12 Chapter 12 – Why do some planets have atmospheres?
OpenStax Astronomy Chapter 8 (Earth) & Chapter 10 (Venus & Mars)
Origin of Atmospheres
I. Atmospheres
A. Formed in the disk
B. Made primarily of gases:
C. still have atmospheres
D. All the planets primary atmospheres
E. Terrestrial planets light gases because:
1. Young planet was
a. Hot gas molecules move and reach (speed needed to escape gravity of planet)
2. Planet has and
a. Easier for molecules to gravity
F. A planet is able to keep gases in its atmosphere
II. Atmospheres
A. Acquired primary atmosphere was
B. of Secondary Atmosphere:
1. brought gases to
a. Minerals containing (CO2) collected in interior as planet formed, volcanoes melt rock and release gases into air
2. Impacts of on the planet brought water and volatiles, like , from outer Solar System
Current Atmospheres
Section 8.3, Section 10.3 & Section 10.5
III. Atmospheres
A. Mercury and Moon: , lost atmosphere too
1. : too and too (near Sun)
2. : even smaller, less and all molecules can escape
Why doesn’t the Moon have an atmosphere?
B. Earth: mostly
1. Gas molecules in secondary atmosphere changed by light from Sun to get
a. Example: Ammonia (NH3) breaks down to H and N, H escapes, N stays
2. from life
C. Venus and Mars: Still mostly from extensive volcanism
The Greenhouse Effect
IV.
A. Planet’s surface temperature is based on between:
1. Amount of energy from in light (heat gained)
2. Amount of energy by (heat lost)
B. But, this balance suggests Earth and Venus be much
1. Earth is about warmer than , should be frozen
2. Venus is of degrees hotter
V. Atmospheric
A. Gases in atmosphere, especially , heat, cooling to space
B. heat in then heats the
1. CO2 and water in atmosphere, the the surface
C. has a greenhouse effect, water vapor and CO2 in atmosphere to trap heat
1. Early Venus: than Earth, so water from surface into atmosphere
2. Early Earth: Water is mostly and CO2 went in and life, not atmosphere
D. Heating from greenhouse effect is as humans add more to Earth’s atmosphere
If it were not for the greenhouse effect on Earth:
A. There would be no liquid water
B. Life as we know it would not have developed
C. It would be much colder
D. All of the above
Surface Conditions on Venus
VI.
A. Hot, , , and mostly CO2
B. Covered in clouds
VII. conditions
A. Daytime: , , sky
B. Very (weight of air above surface)
C. Lots of gas from volcanoes
D. Temperature about because of greenhouse effect
E. temperature over planet even at
1. at surface because planet very
2. atmosphere acts like convection
F. because axis is
Venus’s surface temperature is about the same everywhere all the time because:
A. Venus rotates very rapidly, which causes strong winds
B. Venus is covered by a thick cloud layer that absorbs most of the sunlight that falls on it
C. The carbon dioxide in Venus’s atmosphere emits infrared radiation
D. The thick atmosphere and slow winds allow for convection to slowly circulate the heat
Surface Conditions on Mars
VIII.
A. and because of less gravity
B.
1. No ozone (O3) to from dangerous
IX. conditions
A. due to (oxidation) of iron minerals
B. surface pressure, thin air
C. daily due to thin atmosphere
D. axis and extreme
E. Temperature variations create
1. Planet-covering in spring
2. Turns sky from dark blue to , because of dust in air
3. Changes look of , covering dark rocky areas
Humans cannot survive on the surface of Mars for long periods of time because:
A. There is not enough oxygen in the atmosphere
B. The range in temperature between day and night is too large
C. Too much ultraviolet radiation gets through the thin atmosphere
D. All of the above are valid reasons
Tutorial Activity – Atmospheres
“Elementary Astronomy Worksheet Handout 13: Terrestrial Geology, Atmospheres and Handout 14: Venus, Mars, Climate”(modified by Kaisa E. Young) by Catherine Whiting via OER Commons, licensed under CC BY 4.0, https://oercommons.org/courses/elementary-astronomy-worksheets
1. What are some ways secondary atmospheres are formed?
2. What does a planet need in order to hold onto an atmosphere?
3. Suppose another star system has a rocky terrestrial planet that is half the size of Earth, 1/5 the mass, and at the same distance from its star, which is similar to our Sun. Would you expect it to have an atmosphere?
4. Mars is about half the size and about 1/10th the mass of the Earth.
(a) What is the atmosphere of Mars like?
(b) Why do you think Mars lost most of its secondary atmosphere?
5. Venus and the Earth are almost identical in size, so we should expect them to have similar geologies and atmospheres. However, Venus is located closer to the Sun than Earth.
(a) What is the atmosphere of Venus like?
(b) Why is Venus’ atmosphere so different from Earth?
6. (a)What is the greenhouse effect?
(b) What gasses are the main greenhouse gasses?
(c) What type of light (visible, infrared, or UV) is absorbed by greenhouse gasses in the atmosphere? Where does the heat energy from that light go (space, atmosphere, surface)?
(d) What is the effect of adding more greenhouse gasses into an atmosphere?
