Jovian Planet Systems

Jovian Planet Formation

•Beyond the frost line, planetesimals couldaccumulate ___.

•Hydrogen compounds are more abundantthan rock/metal so jovian planets got biggerand acquired H/He atmospheres.

Jovian Planet Formation

•The jovian cores are very similar:~ mass of 10 Earths

•The jovian differences are in the amount ofH/He gas accumulated.

Why did that amount differ?

Differences in Jovian PlanetFormation

•_______: The planet that forms earliestcaptures the most hydrogen and helium gas.Capture _______ after the first solar windblew the leftover gas away.

•________: The planet that forms in a denserpart of the nebula forms its core first.

Density Differences

•Uranus and Neptuneare denser than Saturnbecause they have lessH/He, proportionately.But that explanationdoesn’t work forJupiter

Sizes of Jovian Planets

•Adding mass to ajovian planetcompresses theunderlying gaslayers.

Sizes of Jovian Planets

•Greater compressionis why Jupiter is notmuch larger thanSaturn even though itis three times moremassive.

•Jovian planets witheven more mass canbe smaller thanJupiter.

Interiors of Jovian Planets

•No solid surface

•Layers under high pressure andtemperatures

•Cores (~10 Earth masses) made of hydrogencompounds, metals, and rock

•The layers are different for the differentplanets — WHY?

Comparing Jovian Interiors

•Models suggest that cores of jovian planets havesimilar composition.

•Lower _________ inside Uranus and Neptune meanno metallic hydrogen.

Inside Jupiter

•High pressure insideof Jupiter causes thephase of hydrogento change withdepth.

•Hydrogen ____ likea metal at greatdepths because itselectrons movefreely.

Jupiter’s Magnetosphere

•Jupiter’s strong magnetic field gives it an enormousmagnetosphere.

•Gases escaping Io feed the donut-shaped Io torus.

Aurora on Jupiter

What is the weather like onjovian planets?

Jupiter’s Atmosphere

•Hydrogen compounds inJupiter form clouds.

•Different cloud layerscorrespond to freezingpoints of differenthydrogen compounds.

•Other jovian planets havesimilar cloud layers.

Methane on Uranus and Neptune

•Methane gas onNeptune and Uranusabsorbs red light buttransmits blue light.

•Blue light reflectsoff methane clouds,making thoseplanets look blue.

Jupiter’sGreatRedSpot

•A storm ______ as wide as Earth

•Has existed for at least __ centuries

Weather on Jovian Planets

•All the jovian planets have strong winds andstorms.

Sizes of Moons

•Small moons (< 300 km)

—No geological activity

•Medium-sized moons (300–1,500 km)

—Geological activity in past

•Large moons (> 1,500 km)

—Ongoing geological activity

Small Moons

•Far morenumerous thanthe medium andlarge moons

•Not enough_______ to bespherical:“potato-shaped”

Medium andLarge Moons

•Enough self-gravity tobe spherical

•Have substantialamounts of ice

•Formed ________around jovian planets

•Circular orbits in samedirection as planetrotation

Io’s Volcanic Activity

•Io is the most volcanically active body in thesolar system, but why?

Io’s Volcanoes

•Volcanic eruptions continue to change Io’ssurface.

______________

Io is squished andstretched as it orbitsJupiter.

But why is itsorbit soelliptical?

Orbital__________

Every 7 days,these threemoons line up.

The tugs add up overtime, making all threeorbits elliptical.

Europa’s Ocean: Waterworld?

Tidal Stresses Crack Europa’sSurface Ice

Tidal stresses crack Europa’ssurface ice

Tidal flexingcloses crack,grinds up ice

Tidal flexingopens crack,leaving tworidges

Europa’s Interior Also Warmed by Tidal Heating

Europa

•Europa

•Diameter 3138 km

•Mass 4.8 x 1022kg

•Smooth youngsurface

•Oxygen atmosphere(not of biologicorigin)

•Ices and water?

•Second possible placefor life in our solarsystem.

Ganymede

•Largest moon in thesolar system

•Clear evidence ofgeological activity

•Tidal heating plusheat from radio-active decay?

Callisto

•“Classic” craterediceball

•No tidal heating,no orbitalresonances

•But it hasmagnetic field !?

Titan’s Atmosphere

•Titan is the onlymoon in the solarsystem which has athick atmosphere.

•It consists mostly ofnitrogen with someargon, methane, andethane.

Why are jovian planet moonsmore geologically active thansmall rocky planets?

Rocky Planets vs. Icy Moons

•Rock melts at _____temperatures.

•Only large rockyplanets have enoughheat for activity.

•Ice melts at _____temperatures.

•Tidal heating canmelt internal ice,driving activity.

•Much fartherfrom Sun thaninner planets

•Mostly H/He;no solid surface

•___ times moremassive thanEarth

•Many moons,rings

Jupiter

Jupiter’s moonscan be asinteresting asplanetsthemselves,especiallyJupiter’s fourGalilean moons

• ___ (shown here): Active volcanoes all over

• ______: Possible subsurface ocean

• ________: Largest moon in solar system

• ________: A large, cratered “ice ball”

Saturn

•Giant and gaseous like Jupiter

•Spectacular _____

•Many moons, including cloudy Titan

•Cassini spacecraft currently studying it

Rings are ___solid; they aremade ofcountlesssmall chunksof ice androck, eachorbiting like atiny moon.

Artist’s conception

The Rings of Saturn

What are Saturn’s rings like?

•They are made up of numerous, tinyindividual particles.

•They orbit over Saturn’s equator.

