AnnouncementsAnnouncements

● Mar 31Mar 31stst – last day to withdraw from course with a – last day to withdraw from course with a `W' grade`W' grade

● If you don't know your current mark in this course, If you don't know your current mark in this course, email Jonathan (email Jonathan (jdursi@artic.edujdursi@artic.edu))

● Less than ½ of total marks assigned so far in this Less than ½ of total marks assigned so far in this course; still time to make up points course; still time to make up points

● Reading Quiz Marks:Reading Quiz Marks:● Assignment Marks:Assignment Marks:

Review: Multicellular life vs. ColoniesReview: Multicellular life vs. Colonies● Some confusion in Some confusion in

assignment: `when did assignment: `when did multicellular life first arrive?'multicellular life first arrive?'

● One common answer: 2.7 One common answer: 2.7 BYABYA

● Stromatalite fossils?Stromatalite fossils?● Colonies of prokaryotes, not Colonies of prokaryotes, not

multicellular organismsmulticellular organisms● Like mold on bread, yeastLike mold on bread, yeast● Colony of independent single-Colony of independent single-

celled organismcelled organism● Could take any organism and Could take any organism and

transplant it – doesn't depend transplant it – doesn't depend on otherson others

The Search: Our Solar SystemThe Search: Our Solar System● History Of The Solar SystemHistory Of The Solar System

– Planet formationPlanet formation● The MoonThe Moon

– HistoryHistory– ExplorationExploration

● VenusVenus

– Greenhouse effectGreenhouse effect– ExplorationExploration

History of the Solar SystemHistory of the Solar System

● Planets, Comets, Asteroids, MeteoritesPlanets, Comets, Asteroids, Meteorites● Protoplanetary diskProtoplanetary disk● InstabilitiesInstabilities

PlanetsPlanets

● All but Pluto inhabit a plane --- All but Pluto inhabit a plane --- the eclipticthe ecliptic

● From Earth's point of view From Earth's point of view (tilted axis), Sun, Moon, planets (tilted axis), Sun, Moon, planets all trace out a single arc along all trace out a single arc along the skythe sky

● Dense, rocky planets near the Dense, rocky planets near the sun, large fluffy gas giants sun, large fluffy gas giants further outfurther out

OrbitsOrbits

● Planets are falling towards Sun Planets are falling towards Sun due to gravitational accelerationdue to gravitational acceleration

● Moving toward the side fast Moving toward the side fast enough that they missenough that they miss

● Moving too fast – escape entirely, Moving too fast – escape entirely, leave Sunleave Sun

● Move too slowly – fall into SunMove too slowly – fall into Sun● Same with satellites circling Earth, Same with satellites circling Earth,

or Sun orbiting in our galaxy, or...or Sun orbiting in our galaxy, or...

GravityGravity

● Gravity acts between all massive Gravity acts between all massive objectsobjects

● Gravitational force is equal on Gravitational force is equal on both objectsboth objects

● If orbiting, both objects move, not If orbiting, both objects move, not just one, since both are being just one, since both are being acted on by gravityacted on by gravity

● Both orbit the center of mass of Both orbit the center of mass of the systemthe system

● Equal mass objects; center of mass Equal mass objects; center of mass is at the center of the two objectsis at the center of the two objects

GravityGravity

● If one body is more massive, If one body is more massive, then gravitational force is then gravitational force is increasedincreased

● Center of mass tilts towards Center of mass tilts towards more massive bodymore massive body

● Forces still equalForces still equal● Equal force on lighter body Equal force on lighter body

moves it more than the same moves it more than the same force on the heavier bodyforce on the heavier body

● Lighter object moves larger Lighter object moves larger distance than heavier objectdistance than heavier object

GravityGravity

● Force of gravity also increases Force of gravity also increases as objects get neareras objects get nearer

● Inverse Square Law (same as Inverse Square Law (same as light)light)

OrbitsOrbits

● Kepler's Laws: (EMPERICAL)Kepler's Laws: (EMPERICAL)

– Planets travel in ellipses, Planets travel in ellipses, with sun at one focus of with sun at one focus of ellipseellipse

– Area swept out by radius is Area swept out by radius is equal over any equal amount equal over any equal amount of timeof time

– Square of the planet's period Square of the planet's period (the `year' for that planet) (the `year' for that planet) proportional to the distance proportional to the distance to the sun cubed.to the sun cubed.

