© Sierra College Astronomy Department The Terrestrial Worlds

© Sierra College Astronomy Department© Sierra College Astronomy Department

The Terrestrial WorldsThe Terrestrial Worlds

© Sierra College Astronomy Department© Sierra College Astronomy Department 22


OverviewOverview

We will be comparing the Earth to the other We will be comparing the Earth to the other terrestrial planets and the Moonterrestrial planets and the MoonWhile there are obvious differences as one looks While there are obvious differences as one looks at the surface features:at the surface features:– Moon and Mercury: barren, crater filled worldsMoon and Mercury: barren, crater filled worlds– Mars: Large canyons and volcanoes, some cratersMars: Large canyons and volcanoes, some craters– Venus: Thick atmosphere, some volcanoes, and Venus: Thick atmosphere, some volcanoes, and

features indicating activity, some cratersfeatures indicating activity, some craters– Earth: Modest atmosphere, volcanoes, water, life, Earth: Modest atmosphere, volcanoes, water, life,

great geological activitygreat geological activity

So why is the Earth geologically active?So why is the Earth geologically active?



Earth’s Structure & CompositionEarth’s Structure & CompositionSome Basic Facts:Some Basic Facts:– Earth bulges at equator about 21 km more than at Earth bulges at equator about 21 km more than at

poles.poles.– The earth velocity at the equator is ~1600 km/hr The earth velocity at the equator is ~1600 km/hr

(1000 miles/hr), whereas at mid-latitudes the velocity (1000 miles/hr), whereas at mid-latitudes the velocity is 1100 km/hr (700 miles/hr).is 1100 km/hr (700 miles/hr).

– DensityDensity - ratio of mass to volume - of the Earth is - ratio of mass to volume - of the Earth is 5.525.52 g/cmg/cm33. (Water’s density is 1 g/cm. (Water’s density is 1 g/cm33, aluminum is 2.7 , aluminum is 2.7 g/cmg/cm33, and iron is 7.8 g/cm, and iron is 7.8 g/cm33.).)

Overall CompositionOverall Composition– The The crust of thecrust of the earth is mostly (73%) composed of earth is mostly (73%) composed of

silicatessilicates - (silicon and oxygen). - (silicon and oxygen).– Other elements are aluminum, iron, calcium, Other elements are aluminum, iron, calcium,

magnesium, sodium, potassium, titanium and others magnesium, sodium, potassium, titanium and others (1%).(1%).



Earth’s Structure & CompositionEarth’s Structure & Composition

The Interior of the Earth (The Interior of the Earth (overall density = 5.5 g/cmoverall density = 5.5 g/cm33))Earth’s interior is determined by analyzing travel times Earth’s interior is determined by analyzing travel times of two types of waves generated by earthquakes.of two types of waves generated by earthquakes.Earth’s interior is made up of three layers:Earth’s interior is made up of three layers:– CrustCrust is the thin (<100 km) outermost layer of the Earth and is the thin (<100 km) outermost layer of the Earth and

has a density of has a density of 2.5–3 g/cm2.5–3 g/cm33. The top part of the crust is . The top part of the crust is relatively cool region of rock called the relatively cool region of rock called the lithosphere.lithosphere.

– MantleMantle is the thick (2,900 km), solid layer between the crust is the thick (2,900 km), solid layer between the crust and the Earth’s core. Density of the mantle is and the Earth’s core. Density of the mantle is 3–9 g/cm3–9 g/cm33. The . The crust “floats” on top of the mantle.crust “floats” on top of the mantle.

– CoreCore is the central part of the Earth, composed of a is the central part of the Earth, composed of a solid inner solid inner corecore and a and a liquid outer coreliquid outer core. Density of the core ranges from . Density of the core ranges from 9–13 g/cm9–13 g/cm33 and is probably composed of iron and nickel. and is probably composed of iron and nickel.

Increasing density trend is called Increasing density trend is called differentiationdifferentiation - - sinking of denser materials toward the center of planets sinking of denser materials toward the center of planets or other objects.or other objects.



Earth’s Structure & CompositionEarth’s Structure & Composition

Interior temperature increases ~ 2Interior temperature increases ~ 2o o K/100 K/100 meters of depth. The Earth’s core is believed to meters of depth. The Earth’s core is believed to be ~ 6500 K.be ~ 6500 K.The Earth and other planets gained heat form The Earth and other planets gained heat form the process of formationthe process of formationCore is heated by Core is heated by radioactive decayradioactive decay which which releases heat and is contained in the core by releases heat and is contained in the core by the outer layers.the outer layers.Recall that through radioactive dating, the Earth Recall that through radioactive dating, the Earth is about 4.5 billion years old.is about 4.5 billion years old.



