Lecture 29 - Planetary Atmosphere - Basics

ASTR 1210 (Exam 3)

Erosion

• Earth has been eroded at —> re-shaping its surface — not a good data point for what solar system looked like 

• Very geologically active — most eroded than other terrestrial worlds

• Has a lot of water (liquid, solid, and vapor) — reshapes the Earth

  • Grand Canyon - formed from water erosion 

  • Uplift causes the Earth to rise 

    • Relatively young 

    • Tributaries shape it 

• Rivers, rocks, mud create deltas — like Mars & Earth 

Yosemite Valley

• Ice river or glaciers flowing through the rock - carving at the land

Wind Erosion

Can create giant sand dunes

Ex. Great Sand Dunes National Park 

Why don’t we see a lot of wind erosion on Venus? 

• Has flat rocks

• Because it rotates slowly - weaker winds - less wind erosion 

Role of Planetary Size 

• Smaller worlds cool off faster and harden earlier

• Larger worlds remain warm inside - promoting volcanism and tectonics

• Larger worlds also have more erosion because their gravity retains an atmosphere 

Role of Distance from Sun

Too close to Sun - no atmosphere, no water

• Earth is in Goldilocks zone for water to exist on surface

• If we move closer to Sun, wouldn’t retain water — Venus

• Earth has liquid water —> glacial erosion

  • Spins fast —> stronger magnetic field / atmosphere

  • Faster wind spins - stronger winds

Role of Rotation

• Jupiter spins the fastest - lots of wind in equatorial regions (more weather, erosion, stronger magnetic field)

• Planets with slower rotations have less weather, erosion and a weaker magnetic field 

What is an Atmosphere?

Layer of gas that surrounds planets - atoms and molecules in gaseous vapor form

• Considers clouds too

• Venus has an incredibly thick atmosphere, thicker than Earth

• Mars has thinner atmosphere

• Moon and Mercury has no atmosphere

What’s the primary component of the Earth’s atmosphere?

• Nitrogen (N2)

• Makes up 80% of our atmosphere

• Use oxygen to create energy though

• Nitrogen doesn’t react with things - inert gas

• Can use oxygen to cause chemical reactions to create energy - fire uses oxygen

  • Body can use it 

• Nitrogen will stick there and not get taken out of atmosphere

• Oxygen gets removed quickly - but we still have a lot of oxygen in our atmosphere

  • Plants 

  • Plankton, phytoplankton — life creates oxygen

What is in the Atmosphere? 

• Atmospheric pressure - weight of atmosphere pushing on surface of Earth

• Weight: 1 atm or 1 bar 

• Higher/lower pressure region (lower) — hurricane 

• Pressure pushes in on you - all a result of the stuff above our heads

• Can impact weather, climate, and gas giant planets 

• Gas pressure depends on temp and density - can change composition of states of matter 

• Pressure forces on Venus are higher than pressure forces on Earth

Pressure and Altitude 

• Less stuff, lower pressure 

• Higher and higher, pressure gets lower - not necessarily because of temp 

  • Temp is higher at higher points

• Density —> more gas particles at the bottom

Auroras

Particles smacking into Earth’s atmosphere

Effects of Atmosphere

• Create pressure that determines whether liquid water can exist on the surface

• Absorb and scatter light

• Create wind, weather, and impact climate

• Can make planetary surfaces warmer through the greenhouse gas

• At 0 C - water freezes, 100 C - water boils

• Change the pressure - change the freezing/boiling point

• Triple point of water (6% of an atm pressure and 0.01 degrees C), water is a solid, liquid, and vapor

• Any small changes can cause that solid to boil or to turn into a liquid as a result of pressure

Greenhouse Effect

• Greenhouse gas is vital towards life on Earth

• Heats up temp of Earth so liquid water could exist

• Any gas that is transparent to visible but opaque to infrared — visible hits Earth and makes it warmer

  • When it radiates, radiates infrared

  • Layer holds onto infrared

• Holds onto the energy

Which greenhouse gas contributes to the effect? 

CO2, H2O, and methane (cows farting)

Planetary Temperature

Surface temperature is determined by balance between energy from sunlight it absorbs and energy of outgoing thermal radiation

Glaciers or Ice  

• Reflecting a lot of light 

• As Earth gets colder - icier - reflects more light - gets more colder - reflects more light

• GHG effect makes it hotter

Planetary Temp: Rotation and Reflectivity

Planet’s rotation rate affects the temp differences between day and night

• Planet’s albedo is fraction of incoming sunlight it reflects (0 = absorb, 1 = reflect)

• Low albedo = absorb more light, leading to hotter temperatures

  • Black pavement = 0

  • White pavement = 1

• Clouds reflect a lot of light

If Earth didn’t have an atmosphere, what would happen to its temp?

