Prof. Miller's Astronomy 1 lecture notes on Venus and Mars's Atmosphere

1. Venus’s Atmosphere
LACC: §9.3, 9.5, 9.6
• Venus’s surface environment
• Venus’s atmospheric evolution = run-away
greenhouse
• Venus’s cloud cover
An attempt to answer the “big questions”: what is out
there? Are we alone?
Thursday, March 11, 2010 1

2. Venus
http://www.astrosurf.com/nunes/explor/explor_m10.htm
Thursday, March 11, 2010 2

3. Venus: Atmosphere
90 bars surface
Composition pressure
• CO2 96% 850°F average
• N2 3.5% surface temperature
(hotter than
• Ar 0.006% Mercury due to a
• O2 0.003% 920°F greenhouse
effect)
• Ne 0.001%
winds of a few mph
Thursday, March 11, 2010 3

4. Venus: Greenhouse Effect
http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap09/FG09_19.jpg
Thursday, March 11, 2010 4

5. Venus: Runaway
Greenhouse Effect
Due to high temperatures, some (all?) of Venus’s H2O was in a
gaseous state instead of a liquid state.
As an atmospheric gas, the sun’s uv light broke the H2O
molecules apart--photodissociation.
The lighter H left the atmosphere--thermal escape; the heavier O
is quite reactive and bonded with C (to make CO2), surface rocks
(e.g. rust), or left the atmosphere via thermal escape.
Less water in general means less liquid water for the CO2 to
dissolve in to, so atmospheric CO2 levels increase.
Higher atmospheric CO2 levels increase the surface
temperature--greenhouse effect. Higher temperatures convert
more liquid H2O into a gas. (Return to top and repeat.)
Thursday, March 11, 2010 5

6. Venus: H2SO4 Clouds
http://lasp.colorado.edu/~bagenal/3720/CLASS16/16EVM-Dyn2.html
Thursday, March 11, 2010 6

7. Venus: Atmosphere
Sulfuric acid, H2SO4, clouds!
Sulfur dioxide SO2 and H2O can combine to
make H2SO4.
SO2 comes from volcanoes; but on Venus,
SO2 becomes sulfuric acid clouds because
there is no liquid water to dilute it.
Thursday, March 11, 2010 7

8. Venus: Venera 13 & 14
Even though it’s
covered by
sulfuric acid
clouds and has a
surface air
pressure of 90
bar, the Soviets
managed several
probe landings:
Venera and Vega
probes.
http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-venus.html
Thursday, March 11, 2010 8

9. Venus’s Atmosphere
LACC: §9.3, 9.5, 9.6
• Venus’s surface environment: 96% CO2, 90 bars,
850°F (planet-wide), slow rotation so less wind/
erosion, constant cloud cover
• Venus’s atmospheric evolution = run-away
greenhouse: high temperatures result in H2O gas
which photodissociates, less liquid water so less
CO2 dissolves out, high CO2 levels raise the
temperature because of greenhouse effect...
• Venus’s cloud cover: sulfuric acid clouds
An attempt to answer the “big questions”: what is out
there? Are we alone?
Thursday, March 11, 2010 9

10. LACC HW: Franknoi, Morrison, and Wolff,
Voyages Through the Universe, 3rd ed.
• Ch. 9, pp. 219-220: 4.
Due at the beginning of the next class period.
Test covering chapters 6-9 next class period.
Be thinking about the Solar System Project.
Thursday, March 11, 2010 10

11. Mars’s Atmosphere
LACC: §9.3, 9.5, 9.6
• Mars’s surface environment
• Mars’s atmospheric evolution = run away
refrigerator
• Mars’s clouds
An attempt to answer the “big questions”: what is out
there? Are we alone?
Thursday, March 11, 2010 11

12. Mars
http://rosetta.jpl.nasa.gov/dsp_images.cfm?buttonSel=gallery&buttonSelL2=images&category=mars
Thursday, March 11, 2010 12

13. Mars: Atmosphere
Composition -67°F surface
temperature
• CO2 95.3%
• 80°F hot day
• N2 2.7%
• -200°F cold night
• Ar 1.6%
(11°F greenhouse)
• O2 0.15%
• Ne 0.0003%
winds of a few mph;
0.007 bar pressure massive dust storms
Thursday, March 11, 2010 13

14. Mars’ Surface
Polar caps of H2O and CO2 ice.
Channels and gullies indicate liquid
water flowed, but over 3 billion years
ago.
Wind erosion occurs.
Thursday, March 11, 2010 14