Internal Heat and Geologic ActivityInternal Heat and Geologic Activity

Interior heat drives the geologic activity on the Interior heat drives the geologic activity on the terrestrial planetsterrestrial planetsConvectionConvection is the process by which hot is the process by which hot material expands and rises while cooler material expands and rises while cooler material contracts and fallsmaterial contracts and falls– Air does this very quicklyAir does this very quickly– The Earth’s mantle moves a few cm/yearThe Earth’s mantle moves a few cm/year

Internal heat depends on the size of the planet Internal heat depends on the size of the planet (actually the surface-area-to-volume ratio, (actually the surface-area-to-volume ratio, see see Cosmic Calculations 7.1Cosmic Calculations 7.1), so Earth and Venus ), so Earth and Venus have a great left over, while Mercury and the have a great left over, while Mercury and the Moon have little and Mars has someMoon have little and Mars has some



Earth’s MagnetosphereEarth’s Magnetosphere

Earth’s Magnetic FieldEarth’s Magnetic FieldA A magnetic fieldmagnetic field is a region of space where is a region of space where magnetic forces can be detected. The region magnetic forces can be detected. The region around a planet is called a around a planet is called a magnetospheremagnetosphereEarth’s magnetic poles are not located at its Earth’s magnetic poles are not located at its poles of rotation. The location of the poles of rotation. The location of the magnetic poles changes with time.magnetic poles changes with time.Dynamo effectDynamo effect is the model that explains is the model that explains the Earth’s and other planets’ magnetic the Earth’s and other planets’ magnetic fields as due to currents within a fields as due to currents within a liquidliquid iron iron core core and a rapidly spinning planetand a rapidly spinning planet..



Earth’s MagnetosphereEarth’s Magnetosphere

TheThe Van Allen belts Van Allen belts are doughnut-shaped are doughnut-shaped regions composed of charged particles regions composed of charged particles (protons & electrons) emitted by the Sun & (protons & electrons) emitted by the Sun & captured by the magnetic field of the Earth.captured by the magnetic field of the Earth.AurorasAuroras result from disturbances in the result from disturbances in the Earth’s magnetic field that cause some of Earth’s magnetic field that cause some of the particles to follow the magnetic field lines the particles to follow the magnetic field lines down to the atmosphere, where their down to the atmosphere, where their collisions with atoms of the air cause it to collisions with atoms of the air cause it to glow.glow.



Shaping the EarthShaping the Earth

There are 4 processes which shape the There are 4 processes which shape the virtually all features on Earthvirtually all features on Earth

1.1. Impact CrateringImpact Cratering Bowl shaped from asteroids or meteorsBowl shaped from asteroids or meteors

2.2. VolcanismVolcanism Eruption of lava from planet’s interiorEruption of lava from planet’s interior

3.3. TectonicsTectonics Disruption of planet’s surface by internal forcesDisruption of planet’s surface by internal forces

4.4. ErosionErosion Wearing down or building of geological Wearing down or building of geological

features by wind, water, ice etc…features by wind, water, ice etc…



Impact CrateringImpact Cratering

As a general rule the craters made by meteors As a general rule the craters made by meteors are 10 times bigger than the impactor and 10-are 10 times bigger than the impactor and 10-20% as deep as the crater is wide.20% as deep as the crater is wide.Most impacts happened very early in the history Most impacts happened very early in the history of the solar systemof the solar systemThe most prominent impact crater on Earth is The most prominent impact crater on Earth is Meteor Crater near Winslow, Arizona (only Meteor Crater near Winslow, Arizona (only 50,000 years ago).50,000 years ago).Many of the craters on the Earth have been Many of the craters on the Earth have been wiped out by erosion processeswiped out by erosion processes– Not true for Moon and MercuryNot true for Moon and Mercury


The number of craters in a given region The number of craters in a given region can tell one the age of the planet/moon can tell one the age of the planet/moon since the last major change on surfacesince the last major change on surface– Does not necessarily indicate formation ageDoes not necessarily indicate formation age

Erosion from wind, water, and lava will Erosion from wind, water, and lava will wipe out craters in a given regionwipe out craters in a given region– This led to determining the development of This led to determining the development of

different parts of the planet/moondifferent parts of the planet/moon


Impact Cratering



VolcanismVolcanism

Volcanism occurs when underground molten Volcanism occurs when underground molten rock finds it way through the lithosphere. This is rock finds it way through the lithosphere. This is due for 3 reasons:due for 3 reasons:– Molten rock is generally less dense than solid rockMolten rock is generally less dense than solid rock– Most of the Earth’s interior is not molten and it Most of the Earth’s interior is not molten and it

requires a chamber of molten rock to be squeezed requires a chamber of molten rock to be squeezed up the surfaceup the surface

