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Lecture

AST251 MARCH 12.docx


Department
Astronomy & Astrophysics
Course Code
AST251H1
Professor
Susan Pfieffer

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AST251 MARCH 12, 2012
LECTURE 9
WHEN WE SAY LIQUID WATER IS UNSTABLE ON MARS WE MEAN
MARS USED TO HAVE MAGNETIC FIELD ITS ROTATION IS SLOWER
MARS
- Retrograde is key defining feature
- The dots in background is Uranus moves much more slowly bc further away, fainter despite
bigger size then mars
- Mars and Uranus close together indication planets in same plane, follow same track as other
planets and the sun
Mars visibility
- Opposoition as close to earth as possible, good time to travel to mars
- Mars on eccentric orbit
- Every two years bc mars move slowler around sun then earh does
Mars opp
Mars essential facts
- Average distance is 1.5 au
- Amount sunslight per sa down as distance squared , a lot less light energy to heat planet
- Elliptical
- Eccentricity measured by e closest 9 percent closer and 9 percent further dramatic difference in
sunlight received
- 1.98 vs 2.8 varies by almost 1.5
- Rotation rate is like earth 24hrs 40 min longer, curious to mars rover bc active day time not
night, they live on a 24 hr 40 min clock on mars when rises and sets
- Slower but not significant
- Rot axis is inclined to orbit by 25 degrees like earth 23.5 degrees
- 25 is current and changes earyh always around 23,4 decrss
- Mars smaller then earth, half radius so volume is one eight and mass is one tenth
- Smaller volume less gravity, 40 percent that of earth, moon is 16% still jum around
- Gravity easier to lose atmosphere
Moons of mars
- Phobos and deimos, once said artificial by martian civ, not special capture by asteroid belt
In pop culture

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- Believed to see canals and other features
- Lowell observatory observed 10s of years
- Depend on what they wanted to see
- Orson wells war of the worlds
Modern exploration of mars
- Satilets started in 60s, fly by Americans
- Viking landed looked for micropes and look for soil chem.
- Queit time then late 90s large number of missions
- Spirit and opp successful
- 2008 lander to polar caps
- 2012 mars science lab on way
- Spirt opp quite massive rovers
- 2012 is size of small car, serious pieces of equipement
Old pics vs radar altimetry
- Not overlap before and now
- Color coded by height red high and blue low
Viking 2 landscape
- First to land
- All dust various sizes
- Forst on shadow side of
- Skies should not orange should be blue and dark bc thin, orange bc of dust in atmsphore
scatters light
- Unpleasant desert
Pathfinder landscape
- Stoney desert
- Might think desert on earth
- More and more dramatic and improves
- Phoenix lander 160 megapixel panorama
- Big desert not much happening
Mars surface
- Cold average temp is -50c
- Summer during day time rise to above freezing
- Atmospeher thin 100th of density atmopspher of earth
- Pressure changes strongly between 30% by co2 condense in polar caps in winter season
- Atmpsphere 90% co2 rest is n2 and ar

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- Co2 greenhouse but thin atmosphere and far from sun
Contd…
- Atmosphere comparision number of molecules earth is 1 venus is 90 times mars 1 percent of
earth
- C02 earth minute amount .0003 venus is 2 thirds and mars is almost completely co2 relative to
total amount
- Other gases 02 20 pwecent on earyh little venus and mars
- Venus and mars similar atmospheres c02 and other elements
Surface conditions
- Cld in winter -80 and above freezing in summer
- Low pressure what means for other liquids
- Pahse temp on x pressure on y
- When water is s l or gasesous
- Critical abive temp and pressure can distinguish between solid and liquid, liquid on above
certain minimum pressure which is close to 1
- With mars pressure below number cold temp solid ice and increase temp turn to gas water
vapor never liquid,
- Same co2 gas or solid no liquid on mars
Liquid water is unstable
- Liquid water either freezes or evap called unstable bc low pressure solid or vapor
Martian season
- On earth what causes seasons is tilt
- Northen summer north hemp pointed toward sun
- In winter points away and lower solar incidence less sunlight and temp drops
- Mars summer when pointing towards and winter when away
- Earth circular
- Second feature for mars is eliiptic orbit
- Summer of south very hot bc close to sun and north summer further away from sun not
pronounced
- Distance changes by 20 percent 9 percent more and less
- And light distance squared
- Closer to sun moves faster, close to sun season is shorter sout summer and further away moves
slower
Seasonal polar caps
- In south co2 condenses and north evaporates blow from north to south and reverses
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