15. Mars: Runaway
Refrigerator Effect
Mars’s lower surface gravity (0.38g) means it lost it’s
atmospheric gases more readily--thermal escape.
As the planet’s atmosphere thinned, the greenhouse
effect became less significant, so Mars grew colder.
Mars became so cold, even CO2 began to condense out
of the atmosphere.
As CO2 condensed out of the atmosphere, the
greenhouse effect became less significant so Mars
grew even colder... i.e. a runaway refrigerator effect.
Eventually Mars became so cold and the air pressure too
low for liquid H2O to exist on its surface.
Thursday, March 11, 2010 15

16. Mars: Atmosphere
Occasionally, clouds of dust, H2O, and/or CO2
form.
The surface pressure is too low for liquid H2O,
even when the temperature does get above
freezing.
CO2 freezes at about -190°F. Much of Martian
polar ice-caps are frozen CO2 (a.k.a. dry ice).
Thursday, March 11, 2010 16

17. Mars: Dust Storms
http://antwrp.gsfc.nasa.gov/apod/ap030602.html
http://abyss.uoregon.edu/~js/images/mars_dust_storm.gif
http://www.nasa.gov/mov/330028main_close_720p_A.mov
Because the martian atmosphere is thin--about 1% as dense as Earth's at
sea level--only the smallest dust grains hang in the air. "Airborne dust on
Mars is about as fine as cigarette smoke," says Bell.
http://science.nasa.gov/headlines/y2003/09jul_marsdust.htm
Thursday, March 11, 2010 17

18. Mars: Landslide
http://photojournal.jpl.nasa.gov/catalog/PIA10245
Thursday, March 11, 2010 18

19. Mars: Landslide
The scarp in this image is on the edge of the dome of
layered deposits centered on Mars' north pole. From top
to bottom this impressive cliff is over 700 meters (2300
feet) tall and reaches slopes over 60 degrees. The top part
of the scarp, to the left of the images, is still covered with
bright (white) carbon dioxide frost which is disappearing
from the polar regions as spring progresses.
The largest cloud (upper images) traces the path of the
debris as it fell down the slope, hit the lower slope, and
continues downhill, forming a billowing cloud front. This
cloud is about 180 meters (590 feet) across and extends
about 190 meters (625 feet) from the base of the steep
cliff.
http://photojournal.jpl.nasa.gov/catalog/PIA10245
Thursday, March 11, 2010 19

20. Mars: Liquid Water
http://www.msss.com/mars_images/moc/2006/12/06/gullies/sirenum_crater/index.html
Thursday, March 11, 2010 20

21. Mars: Faces On Mars
http://stardate.org/resources/gallery/gallery_detail.php?id=71 http://apod.nasa.gov/apod/ap990315.html
Thursday, March 11, 2010 21

22. Mars: Deep Holes On Mars
In a close-up from the HiRISE instrument
onboard the Mars Reconnaissance
Orbiter, this mysterious dark pit, about
150 meters across....Lacking raised rims
and other impact crater characteristics,
this pit and others like it were originally
identified in visible light and infrared
images from the Mars Odyssey and Mars
Global Surveyor spacecraft. While the
visible light images showed only darkness
within, infrared thermal signatures
indicated that the openings penetrated
deep under the martian surface and
perhaps were skylights to underground
caverns. In this later image, the pit wall is
partially illuminated by sunlight and seen to
be nearly vertical, though the bottom, at
least 78 meters below, is still not visible.
The dark martian pits are thought to be
related to collapse pits in the lava flow,
similar to Hawaiian volcano pit craters.
http://apod.nasa.gov/apod/ap070928.html
Thursday, March 11, 2010 22

23. Mars: Martian Meteorites
Splotches of glassy material Comparison of Viking-measured
contain trapped martian Mars atmosphere to trapped gases
atmosphere. in EETA79001 Shergottite glass.
Rock is 16 cm across. Figure is from Pepin, R. O., 1985,
Evidence of Martian Origins,
Nature, 317, p. 473-475.
http://www.psrd.hawaii.edu/July99/EETA79001.html
Thursday, March 11, 2010 23

