The Goldilocks Problem?

Astronomical!

Why is Venus so hot…

and Mars so cold… and Mars so cold…

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

Thought Question What is the main reason why Venus is hotter than Earth? A. Venus is closer to the Sun than Earth. B. Venus is more reflective than Earth. C. Venus is less reflective than Earth. D. Rain stopped, but volcanoes didn’t E. Human activity has led to declining temperatures on Earth.

Thought Question What is the main reason why Venus is hotter than Earth? A. Venus is closer to the Sun than Earth. # 1 Answer given by most people… and it’s not correct!

Thought Question What is the main reason why Venus is hotter than Earth? A. Venus is closer to the Sun than Earth. B. Venus is more reflective than Earth. C. Venus is less reflective than Earth. D. Rain stopped, but volcanoes didn’t E. Human activity has led to declining temperatures on Earth.

Thought Question What is the main reason why Mars is no longer considered habitable (on its surface) A. Mars is farther from the Sun than Earth, and too cold B. Mars doesn’t have a thick atmosphere C. Mars’ volcanoes stopped erupting D. The greenhouse effect is not as strong on Mars compared to Earth. E. Martians screwed up the climate long ago.

Thought Question What is the main reason why Mars is no longer considered habitable (on its surface) A. Mars is farther from the Sun than Earth, and too cold # 1 Answer given by most people… and it’s not correct!

Thought Question What is the main reason why Mars is no longer considered habitable (on its surface) A. Mars is farther from the Sun than Earth, and too cold B. Mars doesn’t have a thick atmosphere C. Mars’ volcanoes stopped erupting D. The greenhouse effect is not as strong on Mars compared to Earth. E. Martians screwed up the climate long ago.

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

Venus in UV light

Venus mapped with Radar

The surface of Venus

Venus’ surface Venera Probes from 1970’s survived for minutes…

Venus’ surface Venera Probes from 1970’s survived for minutes…

Why is Venus so hot?

Venus’ Atmosphere What is it made of? How does it change in height? How does it circulate?

Atmosphere of Venus Venus has very thick carbon dioxide atmosphere with surface pressure 90 times larger than Earth. Venus has very thick carbon dioxide atmosphere with surface pressure 90 times larger than Earth.

Atmosphere of Venus Reflective clouds contain droplets of sulfuric acid. Reflective clouds contain droplets of sulfuric acid. The upper atmosphere has fast winds that remain unexplained. The upper atmosphere has fast winds that remain unexplained.

Venus’ Atmosphere

Water condenses into clouds, allowing for rain around 0 C Sun’s UV light disassociates H 2 0 at this height!

Greenhouse Effect on Venus Thick CO2 atmosphere produces an extremely strong greenhouse effect. Thick CO2 atmosphere produces an extremely strong greenhouse effect. Earth escapes this fate because most of its carbon and water are in rocks and oceans. Earth escapes this fate because most of its carbon and water are in rocks and oceans.

Why is Venus so hot? The greenhouse effect on Venus keeps its surface temperature at 470°C. But why is the greenhouse effect on Venus so much stronger than on Earth?

Runaway Greenhouse Effect The runaway greenhouse effect would account for why Venus has so little water. The runaway greenhouse effect would account for why Venus has so little water. Greater heat, more evaporation More evaporation, stronger greenhouse effect

Explaining Venus’ Atmosphere Lots of Volcanoes CO 2, H 2 S0 4 are outgassed CO 2 traps infrared heat from Sun Atmosphere heats up Water can’t condense => No Rain!

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

Carbon 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 CO 2 in atmosphere

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 1: Evaporation/Rain Liquid water evaporates Liquid water evaporates Condenses into clouds in lower atmosphere Condenses into clouds in lower atmosphere Rain falls through atmosphere forming Carbonic Acid (H 2 CO 3) Rain falls through atmosphere forming Carbonic Acid (H 2 CO 3)  CO2 gas is absorbed 1

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

Water & CO 2 … How do you fill lots of bottles with syrup quickly? How do you fill lots of bottles with syrup quickly? PUSH it in with a propellant PUSH it in with a propellant CO 2 is a good choice! CO 2 is a good choice! People like the bubbles! People like the bubbles!

