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Chapter

The Planets: An Overview

23.1 The Solar System

The terrestrial planets areplanets that are small androcky—Mercury, Venus, Earth,rocky—Mercury, Venus, Earth,and Mars.

The Planets: An Overview

23.1 The Solar System

The Jovian planets arethe huge gas giants— The Jovian planets are

the huge gas giants—Jupiter, Saturn, Uranus,and Neptune.

Jovian planets

23.1

Pluto does not fit into either theJovian or the terrestrial category.

Pluto used to be known as thefurthest planet from the Sun. Ithas now been reclassified bythe International Astronomicalthe International AstronomicalUnion as a dwarf planet,because although it is sphericaland orbits the sun, it shares itsorbit with many smaller bodies.

Orbits of the Planets

The Planets: An Overview

23.1 The Solar System

Size is the most obviousdifference between theterrestrial and Jovian planets.terrestrial and Jovian planets.

Density, chemical makeup,and rate of rotation are otherways in which the two groupsof planets differ.

Planetary Data

The Planets: An Overview

23.1 The Solar System

The Interiors of the Planets

• The substances that• The substances thatmake up the planets aredivided into three groups:gases, rocks, and ices.

The Planets: An Overview

23.1 The Solar System

The Atmosphere of the Planets

• The Jovian planets have verythick atmospheres of hydrogen,

• The Jovian planets have verythick atmospheres of hydrogen,helium, methane, and ammonia.

• By contrast, the terrestrialplanets, including Earth, havemeager atmospheres at best.

Scale of the Planets

Formation of the Solar System

23.1 The Solar System

Nebular Theory• A nebula is a cloud of gasand/or dust in space.and/or dust in space.

• According to the nebulartheory, the sun and planetsformed from a rotating diskof dust and gases.

Formation of the Universe

Formation of the Solar System

23.1 The Solar System

Planetesimals

• Planetesimals are small,• Planetesimals are small,irregularly shaped bodiesformed by collidingmatter.

Planetary Composition, Distancefrom the Sun, and Melting Point

Mercury

Mercury’s Surface

Mercury: The Innermost Planet

23.2 The Terrestrial Planets

Mercury is the innermost andsecond smallest planet; it ishardly larger than Earth’s moon.hardly larger than Earth’s moon.

• Mercury has cratered highlands,much like the moon, and vastsmooth terrains that resemblemaria.

Surface Features

23.2 The Terrestrial Planets

• Mercury hasthe greatest

Surface Temperatures

the greatesttemperatureextremes ofany planet.

Venus

Venus: The Veiled Planet

23.2 The Terrestrial Planets

• The surface temperature of

Surface Temperatures• The surface temperature ofVenus reaches 475oC, and itsatmosphere is 97 percentcarbon dioxide.

Venus

Venus: The Veiled Planet

23.2 The Terrestrial Planets

Venus is similar to Earthin size, density, mass,in size, density, mass,and location in the solarsystem. Thus, it has beenreferred to as “Earth’stwin.”

Venus: The Veiled Planet

23.2 The Terrestrial Planets

• Venus is covered in thickclouds that visible light cannot

Surface Features

clouds that visible light cannotpenetrate.

• About 80 percent of Venus’ssurface consists of plainscovered by volcanic flow.

Mars

Mars: The Red Planet

23.2 The Terrestrial Planets

The Martian Atmosphere

• The Martian atmosphere has only 1• The Martian atmosphere has only 1percent of the density of Earth’s.

• Although the atmosphere of Marsis very thin, extensive dust stormsoccur and may cause the colorchanges observed from Earth.

Mars: The Red Planet

23.2 The Terrestrial Planets

Surface Features

• Most Martian surface features are• Most Martian surface features areold by Earth standards. The highlycratered southern hemisphere isprobably 3.5 billion to 4.5 billionyears old.

Mars

Surface of Mars in polar region

Moons of Mars: Phobos andDeimos

23.2 The Terrestrial Planets

Water on Mars• Some areas of Mars exhibitdrainage patterns similar tothose created by streams onthose created by streams onEarth.

• Images from the Mars GlobalSurveyor indicate thatgroundwater has recentlymigrated to the surface.

Although predominantly red due to thehigh quantities of iron oxide on thesurface, ice-caps can be seen at bothpoles similar in nature to our Arcticand Antarctic. These are howevercomposed mostly of dry ice (frozencomposed mostly of dry ice (frozencarbon dioxide as opposed to water),although in the north it is known thatthe dry ice turns to a gas during thesummer, leaving some water icebehind, but it is not known whetherthis happens in the south.

Water on Mars

Jupiter: Giant Among Planets

23.3 The Outer Planets

Jupiter has a massthat is 2 1/2 timesthat is 2 1/2 timesgreater than the massof all the other planetsand moons combined.

Jupiter: Giant Among Planets

23.3 The Outer Planets

• Jupiter’s hydrogen-helium Structure of Jupiter• Jupiter’s hydrogen-heliumatmosphere also containssmall amounts of methane,ammonia, water, and sulfurcompounds.

Jupiter and the Great Red Spot

Jupiter: Giant Among Planets

23.3 The Outer Planets

• Jupiter’s satellite

Jupiter’s Moons• Jupiter’s satellitesystem, including the 28moons discovered so far,resembles a miniaturesolar system.

Jupiter’s Largest Moons

Jupiter: Giant Among Planets

23.3 The Outer Planets

Jupiter’s Rings• Jupiter’s ring system• Jupiter’s ring systemwas one of the mostunexpecteddiscoveries made byVoyager 1.

Saturn

Moons

Saturn: The Elegant Planet

23.3 The Outer Planets

The most prominentfeature of Saturn is itssystem of rings.feature of Saturn is itssystem of rings.