24. Mars: Martian Meteorites
http://www.aerospaceweb.org/question/astronomy/q0193.shtml
Thursday, March 11, 2010 24

25. Mars: Martian Meteorites
The most tantalizing clue found so far came from a meteorite
discovered in Antarctica. Named ALH 84001, this hunk of space
debris is believed to have been blasted off the surface of Mars about
16 million years ago. The rock survived the perils of space and a fiery
trip through the Earth's atmosphere to land in Antarctica some
13,000 years ago.
The meteorite was discovered in 1984, but it was not until 1996 that
scientists announced evidence of life in the ancient rock. Though the
findings are still controversial, the meteorite contains fossilized
remains that could be a primitive form of bacteria. If so, ALH 84001 is
the first hard evidence that life of any kind evolved on a planet other
than Earth.
http://www.aerospaceweb.org/question/astronomy/q0193.shtml
Thursday, March 11, 2010 25

26. Mars’s Atmosphere
LACC: §9.3, 9.5, 9.6
• Mars’s surface environment: 95% CO2, 0.007 bars,
-67°F (±100+), winds of a few mph, massive (fine)
dust storms, wispy clouds
• Mars’s atmospheric evolution = run away
refrigerator: low surface gravity (0.38g) means
thermal escape of atmosphere; less atmosphere
means less greenhouse effect, so temperatures fall;
H2O, CO2 condense, so temperatures fall...
• Mars’s clouds: H2O, CO2, fine dust
An attempt to answer the “big questions”: what is out
there? Are we alone?
Thursday, March 11, 2010 26

27. LACC HW: Franknoi, Morrison, and Wolff,
Voyages Through the Universe, 3rd ed.
• Ch. 9, pp. 219-220: 7.
• Study for the test on the Inner Planets
(Chapters 6-9)
Due at the beginning of the next class period.
Test covering chapters 6-9 next class period.
Be thinking about the Solar System Project.
Thursday, March 11, 2010 27

28. Review for the Test 2 of 5:
The Terrestrial Planets
[10 pts] Compare and contrast the physical properties of Mercury, [10 pts] Compare and contrast the atmospheric properties of Venus,
Venus, Earth, Luna, and Mars. Earth, and Mars.
• mass, size, density, notable surface features (Caloris Basin, • Composition and Surface Pressure: Venus--90-bar 850°F
Chicxulub crater, maria, highlands, Tycho, Tharsis Bulge, CO2, Earth--1-bar 59°F N2 (and O2), Mars--0.007-bar
Olympus Mons, Valles Marineris) -58°F CO2
• Interiors: core (inner/outer, (Mercury’s vs Luna’s). mantle, • Clouds: Venus--H2SO4 sulfuric acid (radar ranging),
crust); seismic waves Earth--H2O water, Mars--H2O water, CO2 carbon dioxide,
• orbits (distance from the sun, eccentricity, inclination, fine dust
length of a year) and rotational properties (axial tilt, solar • Temperature--Mercury 797°F to -283°F, Venus 850°F
vs. sidereal day, spin:orbit resonance, tide locking) (hotter than Mercury), Earth--59°F average, Moon--257°F
to -283°F, Mars-- -67±100+°F
[10 pts] Understand the processes that shaped the terrestrial planet’s
surfaces. [10 pts] Understand the processes that shape the terrestrial planet’s
• Collapse of solar nebula, Condensation (frost line), atmosphere.
Accretion (planetesimals, differentiation), Heavy • How early atmospheres (CH4, NH3, H2O, CO2) become
Bombardment, Cooling (don’t forget scarps), clearing an mature atmospheres (N2 w/ H2O oceans or CO2):
orbit of debris outgassing by volcanoes, dissociation by solar uv,
• Tectonic Activity: Core-Interior Heat (radioactive decay), thermal escape, liquid water?, condensation
Mantel-Convection, Crust (coronae, ridges and cracks, • Greenhouse Effect (Venus--runaway greenhouse, Mars--
Plate Tectonics, maria, Valles Marineris) runaway refrigerator, Earth--just right)
• Age of planetary surface: radiometric dating (Earth, Luna), • Evidence and effect of life on the planets (Martian
number of impact craters, erosion, resurfacing--extensive meteorites, oldest fossils, extinction events, O2)
volcanic activity or plate tectonics
[10 pts] Identify objects from a picture.
• Mercury, Venus, Earth, Luna, Mars, Phobos, and Deimos
from space
• Venus, Earth, Luna, Mars from the surface
• Shield Volcanoes, “Pancake” Lava Domes, Scarps, impact
craters, coronae
Thursday, March 11, 2010 28