– PP22 ~ a ~ a33

PlanetsPlanets● Almost all planets are in same Almost all planets are in same

planeplane● All planets (except Uranus) All planets (except Uranus)

rotate more or less in the same rotate more or less in the same plane, as does Sunplane, as does Sun

● Very suggestive of the idea that Very suggestive of the idea that planets, Sun formed from a planets, Sun formed from a disk, as we discussed beforedisk, as we discussed before

● Suggested by Laplace in 1600s.Suggested by Laplace in 1600s.● Disk near star is depleted in Disk near star is depleted in

Hydrogen, Helium by Hydrogen, Helium by evaporationevaporation

Planet FormationPlanet Formation● As disk cools, gas/dust disk can begin As disk cools, gas/dust disk can begin

condensingcondensing● Grains form, which themselves Grains form, which themselves

agglomerate to larger particlesagglomerate to larger particles● Regions where disk is originally dense Regions where disk is originally dense

condense faster, gravitationally attract condense faster, gravitationally attract more materialmore material

● Process of continued agglomeration can Process of continued agglomeration can form planetsform planets

InstabilityInstability● Some processes are naturally stableSome processes are naturally stable

– Burning in main sequence starsBurning in main sequence stars– Core heats up – outer layers puff Core heats up – outer layers puff

up – core cools downup – core cools down– Automatically stabilizes itselfAutomatically stabilizes itself– Ball in a right-side-up bowlBall in a right-side-up bowl

● Once there's a region of high density in Once there's a region of high density in a gas cloud or disk, increase in a gas cloud or disk, increase in gravitational attraction to that region...gravitational attraction to that region...

● UnstableUnstable

– Ball on an up-side-down bowlBall on an up-side-down bowl

Planet FormationPlanet Formation

● Proto-planetary-core starts Proto-planetary-core starts sweeping out material and sweeping out material and planetesimals at its radiusplanetesimals at its radius

● Accrete material streams in from Accrete material streams in from just outside or inside its radiusjust outside or inside its radius

● There is a limit to this process; if There is a limit to this process; if there are planets forming on either there are planets forming on either side, eventually the gaps collide – side, eventually the gaps collide – no more new materialno more new material

● This process of slowly sweeping This process of slowly sweeping up and accreting material can take up and accreting material can take millions of yearsmillions of years

Mystery: `Hot Jupiters'Mystery: `Hot Jupiters'

● A Jupiter couldn't form at 1AU; A Jupiter couldn't form at 1AU; evaporation would prevent such a evaporation would prevent such a gas giant from forminggas giant from forming

● Many of the extra-solar planets Many of the extra-solar planets observed are gas giants at observed are gas giants at distances ~ 1AUdistances ~ 1AU

● What happened?What happened?● Two possibilities:Two possibilities:

– MigrationMigration– Different formation Different formation

mechanismmechanism

Planet FormationPlanet Formation

● Migration is possibleMigration is possible● As planets form and As planets form and

accrete material, they accrete material, they experience a drag forceexperience a drag force

● Drag takes energy from Drag takes energy from planets motion and they planets motion and they fall inwardsfall inwards

Planet FormationPlanet Formation

● Fast formation is also Fast formation is also possiblepossible

● In sufficiently massive disk, In sufficiently massive disk, instabilities can occur much instabilities can occur much faster, and on larger scalesfaster, and on larger scales

● Can happen quickly enough Can happen quickly enough that perhaps giants can form that perhaps giants can form near starnear star

AsteroidsAsteroids

● Failed planet formation Failed planet formation between Mars and Jupiterbetween Mars and Jupiter

● Remnants are thought to be Remnants are thought to be similar to the planetesimals similar to the planetesimals that existed in the rocky-that existed in the rocky-planet zoneplanet zone

● Orbit in the same plane as Orbit in the same plane as the planetsthe planets

CometsComets

● `Dirty snowballs'`Dirty snowballs'● Similar to planetesimals of outer Similar to planetesimals of outer

solar systemsolar system● Two regions: Kuiper BeltTwo regions: Kuiper Belt

– `Asteroid Belt' past Neptune`Asteroid Belt' past Neptune● Oort CloudOort Cloud

– Much much further out Much much further out (100,000 AU)(100,000 AU)

– Perhaps objects kicked out of Perhaps objects kicked out of solar system in early solar system in early formation??formation??

