Transcript Earth and the Terrestrial Worlds/Chapter 8

Homework #4
 Due today, 11:59PM
 Covers Chapters 6 and 7
 Estimated time to complete: 1 hour
 Read chapters, review notes before starting
Homework #5
 Due Thursday, March 3, 11:59PM (Exam #2 will be the
following day)
 Covers Chapters 8, 9, and 10
 Estimated time to complete: 1 hour
 Read chapters, review notes before starting
Midterm Grades
 Midterm grades will be posted tonight
 Homework #4 will not be included in your midterm
grade
 Be sure to do Homeworks #1, #2, #3 for partial credit
if you have not completed them
 If you did not take Exam #1, your midterm grade won’t
be based on much!
What makes a planet habitable?
Large enough for geological activity to release gas
and retain water and atmosphere (size is most
important factor)
What makes a planet habitable?
Located at an optimal distance from the Sun for
liquid water to exist (location, location, location)
Earth’s Destiny
Earth is habitable
because it is large
enough to remain
geologically active,
and it is at the right
distance from the
Sun so liquid water
survive on the
surface.
Chapter 7 Study Guide
1) Terrestrial planets have radically different geologies,
atmospheres despite common origin inside frost line
2) Core (high density iron/nickel)  mantle (moderate
density silicate rocks)  crust (low density rocks)
3) When planets were still molten, denser material sunk to
the center  called differentiation
4) Lithosphere – crust + outer part of mantle – cool rigid rock
that floats on top of soft, warm rock of inner part of
mantle
5) A planet’s internal heat determines level of geological
activity
Chapter 7 Study Guide
6) Early times: differentiation + accretion  heat
Now: radioactive decay in core  heat
7) Size is most important factor in determining how long a
planet’s interior stays hot; when heat is gone, geological
activity is gone, rock hardens, atmosphere goes away
8) Impact cratering, volcanism, tectonics, erosion all shape the
surfaces of worlds
9) During volcanic eruptions, copious amount of gas is released
 outgassing  replenishes gas in atmospheres
10) Earth’s atmosphere creates erosion, protects from radiation,
responsible for greenhouse effect, makes sky blue
Chapter 7 Study Guide
11) Greenhouse gases (CO2, H2O, CH4) trap in infrared photons
emitted by blackbody Earth  make surface warmer
12) Moon and Mercury had geological activity (~3 billion years ago)
– maria on Moon – but not any longer (too small, lost internal
heat) – no atmospheres because no more outgassing
13) Mars – thin atmosphere, recent geological activity which is
probably dying down now, good evidence for much liquid water
in past (know the evidence)  probably lost much of internal
heat because of moderate/small size
14) Venus – extremely thick atmosphere, very recent geological
activity, greenhouse effect run wild
15) Earth – broken lithosphere allows plates to drift  continents
move slowly
Chapter 7 Study Guide
16) Continental motion – caused by spreading of sea floor  hot
rock pushes up from mantle pushing plates apart
17) CO2 cycle keeps CO2 levels stable  good for climate
stability
18) Fossil fuel burning is raising CO2 levels to unprecedented
levels  can Earth’s CO2 cycle compensate?
19) A planet’s chance to harbor life depends on its distance from
the Sun (not too hot, not too cold) and size (large enough to
maintain internal heat for geological activity)  Lucky Earth!
Chapter 8
Jovian Planet Systems
Jovian Planet Composition
 Jupiter and Saturn - mostly H and He gas, with small
amounts of hydrogen compounds (ices), rock, and metal
 Uranus and Neptune - majority hydrogen compounds:
water (H2O), methane (CH4), ammonia (NH3),
some H, He, and rock/metal (better named “ice giants”)
Jovian Planet Formation
Beyond the frost line, planetesimals could
accumulate ICES (hydrogen compounds) in
addition to rock/metal (these ices were not
available in the inner Solar System where the
terrestrials formed due to high temperatures).
Hydrogen compounds were more abundant
than rock/metal so proto-Jovian planets got
more massive and acquired H/He atmospheres.
Comparing Jovian Interiors
Models suggest cores of Jovian planets are made
of similar materials, but different layer ratios.
More H/He in Jupiter/Saturn, more ices in
Uranus/Neptune (by percentage)
Jovian Planet Formation
No solid surface
Layers under high pressure and temperatures
The Jovian cores are all very similar:
mass of ~5-10 Earths (made of
ices/rock/metal)
The Jovian planets differ 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 hydrogen and helium
gas. Capture ceases after the solar wind
blows the leftover gas away.
LOCATION: The planet that forms in a
denser part of the nebula forms its core
first  favors Jupiter, then Saturn, but
disfavors Uranus, Neptune
Inside Jupiter
 Core is thought to be
made of rock, metals,
and hydrogen
compounds.
