Astronomical!

Why is Venus so hot…

and Mars so cold …

and Earth just right….?

Thought Question
What is the main reason why Venus is hotter than Earth?
A.
B.
C.
D.
E.
Venus is closer to the Sun than Earth.
Venus is more reflective than Earth.
Venus is less reflective than Earth.
Rain stopped, but volcanoes didn’t
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.
B.
C.
D.
E.
Venus is closer to the Sun than Earth.
Venus is more reflective than Earth.
Venus is less reflective than Earth.
Rain stopped, but volcanoes didn’t
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.
B.
C.
D.
E.
Mars is farther from the Sun than Earth, and too cold
Mars doesn’t have a thick atmosphere
Mars’ volcanoes stopped erupting
The greenhouse effect is not as strong on Mars compared to Earth.
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.
B.
C.
D.
E.
Mars is farther from the Sun than Earth, and too cold
Mars doesn’t have a thick atmosphere
Mars’ volcanoes stopped erupting
The greenhouse effect is not as strong on Mars compared to Earth.
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.

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

Venus’
Atmosphere

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

Greenhouse Effect on Venus
 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.

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

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

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

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

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

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

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

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

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

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

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

Carbon Dioxide Cycle
Step 5: Volcanic Outgassing!

5
Carbon Dioxide Cycle
Step 5: Volcanic Outgassing!
• Eventual Volcanic
Activity pushes CO2 back into atmosphere
 CO2 now in atmosphere again!

Carbon Dioxide Cycle
Venus Feedback Loop Failure
5
1
 Too Hot for clouds to form low enough
But…
 Volcanoes don’t stop!

Carbon Dioxide Cycle
Venus Feedback Loop Failure
1
•
•
•
•
No Rain
NO CO2 gas absorbed
More CO2 added!
Runaway
Greenhouse Effect!

Mars

Schiaparelli’s “Canals”

Is just an illusion…
“The Face”
:

Pyramids
Happy Faces!
More illusions
:

What is real?
A Martian Sunset…

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

Mars IS smaller…

And Earth has life!

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

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

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.
 Greenhouse effect probably kept surface warmer before.
 Somehow Mars lost most of its atmosphere.

Climate Change on Mars

Climate Change on Mars
 Magnetic field may have preserved early
Martian atmosphere.
 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.

Storms on Mars
 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.

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”

… & Earth!
Rivers on Mars

… More evidence of water