Meteors, MeteoritesMeteors, Meteorites

● Meteors: `falling stars'Meteors: `falling stars'● Caused by incoming object Caused by incoming object

burning up in Earth's atmosphereburning up in Earth's atmosphere● 20,000 – 150,000 mph20,000 – 150,000 mph● Sometimes remnant survives: Sometimes remnant survives:

meteoritemeteorite● Easiest form of space exploration: Easiest form of space exploration:

bits of space come to us!bits of space come to us!● Meteors have contained amino Meteors have contained amino

acidsacids

MeteoritesMeteorites● Different kinds of meteoritesDifferent kinds of meteorites● Carbonaceous Chondrite: very Carbonaceous Chondrite: very

nearly solar composition, minus nearly solar composition, minus volatilesvolatiles

– Most commonMost common– Most primitive?Most primitive?

● Achondrites: likely from Mars, Achondrites: likely from Mars, MoonMoon

● Chondrites: like crusts of Chondrites: like crusts of terrestrial planetsterrestrial planets

● Stony-IronStony-Iron● IronIron

Meteorite ImpactsMeteorite Impacts● Occasionally Earth, other planet Occasionally Earth, other planet

hit by meteor/asteroid/comethit by meteor/asteroid/comet● Chances of two solar system Chances of two solar system

objects colliding objects colliding veryvery small, but small, but there are a lot of objects out therethere are a lot of objects out there

● Even more objects in early solar Even more objects in early solar system; many have been swept system; many have been swept up/accreted/kicked out since thenup/accreted/kicked out since then

● Earth's atmosphere protects Earth's atmosphere protects against smaller objectsagainst smaller objects

Meteorite-House impact Park Forest, IL, Mar 2003

Meteorite ImpactsMeteorite Impacts

● Often does damage to far more Often does damage to far more than just drywallthan just drywall

● Large objects rare but if they do Large objects rare but if they do collide, can be catastrophiccollide, can be catastrophic

● Effect weather on surface of Effect weather on surface of planetplanet

● Even tear planet in two?Even tear planet in two?

The MoonThe Moon

● What the Moon is likeWhat the Moon is like● How it formedHow it formed● Exploration of the moonExploration of the moon

The MoonThe Moon

● No atmosphereNo atmosphere● No geological activityNo geological activity● No waterNo water● -> no erosion-> no erosion● Can provide information Can provide information

about formation of solar about formation of solar system that is absent from system that is absent from EarthEarth

MercuryMercury

● Similar to moonSimilar to moon● Similar sizeSimilar size● Small, empty, simpleSmall, empty, simple● Very close to SunVery close to Sun● No atmosphere to mediate No atmosphere to mediate

temperature swings:temperature swings:

– +750+750oo F in sun F in sun– -230-230o o F in shadeF in shade

Moon's CrateringMoon's Cratering

● Nothing to alter surfaceNothing to alter surface● Complete history of Complete history of

cratering in Moon's historycratering in Moon's history● From predicted cratering From predicted cratering

rate, one expects that crust of rate, one expects that crust of moon formed very quickly moon formed very quickly in solar system historyin solar system history

Exploration of MoonExploration of Moon

● Closeness means best explored Closeness means best explored extraterrestrial bodyextraterrestrial body

● USA,USSR began sending USA,USSR began sending flyby probes, impact probes to flyby probes, impact probes to moon in 1959 (Luna, Ranger)moon in 1959 (Luna, Ranger)

● In 1960s, began sending In 1960s, began sending landers (Luna, Surveyor), landers (Luna, Surveyor), return probes (Zond)return probes (Zond)

● 1968, Apollo 8 – Manned 1968, Apollo 8 – Manned missionmission

● 1969, Apollo 11 – Manned 1969, Apollo 11 – Manned landinglanding

Exploration of MoonExploration of Moon

● Exploration continued through Exploration continued through the 1970s, with probes sent the 1970s, with probes sent with increasingly sophisticated with increasingly sophisticated science equipment, camerasscience equipment, cameras

● Return probes, astronauts Return probes, astronauts brought many lunar samples brought many lunar samples back for analysisback for analysis

Exploration of MoonExploration of Moon

● Earliest probes took better pictures of surface, Earliest probes took better pictures of surface, determined no magnetic fielddetermined no magnetic field

● Once landed on surface, could observe Once landed on surface, could observe abundancesabundances