•They are very thin.

Spacecraft View of Ring Gaps

Gap Moons

•Some small moonscreate gaps withinrings.

Jovian Ring Systems

•All four jovian planets have ring systems.

•Others have smaller, darker ring particles than does Saturn.

Why do the jovian planets haverings?

•They formed from dust created in impactson moons orbiting those planets.

How do we know this?

How do we know?

•Rings aren’t leftover from planet formationbecause the particles are too small to havesurvived this long.

•There must be a continuous replacement oftiny particles.

•The most likely source is impacts with thejovian moons.

Ring Formation

•Jovian planets all have rings because theypossess many small moons close-in.

•Impacts on these moons are random.

•Saturn’s incredible rings may be an “accident”of our time.

•Smaller thanJupiter/Saturn;much larger thanEarth

•Made of H/He gasand hydrogencompounds (H2O,NH3, CH4)

•Extreme ________

•Moons and rings

Uranus

•Similar to Uranus(except for axistilt)

•Many moons(including Triton)

Neptune

Radiation andoutflowingmatter fromthe Sun —the___________— blew awaythe leftovergases.

The Solar Wind

Swarms of Smaller Bodies

•Many rockyasteroids andicy cometspopulate thesolar system.

Asteroids and Comets

•Leftovers from the accretion process

•Rocky _________ inside frost line

•Icy ______ outside frost line

Asteroid Facts

•Asteroids are rocky leftovers of planet formation.

•The largest is Ceres, diameter ~1,000 km.

•There are 150,000 in catalogs, and probably over amillion with diameter >1 km.

•Small asteroids are more common than large asteroids.

•All the asteroids in the solar system wouldn’t add up toeven a small terrestrial planet.

Asteroids are cratered and not round.

Asteroids with Moons

•Some large asteroidshave their ownmoon.

•Asteroid Ida has atiny moon namedDactyl.

Asteroid Orbits

•____ asteroids orbitin a belt betweenMars and Jupiter.

•______ asteroidsfollow Jupiter’sorbit.

•Orbits of ____-Earth asteroidscross Earth’s orbit.

Orbital Resonances

•Asteroids in orbitalresonance withJupiter experienceperiodic nudges.

•Eventually thosenudges moveasteroids out ofresonant orbits,leaving gaps in thebelt.

Origin of Asteroid Belt

•Rocky planetesimalsbetween Mars andJupiter did notaccrete into a planet.

•Jupiter’s gravity,through influence oforbital resonances,stirred up asteroidorbits and preventedtheir accretion into aplanet.

Origin of Meteorites

•Most meteorites are pieces of _________.

Meteor Terminology

•_________: A rock from space that fallsthrough Earth’s atmosphere.

•______: The bright trail left by a meteoroid.

•_________: The rock that hits the ground.

Meteorite Types

1._________: Unchanged in compositionsince they first formed 4.6 billion yearsago

2._________: Younger, have experiencedprocesses like volcanism or differentiation

Primitive Meteorites

Processed Meteorites

Meteorites from Moon and Mars

•A few meteorites arrive from the Moon andMars

•Composition differs from the asteroidfragments

•A cheap (but slow) way to acquire moon rocksand Mars rocks

Comet Facts

•Formed beyond the frost line, comets are icycounterparts to asteroids.

•The nucleus of a comet is like a “dirty snowball.”

•Most comets do ___ have tails.

•Most comets remain perpetually frozen in theouter solar system.

•Only comets that enter the _____ solar systemgrow tails.

_______ of Comet

•A “dirty snowball”

•Source of materialfor comet’s tail

Anatomy of a Comet

•____ is atmospherethat comes fromheated nucleus.

•______ tail is gasescaping from coma,pushed by solarwind.

•____ tail is pushedby photons.

Growth of Tail

Origin of Earth’s Water

•Water mayhave come toEarth by wayof icyplanetesimalsfrom the outersolar system.

Famous Comets

•Halley’s Comet

–Edmund Halley

–76 year period

–Nucleus 15x8 km

–Next appearance 2062

•Hale Bopp

–Alan Hale and Thomas Bopp

–4200 year period

–50-60 million mile tail

–Orbital speed

•98,000 mph at perihelion

•250 mph at aphelion

Photograph made by the Giotto spacecraft of the nucleus of Halley's comet. Thespacecraft was approximately 1000 kilometers (about 620 miles) from the nucleus—deep inside Halley's coma of gas—during the time this picture was made. (Copyright1986, Max Planck Institute for Aeronomy; courtesy Harold Reitsema, Ball Aerospace.)

Comet Hale-Bopp

•Shoemaker-Levy 9

–Collided with Jupiter

–400 km nucleus

–Broke into 21 pieces before impact (A-W)

•Frag A generated an energy equivalent to225,000,000,000 tons of TNT

–Crater ½ Earth’s diameter

Comets eject small particles that follow the comet around in itsorbit and cause meteor showers when Earth crosses the comet’sorbit.

Meteors in a shower appear to emanate from the same area of skybecause of Earth’s motion through space.

______ belt:

On orderly orbitsfrom 30–100 AU indisk of solar system

____ cloud:

On random orbitsextending to about50,000 AU

Only a tiny number ofcomets enter the innersolar system; moststay far from the Sun.

How did they get there?

•Kuiper belt comets formed in the Kuiper belt: flat plane,aligned with the plane of planetary orbits, orbiting in thesame direction as the planets.

•Oort cloud comets were once closer to the Sun, but theywere kicked out there by gravitational interactions withjovian planets: spherical distribution, orbits in anydirection.