Dust Storms Mars and Earth. Bit of Administration …. ReadingReading –BSNV Chaps. 10, 11 12-week exam!12-week exam! –Tonight, 7:15-8:30 pm, 3425 Sterling

Dust StormsDust StormsMars and EarthMars and Earth

Bit of Administration ….Bit of Administration ….

• ReadingReading– BSNV Chaps. 10, 11BSNV Chaps. 10, 11

• 12-week exam!12-week exam!– Tonight, 7:15-8:30 pm, 3425 Sterling HallTonight, 7:15-8:30 pm, 3425 Sterling Hall

• Mathieu office hours for pre-test questionsMathieu office hours for pre-test questions– All day todayAll day today

Nuclear Fusion - A DigressionNuclear Fusion - A Digression

Thermonuclear Hydrogen Fusion 4 H => HeThermonuclear 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


Thermonuclear Hydrogen Fusion D + T => He + nThermonuclear Hydrogen Fusion D + T => He + n







AdvantagesAdvantages

• 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 pollution No air pollution • Minimal radioactivity?Minimal radioactivity?

The “Big Idea” of Solar System EvolutionThe “Big Idea” of Solar System Evolution

The Second Law of ThermodynamicsThe Second Law of Thermodynamics

Heat can never pass spontaneously from a colderHeat can never pass spontaneously from a colderto a hotter body. to a hotter body.

As a result of this fact, As a result of this fact, natural processes that involve energy transfer natural processes that involve energy transfer

must have one direction, must have one direction, and all natural processes are and all natural processes are

irreversible.irreversible.

Profound Consequence:Profound Consequence:Equilibrium requires an Energy SourceEquilibrium requires an Energy Source

Planetary AtmospheresPlanetary Atmospheres

MercuryMercury

Trace ofTrace ofHe, Na, OHe, Na, O

VenusVenus

96% CO96% CO22

470 470 ooCC90 atmospheres90 atmospheres

EarthEarth

77% N77% N22, 21% O, 21% O22

15 15 ooCC1 atmosphere1 atmosphere

Moon Trace of He, Na, ArMoon Trace of He, Na, Ar

MarsMars

95% CO95% CO22

-50 -50 ooCC0.01 atmospheres0.01 atmospheres


• Retention of AtmosphereRetention of Atmosphere

• Atmospheric particles (atoms, molecules, dust) Atmospheric particles (atoms, molecules, dust) respond to gravity in same way as any bodyrespond to gravity in same way as any body

Atmosphere will escape Atmosphere will escape if velocities of atmospheric particlesif velocities of atmospheric particles

((THERMAL VELOCITYTHERMAL VELOCITY) ) are greater than are greater than

ESCAPE VELOCITYESCAPE VELOCITY of planet of planet

• Escape Velocity - “a threshold velocity”Escape Velocity - “a threshold velocity”

• Escape Velocity - Minimum speed at which two objects willEscape Velocity - Minimum speed at which two objects will not be held together by their mutual gravitynot be held together by their mutual gravity

€

Vescape =2GM

R RM


• Thermal Velocities of Atmospheric ParticlesThermal Velocities of Atmospheric Particles


Values for speeds are just for example - depends on temperature

• Peak Thermal VelocityPeak Thermal Velocity

€

Vthermal =2kT

mparticle


mparticle = mass of atom or moleculeT = temperature in oKk = Boltzmann constant = 1.4 x 10-23 joules/K

• Note VNote Vthermalthermal increases with higher T increases with higher T• Note VNote Vthermalthermal decreases with higher m decreases with higher mparticleparticle


Same mass particlesSame mass particles


0 Velocity of particles

Num

ber

of p

arti

cles

Low temperature

Medium temperature

High temperature


Same temperatureSame temperature



Num

ber

of p

arti

cles

High mass particles (e.g., CO2)

Medium mass particles (e.g., H2O)

Low mass particles (e.g., H)



• Retention of AtmosphereRetention of Atmosphere



Num

ber

of p

arti

cles

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 VRule of Thumb - if Vescesc > 5 x V > 5 x Vthermalthermal, then retain an atmosphere, then retain an atmosphere

• Retention of AtmosphereRetention of Atmosphere• Example - consider Earth and Moon - T ≈ 300 KExample - consider Earth and Moon - T ≈ 300 K

H = 1.7 x 10H = 1.7 x 10-27-27 kg kgO = 2.7 x 10O = 2.7 x 10-26-26 kg kg HH22O = 3.0 x 10O = 3.0 x 10-26-26 kg kg


€

Vthermal = 2 x 1.4x10-23 x 300

1.7 x 10-27= 2300 m/sec = 2.3 km/secFor H,

For H2O,

€

Vthermal = 2 x 1.4x10-23 x 300

3.0 x 10-26= 500 m/sec = 0.5 km/sec

• Retention of AtmosphereRetention of Atmosphere• Example - consider Earth and Moon - T ≈ 300 Example - consider Earth and Moon - T ≈ 300 KK


For H, Vthermal = 2.3 km/sec

For H2O, Vthermal = 0.5 km/sec

VVescape, Earthescape, Earth = 11.2 km/sec No H, retains H = 11.2 km/sec No H, retains H2200

VVescape, Moonescape, Moon = 2.4 km/sec No H, no H = 2.4 km/sec No H, no H2200

The escape velocity of Mercury is 4.3 km/sec. The escape velocity 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 of Mars is 5.0 km/sec. Mercury does not have a substantial atmosphere; Mars has an atmosphere. This is primarily because atmosphere; Mars has an atmosphere. This is primarily because

A) Mars is further from the Sun so any gases are much colderA) Mars is further from the Sun so any gases are much colder B) Mars has a 20% higher escape velocityB) Mars has a 20% higher escape velocity C) COC) CO22 has more mass on Mars than on Mercury has more mass on Mars than on Mercury

D) Mars is a dynamically active planet with active volcanoesD) Mars is a dynamically active planet with active volcanoes

ConcepTest!ConcepTest!


• Greenhouse EffectGreenhouse Effect

90 atmospheres!90 atmospheres!

Planetary AtmospheresPlanetary Atmospheres• Greenhouse EffectGreenhouse Effect

COCO22

HH2200

240 240 watts/mwatts/m22

inin

240 240 watts/mwatts/m22

outout50% reflected by50% reflected by

clouds and surfaceclouds and surface

Small fractionSmall fractionescapes intoescapes into

spacespace


Energy In Energy Out

100 energy units 100 energy units

100% gate 50% gate

200 energy unitsstored

in equlibrium


Energy In Energy Out

100 energy units 100 energy units

100% gate 1% gate

10, 000 energy unitsstored

in equlibrium


Documents

Dust Storms Mars and Earth. Bit of Administration …. ReadingReading –BSNV Chaps. 10, 11 12-week exam!12-week exam! –Tonight, 7:15-8:30 pm, 3425 Sterling