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 Venus Very 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 planet in 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 CO 2 in our atmosphere at a reasonable level? The CO 2 cycle

The CO 2 cycle is Earth’s thermostat

While Earth has gone through ice ages and even “snowball” phases, the CO 2 thermostat has pulled Earth out of those cold times

And now we’re interfering with that thermostat We’re releasing CO 2 at a rate over 100 times faster than volcanoes The rise in CO 2 is undeniable – as is the fact that it has never happened so fast

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 CO 2 cycle has pulled Earth out of “snow ball” phases because … A) The rate of CO 2 removal from the atmosphere goes down slightly, increasing greenhouse gas concentrations in the atmosphere. B) CO 2 removal stops completely, increasing greenhouse gas concentrations in the atmosphere. C) The rate of CO 2 removal from the atmosphere goes up slightly, decreasing greenhouse gas concentrations in the atmosphere. D) CO 2 outgassing stops completely, decreasing greenhouse gas concentrations in the atmosphere.