Atmospheres of the Planets

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Atmospheres of the Planets

• By Danielle Stroup

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Introduction-Definitions

• Atmosphere consists of molecules and atoms moving
  at various speeds
• Temperature of gas is the measure of the average
  kinetic energy of particles, K½mv² ? kT
• gt larger mass gt smaller speed at given
  temp.
• Atmospheric escape gravity holds down any
  atmosphere of a celestial body
• Thin layers of the atmosphere, far fewer
  collisions occur if escape speed reached here,
  the particles speed into outer space
• Main constituent of lunar atmosphere? Ne-very
  massive

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Our Moon

• Moon escape speed is only 2.4 km/s
• Most gases have escaped the moon since its
  formation
• Some material from solar wind stays around
  briefly, but this does not amount to much
• Moon has no shield from lethal X-rays and
  ultraviolet radiation from the sun and from other
  particles in space

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Mercury

• Long hot solar days and low escape speed 4.3
  km/s
• Escape speed makes it unlikely for Mercury to
  have an atmosphere but a helium and hydrogen
  atmosphere has been detected, which was probably
  picked up by solar wind
• Na and K vapor exists in the atmosphere on the
  day side
• No atmosphere? No insulation from space noon to
  midnight temperatures are severe

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Venus-Atmosphere Statistics

• Atmosphere 60 CO2, 3 N2, some Ar and traces of
  water vapor
• Surface pressure 90 atm
• Surface temperature 740 K probably results from
  the effective trapping of surface heat by CO2 and
  water vapor
• Temperatures vary about 10 K or less from day to
  night
• Has to be a good insulator to result in the high
  temperatures recorded

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Venus Clouds and Wind

• Yellowish-white clouds conceal Venuss surface
  flow at 100 m/s with the upper atmosphere in
  patterns similar to the jet streams of the earth
• 90 Sulfuric acid, H2SO4 mixed with water
• Wind blows from the Equator to the poles in large
  cyclones that culminate in two giant vortices
  that cap the polar regions
• What drives the wind? Solar heating (not unlike
  Earth)
• The wind flows carry heat which helps to keep
  temperatures fairly constant

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Mars - Statistics

• Thin atmosphere
• 95 CO2, 0.10.4 O2, 2-3 N2, 1-2 Ar
• Very similar composition to Venus
• Very dry planet
• Water vapor in atmosphere is found in the
  greatest amounts in high northern latitudes in
  the summer
• Low density of atmosphere, even though it
  contains CO2, limits greenhouse effect
• Surface temperature remains below the freezing
  point of water both day and night
• Temp. difference between day and night? 100 K

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Mars - Atmosphere

• Cannot rain because of low surface pressure,
  about 0.005 times the Earths
• Only in canyons could liquid water exist on the
  surface
• Water may exist in a permafrost layer beneath the
  surface
• A layer of water ice coats the rocks and soil in
  the winter is extremely thin, less than a mm

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Jupiter

• Visible disk of Jupiter is the upper atmosphere
• Has alternating strips of light and dark regions
  (zones and belts) running parallel to the equator
• Light and dark implies that zones are higher than
  the belts because temperature in planets
  atmosphere decreases with altitude

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Jupiter-Atmosphere

• Convective atmospheric flow transports energy out
  to space from the planets interior indicates
  hot interior
• Jupiters upper atmosphere, by mass contains 82
  H2, 18 He, and traces of other elements
  essentially the same composition as the Sun
• Clouds in zones are probably ammonia crystals
• Entire atmosphere? 1000 km thick
• There is no distinct boundary between atmosphere
  and interior

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Jupiter Differential rotation

• Indicates Jupiter acts like a fluid
• Jupiter spins in 9h 50 min at its equator and 9h
  55 min at the poles
• Solid body like the Earth will rotate so each
  point in the surface has same rotational period
• Rapid rotation and large radius produces an
  equatorial speed of 43,000 km/s makes planet
  fairly oblate
• Rotation drives the circulation
• in Jupiters atmosphere
• Wind speeds are about 100 m/s

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Saturn

• Resembles Jupiters atmosphere
• Belts running parallel to equator, driven by
  rapid rotation
• Rotational period 10h 14 min at the equator and
  varies with latitude
• Also shows differential rotation
• Composition mostly H2 and He
• Also has methane, water vapor, and ammonia

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Saturns clouds

• Appear far less colorful than those of Jupiter
  (mostly a faint yellow and orange)
• Lie lower in atmosphere than Jupiter
• Wind speeds are up to 500 m/s near the equator

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Uranus

• Upper atmosphere very cold 58 K
• Atmosphere consists of 15 H2 and He, 60 icy
  materials (water, methane, and ammonia) and 25
  earthy materials (silicates and iron)
• Ammonia clouds
• Low bulk density implies mostly lightweight
  elements exist

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Neptune

• Great Dark Spot storm 30,000 km across, rotating
  counter clockwise in a few days lacks the
  typical atmospheric methane
• Bright cirrus-like clouds accompany the Dark spot
• Most of the clouds change size or shape from one
  rotation from the next
• Atmosphere is likely driven by the outflow of
  Neptunes internal heat

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Pluto

• Atmosphere stretches over 600 km from the
  planets surface
• Probably consists of N2, CO, and methane gas that
  has been released from the ice on the surface as
  the planet is heated
• Surface pressure of a mere 10-8 atm

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Conclusion

• Temperature, clouds, and composition of the
  atmosphere differs from planet to planet
• Escape speed determines whether a planet will be
  able to keep in the atmospheric elements that are
  present
• Rotational speed and internal heat can drive the
  atmospheric circulation