ASTR100 (Spring 2006)
Introduction to Astronomy
Earth as a Living Planet
Prof. D.C. Richardson
Sections 0101-0106
Extra Credit Opportunities
 The first 10 astronomy-related posts to
the course discussion board or blog.
 Existing posts will earn retroactive credit
and not count against the 10.
 Maximum 3 points per student.
 Comments/replies can count too!
 Homework #6.5 on
MasteringAstronomy.com.
 Not due for a couple of weeks.
 Ask me an astronomy question in class,
right now!
A Word About the Greenhouse Effect
 The “greenhouse” part is misleading:
 A real greenhouse works by heating and
trapping the air inside the structure.
 The same principle explains why the inside
of a car gets hot so fast on a sunny day.
 The greenhouse “effect” is trapping of
heat by the air (atmosphere) itself.
 No glass needed!
What unique features of Earth are
important to human life?
1)
2)
3)
4)
Surface liquid water.
Atmospheric oxygen.
Plate tectonics.
Climate stability.
What unique features of Earth are
important to human life?
Earth’s distance from
the Sun and
1) Surface liquid water. moderate greenhouse
2) Atmospheric oxygen. effect make liquid
water possible.
3) Plate tectonics.
4) Climate stability.
What unique features of Earth are
important to human life?
1)
2)
3)
4)
PHOTOSYNTHESIS
Surface liquid water. (plant life) is required
Atmospheric oxygen. to make high
concentrations of O2,
Plate tectonics.
which produces the
protective layer of O3.
Climate stability.
What unique features of Earth are
important to human life?
1)
2)
3)
4)
Surface liquid water.
Atmospheric oxygen.
Plate tectonics.
Climate stability.
Plate tectonics
are an
important step
in the carbon
dioxide cycle.
The Carbon Dioxide Cycle
1. Atmospheric CO2
dissolves in
rainwater.
2. Rain erodes
minerals that flow
into the ocean.
3. Minerals combine
with carbon to make
rocks on ocean
floor.
The Carbon Dioxide Cycle
4. Carbonate rocks
carried down into
the mantle by
subduction.
5. Rocks melt in
mantle and outgas
CO2 back into
atmosphere through
volcanoes.
What unique features of Earth are
important to human life?
1)
2)
3)
4)
Surface liquid water.
Atmospheric oxygen.
Plate tectonics.
The CO2 cycle acts like a
Climate stability. thermostat for the
Earth’s temperature.
The Thermostat
 If Earth heats up a bit, increased rainfall
dissolves more CO2, reducing greenhouse effect.
 If Earth cools down a bit, decreased rainfall
dissolves less CO2, building up greenhouse gas.
 Everything is OK if swings are slow and small…
These unique features are
intertwined…
 Plate tectonics creates climate stability.
 Climate stability allows liquid water.
 Liquid water is necessary for life.
 Life is necessary for atmospheric
oxygen.
 More?
How is human activity changing our
planet?
Dangers of Human Activity
 Human-made CFCs in the atmosphere
destroy ozone, reducing protection from
UV radiation.
 Human activity is driving many other
species to extinction.
 Human use of fossil fuels produces
greenhouse gases that can cause global
warming.
Global Warming
 Earth’s average temperature has
increased by 0.5°C in the past 50 years.
 The concentration of CO2 is rising
rapidly.
 An unchecked rise in greenhouse gases
will eventually lead to global warming.
CO2 Concentration
 Global temperatures
have tracked CO2
concentration for the
last 500,000 years.
 Antarctic air bubbles
indicate the current
CO2 concentration is
at its highest level in
at least 500,000
years.
CO2 Concentration
 Most of the CO2 increase has happened in the
last 50 years!
Modeling of Climate Change
 Complex models of
global warming
suggest that the
recent temperature
increase is indeed
consistent with
human production of
greenhouse gases.
Consequences of Global Warming
QuickTime™ and a
H.264 decompressor
are needed to see this picture.
 Melting of polar ice.
 More extreme weather.
 Rising sea levels.
What can we do about it?
 Reduce greenhouse emissions by improving
energy efficiency, especially car gas mileage.
 Invest in alternative energy sources.
 Bury the CO2.
What makes a planet habitable?
 Located at an optimal distance from the Sun
for liquid water to exist.
What makes a planet habitable?
 Large enough for geological activity to release
and retain water and atmosphere.