● Difference between deep craters and surfaceDifference between deep craters and surface● Much lower than even Earth's crust in volatiles Much lower than even Earth's crust in volatiles

(Hydrogen, Carbon, Nitrogen...)(Hydrogen, Carbon, Nitrogen...)● Oxygen isotopes very similar to those in Earth's Oxygen isotopes very similar to those in Earth's

CrustCrust

Exploration of MoonExploration of Moon

● Earliest probes took better pictures of surface, Earliest probes took better pictures of surface, determined no magnetic fielddetermined no magnetic field

● Once landed on surface, could observe Once landed on surface, could observe abundancesabundances

● Difference between deep craters and surfaceDifference between deep craters and surface● Much lower than even Earth's crust in volatiles Much lower than even Earth's crust in volatiles

(Hydrogen, Carbon, Nitrogen...)(Hydrogen, Carbon, Nitrogen...)● Oxygen isotopes very similar to those in Earth's Oxygen isotopes very similar to those in Earth's

CrustCrust

Possible Moon Formation ScenarioPossible Moon Formation Scenario

Possible Moon Formation ScenarioPossible Moon Formation Scenario

● Explains similar Oxygen abundancesExplains similar Oxygen abundances

– Very different from meteoritesVery different from meteorites● Explains fewer volatilesExplains fewer volatiles

– If Earth's iron core had already settled, If Earth's iron core had already settled, impact would have dislodged crust materialimpact would have dislodged crust material

– Heat of impact would have vaporized Heat of impact would have vaporized volatiles volatiles

Moon Effect on Earth LifeMoon Effect on Earth Life

● Tides:Tides:

– Helps drive ocean life to landHelps drive ocean life to land– Helps form tidal pools Helps form tidal pools

(`cells')(`cells')● Moon's effect on tides stronger Moon's effect on tides stronger

than Sun'sthan Sun's● Orbital tilt:Orbital tilt:

– Moon's presence helps Moon's presence helps stabilize Earth's tiltstabilize Earth's tilt

● Both may be helpful, but neither at Both may be helpful, but neither at moment seem crucialmoment seem crucial

VenusVenus

● What Venus is likeWhat Venus is like● The Greenhouse EffectThe Greenhouse Effect● The Runaway Greenhouse EffectThe Runaway Greenhouse Effect

VenusVenus

● Closest to EarthClosest to Earth● ¾ as far away from Sun as ¾ as far away from Sun as

Earth isEarth is● Very similar to Earth's size, Very similar to Earth's size,

densitydensity● Covered by thick, opaque Covered by thick, opaque

cloudsclouds● Clouds opaque to visible, Clouds opaque to visible,

infrared light, but transparent to infrared light, but transparent to radio; can use radar to map radio; can use radar to map surfacesurface

Venus: Inverse Square LawVenus: Inverse Square Law● Venus ¾ as far away from sun, Venus ¾ as far away from sun,

so gets (4/3)so gets (4/3)22 ~ 1.8 times as ~ 1.8 times as much lightmuch light

● Blackbody radiation in radio Blackbody radiation in radio from surface -> 850from surface -> 850oo F on F on surface!surface!

● Much hotter on surface than Much hotter on surface than inverse-square law accounts inverse-square law accounts for.for.

● Heat from surface/geologic Heat from surface/geologic activity? Radar, Soviet probes activity? Radar, Soviet probes say no.say no.

Planet TemperaturesPlanet Temperatures● Earth is continuously Earth is continuously

bombarded by radiation from bombarded by radiation from SunSun

● Why doesn't Earth get hotter Why doesn't Earth get hotter and hotter?and hotter?

Planet TemperaturesPlanet Temperatures

● Earth is continuously bombarded Earth is continuously bombarded by radiation from Sunby radiation from Sun

● Why doesn't Earth get hotter and Why doesn't Earth get hotter and hotter?hotter?

● As Earth warms, glows as a As Earth warms, glows as a blackbodyblackbody

● Heats up more, glows moreHeats up more, glows more● Equilibrium is reached when Equilibrium is reached when

energy coming from Sun equals energy coming from Sun equals energy given off by Earthenergy given off by Earth

● (Stable or Unstable?)(Stable or Unstable?)● Can calculate this eq: -22Can calculate this eq: -22ooFF

Planet TemperaturesPlanet Temperatures

● Not bad, but Earth is on average Not bad, but Earth is on average warmer than that (~60warmer than that (~60ooF)F)

● What happens?What happens?

