MARS

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MARS: EARTH'S LITTLE BROTHER

  • Mass is 0.106 that of Earth (via Phobos & Deimos)
  • Radius is 3394 km or 0.53 of Earth (angular diameter at opposition)
  • Density is 3.93 g/cm^3 or 0.71 of Earth;
    implies a different interior from Earth, Venus or Mercury.

    As seen from Earth, Mars is:

  • Closest at opposition; some details visible from Earth.
  • Much fainter than Venus: further from Sun, smaller and
    lower albedo (.15 vs .70) all make Mars fainter.
  • Martian day = 24.6 h
  • equatorial tilt = 24.0 degrees -- both close to Earth
    THEREFORE MARS HAS SEASONS TOO.
  • Mainly red surface with variable markings
  • Polar caps: variable parts are mostly CO_2, not H_2 O
  • But latest measurements indicate most of both caps is water ice
  • Shifting dunes change markings --- not canals and vegetation

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    MARTIAN TOPOGRAPHY

  • Southern Hemisphere higher by several km; heavily cratered
  • Northern Hemisphere mostly volcanic plains (maria);
    probably only 3 billion years old, vs. 4 billion years for S.

  • Tharsis bulge --- near equator and 10 km higher
  • 4 big volcanoes on Tharsis and 100s of good sized ones
  • One, of these, the SS's biggest, is Olympus Mons:
    700 km diameter;
    25 km high;
    80 km wide caldera -- way bigger than biggest on earth.
  • WHY? Lower gravity allows greater height and
    lack of tectonic motion allows huge build-up.

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    MARTIAN ATMOSPHERE

  • P_Mars = 0.006 P_Earth;
  • T = 100-300 K (night to day)
  • Windy and dusty --- dust storms frequent
  • COMPOSITION: 95.3% CO_2; 2.7% N_2; 1.6%Ar
  • Clearly much denser and hotter when young, but water dissolved
    most CO_2 (like on earth) so less greenhouse effect.

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    MARS'S INTERIOR

  • CRUST some 100 km thick
  • MANTLE some 2050 km thick -- not plastic now
  • CORE some 1250 km in radius --- FeS
  • No bulk MAGNETIC FIELD ---> no liquid and/or no Fe/Ni
  • Cooled off too fast to establish tectonics

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    CANYONS and WATER

    Many images from Mariners 4 and 7, Viking, Global Surveyor, and
    Pathfinder showed Mars has:

    Some large ``Canyons'' due to TECTONIC FRACTURES
    e.g., Valles Marineris, near Tharsis bulge

  • 2 billion yrs old; 4 km deep
  • 4000 km long; 120 km across

    Real CANYONS ---> RUNNING WATER

  • RUNOFF CHANNELS, that merge like river valleys
  • OUTFLOW CHANNELS, relics of huge floods

    FLUIDIZED EJECTA near IMPACT CRATERS

  • Recent images MAY indicate CURRENT SEEPAGE OF WATER
    from PERMAFROST
  • Some WATER is permanently FROZEN in POLAR CAPS
  • The latest measurements indicate most of BOTH polar caps are water ice.

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    MARS HAS PUNY MOONS

    Discoverd by Asaph Hall in 1877, these are probably captured
    asteroids since densities are low (2 g/cm^3).

    Phobos

  • 28 x 20 x 8 km
  • a = 9378 km; P = 7h 39m --> ``backwards'' orbit

    Deimos

  • 16 x 10 x 6 km
  • a = 23,459 km; P = 30h 18m --> ``slow''

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    MARS LANDINGS

    Vikings in 1976; Pathfinder/Sojourner in 1997; Spirit and Opportunity in 2004-5

  • Red color from Fe_2 O_3 --- rust
  • Plains covered with boulders and rocks
  • Some sharp, some smooth and eroded
  • Pathfinder site: rocks deposited by old flood; Sojourner was the rover
  • Spirit and Opportunity rovers found clear chemical evidence for liquid water in the past

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    LIFE ON MARS?

    Viking (and subsequent) photos showed nothing moving.

    Viking: Gas-chromatograph/mass-spectrometer showed no organic compounds.

    Viking: Gas-exchange and pyrolytic release experiments search for metabolism
    and gave ``positive'' results (O_2 and C, respectively),
    but sterilized samples also gave off gases;
    both anomalous results are probably due to UV irradiated
    soil and water yielding hydrogen peroxide.

    Viking: Labeled release experiment gave off radioactive gas while
    sterilized soil didn't. Probably due to C_2 O_3 -- carbon suboxide.

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    Meteorite ALH84001 found in Antarctica came from Mars; controversial
    evidence for bacterial fossils.

  • Rock structures similar to bacterial; PAHs
  • Magnetite found where carbonate dissolved
  • Rod-like structures --- but very small!

    Most investigators think that ALL this "EVIDENCE" of life on Mars
    is NOT CONCLUSIVE and could be explained by INORGANIC CHEMISTRY.
    But the chance that there was once life on Mars, or that some
    primitive form exists below the Martian surface, cannot be absolutely
    ruled out.