About same
temperature as
surface of Sun!
 Core is about same
size as Earth but 5-10
times as massive.
 Tremendous pressure
within inner layers
leads to extremely
high temperatures
Inside Jupiter
High pressures
inside Jupiter cause
phase of hydrogen
to change with
depth.
Hydrogen acts like a
metal at great
depths because its
electrons move
freely (metallic
hydrogen).
What is the weather like on
Jovian planets?
Jupiter’s
Colors
Ammonium hydrosulfide clouds (NH4SH) reflect
red/brown.
Ammonia, the highest, coldest layer, reflects
yellowish-white.
Jupiter’s Atmosphere
Hydrogen
compounds in
Jupiter form
clouds (H/He are
colorless).
ammonium
hydrosulfide
Different cloud
layers correspond
to freezing points
of different
hydrogen
compounds.
Saturn’s
Colors
 Saturn’s layers are similar, but sunlight is
reflected at a deeper depth. More absorption of
light on the way back out leads to more subdued
colors.
Methane on Uranus and Neptune
 Methane gas (20x more abundant by percentage than on
Jupiter/Saturn) of Neptune and Uranus absorbs red light but
transmits blue light .
 Blue light reflects off methane clouds, making those planets
look blue.
Jupiter’s
Great
Red Spot
Is a storm twice as wide as Earth
Has existed for at least three centuries
Why does storm last so long? Unknown!
Weather on Jovian Planets
All the Jovian planets have strong winds
and storms.
All the Jovian planets have strong magnetic
fields (much stronger than Earth’s)
All the Jovians share the following
properties except:
A) A mostly H/He composition
B) Strong winds and storms in their atmospheres
C) Magnetic fields much greater than Earth’s
D) ~5-10 Earth-mass cores of ice/rock/metal
All the Jovians share the following
properties except:
A) A mostly H/He composition
B) Strong winds and storms in their atmospheres
C) Magnetic fields much greater than Earth’s
D) ~5-10 Earth-mass cores of ice/rock/metal
Only Jupiter and Saturn are made mostly of H/He,
Uranus and Neptune are majority hydrogen
compounds, with lesser amounts of H/He.
What kinds of moons orbit the
Jovian planets?
Moons might be more interesting than their host planets!
Sizes of Moons
Small moons (< 300 km)
No geological activity
Medium-sized moons (300–1500 km)
Geological activity in past
Large moons (> 1500 km)
Ongoing geological activity  why not dead?!?
Medium and
Large Moons
Enough self-gravity to
be spherical
Most have substantial
amounts of ice
Formed in orbit
around Jovian planets
(like solar nebula)
Mostly circular orbits
in same direction as
planet rotation (except
Triton)
Small
Moons
These are far more numerous than the
medium and large moons.
They do not have enough gravity to be
spherical: most are “potato-shaped”.
Small
Moons
They are probably captured comets, so their
orbits do not follow usual patterns (orbit in
wrong direction, or highly elliptical orbit).
Why are Jupiter’s Galilean
moons so geologically active?
All large Jovian moons (except Ganymede) are smaller
than Mercury, and some are smaller than Earth’s Moon.
So why haven’t they lost their internal heat and become
geologically dead??
Io’s Volcanic Activity
 Io is the most volcanically active body in the solar system,
but why?
 Only Jovian moon made entirely of rock/metal (area close
to young Jupiter was hot  only rock/metal survived)
Io’s Volcanoes
Volcanic eruptions continue to change Io’s
surface. No impact craters at all.
Io’s Volcanoes
Tupan Patera,
a caldera
surrounded by
1 km high cliff
Currently
active and
venting sulfur
gas
warm red sulfur deposits
hot black lava
What does the lack of craters on Io tell
us?
A) Few comets have hit Io because it is far from the
Sun.
B) Io’s very thick atmosphere burns up comets before
they can make an impact.
C) Io’s surface must be very young.
D) Io is a water world, so craters are covered by liquid
water.
What does the lack of craters on Io tell
us?
A) Few comets have hit Io because it is far from the
Sun.
B) Io’s very thick atmosphere burns up comets before
they can make an impact.
C) Io’s surface must be very young.
D) Io is a water world, so craters are covered by liquid
water.
Io is repaved constantly by ongoing volcanic activity 
any craters are quickly erased.
Tidal Heating
Io is squished and
stretched as it orbits
Jupiter from tidal forces
(recall minor effect of
Moon on Earth’s tides).
Very elliptical orbit makes
squishing more extreme.
This extreme squishing
heats the internal
material and keeps it
warm without radioactive
decay  so not
geologically dead!
Effect highly exaggerated in diagram
But why is its orbit so elliptical?