The Goldilocks Problem?The Goldilocks Problem?

The Goldilocks Problem?The Goldilocks Problem?Astronomical!

Why is Venus so hot…Why is Venus so hot…

and Mars so and Mars so coldcold……

and Earth just right….?and Earth just right….?

Thought QuestionThought Question

What is the main reason why Venus is hotter What is the main reason why Venus is hotter than Earth?than Earth?

A.A. Venus is closer to the Sun than Earth.Venus is closer to the Sun than Earth.B.B. Venus is more reflective than Earth.Venus is more reflective than Earth.

C.C. Venus is less reflective than Earth.Venus is less reflective than Earth.

D.D. Rain stopped, but volcanoes didn’tRain stopped, but volcanoes didn’t

E.E. Human activity has led to declining temperatures on Human activity has led to declining temperatures on Earth.Earth.

Thought QuestionThought Question

What is the main reason why Venus is hotter What is the main reason why Venus is hotter than Earth?than Earth?

A.A. Venus is closer to the Sun than Earth.Venus is closer to the Sun than Earth.

# 1 Answer given by most people… # 1 Answer given by most people… and it’s not correct!and it’s not correct!

Thought QuestionThought Question

What is the main reason why Venus is hotter What is the main reason why Venus is hotter than Earth?than Earth?

A.A. Venus is closer to the Sun than Earth.Venus is closer to the Sun than Earth.B.B. Venus is more reflective than Earth.Venus is more reflective than Earth.

C.C. Venus is less reflective than Earth.Venus is less reflective than Earth.

D.D. Rain stopped, but volcanoes didn’tRain stopped, but volcanoes didn’t

E.E. Human activity has led to declining temperatures on Human activity has led to declining temperatures on Earth.Earth.

Thought QuestionThought Question

What is the main reason why Mars is no longer What is the main reason why Mars is no longer considered habitable (on its surface)considered habitable (on its surface)

A.A. Mars is farther from the Sun than Earth, and too Mars is farther from the Sun than Earth, and too coldcold

B.B. Mars doesn’t have a thick atmosphereMars doesn’t have a thick atmosphere

C.C. Mars’ volcanoes stopped eruptingMars’ volcanoes stopped erupting

D.D. The greenhouse effect is not as strong on Mars The greenhouse effect is not as strong on Mars compared to Earth.compared to Earth.

E.E. Martians screwed up the climate long ago.Martians screwed up the climate long ago.

Thought QuestionThought Question

What is the main reason why Mars is no longer What is the main reason why Mars is no longer considered habitable (on its surface)considered habitable (on its surface)

A.A. Mars is farther from the Sun than Earth, and too Mars is farther from the Sun than Earth, and too coldcold

# 1 Answer given by most people… # 1 Answer given by most people… and it’s not correct!and it’s not correct!

Thought QuestionThought Question

What is the main reason why Mars is no longer What is the main reason why Mars is no longer considered habitable (on its surface)considered habitable (on its surface)

A.A. Mars is farther from the Sun than Earth, and too Mars is farther from the Sun than Earth, and too coldcold

B.B. Mars doesn’t have a thick atmosphereMars doesn’t have a thick atmosphere

C.C. Mars’ volcanoes stopped eruptingMars’ volcanoes stopped erupting

D.D. The greenhouse effect is not as strong on Mars The greenhouse effect is not as strong on Mars compared to Earth.compared to Earth.

E.E. Martians screwed up the climate long ago.Martians screwed up the climate long ago.

Carbon Dioxide CycleCarbon Dioxide Cycle• Terrestrial Planets

can “Recycle” CO2 from atmosphere to crust to atmosphere over time

• Estimate ~25 million years or more for this to occur on Earth

Carbon Dioxide CycleCarbon Dioxide Cycle• How do

atmospheres of Venus & Mars differ in their ability to cycle CO2 from atmosphere to crust and back??

Venus in UV lightVenus in UV light

Venus mapped with RadarVenus mapped with Radar

The surface of VenusThe surface of Venus

Venus’ surfaceVenus’ surface

Venera Probes from 1970’s survived for minutes…

Venus’ surfaceVenus’ surface

Venera Probes from 1970’s survived for minutes…

Why is Venus so hot?Why is Venus so hot?

Venus’ AtmosphereVenus’ Atmosphere

•What is it made of?

•How does it change in height?

•How does it circulate?

Atmosphere of VenusAtmosphere of Venus Venus has Venus has

very thick very thick carbon dioxide carbon dioxide atmosphere with atmosphere with surface pressure surface pressure 90 times larger 90 times larger than Earth.than Earth.

Atmosphere of VenusAtmosphere of Venus Reflective clouds Reflective clouds

contain droplets of contain droplets of sulfuric acidsulfuric acid..