– Molten rock often has gas inside of it, leading to Molten rock often has gas inside of it, leading to dramatic eruption and to dramatic eruption and to outgassingoutgassing

The most common gasses released are water The most common gasses released are water vapor, carbon dioxide, nitrogen, and sulfur vapor, carbon dioxide, nitrogen, and sulfur gasses (Hgasses (H22S or SOS or SO22))



Plate TectonicsPlate Tectonics

Plate TectonicsPlate TectonicsAlfred Wegener is credited with first Alfred Wegener is credited with first developing the idea of developing the idea of continental driftcontinental drift - - the gradual motion of the continents relative the gradual motion of the continents relative to one another.to one another.Rift zoneRift zone is a place where tectonic plates is a place where tectonic plates are being pushed apart, normally by molten are being pushed apart, normally by molten material being forced up out of the mantle.material being forced up out of the mantle.

Subduction ZoneSubduction Zone is where two plates are is where two plates are forced together.forced together.



ErosionErosion

The surface of the Earth is changed by The surface of the Earth is changed by erosionerosion, the processes that break down or , the processes that break down or transport rock through the action of ice, liquid, transport rock through the action of ice, liquid, or gasor gas– Valleys shaped by glaciersValleys shaped by glaciers– Canyons carved by riversCanyons carved by rivers– Shifting of sand dunes by the airShifting of sand dunes by the air

Erosion can pile up sediments into layers called Erosion can pile up sediments into layers called sedimentarysedimentary rocks (Ex. Grand Canyon) rocks (Ex. Grand Canyon)The Earth has the most erosion of any The Earth has the most erosion of any terrestrial planetterrestrial planet



Earth’s AtmosphereEarth’s Atmosphere

The Earth’s atmosphere formed in two ways.The Earth’s atmosphere formed in two ways.– Heating the solid material by volcanic action or Heating the solid material by volcanic action or

by violent asteroid impacts. This released the by violent asteroid impacts. This released the gases from the rocks.gases from the rocks.

– Gases were brought here by comets.Gases were brought here by comets.

Both hypotheses are difficult to validate, but a Both hypotheses are difficult to validate, but a combinationcombination of both is most probable. of both is most probable.

Biological activity then altered the original Biological activity then altered the original atmosphere.atmosphere.




Earth’s atmosphere consists of about 77% Earth’s atmosphere consists of about 77% nitrogen (Nnitrogen (N22), 21% oxygen (O), 21% oxygen (O22), with minor ), with minor amounts of water vapor (Hamounts of water vapor (H22O), carbon O), carbon dioxide (COdioxide (CO22), argon (Ar), and trace amounts ), argon (Ar), and trace amounts of ozone (Oof ozone (O33).).The Earth’s atmosphere is “layered” The Earth’s atmosphere is “layered” according to temperature and composition.according to temperature and composition.– 2/32/3 of the atmospheric is only 10 km (6 mi) from of the atmospheric is only 10 km (6 mi) from

the surface of the Earththe surface of the Earth

The Earth’s atmosphere absorbs certain The Earth’s atmosphere absorbs certain amounts of light and allow other to passamounts of light and allow other to pass




About 25-50 km above the surface of the About 25-50 km above the surface of the Earth (in the Earth (in the stratospherestratosphere) is the ) is the ozone ozone layerlayer, which is an efficient absorber of , which is an efficient absorber of UV radiation from the Sun. This UV radiation from the Sun. This absorption causes the temperature of absorption causes the temperature of the atmosphere to peak at the ozone the atmosphere to peak at the ozone layer.layer.




The The greenhouse effectgreenhouse effect is the atmosphere’s is the atmosphere’s process of “trapping” heat emanating from the process of “trapping” heat emanating from the ground (originally captured from the sun).ground (originally captured from the sun).– The atmosphere becomes another source of heat (in The atmosphere becomes another source of heat (in

addition to the sun)addition to the sun)

The greenhouse effect is enhanced by so-called The greenhouse effect is enhanced by so-called greenhouse gassesgreenhouse gasses : mainly water vapor, carbon : mainly water vapor, carbon dioxide, and methanedioxide, and methane



The Moon and MercuryThe Moon and Mercury

The Moon’s geologyThe Moon’s geologyThe Moon’s surface can be divided into The Moon’s surface can be divided into two main landforms: two main landforms: lunar marialunar maria and and highlandshighlands (mountainous and cratered) (mountainous and cratered) regions.regions.MariaMaria (plural of (plural of maremare) are any of the ) are any of the lowlands of the Moon (some circled by lowlands of the Moon (some circled by mountains) that resemble a sea when mountains) that resemble a sea when viewed from Earth.viewed from Earth.