23.3 The Outer Planets

Features of Saturn

• Saturn’s atmosphere is veryactive, with winds roaring at upto 1500 kilometers per hour.to 1500 kilometers per hour.

• Large cyclonic “storms” similarto Jupiter’s Great Red Spot,although smaller, occur inSaturn’s atmosphere.

Saturn: The Elegant Planet

23.3 The Outer Planets

Saturn’s Rings

• Until the discovery that Jupiter,Uranus, and Neptune have ring

• Until the discovery that Jupiter,Uranus, and Neptune have ringsystems, this phenomenon wasthought to be unique to Saturn.

• Most rings fall into one of twocategories based on particledensity.

Saturn’s Rings

23.3 The Outer Planets

Saturn’s Moons• Saturn’s satellite systemconsists of 31 moons.

• Titan is the largest moon, and it• Titan is the largest moon, and itis bigger than Mercury.

Uranus

Uranus: The Sideways Planet

23.3 The Outer Planets

Instead of being generallyperpendicular to the plane ofperpendicular to the plane ofits orbit like the otherplanets, Uranus’s axis ofrotation lies nearly parallelwith the plane of its orbit.

Uranus

Neptune: The Windy Planet

23.3 The Outer Planets

Winds exceeding 1000kilometers per hour encirclekilometers per hour encircleNeptune, making it one ofthe windiest places in thesolar system.

Neptune

Neptune'sblue color isdue tomethane inmethane intheatmosphere,whichabsorbs redlight.

Pluto: Planet X

23.3 The Outer Planets

Pluto’s orbit is highlyeccentric, causing it toeccentric, causing it tooccasionally travel inside theorbit of Neptune, where itresided from 1979 throughFebruary 1999.

Pluto and its moon Charon

Formerly planet X

Pluto's identity crisisThe International

Astronomical Union (IAU)announced Pluto should nowannounced Pluto should now

be called a "plutoid," twoyears after the organization

voted to demote Pluto to"dwarf planet" status.

The two known and named plutoidsare Pluto and Eris. Plutoids arecelestial bodies in orbit around theSun at a distance greater than that ofNeptune that have sufficient mass fortheir self-gravity to overcome rigidbody forces so that they assume ahydrostatic equilibrium (near-spherical) shape, and that have notspherical) shape, and that have notcleared theneighborhoodaround theirorbit.

Ceres

New Planets? The Future of our solar system!

Sedna

In March 2004, researchers at theCalifornia Institute of technology (Caltech)discovered a body orbiting the sun that isthree times further away from the Earththree times further away from the Earththan Pluto. This puts it well beyond thebounds of the Kuiper Belt as far as weknow, and yet it is approximately three-quarters of the size of Pluto, larger thanQuaoar.

Makemake Named the Newest PlutoidThe red methane-covered dwarf planet,formerly known as 2005 FY9 or“Easterbunny,” is named after a Polynesiancreator of humanity and god of fertility.“The orbit is not particularly strange, but theobject itself is big, probably about two-thirdsthe size of Pluto,” said Michael E. Brown,the size of Pluto,” said Michael E. Brown,who discovered and named Makemake(pronounced MAH-keh MAH-keh).Dr. Brown said the name came to him whenhe was looking for a mythological god andthought of Easter Island in the South Pacific.Makemake was the chief god among peoplewho settled the island.

Asteroids: Microplanets

23.4 Minor Members of the Solar System

An asteroid is a small, rockybody whose diameter can rangefrom a few hundred kilometersfrom a few hundred kilometersto less than a kilometer.

Most asteroids lie between theorbits of Mars and Jupiter. Theyhave orbital periods of three tosix years.

Irregular Orbits of Asteroids

Comets

23.4 Minor Members of the Solar System

Comets are small bodiesmade of rocky and metallicmade of rocky and metallicpieces held together byfrozen gases. Cometsgenerally revolve about thesun in elongated orbits.

23.4 Minor Members of the Solar System

Coma• A coma is the fuzzy, gaseous

component of a comet’s head.

• A small glowing nucleus with a• A small glowing nucleus with adiameter of only a few kilometerscan sometimes be detected withina coma. As comets approach thesun, some, but not all, develop atail that extends for millions ofkilometers.

Comet’s Tail Points Away from the Sun

23.4 Minor Members of the Solar System

Halley’s Comet 1986• The mostfamous short-famous short-period comet isHalley’s comet.Its orbital periodis 76 years.

Comets

23.4 Minor Members of the Solar System

Kuiper Belt

• Like the asteroids in theinner solar system, most

• Like the asteroids in theinner solar system, mostKuiper belt comets move innearly circular orbits that lieroughly in the same plane asthe planets.

Comets

23.4 Minor Members of the Solar System

Oort Cloud• Comets with long orbitalperiods appear to beperiods appear to bedistributed in all directionsfrom the sun, forming aspherical shell around thesolar system called the Oortcloud.

Meteoroids

23.4 Minor Members of the Solar System

A meteoroid is asmall, solid particlesmall, solid particlethat travels throughspace.

Meteoroids

23.4 Minor Members of the Solar System

A meteor is theluminous phenomenonobserved when aluminous phenomenonobserved when ameteoroid enters Earth’satmosphere and burnsup, popularly called ashooting star.

Meteoroids

23.4 Minor Members of the Solar System

A meteorite is anyportion of aportion of ameteoroid thatreaches Earth’ssurface.

Meteor lake Kaali, Estonia

Crater Lake Oregon

23.4 Minor Members of the Solar System

Most meteoroids originate fromany one of the following threesources: (1) interplanetary debristhat was not gravitationally sweptthat was not gravitationally sweptup by the planets during theformation of the solar system, (2)material from the asteroid belt, or(3) the solid remains of cometsthat once traveled near Earth’sorbit.

Major Meteor Showers