Dust Storms Mars and Earth

Bit of Administration …. ReadingReading –BSNV Chaps. 10, week exam!12-week exam! –Tonight, 7:15-8:30 pm, 3425 Sterling Hall Mathieu office hours for pre-test questionsMathieu office hours for pre-test questions –All day today

Nuclear Fusion - A Digression Thermonuclear Hydrogen Fusion 4 H => He Positron Neutrino Deuterium Hydrogen Helium 4 Helium 3 Why “Thermonuclear”? Bringing two positive charges together Requires high velocity = high temperature

Nuclear Fusion - A Digression Thermonuclear Hydrogen Fusion D + T => He + n

Nuclear Fusion - A Digression Thermonuclear Hydrogen Fusion D + T => He + n

Nuclear Fusion - A Digression Thermonuclear Hydrogen Fusion D + T => He + n

Nuclear Fusion - A Digression Thermonuclear Hydrogen Fusion D + T => He + n Advantages Fuel source - deuterium, tritium from waterFuel source - deuterium, tritium from water - tritium also from reactors - tritium also from reactors No risk of nuclear accidentNo risk of nuclear accident No air pollutionNo air pollution Minimal radioactivity?Minimal radioactivity?

The “Big Idea” of Solar System Evolution The Second Law of Thermodynamics Heat can never pass spontaneously from a colder to a hotter body. As a result of this fact, natural processes that involve energy transfer must have one direction, and all natural processes are irreversible.

Profound Consequence: Equilibrium requires an Energy Source

Planetary Atmospheres Mercury Trace of He, Na, O Venus 96% CO o C 90 atmospheres Earth 77% N 2, 21% O 2 15 o C 1 atmosphere Moon Trace of He, Na, Ar Mars 95% CO o C 0.01 atmospheres

Planetary Atmospheres Retention of Atmosphere Retention of Atmosphere Atmospheric particles (atoms, molecules, dust) Atmospheric particles (atoms, molecules, dust) respond to gravity in same way as any body respond to gravity in same way as any body Atmosphere will escape if velocities of atmospheric particles (THERMAL VELOCITY) (THERMAL VELOCITY) are greater than ESCAPE VELOCITY of planet ESCAPE VELOCITY of planet

Escape Velocity - “a threshold velocity” Escape Velocity - “a threshold velocity” Escape Velocity - Minimum speed at which two objects will Escape Velocity - Minimum speed at which two objects will not be held together by their mutual gravity not be held together by their mutual gravity R M Planetary Atmospheres

Thermal Velocities of Atmospheric Particles Thermal Velocities of Atmospheric Particles Planetary Atmospheres Values for speeds are just for example - depends on temperature

Peak Thermal Velocity Peak Thermal Velocity Planetary Atmospheres m particle = mass of atom or molecule T = temperature in o K k = Boltzmann constant = 1.4 x joules/K Note V thermal increases with higher T Note V thermal increases with higher T Note V thermal decreases with higher m particle Note V thermal decreases with higher m particle

Peak Thermal Velocity Peak Thermal Velocity Same mass particles Planetary Atmospheres 0 Velocity of particles Number of particles Low temperature Medium temperature High temperature

Peak Thermal Velocity Peak Thermal Velocity Same temperature Planetary Atmospheres 0 Velocity of particles Number of particles High mass particles (e.g., CO 2 ) Medium mass particles (e.g., H 2 O) Low mass particles (e.g., H)

Peak Thermal Velocity Peak Thermal Velocity Planetary Atmospheres

Retention of Atmosphere Retention of Atmosphere Planetary Atmospheres 0 Velocity of particles Number of particles Low temperature Medium temperature High temperature Escape Velocity Escape from Planet Surface Tension of drop of Water Evaporation Escape Velocity Escape from Planet Rule of Thumb - if V esc > 5 x V thermal, then retain an atmosphere Rule of Thumb - if V esc > 5 x V thermal, then retain an atmosphere

Retention of Atmosphere Retention of Atmosphere Example - consider Earth and Moon - T ≈ 300 K Example - consider Earth and Moon - T ≈ 300 K H = 1.7 x kg O = 2.7 x kgH 2 O = 3.0 x kg Planetary Atmospheres For H, For H 2 O,

Retention of Atmosphere Retention of Atmosphere Example - consider Earth and Moon - T ≈ 300 K Example - consider Earth and Moon - T ≈ 300 K Planetary Atmospheres For H, V thermal = 2.3 km/sec For H 2 O, V thermal = 0.5 km/sec V escape, Earth = 11.2 km/sec No H, retains H 2 0 V escape, Earth = 11.2 km/sec No H, retains H 2 0 V escape, Moon = 2.4 km/sec No H, no H 2 0 V escape, Moon = 2.4 km/sec No H, no H 2 0

The escape velocity of Mercury is 4.3 km/sec. The escape velocity of Mars is 5.0 km/sec. Mercury does not have a substantial atmosphere; Mars has an atmosphere. This is primarily because A) Mars is further from the Sun so any gases are much colder A) Mars is further from the Sun so any gases are much colder B) Mars has a 20% higher escape velocity B) Mars has a 20% higher escape velocity C) CO 2 has more mass on Mars than on Mercury C) CO 2 has more mass on Mars than on Mercury D) Mars is a dynamically active planet with active volcanoes D) Mars is a dynamically active planet with active volcanoes ConcepTest!

Planetary Atmospheres Greenhouse Effect Greenhouse Effect 90 atmospheres!

Planetary Atmospheres Greenhouse Effect Greenhouse Effect CO 2 CO 2 H 2 0 H watts/m 2 in 240 out 50% reflected by clouds and surface Small fraction escapes into space

Planetary Atmospheres Greenhouse Effect Greenhouse Effect Energy In Energy Out 100 energy units 100% gate 50% gate 200 energy units stored in equlibrium

Planetary Atmospheres Greenhouse Effect Greenhouse Effect Energy In Energy Out 100 energy units 100% gate 1% gate 10, 000 energy units stored in equlibrium

Planetary Atmospheres Greenhouse Effect Greenhouse Effect