The Moon’s SurfaceThe Moon’s Surface

The The MariaMaria were caused (3 to 4 billion years ago, just after the were caused (3 to 4 billion years ago, just after the Moon was formed) by large impacts cracking through the crust Moon was formed) by large impacts cracking through the crust and the consequent magma flow from the Moon’s mantle.and the consequent magma flow from the Moon’s mantle.Asymmetry of maria between the two sides of Moon is caused Asymmetry of maria between the two sides of Moon is caused by differences in crust thickness (which ranges in depth from by differences in crust thickness (which ranges in depth from 60-100 km and is thinner on Earth-facing side).60-100 km and is thinner on Earth-facing side).This asymmetry also lead to the “locking” of one face of the This asymmetry also lead to the “locking” of one face of the Moon always towards the Earth (since the maria are made of Moon always towards the Earth (since the maria are made of denser materials).denser materials).The interior of the Moon has cooled too much for this to occur The interior of the Moon has cooled too much for this to occur againagainMicrometeoritesMicrometeorites, sand sized particles from space, remain as , sand sized particles from space, remain as the only major erosion processthe only major erosion process



The Moon and MercuryThe Moon and Mercury

Mercury’s geology – extreme conditionsMercury’s geology – extreme conditionsRadar observations show that Mercury rotates once Radar observations show that Mercury rotates once very 58.65 Earth days, which is precisely 2/3 of its very 58.65 Earth days, which is precisely 2/3 of its orbital period.orbital period.Mercury’s solar day is quite different from its sidereal Mercury’s solar day is quite different from its sidereal day. The solar day is 176 Earth days long (two day. The solar day is 176 Earth days long (two Mercurian years.)Mercurian years.)Only 2 longitudes on Mercury experience noon while Only 2 longitudes on Mercury experience noon while the planet is at perihelionthe planet is at perihelionHigh temperatures on Mercury can reach 425°C High temperatures on Mercury can reach 425°C (790°F), well above the melting point of lead (330°C (790°F), well above the melting point of lead (330°C or 626°F).or 626°F).On the night-side of Mercury, temperatures can fall to On the night-side of Mercury, temperatures can fall to -150°C (-250°F).-150°C (-250°F).



Mercury and the MoonMercury and the Moon

Mercury’s geology Mercury’s geology - - Moon ComparisonMoon Comparison

Mariner 10Mariner 10 flew by Mercury in 1974 (and flew by Mercury in 1974 (and subsequently twice more), returning a total of 4,000 subsequently twice more), returning a total of 4,000 photographs for the three fly-bys.photographs for the three fly-bys.Mercury appears similar to our Moon; both are Mercury appears similar to our Moon; both are covered with many impact craters.covered with many impact craters.Mercury’s craters are less prominent; the planet’s Mercury’s craters are less prominent; the planet’s surface gravity is twice that of the Moon so loose surface gravity is twice that of the Moon so loose material will not stack as steeply.material will not stack as steeply.Ray patterns are also less extensive on Mercury Ray patterns are also less extensive on Mercury because of the higher gravity.because of the higher gravity.



Mercury’s SurfaceMercury’s Surface

Mercury’s surface history is thought be:Mercury’s surface history is thought be:– Mercury was hot and melted due to radioactive Mercury was hot and melted due to radioactive

decay and expanded in sizedecay and expanded in size– This fractured the crust and allowed lava to reach This fractured the crust and allowed lava to reach

the surface to form the the surface to form the intercrater plainsintercrater plains– Lava eruptions in impact basins formed theLava eruptions in impact basins formed the

smooth plainssmooth plains– Then the interior cooled and the planet shrunk Then the interior cooled and the planet shrunk

cracking the surface forming thecracking the surface forming the scarpsscarps– This probably happened in the first 700 million This probably happened in the first 700 million

years after Mercury formedyears after Mercury formed



Mercury and the MoonMercury and the Moon

A large “bulls-eye” impact crater called A large “bulls-eye” impact crater called Caloris Basin is visible.Caloris Basin is visible.

