PES 105        Fall 2001
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General Astronomy I
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Lecture Notes:

Mars

text: Chapter 8: Section 8.4, 8.6

Introduction and General Properties

Here is a good link for information about the Mars: http://seds.lpl.arizona.edu/billa/tnp/mars.html

Here is another good link with information, pictures and animations about Mars: http://www.planetscapes.com/solar/eng/mars.htm

Here is a link with pictures of Mars: http://antwrp.gsfc.nasa.gov/apod/index/Mars.html

Mars is our other neighbor in space.

 

albedo = 0.15 . . . . similar to Moon and Mercury

few clouds

density = 4.0 g/cm3 . . . slightly lower than other terrestrial planets

=> more rock and less metal ?

size: much smaller than Earth (but bigger than Mercury)

lots of information from spacecraft

Motions

orbit:

  • orbital period = 687 days (about 2 years)
  • elongated elliptical orbit

rotation:

  • rotation period = 24.5 hours
  • tilt of axis = 25 degrees
    • seasons ?
  • both of these are similar to Earth

Interior

observe NO magnetic field

since it rotates quickly, there must be NO liquid inside

consistent with small size (and fast cooling rate)

cross-section of Mars

Mars is less differentiated => was not molten for very long

some evidence for past seismic activity and past volcanoes

Surface

Observe:

  • plains (40 %)
    • mainly northern hemisphere
  • rough areas with craters (60%)
    • mainly southern hemisphere

Interesting features (within these regions):

 

  • Polar caps
    • frozen carbon dioxide (dry ice) on top of water ice
    • some melting in summers
      • caps visibly change appearance
    • Figure 8.17 shows the polar caps. [Link to Figure 8.17]
  • Valles Marineris
  • Olympus Mons
    • high volcano
    • 6 1/2 times higher than Pikes Peak (which is not a volcano)
    • 3 times higher than Mount Everest (which is not a volcano)
    • volcanos on Earth do grow so large because continental drift moves the mountain off of the hot spot.
    • no continental drift on Mars, so mountains keep getting higher and higher
    • Figure 8.19 B shows Olympus Mons. [Link to Figure 8.19]
    • This animation shows Olympus Mons: http://www.planetscapes.com/solar/cap/mars/vidmars4.htm
  • channels
    • appear to be from running water
    • Where is the water now?
      • not liquid - pressure is too low and too cold
      • not gas - water escapes from Martian atmosphere
      • maybe solid - at poles and permafrost under ground ?
      • Figure 8.20 and 8.23 show channels. [Link to Figure 8.20] [Link to Figure 8.23]
      • [demo with vacuum system]
  • sand dunes
    • from wind

Atmosphere

very thin

pressure at surface is 1/200 pressure on Earth

Composition:

  • carbon dioxide - 95 %
  • nitrogen - 3 %
    • from volcanoes ?
  • others - 2 %

similar to Venus - probably no life on Mars

some thin clouds of dust, water vapor and carbon dioxide droplets

Mars atmosphere

 

Ciculation

fast rotation and convection

rotation dominates

Mars circulation

winds are typically parallel to equator

can be strong (35 - 200 km / hr)

not much erosion since atmosphere is very thin

Seasons

caused by:
  1. tilt of axis (simlar to what happens on Earth)
  2. elongation of orbit (not a factor on Earth)

 

seasons on Mars

During hot Southern summer strong winds can create global dust storms (weeks long)

History

4.5 billion years ago

planetisimals combine

planet is molten - some differentiation occurs

4 billion years ago

crust cools quickly - before complete differentiation

craters form from impacts

seismic activity

3.5 billion years ago . . . . .

flowing water

thicker atmosphere (warmer)

life on Mars ?????

3 billion years ago

major volcanic activity - lava flows

lava covers old craters in Northern hemisphere

since then

continuing wind erosion

Moons:

two very small moons:

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