• Got rid of its greenhouse layer and blanket - colder 

Temperature of the Earth vs. Altitude 

• Higher you go, hotter and hotter temp - then colder and colder 

• Impacts where clouds can be, what types of clouds can form

• Stratosphere: unique for terrestrial planets 

  • Ozone layer creates this - absorbs energy in the stratosphere

  • 3 oxygen molecules bound together

  • Ozone absorbs a lot of UV energy - UV blanket to hold It all together

Why Do Atmospheric Properties Vary with Altitude?

• Convection - hotter at bottom, cold at top - cycle - troposphere 

• Doesn’t do it stratosphere - inverts it (no ice forming) 

Light’s Effects on Atmosphere

• Ionization: removal of an electron

• Dissociation: destruction of a molecule

• Scattering: change in photon’s direction

• Absorption: photon’s energy is absorbed

Magnetosphere

A magnetosphere is the region of space around a planet that is controlled by its magnetic field. This magnetic field acts as a shield, deflecting the solar wind and protecting the planet from the charged particles from the sun

Exosphere

The exosphere is the outermost layer of Earth's atmosphere, starting around 600 km (375 miles) above the surface and gradually fading into space. It is extremely thin, composed mainly of hydrogen and helium, and is where satellites orbit Earth. Particles in this layer are so spread out they rarely collide, and the lightest ones can escape into outer space. 

Thermosphere

The thermosphere is a layer of Earth's atmosphere above the mesosphere where temperatures increase with altitude, reaching thousands of degrees Celsius due to absorption of high-energy solar radiation. Despite the high temperatures, the air is so thin that it would feel cold to us. This layer is also where the aurora borealis and aurora australis occur and where satellites like the International Space Station orbit. 

Which planet(s) have an atmosphere that consists mostly of carbon dioxide?

Venus and Mars

Which of the following is not caused by the Coriolis effect on Earth?

Water going down a drain swirls in opposite directions in the Northern and Southern hemispheres.

Why is the Coriolis effect so weak on Venus?

Because Venus rotates so slowly.

Why is thermal escape of atmospheric gas much easier from the Moon than from Earth?

Because the Moon's gravity is so much weaker than Earth's.

This diagram represents the carbon dioxide cycle. Which position in the diagram represents the part of the cycle in which carbon dioxide is turned into carbonate minerals and rock?

Position 3

Which of the following best describes the nature and origin of the atmospheres of the Moon and Mercury?

They have thin exospheres only, with gas coming from impacts of subatomic particles and photons.

What is the connection between core convection and a strong magnetosphere?

Core convection helps generate a magnetic field, and the magnetic field creates the magnetosphere.

What key process underlies why Mars changed so much from its early conditions to its conditions today?

Interior cooling

Why is Mars red?

Chemical reactions between surface rock and atmospheric oxygen literally rusted the surface.

What would happen to Earth if we somehow moved our planet to the orbit of Venus?

Earth would suffer a runaway greenhouse effect and become as hot as or hotter than Venus.

Which characteristic of Earth explains why Earth has the ozone necessary for an ultraviolet-absorbing stratosphere?

the existence of photosynthetic life

Why does Earth have so little carbon dioxide in its atmosphere compared to Venus?

Earth has just as much carbon dioxide as Venus, but most of it is locked up in carbonate rocks rather than being free in the atmosphere.

Which two factors are critical to the existence of the carbon dioxide (CO₂) cycle on Earth?

plate tectonics and liquid water oceans

Listed following are characteristics of the atmospheres of Venus, Earth, and Mars. Match each atmospheric characteristic to the appropriate planet.

Venus - almost no surface winds, runaway greenhouse effect, sulfuric acid clouds; Earth - atmosphere composed primarily of nitrogen, ultraviolet-absorbing stratosphere; Mars - global dust storms, extremely low density atmosphere

All the following statements about Mars are true. Which one might have led to a significant loss of atmospheric gas to space?

Mars lost any global magnetic field that it may once have had. - This allowed the solar wind to strip atmospheric gas into space.

All the following statements are true. Which two represent the two facts that lead us to expect Earth to be warming up as a result of human activity? Be sure to choose two of the statements below.

• Human activity is increasing the concentration of carbon dioxide and other greenhouse gases in the atmosphere.

• Greenhouse gases make Earth warmer than it would be otherwise.