The Moon has a similar impact regionThe Moon has a similar impact region

This impact was so intense that there is This impact was so intense that there is broken terrain in the region opposite of broken terrain in the region opposite of the Caloris basinthe Caloris basin



MarsMars

Mars’s BasicsMars’s BasicsMars orbits the Sun at an average of 1.524 AU Mars orbits the Sun at an average of 1.524 AU (about 228 million km).(about 228 million km).Mars’ orbit is more eccentric than Earth’s, so Mars’ orbit is more eccentric than Earth’s, so Mars’ distance from the Sun varies from 210 Mars’ distance from the Sun varies from 210 million km to 250 million km.million km to 250 million km.Mars takes 1.88 Earth years to complete its Mars takes 1.88 Earth years to complete its orbit around the Sun.orbit around the Sun.Polar caps of water-ice and carbon dioxide can Polar caps of water-ice and carbon dioxide can be seenbe seen



MarsMars

Mars’ sidereal period is 24Mars’ sidereal period is 24hh3737mm; its ; its solarsolar day is day is 2424hh4040mm long, very similar to that of Earth. long, very similar to that of Earth.Mars’ equator is tilted 25.2° with respect to its Mars’ equator is tilted 25.2° with respect to its orbital plane, close to Earth’s 23.4°.orbital plane, close to Earth’s 23.4°.We see seasons on Mars as we do on Earth.We see seasons on Mars as we do on Earth.– The polar caps grow and shrink accordinglyThe polar caps grow and shrink accordingly

Because of Mars’ eccentric orbit, the southern Because of Mars’ eccentric orbit, the southern hemisphere exhibits greater seasonal shifts in hemisphere exhibits greater seasonal shifts in temperature than does the northern temperature than does the northern hemisphere.hemisphere.– These can have significant effect on the winds of These can have significant effect on the winds of

MarsMars


Geology of MarsGeology of MarsBesides the polar caps, Mars has other Besides the polar caps, Mars has other remarkable featuresremarkable featuresThe southern hemisphere has most of the The southern hemisphere has most of the higher elevation and the great impact region higher elevation and the great impact region called Hellas Basin and most of the impact called Hellas Basin and most of the impact craterscratersThe northern hemisphere has the lower The northern hemisphere has the lower elevation, few impact craters and most of elevation, few impact craters and most of the volcanoesthe volcanoes


MarsMars



MarsMars

The largest volcano is Olympus Mons, who The largest volcano is Olympus Mons, who height of 24 km (15 mi) is twice that of Earth’s height of 24 km (15 mi) is twice that of Earth’s largest mountain.largest mountain.– Several other large volcanoes can be found in the Several other large volcanoes can be found in the

surrounding surrounding Tharsis RegionTharsis Region

One reason Mars can “grow” larger volcanoes One reason Mars can “grow” larger volcanoes than Earth is because they lack Earth-like than Earth is because they lack Earth-like tectonic plates. Formed over a hot spot of lava tectonic plates. Formed over a hot spot of lava that wells up from within a planet, a volcano that wells up from within a planet, a volcano can grow to enormous size if it does not move can grow to enormous size if it does not move off the hot spot.off the hot spot.



MarsMars

There were some tectonic activities in Mars’ past: There were some tectonic activities in Mars’ past: Valles MarinerisValles Marineris is an enormous canyon on Mars is an enormous canyon on Mars that stretches nearly 4,800 km (3,000 mi).that stretches nearly 4,800 km (3,000 mi).– However, it was not carved out by a river nor a result of However, it was not carved out by a river nor a result of

Earth-like plate tectonicsEarth-like plate tectonics

– Instead it is a split in the crust which caused the Tharsis Instead it is a split in the crust which caused the Tharsis Region to bulge outwardRegion to bulge outward

– There do appear to be runoff channels on the edges of the There do appear to be runoff channels on the edges of the canyon which may have been formed by the outpouring of canyon which may have been formed by the outpouring of subsurface watersubsurface water

There may be current geologic actively, though Mars There may be current geologic actively, though Mars will “die” in the next few billion yearswill “die” in the next few billion years


Ancient Water on MarsAncient Water on MarsCould Mars have been water filled in its past?Could Mars have been water filled in its past?– Outflow channel seem to imply that water flowed 2-3 Outflow channel seem to imply that water flowed 2-3

billion years agobillion years ago

RoversRovers Spirit Spirit and and OpportunityOpportunity (Mars Exploration (Mars Exploration Missions: Missions: MER-MER-AA and MER- and MER-B; B; RoversRovers) landed on ) landed on Mars in 2004 looking for evidence of ancient waterMars in 2004 looking for evidence of ancient water– OpportunityOpportunity found rocks that must have been soaking found rocks that must have been soaking

in water at some time: Jarosite and the “blueberries” in water at some time: Jarosite and the “blueberries” containing hematitecontaining hematite