The upper The upper atmosphere has atmosphere has fast winds that fast winds that remain remain unexplained.unexplained.

Venus’ Venus’ AtmosphereAtmosphere

Venus’ AtmosphereVenus’ Atmosphere

Water condenses into clouds, allowing for rain around 0 C

Sun’s UV light disassociates H20 at this height!

Greenhouse Effect on VenusGreenhouse Effect on Venus Thick CO2 Thick CO2

atmosphere atmosphere produces an produces an extremely strong extremely strong greenhouse effectgreenhouse effect..

Earth Earth escapes this escapes this fate because most fate because most of its carbon and of its carbon and water are in water are in rocks rocks and oceans.and oceans.

Why is Venus so hot?Why is Venus so hot?

The greenhouse effect on Venus keeps its The greenhouse effect on Venus keeps its surface temperature at 470°C.surface temperature at 470°C.

But why is the greenhouse effect on Venus But why is the greenhouse effect on Venus so much stronger than on Earth?so much stronger than on Earth?

Runaway Greenhouse EffectRunaway Greenhouse Effect

The runaway greenhouse effect would account The runaway greenhouse effect would account for why Venus has so little water.for why Venus has so little water.

Greater heat, more evaporation

More evaporation, stronger greenhouse effect

Explaining Venus’ AtmosphereExplaining Venus’ Atmosphere

•Lots of Volcanoes

•CO2, H2S04 are outgassed

•CO2 traps infrared heat from Sun

•Atmosphere heats up

•Water can’t condense => No Rain!

Carbon Dioxide CycleCarbon Dioxide Cycle• “Recycle” CO2

from atmosphere to crust to atmosphere over time

• Estimate ~25 million years or more for this to occur on Earth

Carbon Dioxide CycleCarbon Dioxide Cycle• How do

atmospheres of Venus & Mars differ in their ability to cycle CO2 from atmosphere to crust and back??

Carbon Dioxide CycleCarbon Dioxide Cycle• Assume all 3 planets had

similar compositions and conditions “early” in the solar system’s history…

• Assume all 3 had liquid water, active volcanoes, and CO2 in atmosphere

Carbon Dioxide CycleCarbon Dioxide CycleStep 1: Evaporation/Rain

• Liquid water evaporatesLiquid water evaporates

• Condenses into clouds Condenses into clouds in lower atmospherein lower atmosphere

• Rain falls through Rain falls through atmosphere forming atmosphere forming Carbonic Acid (HCarbonic Acid (H22COCO3)3)

CO2 gas is absorbedCO2 gas is absorbed

1

Aside – what does Coca Cola Aside – what does Coca Cola have to do with Astronomy?have to do with Astronomy?

Aside – what does Coca Cola Aside – what does Coca Cola have to do with Astronomy?have to do with Astronomy?

Aside – what does Coca Cola Aside – what does Coca Cola have to do with Astronomy?have to do with Astronomy?

Water & COWater & CO22……

• How do you fill How do you fill lotslots of of bottles with syrup quickly?bottles with syrup quickly?

• PUSHPUSH it in with a it in with a propellantpropellant

• COCO22 is a good choice! is a good choice!

• People like the bubbles!People like the bubbles!

Carbon Dioxide CycleCarbon Dioxide CycleStep 2: Mineral Erosion by Acid Rain

• Carbonic Acid (HCarbonic Acid (H22COCO3) 3) in rivers erodes rocksin rivers erodes rocks

•

2

Carbon Dioxide CycleCarbon Dioxide CycleStep 2: Mineral Erosion by Acid Rain

• Carbonic Acid (HCarbonic Acid (H22COCO3) 3) in rivers erodes rocksin rivers erodes rocks

• Carbonate (COCarbonate (CO332-2-) ion ) ion

picked up in minerals picked up in minerals washed to oceanwashed to ocean

• Calcium easily absorbedCalcium easily absorbed

CO2 is carried to oceansCO2 is carried to oceans

2

Carbon Dioxide CycleCarbon Dioxide CycleStep 3: Tying Carbon into Rocks &

Life!• Calcium from rocks Calcium from rocks

forms CaCOforms CaCO33 (Calcium (Calcium

Carbonate)Carbonate)

• CaCOCaCO33 = Limestone = Limestone

• CaCOCaCO33 = Coral, Mollusk = Coral, Mollusk

shells!shells!

3

CO2 accumulates on CO2 accumulates on seafloorseafloor

Carbon Dioxide CycleCarbon Dioxide CycleStep 3: Tying Carbon to Rocks & Life!

Carbon Dioxide CycleCarbon Dioxide CycleStep 4: Tectonics & Subduction!

