vapour 0.004% .004%-4.0% 0.03%

  8. Partial Pressures Partial pressure of a gas = P total atmospheric× % concentration Examples: N2 on Venus: 3.5% × 90 = 3.15 atm. N2 on Earth: CO2 on Mars: CO2 on Earth: 78% ×1 = 95.3% × 0.01 = 0.035% × 1 = 0.78 atm. 0.00953 atm. 0.00035 atm.

  9. Some Important Gases CO2 Greenhouse gas: temperature Needed for photosynthesis: life H2O Sink for CO2 Liquid Water needed for life on earth Oxygen O2 needed for life on earth O3 (Ozone) Pollutants through human activities (Low atmosphere) Formed by Sun’s radiation (High atmosphere) UV screen

  10. How does a planet GAIN atmospheric gases ? Born 4.5 million years ago without atmospheres • Outgassing • Heating from the core • Volcanic activities • H2O, CO2,N2,H2,S,SO2 • Evaporation/sublimation Water (Earth) /ice (Earth, Mars) and frozen CO2 (Mars)

  11. How does a planet LOSE atmospheric gases ? • Five processes: • Condensation • Chemical Reactions 3) Thermal Escape 4) Impacts 5) Dissociation from solar rays These two can be reversed These three permanent loss

  12. The presence of water affects CO2 levels - CO2 highly soluble in water - Acid rain which reacts with rock - CO2 locked into rocks (over geological timescale) Chemical Reactions • Removal of CO2 from atmosphere • (see next lecture for Oxygen cycle)

  13. Thermal Escape: Gravity and the atmosphere Escape velocity (Ve): G – Gravi. Const. (6.67×10-11m3s-2kg-1) M – Mass of Planet r - Planet radius For Earth Ve = 11km/s

  14. Gravity and the atmosphere No. of molecules Velocity Ve Motion of Gas molecules: - random - temperature dependant velocity R – gas constant (8.31 J mol-1 K-1) T – temperature m – molecular weight (=0.002kg/mol for H2) At 280K, Vmax = 1.5km/s

  15. Temperature & escape velocity of planet are determining factors of atmospheric composition Points show vescape and temperature of each planets Curves show typical highest velocities for different gases Thermal Escape Vescape(km/s) Temperature (K)

  16. Earth’s atmosphere – other constituents Aerosols Types: Dust, Organic matter, Smoke, Salt Sources: Forest/Bush Fire, Volcano, Sea Spray, Dust Storm, Burning fossil Fuel Pollutants Sulphur compounds (acid rain), Nitrogen compounds (NOx), Ozone, CO, Hydrocarbons Water vapour Cloud formation

  17. Earth’s atmosphere – Cloud formation Planetary Albedo Water vapour saturation Temperature Pressure aerosols Many different types of cloud Highly reflective ( 70%-95% Visible range) Efficient scatterer

  18. Example exam questions Q1. List the main differences between atmospheric composition of Mars and Earth? Q2. What are the main factors which affect surface temperature of planets? Q3. How does surface temperature affect the composition of planetary atmosphere? Next lecture – evolution of Earth’s atmosphere

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