MarsMars



MarsMars

Present Water on MarsPresent Water on MarsUnder the current conditions, free flowing water Under the current conditions, free flowing water is unlikely to exist on Mars since the pressure is unlikely to exist on Mars since the pressure and temperature are too low.and temperature are too low.– Water will only exist as a gas or solid on MarsWater will only exist as a gas or solid on Mars– However, there is evidence of “gullies” which seemed However, there is evidence of “gullies” which seemed

to have running water in the recent pastto have running water in the recent past

However, water or water-ice may exist just However, water or water-ice may exist just underneath the surface of the planet.underneath the surface of the planet.– OdysseyOdyssey and and Mars ExpressMars Express orbiter both saw evidence orbiter both saw evidence

for subsurface waterfor subsurface water



MarsMars

Why did Mars Change?Why did Mars Change?Mars’ likely was wetter and possibly warmer some 3 Mars’ likely was wetter and possibly warmer some 3 billion years agobillion years ago– Probably had a thicker atmosphere to allow rainfallProbably had a thicker atmosphere to allow rainfall– Outgassing of water and COOutgassing of water and CO22 from volcanoes would have from volcanoes would have

created a sufficient greenhouse effectcreated a sufficient greenhouse effect– A denser atmosphere would allow liquid water to flow on A denser atmosphere would allow liquid water to flow on

surfacesurface– COCO22

in the atmosphere dissolved in water and into rocks, in the atmosphere dissolved in water and into rocks, causing the atmospheric temperature to drop, freezing all causing the atmospheric temperature to drop, freezing all the water, though much of the water and COthe water, though much of the water and CO22 was lost into was lost into spacespace

– Oxygen formed from water which remained, COOxygen formed from water which remained, CO2 2 rusted the rusted the surface giving Mars the ruddy appearance of todaysurface giving Mars the ruddy appearance of today


Currently there:Currently there:– Mars Global SurveyorMars Global Surveyor andand OdysseyOdyssey (Orbiters;Relays)(Orbiters;Relays)

– SpiritSpirit and and OpportunityOpportunity (Mars Exploration Missions: (Mars Exploration Missions: MER-MER-AA and MER-and MER-B; B; RoversRovers))

– Mars ExpressMars ExpressBeagle 2Beagle 2 roverrover crashed on surface, but crashed on surface, but orbiterorbiter is working fine is working fine and it is taking some of the highest resolution pictures of the and it is taking some of the highest resolution pictures of the Martian surface ever from orbitMartian surface ever from orbit

– Mars Reconnaissance OrbiterMars Reconnaissance Orbiter Even higher resolution of surface, subsurface, atmosphereEven higher resolution of surface, subsurface, atmosphere

– Phoenix Phoenix landerlander (2008) – mission ended(2008) – mission endedDigger arms, oven and portable laboratoryDigger arms, oven and portable laboratoryLanded in polar regions, discovered ice just under the surfaceLanded in polar regions, discovered ice just under the surface


Current and Upcoming Mars MissionsCurrent and Upcoming Mars Missions


Mars Science Laboratory (Landed Aug 2012)Mars Science Laboratory (Landed Aug 2012)Called “Curiosity” Called “Curiosity” Bigger and better rover with many cameras and instrumentsBigger and better rover with many cameras and instruments

Maven (Maven (Mars Atmospheric and Volatile EvolutioN; Mars Atmospheric and Volatile EvolutioN; landed 2014)landed 2014) Exploring the Martian atmosphere and how it is changing today and in Exploring the Martian atmosphere and how it is changing today and in the pastthe past

Up Next:Up Next:

ExoMars/Trace Gas Orbiter (2016 by ESA)ExoMars/Trace Gas Orbiter (2016 by ESA)Includes “demonstration” landerIncludes “demonstration” lander

Orbiting spacecraft that will help with telecommunicationsOrbiting spacecraft that will help with telecommunicationsOrbiter looking for trace gasesOrbiter looking for trace gases

ExoMars/Trace Gas Rover- (2018 ExoMars/Trace Gas Rover- (2018 byby ESA) ESA)Looking for organic materials on Mars.Looking for organic materials on Mars.Prelude to return sample mission.Prelude to return sample mission.


Current and Upcoming Mars MissionsCurrent and Upcoming Mars Missions


Is Venus Geologically Active?Is Venus Geologically Active?Since Venus is only 5% smaller than the Earth, we expect it to be Since Venus is only 5% smaller than the Earth, we expect it to be geologically activegeologically active

Orbiting probes Orbiting probes Pioneer Venus 1Pioneer Venus 1 (1978), (1978), Venera 15 Venera 15 andand 16 16 (1983-84), and (1983-84), and MagellanMagellan (1990-93) have produced detailed (1990-93) have produced detailed radar maps of Venus’s surface.radar maps of Venus’s surface.

