The Solar SystemThe Solar System

09.19.07 / 09.20.0709.19.07 / 09.20.07

Essential QuestionsEssential Questions

What are distinguishing features of solar What are distinguishing features of solar system bodies?system bodies?

What are Kepler’s laws and how do they What are Kepler’s laws and how do they apply to planetary motion?apply to planetary motion?

What is the nebular hypothesis?What is the nebular hypothesis?

Overview of the solar system Overview of the solar system

Solar system includes Solar system includes • SunSun• Eight planets and their satellitesEight planets and their satellites• AsteroidsAsteroids• CometsComets• Meteoroids Meteoroids

Kuiper BeltKuiper Belt

2.8 - 4.6 billion miles away2.8 - 4.6 billion miles awayProbably tens-of-thousands of rocky, icy Probably tens-of-thousands of rocky, icy

objectsobjects Includes PlutoIncludes PlutoDiscovered circa 1992Discovered circa 1992Predicted in 1951 by Gerald Kuiper Predicted in 1951 by Gerald Kuiper

The solar systemThe solar system

The orbits of most asteroids The orbits of most asteroids lie between Mars and Jupiterlie between Mars and Jupiter

Minor members of the Minor members of the solar system solar system

AsteroidsAsteroids• Most lie between Mars and JupiterMost lie between Mars and Jupiter• Small bodies – largest (Ceres) is about 620 Small bodies – largest (Ceres) is about 620

miles in diametermiles in diameter• Some have very eccentric orbitsSome have very eccentric orbits• Irregular shapesIrregular shapes• Origin is uncertain Origin is uncertain

Image of asteroid 951 Image of asteroid 951 (Gaspra)(Gaspra)

Minor members of the Minor members of the solar system solar system

CometsComets• Often compared to large, "dirty snowballs"Often compared to large, "dirty snowballs"• CompositionComposition

• Frozen gasesFrozen gases• Rocky and metallic materialsRocky and metallic materials

Minor members of the Minor members of the solar system solar system

CometsComets• OriginOrigin

• Not well knownNot well known• Form at great distance from the SunForm at great distance from the Sun

Comet Hale-BoppComet Hale-Bopp

Minor members of the Minor members of the solar system solar system

MeteoroidsMeteoroids• CalledCalled meteorsmeteors when they enter Earth's when they enter Earth's

atmosphereatmosphere• A meteor shower occurs when Earth A meteor shower occurs when Earth

encounters a swarm of meteoroids encounters a swarm of meteoroids associated with a comet's pathassociated with a comet's path

• Meteoroids are referred to as Meteoroids are referred to as meteoritesmeteorites when they are found on Earth when they are found on Earth

Overview of the solar system Overview of the solar system

A planet's orbit lies in an A planet's orbit lies in an orbital planeorbital plane • Similar to a flat sheet of paperSimilar to a flat sheet of paper• The orbital planes of the planets are The orbital planes of the planets are

inclinedinclined• Planes of seven planets lie within 3 degrees of Planes of seven planets lie within 3 degrees of

the Sun's equatorthe Sun's equator• Mercury's is inclined 7 degreesMercury's is inclined 7 degrees• Pluto's is inclined 17 degrees (That crazy Pluto's is inclined 17 degrees (That crazy

Pluto)Pluto)

Overview of the solar system Overview of the solar system

Two groups of planets occur in the solar Two groups of planets occur in the solar systemsystem • TerrestrialTerrestrial (Earth-like) planets (Earth-like) planets

• Mercury through MarsMercury through Mars• Small, dense, rockySmall, dense, rocky• Low escape velocitiesLow escape velocities

Overview of the solar system Overview of the solar system

Two groups of planets occur in the solar Two groups of planets occur in the solar systemsystem • JovianJovian (Jupiter-like) planets (Jupiter-like) planets

• Jupiter through NeptuneJupiter through Neptune• Large, low density, gaseousLarge, low density, gaseous• MassiveMassive• Thick atmospheres composed of hydrogen, Thick atmospheres composed of hydrogen,

helium, methane, and ammoniahelium, methane, and ammonia• High escape velocitiesHigh escape velocities

• Pluto not included in either group (oddball)Pluto not included in either group (oddball)

