Atmospheres of the Terrestrial Planets

Atmospheres of the Moon and Mercury

The Moon

Mercury

There is no substantial atmosphere on either body

They probably had outgassing long ago Without replenishment, these gases were lost

But they have been geologically dead for

billions of years

The low surface gravity of the Moon and Mercury make it very easy for molecules to escape

But they do currently have an extremely thin gas around them – an EXOSPHERE(One hundred trillion times thinner than Earth’s atmosphere!)

These images were made by instruments that are sensitive to sodium emission lines

These gases come from impacts by micrometeorites, solar wind particles, and high energy photons

Some of those escape directly into space, others fall back to the surface

Those that fall back typically bounce a few dozen times before being reabsorbed into the

surface

This leads to an interesting phenomenon…

The gas particles are most easily ejected where the

surface is warmed by sunlight

The bouncing will come to an end when a particle hits a very cold part of the surface

Polar craters that are in perpetual shadow

Water ice has been found in many of these craters

What is the source of the exospheres of the Moon and Mercury?

A) evaporation and sublimation from surface ices and liquids

B) impacts on the surface by solar wind particles

C) meteoroid impacts on the surface

D) volcanic outgassing

E) B and C

The Atmospheric History of Mars

Very thin atmosphere

Average temperature ~ – 50° C

No oxygen no ozone layer

UV hits the surface

Astronauts could not survive without a pressurized spacesuit

Mars’ seasons are affected not only by tilt, but also by the high eccentricity of Mars’ orbit.

Dust storms on Mars can engulf the entire planet

Dust devils are very common

Dust devil tracks As seen by MRO

While there can be no liquid water on the surface, there IS water ice.

The Phoenix lander landed right on top of a patch of water ice

So what happened to Mars’ atmosphere?

Warm interior allowed:• Liquid core magnetic field• Active volcanism outgassing• Thicker atmosphere stronger

greenhouse effect• Thick, warm atmosphere liquid water

Cooled interior:• No core convection no magnetic field• No active volcanism no outgassing• Thinner atmosphere weaker

greenhouse effect• Thin, cold atmosphere no liquid water

Size was the primary factor here

How do seasons on Mars differ from seasons on Earth?

A) They are less extreme because of Mars's smaller axis tilt.

B) They are more extreme because of Mars's greater axis tilt.

C) They are less extreme because of Mars's larger orbit.

D) They are more extreme because of Mars's larger orbital eccentricity.

E) Seasons on Earth and Mars are basically the same.

The Atmospheric History of VenusVery thick atmosphere: 90 bar

(Equivalent to 0.6 mi under water)

Average temperature:870° F = 465° C

Everywhere, all the time

At high altitudes, temps are ~ 65° C

Sulfuric acid clouds and rain:It evaporates before reaching the

ground

High altitude winds circle planetin 4 days:

> 200 mph!

Being about the same size as Earth, and forming near it in the solar nebula, Venus should have been made of the same stuff

Why would it end up with LOTS of carbon dioxide in its atmosphere and almost no water?

What would happen if we could move Earth to Venus’s orbit?

The Atmospheric History of Earth

If Earth started out so similar to Venus and Mars, how did

it end up so different?

What is the most abundant gas in Venus’s atmosphere?

A) Oxygen

B) Nitrogen

C) Water vapor

D) Carbon dioxide

E) Argon

What is the most abundant gas in Earth’s atmosphere?

A) Oxygen

B) Nitrogen

C) Water vapor

D) Carbon dioxide

E) Argon

What is the second most abundant gas in Earth’s atmosphere?

A) Oxygen

B) Nitrogen

C) Water vapor

D) Carbon dioxide

E) Argon

Where did the oxygen and ozone come from?

LIFE

What has kept the CO2 in our atmosphere at a reasonable level?

The CO2 cycle

The CO2 cycle is Earth’s thermostat

While Earth has gone through ice ages and even “snowball” phases,the CO2 thermostat has pulled Earth out of those cold times

And now we’re interfering with that thermostatWe’re releasing CO2 at a rate over 100 times faster than volcanoes

The rise in CO2 is undeniable – as is the fact that it has never happened so fast

Average global temperatures are also rising

Average global temperatures are also rising

Only models that include human release of greenhouse

gases match the observed temperature increase

It IS a result of human activity

Where is most of Earth’s carbon dioxide?

A) In the atmosphere

B) In the oceans

C) In the rainforests

D) In rocks

Astro-Cash Cab!

John Beedle

Kaitlin Hoffman

Matt Daniels

Jennifer Maez

Miranda Johnson

1) Where on the Moon can water be found?

2) On which terrestrial world is nitrogen the primary component of the atmosphere?

Mercury

Venus

Earth

The Moon

Mars

3) True or False?

On Venus sulfuric acid rain erodes the surface.

4) Earth’s CO2 cycle has pulled Earth out of “snow ball” phases because …

A) The rate of CO2 removal from the atmosphere goes down slightly, increasing greenhouse gas concentrations in the atmosphere.

B) CO2 removal stops completely, increasing greenhouse gas concentrations in the atmosphere.

C) The rate of CO2 removal from the atmosphere goes up slightly, decreasing greenhouse gas concentrations in the atmosphere.

D) CO2 outgassing stops completely, decreasing greenhouse gas concentrations in the atmosphere.