About two-thirds of Venus’s surface is covered with rolling hills. About two-thirds of Venus’s surface is covered with rolling hills. Highlands occupy <10% of the surface, with lower-lying areas Highlands occupy <10% of the surface, with lower-lying areas making up the rest.making up the rest.

Venus has about 1,000 craters that are larger than a few Venus has about 1,000 craters that are larger than a few kilometers in diameterkilometers in diameter


VenusVenus


Is Venus Geologically Active?Is Venus Geologically Active?While it has volcanoes and a lithosphere contorted While it has volcanoes and a lithosphere contorted by tectonics, Venus has some unique features, such by tectonics, Venus has some unique features, such as as coronaecoronae, probably made of hot rising plumes of , probably made of hot rising plumes of mantle rock.mantle rock.Volcanoes are still active (erupting in the last 100 Volcanoes are still active (erupting in the last 100 million years) since the atmosphere contains sulfuric million years) since the atmosphere contains sulfuric acidacidThere is the lack of erosion on Venus: the winds are There is the lack of erosion on Venus: the winds are very weak.very weak.


VenusVenus


Is Venus Geologically Active?Is Venus Geologically Active?Venus has a lack of Earth-like plate tectonics: no super high Venus has a lack of Earth-like plate tectonics: no super high mountain rangesmountain ranges

Crater counts are uniform across the planet, suggesting an Crater counts are uniform across the planet, suggesting an uniform age for the planet’s surface which is estimated to be uniform age for the planet’s surface which is estimated to be 750 million years old. The uniformity of this age suggest that 750 million years old. The uniformity of this age suggest that the entire planet “repaved” itself at that time.the entire planet “repaved” itself at that time.

Since Venus should be a warm underneath the lithosphere Since Venus should be a warm underneath the lithosphere as the Earth, the lithosphere of Venus must be thicker than as the Earth, the lithosphere of Venus must be thicker than that of the Earth and resists fracturing into piecesthat of the Earth and resists fracturing into pieces– No direct proof of thisNo direct proof of this

– May have come about from higher temperature surfaceMay have come about from higher temperature surface


VenusVenus


Why Is Venus So Hot?Why Is Venus So Hot?Venus surface temperature is about 880Venus surface temperature is about 880°F, hotter than Mercury.°F, hotter than Mercury.

About twice as much sunlight hits Venus as it does EarthAbout twice as much sunlight hits Venus as it does Earth

However, due to the larger abundance of highly reflective clouds of However, due to the larger abundance of highly reflective clouds of Venus today, the Earth actually gets more sunlight to the surface Venus today, the Earth actually gets more sunlight to the surface than Venus.than Venus.– Then why is it hotter on Venus than Earth and Mercury?Then why is it hotter on Venus than Earth and Mercury?

Venus’s closer distance from the Sun created conditions for a Venus’s closer distance from the Sun created conditions for a run-run-awayaway greenhouse effectgreenhouse effect..

Water did not condense out of its atmosphere into oceans that could Water did not condense out of its atmosphere into oceans that could absorb COabsorb CO22 (as happened on Earth). Water vapor also contributed (as happened on Earth). Water vapor also contributed

to the greenhouse effect before it was broken apart the UV radiation to the greenhouse effect before it was broken apart the UV radiation from the Sun and never reformed.from the Sun and never reformed.

Life on Earth may have also help remove COLife on Earth may have also help remove CO22 from the atmosphere from the atmosphere


VenusVenus


The Earth has several unique features The Earth has several unique features for life to existfor life to exist– Surface liquid waterSurface liquid water– Atmospheric oxygenAtmospheric oxygen– Plate tectonicsPlate tectonics– Climate StabilityClimate Stability


Earth as a Living Planet


Our Unique Oceans and AtmosphereOur Unique Oceans and Atmosphere– Water came from outgassing from volcanoes Water came from outgassing from volcanoes

(though the water may have come from (though the water may have come from comet impacts)comet impacts)

– Oxygen did not come from outgassing, but Oxygen did not come from outgassing, but instead came from life itselfinstead came from life itself




Plate TectonicsPlate Tectonics– The lithosphere is broken down into more than a The lithosphere is broken down into more than a

dozen platesdozen plates– These plates get renewed in a process called These plates get renewed in a process called

subduction subduction and so the and so the seafloor crust seafloor crust is never is never more the 100 million years old.more the 100 million years old.