The planets The planets drawn to scaledrawn to scale

Evolution of the planets Evolution of the planets

Nebular hypothesisNebular hypothesis • Planets formed about 5 billion years agoPlanets formed about 5 billion years ago• Solar system condensed from a gaseous Solar system condensed from a gaseous

nebulanebula As the planets formed, the materials As the planets formed, the materials

that compose them separated that compose them separated • Dense metallic elements (iron and nickel) Dense metallic elements (iron and nickel)

sank toward their centerssank toward their centers• Lighter elements (silicate minerals, oxygen, Lighter elements (silicate minerals, oxygen,

hydrogen) migrated toward their surfaceshydrogen) migrated toward their surfaces

Kepler’s LawsKepler’s Laws

Law 1: The planet orbit is ellipses with the Law 1: The planet orbit is ellipses with the Sun at one of two fociSun at one of two foci

Law 2: The line connecting the planet to Law 2: The line connecting the planet to the Sun sweeps equal areas in equal timethe Sun sweeps equal areas in equal time

Law 3: The periods of planets’ revolutions Law 3: The periods of planets’ revolutions is proportional to their distances from the is proportional to their distances from the SunSun

Law 1Law 1

http://astro.isi.edu/notes/gravity.htmlhttp://astro.isi.edu/notes/gravity.html

Law 2Law 2

http://burro.astr.cwru.edu/Academics/Astr221/Gravity/kepler2.htmhttp://burro.astr.cwru.edu/Academics/Astr221/Gravity/kepler2.htm

Law 3Law 3

http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.htmlhttp://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html

Eight or Nine? Eight or Nine?

PlutoPluto• Discovered in 1930Discovered in 1930• Highly eccentric orbit causes it to Highly eccentric orbit causes it to

occasionally travel inside the orbit of occasionally travel inside the orbit of Neptune, where it resided from 1979 Neptune, where it resided from 1979 through February 1999through February 1999

• Moon (Charon) discovered in 1978Moon (Charon) discovered in 1978

Pluto and its Pluto and its moon Charon moon Charon as compared as compared to the size of to the size of

EarthEarth

A decision to makeA decision to make

With the discovery of the Kuiper Belt, With the discovery of the Kuiper Belt, astronomers need to make on of two astronomers need to make on of two choices:choices:allow the possibility of many, many more allow the possibility of many, many more

planetsplanetscreate a more restrictive definition of planetcreate a more restrictive definition of planet

They chose this second option They chose this second option They then created possible definitionsThey then created possible definitions

Potential definition 1Potential definition 1

A planet would need to a) revolve around A planet would need to a) revolve around a star, b) be massive enough to have a star, b) be massive enough to have formed into a round shape, c) not be a formed into a round shape, c) not be a moon, and d) not be another starmoon, and d) not be another star

This option would have resulted in 12 This option would have resulted in 12 planets, with more possible in the future planets, with more possible in the future

Potential definition 2Potential definition 2

The same as the first with one additionThe same as the first with one addition the planet must have “cleared the the planet must have “cleared the

neighborhood around its orbit.”neighborhood around its orbit.”Because Pluto’s orbit crosses paths with Because Pluto’s orbit crosses paths with

Neptune, it would not qualifyNeptune, it would not qualifyThis definition results in 8 planetsThis definition results in 8 planetsThis is the one the International Astronomical This is the one the International Astronomical

Union chose to acceptUnion chose to acceptPluto hasn’t changed, just our definition of Pluto hasn’t changed, just our definition of

planetplanet

Light pollutionLight pollution

http://epod.usra.edu/archive/epodviewer.php3?oid=92448http://epod.usra.edu/archive/epodviewer.php3?oid=92448

Source: University of HawaiiSource: University of Hawaii

Houses cause pollution tooHouses cause pollution too

Better lightingBetter lighting

Source: NASASource: NASAsee also p. 664 in home textsee also p. 664 in home text

ResourcesResources

International Dark-Sky SocietyInternational Dark-Sky Society International Astronomical UnionInternational Astronomical UnionLight Pollution Abatement Program Light Pollution Abatement Program

(LPAP) Canada(LPAP) Canada