Quiz #4 Review

17 November 2011

The Outer or Jovian Planets• Jupiter, Saturn,

Uranus and Neptune share certain characteristics:– All are large,

massive, gaseous bodies.

– All have very thick atmospheres, with possibly liquid interiors and solid cores

– All have rings

• They are called Jovian planets because of their resemblance to Jupiter.

Outer Planets: Gaseous/Liquid

•Gaseous with gradual phase transition to liquid (molecules that have hydrogen: water, ammonia, methane)•Low average density – close to that of liquid water on Earth •Rocky core deduced from spacecraft flybys•Chemical composition similar to that of the Sun

•71% Hydrogen, 27% Helium, 2% other (C,N,O,etc.)

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Outer or Jovian Planets

• All the Jovian planets are larger than the Terrestrial planets.• All have similar compositions and are similar to the Sun.• Solar composition is mostly Hydrogen, some Helium, etc.• All have low average densities,• All have rings and many satellites.• None have surfaces but only increasingly dense atmospheres and

rock and metal cores.

Heating and Condensation of the Solar Nebula

• The heat from the Sun prevents ices from reforming on the dust grains in the region near the Sun.

• Ices condensed only in the cooler outer parts of the Solar nebula.

• In the hotter inner portion of the disk only materials like iron and silicates (rock) can condense into solids. Slowly they form clumps of material.

• In the outer portion of the disk much more material can condense as solids including ice. This extra material allows clumps to grow larger and faster.

Gravity does the job• Within the disk, material is

constantly colliding with one another. If the collisions are not too violent material (planetesimals) may stick together.

• In the outer parts of the Solar Nebula the planets become large enough to have a significant gravitational pull and collect gas around them.– Ice is ten times more abundant

than silicates and iron compounds, therefore there is more planet building material in the outer solar system.

• Planets in the inner nebula can not grow enough to collect much gas.

• Eventually most but not all of the material was swept up by the planets.

Atmospheres

• Outer planets– Captured Hydrogen from solar nebula

• Inner planets (such as the Earth)– Volcanic activity– Captured gas from comets that vaporized on

impact

Jupiter

• Has more than 60 moons• Emits more energy than it receives from the Sun –

leftover formation energy, contraction, differentiation• 300x more massive than the Earth; 1000 times less

massive than the Sun • Upper atmosphere contains hydrogen, helium, methane,

ammonia, and water, giving Jupiter a multi-colored appearance

• Atmosphere shows storm features (great red spot) • Atmosphere shows wind shear features

– Alternating bands move in different directions – Due to convection in atmosphere and Coriolis force

• Rising and falling gases are deflected in opposite directions at cloud tops

Jupiter

• Tidal forces exerted on nearest moon, Io, are responsible for the tremendous volcanic activity on that moon.

• Particles expelled by Io’s volcanoes get trapped in Jupiter’s magnetic field

• Particles accelerated by Jupiter’s magnetic field produce radio wave emissions– Strong magnetic field in part due to rotation speed of 10 hours;

enhanced dynamo effect• Outer moons show evidence of ice locked in surface

– Moon Europa may have an ice crust with an ocean underneath• Jupiter + moons resembles a mini-solar system with

dense inner planets/moons and less dense outer planets

Saturn• Also emits more energy than it receives from the Sun,

but not as much as Jupiter• No atmospheric bands like on Jupiter seen in visible light

due to obscuring ammonia ice clouds (beige/tan color)– Jupiter-like atmospheric bands are apparent in infrared light

observations; penetrates upper atmosphere

• Ring origin: comet/asteroid/moon collisions and moons ripped apart by tidal forces exerted by Saturn – Roche limit: moon that gets to close to its planet will be ripped

apart by tidal forces (forces near side of moon is greater that forces on far side).

• Moon Titan has an atmosphere (nitrogen/methane/ethane clouds + lakes)– Temperature is cold enough so that atmospheric gas velocity

less than Titan’s escape velocity– Surface features known by radar mapping

Uranus

• No atmospheric bands like on Jupiter seen in visible light due to obscuring methane ice clouds (blue color).– Jupiter-like atmospheric bands are apparent in

infrared light observations; penetrates upper atmosphere

• Rotation axis is severely tilted (~90 degrees)– Since moons and rings aligned w/ equator, tilt is likely

due to a massive impact during its formation

Neptune

• Weak atmospheric bands like those on Jupiter are seen in visible light due to obscuring methane ice clouds (blue color).– Jupiter-like atmospheric bands are apparent in

infrared light observations; penetrates upper atmosphere

• Moon Triton orbits backwards – opposite Neptune’s rotation direction – likely captured after formation

• Moon Triton has an atmosphere – temperature is cool enough so that gas particle speeds are less than escape velocity.

Earth

• Atmosphere originally from volcanic activity; vaporized comet impacts– UV sunlight breaks up molecules (photo-

disassociation)– Rain removes carbon-dioxide from

atmosphere– Plants convert carbon dioxide to oxygen

• Interior (size of mantle, core) inferred from seismology observations during earthquakes

Earth

• Magnetic field due to rotating molten iron outer core

• Magnetic field reduces deadly solar wind particle flux on Earth’s surface

• Solar wind particles in Earth’s magnetic field strike atmosphere and produce the auroras near the poles– Higher solar activity yields brighter auroras

The Sun

• Sun is 300,000 times more massive than the Earth

• Composition: 71% Hydrogen, 27% Helium, 2% other (C,N,O)

• All gas, powered by nuclear fusion in core– Hydrogen is combined to form Helium in multi-step

process (6 H produce 1 He)

• Tremendous energy generated by fusion is balanced by massive solar gravity– Hydrostatic equilibrium prevents the Sun from either

collapsing or flying apart

The Sun - Interior

• Four main zones inferred from helioseismology (solar vibrations inferred by measuring absorption lines [gas velocities towards and away from us] on all parts of the solar photosphere: – core: nuclear fusion reactor – emits gamma-rays– radiative zone: fusion energy propagates outward

slowly (10s of thousands of years) in a random walk pattern; original gamma ray energy downgraded to lower energies

– convective zone: energy transfer by rising and falling gas motions (solar granules)

– photosphere: the part of the Sun we see directly

The Sun - Interior

• Gas temperature and density increase from the solar surface toward the core– Photosphere T=6000K– Core T=15,000,000K

Solar Magnetic Activity

• Sunspots are evidence of solar magnetic field– Appear in pairs, each a North or South

magnetic pole– Appear darker than surrounding gas because

the magnetic field traps and slows the gas at and below the photosphere, reducing its temperature

– Caused by kinks in the subsurface magnetic field loops due to solar differential rotation

• Equatorial region takes 25 days for one rotation• Poles take about 30 days for one rotation

Solar Cycle

• Defined by counting sunspots

• Measured from minimum to minimum– 11-years between minima

• Sunspots form closer to poles at beginning of cycle and closer to equator at end of cycle

• Sunspot poles switch every 11-years

• Sunspot polarity cycle is 22-years

The Sun – Atmosphere

• Chromosphere: above the photosphere T=up to 50,000K – Spicules: jets of hot gas in magnetic fields

• Corona: T = up to 1 million degrees• High temperatures are due to high gas velocities• Gas is accelerated (and thus heated) by solar

magnetic field in the solar atmosphere• Gas velocities in corona exceed solar escape

velocity solar wind– Solar corona is not in hydrostatic equilibrium

Solar Cycle Influence on Earth Climate

• Solar wind activity affects Earth’s atmosphere thickness

• Earth’s atmosphere thickness affects jet streams

• Ocean temperature changes correlate with sunspot activity