Download Venus -- Our “sister” planet. Stark atmospheric / surface differences

Venus -- Our “sister” planet.
Stark atmospheric / surface
differences contrast with
an interior that’s quite
similar to Earth’s.
Terra not-so-Firma
The Earth’s lithosphere is fractured into several plates
and the distortions in the crust happen at the edges of
these plates.
These plates drift
slowly relative to
each other over
time.
Continental Drift -- Fossil and Geological evidence of
overlapping continents.
Why do the continents remain on the surface of the
Earth for long (Gyr) periods of time?
A. Being rocky, they stay in one place.
B. The terrestrial magnetic field keeps them at the
surface.
C. The ocean plates are pushed under the continents by
the force of the oceans.
D. The moon’s tidal forces pull them upward.
E. They are less dense than the stuff beneath them.
Why do the continents remain on the surface of the
Earth for long (Gyr) periods of time?
A. Being rocky, they stay in one place.
B. The terrestrial magnetic field keeps them at the
surface.
C. The ocean plates are pushed under the continents by
the force of the oceans.
D. The moon’s tidal forces pull them upward.
E. They are less dense than the stuff beneath them.
The Greenhouse Effect
•This is a misnomer.
Agricultural greenhouses
work by inhibiting convection, not what we’ll
discuss.
•The Earth’s atmosphere contains greenhouse gases
such as water (H2O) and carbon dioxide (CO2)
which are defined by their absorption of infrared
light.
Venus
Earth
Mars
Visible Light incoming
Infrared Light
10.6
Greenhouse Effects
•Some degree of greenhouse effect is
essential for life on Earth. The equilibrium
temperature of Earth without any
greenhouse is -15 °C. Instead it’s a balmy
+15 °C
•On Venus, the greenhouse effect results in
almost 500 °C difference between
equilibrium and actual temperatures.
Losing Atmospheres
Some gas is always escaping from the exosphere
of the planet through thermal escape.
Unless replenished,
most of the
atmospheres will
eventually boil away.
Lighter gases (e.g.
He) leave terrestrial
planets easily.
What would be not be a consequence of the Earth’s
atmosphere’s temperature increasing?
A. More water would evaporate into the
atmosphere.
B. Fewer water molecules could undergo thermal
escape.
C. Helium would continue to escape the planet.
D. More massive molecules would break free of
Earth’s gravity.
E. The atmosphere would expand slightly.
What would be not be a consequence of the Earth’s
atmosphere’s temperature increasing?
A. More water would evaporate into the
atmosphere.
B. Fewer water molecules could undergo thermal
escape.
C. Helium would continue to escape the planet.
D. More massive molecules would break free of
Earth’s gravity.
E. The atmosphere would expand slightly.
Other losses
•Solar wind blows off outer atmosphere
•Giant impacts can blow off the gas layer
•Chemical or phase transition onto the
surface.
1 bar = standard earth atmosphere = 101,325 Pa
Linking Geology to Atmospheres
There is a tight link between geological activity and
atmospheres mediated by two effects.
1.Volcanic activity provides outgassing, increasing the
atmosphere.
2.A molten core creates a magnetic field which shields
the atmosphere from solar wind, reducing the losses.
As Mars dies, geologically, these two effects slow down
and the planet loses its atmosphere.
Losing Water
Without an ozone layer, UV light dissociates water
into O + H + H.
Since H is low mass, it’s thermal velocity is larger than
oxygen and is preferentially lost to thermal escape.
The left-over oxygen then combines with other atoms
to form other molecules (CO2, FeOx)
Gaining atmosphere
•Outgassing (the primary source)
•Evaporation / chemical release
•Volatile impactors such as comets.
Magnetic fields
Of all the terrestrial planets, only Earth
has a significant magnetic field that
shields it from the Solar Wind.
Aurora Borealis (North)
Aurora Australis (South)
Planetary Magnetism
•To have a strong magnetic
field, three ingredients are
key: a (1) rotating (2) liquid (3)
metallic core.
•Such a core drives the
formation of a magnetic field
through some seriously badass
physics (dynamo theory)
A crude
dynamo
simulation
The Solar Cycle
in X-ray Emission
Sunspot number over time
When will the thermosphere of the Earth
reach its maximum temperature next?
A. 2010 B. 2013 C. 2016 D. 2018 E. 2020
When will the thermosphere of the Earth
reach its maximum temperature next?
A. 2010 B. 2013 C. 2016 D. 2018 E. 2020
Based off solar magnetic activity, the aurora activity can
be predicted.
Storms happen at peak of solar activity cycle.
spaceweather.com
spaceweather.ca
My Mass Budget:
A. < 1000 kg
B. 103 - 104 kg
C. 104-105 kg
D. 105-106 kg
6
7
E. 10 -10 kg
The Jovian Planets
The Jovian Planets
(to scale)
The big difference in composition of the Jovian
planets is the dominance of H (specifically H2)
and He.