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 2: Mineral Erosion by Acid Rain Carbonic Acid (H 2 CO 3) in rivers erodes rocks Carbonic Acid (H 2 CO 3) in rivers erodes rocks 2

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 2: Mineral Erosion by Acid Rain Carbonic Acid (H 2 CO 3) in rivers erodes rocks Carbonic Acid (H 2 CO 3) in rivers erodes rocks Carbonate (CO 3 2- ) ion picked up in minerals washed to ocean Carbonate (CO 3 2- ) ion picked up in minerals washed to ocean Calcium easily absorbed Calcium easily absorbed  CO2 is carried to oceans 2

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 3: Tying Carbon into Rocks & Life! Calcium from rocks forms CaCO 3 (Calcium Carbonate) Calcium from rocks forms CaCO 3 (Calcium Carbonate) CaCO 3 = Limestone CaCO 3 = Limestone CaCO 3 = Coral, Mollusk shells! CaCO 3 = Coral, Mollusk shells! 3  CO2 accumulates on seafloor

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 3: Tying Carbon to Rocks & Life!

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 4: Tectonics & Subduction! Tectonics gradually pulls seafloor down Tectonics gradually pulls seafloor down CaCO 3 broken back into CO2 & other minerals CaCO 3 broken back into CO2 & other minerals 4  CO2 now inside crust

Carbon Dioxide Cycle Carbon Dioxide Cycle Step 5: Volcanic Outgassing!

Eventual Volcanic Activity pushes CO2 back into atmosphere Eventual Volcanic Activity pushes CO2 back into atmosphere 5  CO2 now in 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 Rain No Rain NO CO2 gas absorbed NO CO2 gas absorbed More CO2 added! More CO2 added! Runaway Greenhouse Effect! Runaway Greenhouse Effect! 1 Carbon Dioxide Cycle Carbon Dioxide Cycle Venus Feedback Loop Failure

Mars Mars

Schiaparelli’s “Canals”

“The Face” : Is just an illusion…

Pyramids Happy Faces! More illusions :

What is real? A Martian Sunset…

Mars vs. Earth 50% Earth’s radius, 10% Earth’s mass 50% Earth’s radius, 10% Earth’s mass 1.5 AU from the Sun 1.5 AU from the Sun Axis tilt about the same as Earth Axis tilt about the same as Earth Similar rotation period (25 hours/”day”) Similar rotation period (25 hours/”day”) Thin CO 2 atmosphere: little greenhouse effect Thin CO 2 atmosphere: little greenhouse effect =>Main difference: Mars is SMALLER

Mars IS smaller… Mars IS smaller…

And Earth has life!

Carbon Dioxide Cycle Carbon Dioxide Cycle Mars Feedback Loop Failure Evaporation Evaporation Rain Rain CO2 gas flushed out CO2 gas flushed outBut… Interior cools off Interior cools off Volcanoes Stop! Volcanoes Stop! 1 5

Carbon Dioxide Cycle Carbon Dioxide Cycle Mars Feedback Loop Failure Atmosphere CO2 decreases Atmosphere CO2 decreases Planet freezes Planet freezes 1 5

Why did Mars change?

Volcanoes…as recent as 180 million years ago…

Past tectonic activity…

Climate Change on Mars No widespread surface water for 3 billion years. No widespread surface water for 3 billion years. Greenhouse effect probably kept surface warmer before. Greenhouse effect probably kept surface warmer before. Somehow Mars lost most of its atmosphere. Somehow Mars lost most of its atmosphere.

Climate Change on Mars

Magnetic field may have preserved early Martian atmosphere. Magnetic field may have preserved early Martian atmosphere. Solar wind may have stripped atmosphere after field decreased because of interior cooling. Solar wind may have stripped atmosphere after field decreased because of interior cooling.

Recent Polar Climate Change

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

Storms 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 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 Map

A *really* GRAND canyon…

A *even bigger* volcano

Differences in Hemispheres

Low-lying regions may once have had oceans.

Opportunity Spirit 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 Mars

Winds on Mars

Wind trails from “dust devils”

Rivers on Mars … & Earth!

… More evidence of water