Atmospheres of the Atmospheres of the PlanetsPlanets

By Danielle Stroup

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

ConclusionConclusion

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