Jupiter and Saturn have nearly
stellar compositions (70% H,
28% He, 2% other)
Uranus and Neptune are mostly
Hydrogen compounds (H2O, CH4, NH3)
with pure H2 and He forming a smaller
fraction. Note, C, N, O as basis for
compounds.
Jovian Planet Structure
Saturn is the least dense planet (0.73 g/cm3) because
it’s made of light elements (H, He). Jupiter is richer in
light elements but more dense (?).
This is because Jovian
planets are mostly gas
and so their structure is
like that of terrestrial
atmospheres: pressure
balances gravity!
What is one reason why Jupiter could be smaller,
but more massive than Saturn?
A. Jupiter is warmer.
B. Jupiter’s composition is made of lighter
elements.
C. Jupiter has a liquid centre, but Saturn is a gas.
D. Jupiter has a stronger magnetic field
compressing it.
E. Jupiter’s gravity is the strongest of all the
planets.
What is one reason why Jupiter could be smaller,
but more massive than Saturn?
A. Jupiter is warmer.
B. Jupiter’s composition is made of lighter
elements.
C. Jupiter has a liquid centre, but Saturn is a
gas.
D. Jupiter has a stronger magnetic field
compressing it.
E. Jupiter’s gravity is the strongest of all the
planets.
Maximum size
planet
For Hydrogen and Helium planets...
The structure of Jupiter
is determined by the
need to support its own
weight and its
composition.
At high pressure,
hydrogen becomes a
metal! This means,
among other things,
that it conducts
electricity well.
Large metal core? Rapidly rotating? Magnetic Field!!!!
Jupiter has a magnetic field >104 times
stronger than Earth’s, i.e. a lot.
The structure of Jupiter’s
atmosphere.
Thermosphere is heated
by X-ray and UV
ionization (atoms)
The stratosphere is heated
by UV absorption and
dissociation (molecules)
Convection establishes the
temperature gradient in
the troposhere.
Bands on the Jovian planets form from the Coriolis
effect breaking up convection cells.
Since the Coriolis force is stronger (faster rotation)
there are more bands.
Neptune also
shows strong
storms and
banding,
including the
“Great Dark Spot”
Saturn’s weather is like that of
Jupiter (high / low cloud
layers).
The banding is less striking
since all the cloud layers occur
deeper in the atmosphere.
The winds on Saturn are the
stronges in the Solar System
but there are very few obvious
storms (less internal heating?)
Even Uranus shows some storms,
but the weather is weak most of
the time. Because of the ~90° tilt
of the axis, the seasons are thus
quite extreme.
Recent observations indicate new
storms have arisen, probably
because of the “sunrise” for the
Northern hemisphere.
Clouds form at unique
combinations of pressure
and temperature. Jupiter
has three main cloud
“decks.”
Ammonia
Ammonium
hydrosulfide
Water
Convection cells on Earth.
Hot air rises and the water condenses
as the air cools, forming clouds.
Io
Ammonia
Ammonium Hydrosulfide et al.
We don’t see deep enough to see water.
The outer planets, Uranus and
Neptune lack the hot temperature
structures in their tropospheres to
form Ammonia or NH4SH clouds.
Instead, we see
methane cloud layers,
the coldest possible
cloud layers.
Charged particles are trapped in the magnetic fields
from the planets. This creates auroras and a belt of
plasma (charged particles) around the planet.
All of the Jovian
planets have
extensive moon
systems.
These form out of the
disks channelling
material onto the
forming Jovian
planets.
Larger than Mercury!
All massive moons
are spherical
because of gravity,
just like planets.
Their geology is
similar to
terrestrial planets,
but contain large
fractions of ices
because they form
past the frost line!
Planets have also gravitationally captured some
debris. Not massive enough to become spherical.
The most geologically
active object in the
solar system. The
volcanos outgas sulfur
compounds, SO2.
This accounts for the
yellow colour.
Tidal forces with Jupiter and
the other massive moons
keep Io geologically active.
Volcanos!
Io (Jupiter)
An elliptical orbit prompts tidal
stretching and squishing of Io.
The orbit’s ellipticity is
maintained by orbital
resonances with Europa and
Ganymede
Europa (Jupiter) has an
incredibly new, geologically
rich surface that appears to be
mostly water ice.
Geological
features
suggest
liquid water
underneath!
- The surface looks a lot like glacial fracturing.
- Evidence also for liquid water volcanos.
- Tidal stretching keeps the interior hot and liquid.
Titan (Saturn) has is the only
moon to have a thick
atmosphere.
The atmosphere is largely
nitrogen (N2) and
hydrocarbons (CH4, C2H6 etc.)
The hydrocarbons are significant greenhouse gases,
so the surface is a little warmer than expected
(-170° C).
Atmospheric pressure is 1.5 times that of Earth
(which is close!).
The Huygens probe was dropped onto Titan to
explore it. Why?
Titan shows a complex chemistry; plenty of pre-biotic
hydrocarbons.
Moreover, there’s ample evidence for liquid-based
geology on Titan, like erosion from liquid methane.