Planet TemperaturesPlanet Temperatures

● Not bad, but Earth is on average Not bad, but Earth is on average warmer than that (~60warmer than that (~60ooF)F)

● What happens?What happens?● Atmosphere traps some radiation Atmosphere traps some radiation

insideinside● Less heat escaping for a given Less heat escaping for a given

surface temperaturesurface temperature● Pushes equilibrium higherPushes equilibrium higher● Planet is warmer than would be Planet is warmer than would be

without atmospherewithout atmosphere

Greenhouse EffectGreenhouse Effect● This happens in greenhouses, or in This happens in greenhouses, or in

cars on a hot daycars on a hot day● Sunlight streams in through Sunlight streams in through

transparent (to visible light) glass, transparent (to visible light) glass, is absorbed by plants/car seats/etcis absorbed by plants/car seats/etc

● Hot material emits energy as a Hot material emits energy as a blackbody; if outside, would cool blackbody; if outside, would cool somewhatsomewhat

● But glass is But glass is opaqueopaque to infrared to infrared light (where most blackbody light (where most blackbody radiation would be emitted)radiation would be emitted)

● Energy is trapped inside Energy is trapped inside greenhouse/cargreenhouse/car

● Gets hotGets hot

Greenhouse EffectGreenhouse Effect● Earth's Atmosphere, too, Earth's Atmosphere, too,

is transparent to visible is transparent to visible light but largely opaque light but largely opaque to infrared lightto infrared light

● COCO22, water vapor are , water vapor are

`greenhouse gases' `greenhouse gases' which trap some IR in which trap some IR in atmosphereatmosphere

● Much of early COMuch of early CO22 in in

Earth's atmosphere Earth's atmosphere locked up in oceanslocked up in oceans

Greenhouse EffectGreenhouse Effect

● Venus' atmosphere has a huge Venus' atmosphere has a huge amount of Carbon Dioxideamount of Carbon Dioxide

● Traps an enormous amount of heat Traps an enormous amount of heat ● All water completely gone; not All water completely gone; not

merely evaporated, but broken merely evaporated, but broken downdown

● High temperatures make other High temperatures make other compounds more likely than on compounds more likely than on earth – Sulphuric acid, etc.earth – Sulphuric acid, etc.

Runaway Greenhouse EffectRunaway Greenhouse Effect

● Greenhouse effect on a planet with oceans is Greenhouse effect on a planet with oceans is unstable:unstable:

– Planet gets warmerPlanet gets warmer– Increased evaporation of oceansIncreased evaporation of oceans– More water vapor in atmosphereMore water vapor in atmosphere

– (And more CO(And more CO22))

– Greenhouse gas!Greenhouse gas!– Planet gets warmer....Planet gets warmer....

Runaway Greenhouse EffectRunaway Greenhouse Effect

● If Earth were moved to Venus' orbit, runaway If Earth were moved to Venus' orbit, runaway greenhouse effect would occurgreenhouse effect would occur

● And that explains biggest difference between the And that explains biggest difference between the two todaytwo today

● Difference in surface temperature, atmosphere Difference in surface temperature, atmosphere composition,...composition,...

● Much larger effect than naïve estimate from Much larger effect than naïve estimate from distance to Sundistance to Sun

● Large effect of atmosphereLarge effect of atmosphere● Planets as near a Sun-like star as Venus can't Planets as near a Sun-like star as Venus can't

have liquid waterhave liquid water

Assignment for Next Class (Apr 2)Assignment for Next Class (Apr 2)

● Very short (happy break!)Very short (happy break!)● Come up with and consider three processes (at Come up with and consider three processes (at

least one of each) that are either stable or least one of each) that are either stable or unstable.unstable.

● Once something starts happening, either:Once something starts happening, either:

– There's a compensating effect which There's a compensating effect which pushes the system back to where it was, pushes the system back to where it was, (stable) or(stable) or

– There's an effect which pushes whatever's There's an effect which pushes whatever's happening even faster (unstable)happening even faster (unstable)

Reading for Next Class (Apr 2)Reading for Next Class (Apr 2)

● Chapter 13, 14: Mars, and Life on Mars?Chapter 13, 14: Mars, and Life on Mars?

– History of Mars ExplorationHistory of Mars Exploration– Search for WaterSearch for Water– Search for BiologySearch for Biology