Introduction-DefinitionsIntroduction-Definitions 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 MoonOur Moon
Moon escape speed is only 2.4 km/sMost gases have escaped the moon since its
formationSome material from solar wind stays around
briefly, but this does not amount to muchMoon has no shield from lethal X-rays and
ultraviolet radiation from the sun and from other particles in space
MercuryMercury
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 StatisticsVenus-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
Venus – Clouds and WindVenus – Clouds and Wind
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 - StatisticsMars - Statistics
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 - AtmosphereMars - Atmosphere
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
JupiterJupiter 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-AtmosphereJupiter-Atmosphere
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 rotationJupiter – 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 Jupiter’s atmosphere
Wind speeds are about 100 m/s
SaturnSaturn
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 cloudsSaturn’s clouds
Appear far less colorful than those of Jupiter (mostly a faint yellow and orange)
Lie lower in atmosphere than JupiterWind speeds are up to 500 m/s near the
equator
UranusUranus
Upper atmosphere very cold: 58 KAtmosphere 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
NeptuneNeptune
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
PlutoPluto
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