• Tectonics gradually pulls Tectonics gradually pulls seafloor downseafloor down

• CaCOCaCO33 broken back into broken back into

CO2 & other mineralsCO2 & other minerals

4 CO2 now inside crustCO2 now inside crust

Carbon Dioxide CycleCarbon Dioxide CycleStep 5: Volcanic Outgassing!

Carbon Dioxide CycleCarbon Dioxide CycleStep 5: Volcanic Outgassing!

• Eventual Volcanic Eventual Volcanic Activity pushes CO2 Activity pushes CO2 back into atmosphereback into atmosphere

5 CO2 now in CO2 now in atmosphere again!atmosphere again!

1

Too Hot for clouds to form low enough

But… Volcanoes don’t stop!

Carbon Dioxide Cycle Carbon Dioxide Cycle Venus Feedback Loop Failure

5

• No RainNo Rain• NO NO CO2 gas CO2 gas

absorbedabsorbed• More CO2 added!More CO2 added!• Runaway Runaway

Greenhouse Effect!Greenhouse Effect!

1

Carbon Dioxide Cycle Carbon Dioxide Cycle Venus Feedback Loop Failure

MarsMars

Schiaparelli’s “Canals”Schiaparelli’s “Canals”

“The Face” :

Is just an illusion…

Pyramids

Happy Faces!

More illusions:

What is real? What is real? A Martian Sunset…A Martian Sunset…

Mars vs. EarthMars vs. Earth

50% Earth’s radius, 10% Earth’s mass50% Earth’s radius, 10% Earth’s mass1.5 AU from the Sun1.5 AU from the SunAxis tilt about the same as EarthAxis tilt about the same as EarthSimilar rotation period (25 hours/”day”)Similar rotation period (25 hours/”day”)Thin COThin CO22 atmosphere: little greenhouse atmosphere: little greenhouse

effecteffect

=>=>Main difference: Mars is SMALLERMain difference: Mars is SMALLER

Mars IS smaller…Mars IS smaller…

And Earth has life!And Earth has life!

Carbon Dioxide CycleCarbon Dioxide CycleMars Feedback Loop Failure

• EvaporationEvaporation• RainRain• CO2 gas flushed outCO2 gas flushed out

But…But…• Interior cools offInterior cools off• Volcanoes Stop!Volcanoes Stop!

1

5

Carbon Dioxide CycleCarbon Dioxide CycleMars Feedback Loop Failure

• Atmosphere CO2 Atmosphere CO2 decreasesdecreases

• Planet freezesPlanet freezes

1

5

Why did Mars change?Why did Mars change?

Volcanoes…as recent as 180 million years ago…

Past tectonic activity…

Climate Change on MarsClimate Change on MarsNo widespread No widespread

surface water for surface water for 3 billion years.3 billion years.

Greenhouse Greenhouse effect probably effect probably kept surface kept surface warmer before.warmer before.

Somehow Mars Somehow Mars lost most of its lost most of its atmosphere.atmosphere.

Climate Change on MarsClimate Change on Mars

Climate Change on MarsClimate Change on Mars

Magnetic field may have preserved early Martian Magnetic field may have preserved early Martian atmosphere.atmosphere.

Solar wind may have stripped atmosphere after field Solar wind may have stripped atmosphere after field decreased because of interior cooling.decreased because of interior cooling.

Recent Polar Climate ChangeRecent Polar Climate Change

Seasons on MarsSeasons on Mars

Seasons on Mars are more extreme in the Seasons on Mars are more extreme in the southern hemisphere because of its elliptical orbit.southern hemisphere because of its elliptical orbit.

Storms on MarsStorms on Mars

Seasonal winds on Mars can drive huge dust storms.Seasonal winds on Mars can drive huge dust storms.

What geological features tell us What geological features tell us water once flowed on Mars?water once flowed on Mars?

The surface of Mars appears to have ancient riverbeds.

The condition of craters indicates surface history.

Eroded crater

Close-up of eroded crater

The Martian Surface MapThe Martian Surface Map

A *really* GRAND canyon…A *really* GRAND canyon…

A *even bigger* volcanoA *even bigger* volcano

Differences in HemispheresDifferences in Hemispheres

Low-lying regions may once have had oceans.

Low-lying regions may once have had oceans.

OpportunitySpirit

NASA’s SPIRIT & OPPORTUNITY Rovers…still sending data!

• 2004 Opportunity Rover provided strong evidence for abundant liquid water on Mars in the distant past.

• How could Mars have been warmer and wetter in the past?

Today, most water lies frozen underground (blue regions)

Some scientists believe accumulated snowpack melts carve gullies even today.

Exploring MarsExploring Mars

Winds on MarsWinds on Mars

Wind trails Wind trails from “dust from “dust

devils”devils”

Rivers on MarsRivers on Mars

… … & Earth!& Earth!

… … More More evidence evidence of waterof water