– As a result, the continents have been spreading As a result, the continents have been spreading away from each other for 200 million years.away from each other for 200 million years.




Climate StabilityClimate Stability– The Earth’s climate has remained stable The Earth’s climate has remained stable

enough to keep water liquid on the surfaceenough to keep water liquid on the surface– The Earth’s temperature has remained in The Earth’s temperature has remained in

much the same range despite the fact the much the same range despite the fact the Sun has brightened substantially in the last Sun has brightened substantially in the last 4 billion years (by about 30%).4 billion years (by about 30%).




Climate StabilityClimate Stability– The self-regulation of the Earth temperature is done The self-regulation of the Earth temperature is done

by the COby the CO22 cycle: cycle:Atmospheric COAtmospheric CO22 dissolves in rainwater, creating a mild dissolves in rainwater, creating a mild acidacidThis mild acid rain breaks down minerals in the rocks and This mild acid rain breaks down minerals in the rocks and send the material to the oceanssend the material to the oceansThese minerals combine with dissolved COThese minerals combine with dissolved CO22 making making carbonate rocks such as limestonecarbonate rocks such as limestonePlate tectonics carries the carbonate rocks to subduction Plate tectonics carries the carbonate rocks to subduction zones to the mantlezones to the mantleAs these rocks are pushed deeper into the mantle some of As these rocks are pushed deeper into the mantle some of the subducted rock melts and releases COthe subducted rock melts and releases CO2 2 which outgases which outgases back into the atmosphereback into the atmosphere

– So COSo CO2 2 acts like a thermostatacts like a thermostat




Changes made by Human Activity: Global WarmingChanges made by Human Activity: Global Warming– Global Warming seems to be a reality because of Global Warming seems to be a reality because of

three facts:three facts:By burning fossil fuels we are increasing the amount of By burning fossil fuels we are increasing the amount of greenhouse gasesgreenhouse gasesWe understand the greenhouse effect enough to know that We understand the greenhouse effect enough to know that this increase make our planet warm up at some timethis increase make our planet warm up at some timeSophisticated models have matched the climate data quite Sophisticated models have matched the climate data quite well and may be able to accurately predict to future increase well and may be able to accurately predict to future increase in global temperaturesin global temperatures

– Consequences include the raising a water levels due Consequences include the raising a water levels due to slight warmer water temperature and the melting of to slight warmer water temperature and the melting of inland ice.inland ice.





SummarySummary

Major Characteristics for PlanetsMajor Characteristics for Planets– Orbit Parameters (Semi-major Axis, Eccentricity, Orbit Parameters (Semi-major Axis, Eccentricity,

and Orientation)and Orientation)– Planet Parameters (Mass, Radius, Avg. Density, Planet Parameters (Mass, Radius, Avg. Density,

Sidereal & Solar Spin Rates, and Tilt)Sidereal & Solar Spin Rates, and Tilt)– Interiors (Liquid vs Solid)Interiors (Liquid vs Solid)– Surfaces (Structures and Erosion)Surfaces (Structures and Erosion)– Atmospheres (Composition and Altitude Variation)Atmospheres (Composition and Altitude Variation)– Ionospheres and Ionospheres and MagnetospheresMagnetospheres

Depends on what?Depends on what?

– History in the Solar System EvolutionHistory in the Solar System Evolution



Epilogue: Comparative PlanetologyEpilogue: Comparative Planetology

Surface features vs. planet sizeSurface features vs. planet size– A competition between A competition between internallyinternally driven forces driven forces

vs. vs. externalexternal bombardment bombardment– The smaller the planet the more quickly it The smaller the planet the more quickly it

cooledcooled– Major bombardment ended 4 billion years agoMajor bombardment ended 4 billion years ago

Planetary atmospheresPlanetary atmospheres– The key players: planet Mass, distance from The key players: planet Mass, distance from

sun, planet radiussun, planet radius


General principlesGeneral principles::– Larger planets are more likely to have Larger planets are more likely to have

internal geological activityinternal geological activity– The larger the planet is, the younger its The larger the planet is, the younger its

surface features are likely to besurface features are likely to be– The larger and cooler a planet is, the more The larger and cooler a planet is, the more

likely it is to have an atmosphere, and the likely it is to have an atmosphere, and the more likely this atmosphere is to have more likely this atmosphere is to have retained its original gasesretained its original gases


Epilogue: Comparative PlanetologyEpilogue: Comparative Planetology


The EndThe End

Documents

© Sierra College Astronomy Department The Terrestrial Worlds