Planetary Destiny
 Earth is habitable
because it is large
enough to remain
geologically
active, and it is at
the right distance
from the Sun so
oceans could
form.
ASTR100 (Spring 2008)
Introduction to Astronomy
Jovian Planet Systems
Prof. D.C. Richardson
Sections 0101-0106
A Different Kind of Planet




Bigger and more massive.
Lower density, different composition.
Rings.
Numerous moons.
Jovian Planet Composition
 Jupiter and Saturn
 Mostly H and He gas.
 Some hydrogen compounds, metal, rock.
 Uranus and Neptune
 Mostly hydrogen compounds: water (H2O),
methane (CH4), ammonia (NH3).
 Some H, He, metal, and rock.
 Why the difference?
Jovian Planet Formation
 Beyond the frost line, planetesimals
could accumulate ICE.
 H compounds are more abundant than
rock/metal so jovian planets got bigger
and acquired H/He atmospheres.
Jovian Planet Formation
 The jovian cores are very similar: solid
masses of about 10 Earths.
 The jovian differences are in the
amount of H/He gas accumulated.
 Why did that amount differ?
Differences in Jovian Planet
Formation
 TIMING: the planet that forms earliest
captures the most H & He gas. Capture
ceases after the first solar wind blows
the leftover gas away.
 LOCATION: the planet that forms in the
densest part of the nebula forms its
core first.
pi
te
Sa r
tu
U rn
ra
N nu
ep s
tu
ne
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Ju
Density (g/cc)
Density Differences
 Uranus and Neptune
are denser than
Saturn because they
have less H/He,
proportionately.
pi
te
Sa r
tu
U rn
ra
N nu
ep s
tu
ne
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Ju
Density (g/cc)
Density Differences
 But that doesn’t
explain Jupiter’s
density…
Sizes of Jovian Planets
 Adding mass to a
jovian planet
compresses the
underlying gas
layers.
Sizes of Jovian Planets
 Greater compression
is why Jupiter is not
much larger than
Saturn even though
it is 3 times more
massive.
 Jovian planets with
even more mass can
be smaller than
Jupiter.
What are jovian planets like on the
inside?
Interiors of Jovian Planets
 No solid surface.
 Layers under high pressure and
temperature.
 Cores (~10 Earth masses) made of
hydrogen compounds, metals and rock.
 The layers are different for the different
planets. WHY?
Inside Jupiter
 High pressure inside
Jupiter causes phase
of hydrogen to
change with depth.
 Hydrogen acts like a
metal at great
pressures because
its electrons move
freely.
Comparing Jovian Interiors
 Models suggest that cores of jovian planets
have similar composition.
 Lower pressure inside Uranus and Neptune
means no liquid or metallic hydrogen.
Jupiter’s Magnetic Field
 Jupiter has a powerful magnetic field
generated by its rotating, convecting layer of
metallic hydrogen.
Aurora on Jupiter
Aurorae on Saturn
What is the weather like on
jovian planets?
Jupiter’s Atmosphere
 Hydrogen compounds
in Jupiter form
clouds.
 Different cloud layers
correspond to
freezing points of
different hydrogen
compounds.
 Other jovian planets
have similar cloud
layers.
Planet colors
Jupiter’s
Colors
 Ammonium sulfide clouds reflect red/brown.
 Ammonia, the highest coldest layer, reflects
white.
Planet colors
Saturn’s
Colors
 Saturn’s layers are the same, but deeper in
and farther from the Sun—more subdued.
 Uranus and Neptune’s upper layers are colder
still, allowing methane to condense as clouds.
 Methane gas absorbs red light and transmits
blue light reflected by the lower clouds.
Jupiter Winds and Storms
 Earth’s rotation makes storms “spin.”
 Jupiter’s fast rotation stretches storms
into bands that surround the planet.
 High east/west winds (up to 400 km/hr).
Jupiter’s
Great
Red Spot
 A storm twice as wide as Earth.
 Has existed for at least 3 centuries.
Weather on Jovian Planets
 All the jovian planets have strong winds and
storms.
Quiz!
 Take out a sheet of paper.
 Write down your name and section
number.
 That’s it! Ha ha.
 Hand it in (along with HW#6 if needed).
 Have a great Spring Break!
 BUT REMEMBER, THERE IS
DISCUSSION TOMORROW FOR
SECTIONS 105 & 106!