Lecture 31 - Climate of the Earth

ASTR 1210 (Exam 3)

What Factors Can Cause Long-term Climate Change?

• Energy in = energy out 

• When those two things find equilibrium on a planet, that leads to getting the temp of a planet

• Sun creates all the energy in the solar system = affects equilibrium temp 

• Can take a planet and push it closer to the sun = equilibrium temp goes up because energy goes up and vice versa 

• Can make my star hotter = increase energy even if planet is same distance

  • What is happening to the Sun 

• Stars get hotter and hotter as years go on 

Solar Brightening

• Rate at which sun is fusing at = as it runs out of hydrogen, it has to fuse hydrogen faster

• Sun very gradually grows brighter with time, increasing the amount of sunlight warming the planets

• In Goldilocks Zone to allow liquid water exist on the Earth 

• Mars will be pushed into the Goldilocks Zone

Temperature vs Solar Activity

• Sunlight is decreasing and relatively stable

• Sun is getting colder, Earth is getting hotter

• Has to do with the gases around the planet’s atmosphere

Changes in Axis Tilt

• Earth’s climate is affected by seasonal temperature changes

• Has to do with the axial tilt of the Earth - tilt more extreme = seasons more extreme

• Over many years, about 22 to 25 degrees - our tilt is stable because of the Moon

• Moon acts as a gravitational sounding board that allows the tilt to stay the same

• Mars has had more extreme tilts = more extreme climate change because it doesn’t have a big moon

Changes in Reflectivity

• If planet more reflective - energy in going down

• Less reflective - energy in is gonna increase

• Can change energy of the planet

Changes in Greenhouse Gases

• Cause the potential for significant temp change

• Greenhouse gases are also vital for the Earth’s life to thrive

Evolution of the Earth’s Atmosphere 

• When Earth first formed, it was situated in gas and dust that was the solar nebula 

  • Hydrogen and helium made up Earth’s early atmosphere

• Earth eventually lost the H and He over time - has to do with Earth’s gravity - can’t hold on to H and He

  • If planet was bigger, it could retain H and He - gas giants retained it

• Ammonia and methane went away and atmosphere dominated by nitrogen, carbon dioxide, and water

Sources of Gas

1. Impacts — impacts vaporize rock 

2. Outgassing — volcanos can significantly change the amount of gas in our atmosphere 

3. Vaporization — ice or liquid vaporizes 

Losses of Gas

1. Reversible loss

   1. Condensation

   2. Chemical reactions with the surface

      1. Rust removes oxygen from the atmosphere

2. Permanent loss — losing gas to space

   1. Thermal escape due to planet’s temperature

   2. Escape via the Solar World - particles from Sun smack into planet’s atmosphere and the energy can cause particles to escape the planet’s atmosphere

Thermal Escape from an Atmosphere 

• Average speed or thermal velocity of particles move at tells you the temperature 

• Some of those particles travel faster/ some will travel slower

• Some will be traveling GREATER than escape velocity - velocity of an object so that it escapes a planet 

Thermal Velocity Equation

• Particles that have less mass will be moving much faster than the other particle to reach escape velocity

Escape Velocity from Solar System Planets

• Low-mass particles will move fastest at any given speed

• Further from sun - colder you’re going to be 

• Gravity affects escape velocity

Exospheres of the Moon and Mercury

• Very, very thin atmosphere

• Dominated by things smacking into these objects, vaporizing them…

What is Mars like Today?

• Thin atmosphere but it has some stuff

• Impacts of weather on Mars - seasonally has dust storms

• Dust in the Martian atmosphere that’s been blown around as a result of windstorms that has blurred features

Seasonal Ice Caps of Mars

• Polar ice cap biggest during winter, smallest during summer - made up of carbon dioxide (dry ice)

• Going to increase/decrease CO2 seasonally on Mars

How Has Mars’s Climate Differed in the Past? 

• Likely had water on the surface 

Changing Axis Tilt

• layers of ice and rock that Mars goes through freezing and non-freezing periods - these layers were explained by axial tilt from Mars (0 to 60 degrees)

• Could’ve cause Mars to lose atmosphere

Why the Climate Change?

• Loss of atmospheric gas

• Loss of water

• Size is a critical factor in the timescale for climate change on a planet

Climate Change on Mars 

• Magnetic field may have perserved early Martian atmosphere

• Solar winds stripped atmosphere after field decreased because of interior cooling 

What is Venus like today?