Download DStroupTalk4 - FSU High Energy Physics

Atmospheres of the
Planets
By Danielle Stroup
Introduction-Definitions
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Atmosphere consists of molecules and atoms
moving at various speeds
Temperature of gas is the measure of the average
kinetic energy of particles, K=½mv²  kT
=> larger mass => 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
Our Moon
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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
Mercury
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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
Venus-Atmosphere Statistics
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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
Venus – Clouds and Wind
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Yellowish-white clouds conceal Venus’s 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
Mars - Statistics
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Thin atmosphere
 95% CO2, 0.1–0.4% 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
Mars - Atmosphere
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Cannot rain because of low surface pressure, about
0.005 times the Earth’s
 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
Jupiter
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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 planet’s atmosphere decreases with
altitude
Jupiter-Atmosphere
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Convective atmospheric flow transports energy out to
space from the planet’s interior; indicates hot interior
Jupiter’s 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
Jupiter – Differential rotation
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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 Jupiter’s atmosphere
Wind speeds are about 100 m/s
Saturn
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Resembles Jupiter’s 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
Saturn’s clouds
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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
Uranus
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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
Neptune
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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
Neptune’s internal heat
Pluto
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Atmosphere stretches over 600 km from the
planet’s 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
Conclusion
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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