Solar System Geology Part II

New Horizon, Kuiper Belt and Pluto-Charon: #

Learning Outcomes:

  • List the main objects that the New Horizons mission has explored so far

    • Pluto & Charon

  • Describe how Pluto is different from the other planets in our solar system in terms of its orbit, composition and the characteristics of its largest satellite (Charon)

  • Compare and contrast Pluto and Charon in terms of geologic processes, atmospheres, and interior structure

    • Pluto:
      • Nitrogen ice glaciers
      • Convection cells in nitrogen ice
      • Dunes
      • Water-ice rich crust
      • Cryovolcanism
      • Thin nitrogen atmosphere, ~ 1000x thinner than Mars'. Composed mostly of nitrogen, some methane and carbon monoxide.
    • Charon:
      • Water-ice rich, but lacks N2, CH4, and CO
      • Large chasms
        • Indicates extensional tectonics
        • Formed early in its formation, as a result of freezing of a primordial ocean
      • Reddish north pole
        • Formed by methane from Pluto being irradiated and forming hydrocarbons
    • Interiors of both:
      • Radius:
        • Pluto: 1,150-1,200km
        • Charon: 600-610km
      • Density:
        • Pluto: 1.7-2.15 g/cm3
        • Charon: 1.3-1.8 g/cm3
      • Surface Ices:
        • Pluto: N2, CH4, CO, H2O, and presumably organics
        • Charon: NH3, H2O
      • Both are differentiated
        • Charon is geologically dead
        • Pluto is still active, with radiogenic heat as primary source

  • Compare Neptune’s moon Triton to Pluto and Charon

    • Shares similarities with both Pluto and Charon

    • Most likely a captured KBO

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  • Describe comets in terms of their characteristics, their relationships to the Kuiper Belt/KBOs and Oort Cloud, and their significance

    • Comets are small, ice-rich bodies that formed in the outer Solar System
    • Characteristics:
      • Orbital:
        • Highly elliptical
        • Either short-period (years) or long period (>1000 years)
      • Composition:
        • CHON: Carbon-Hydrogen-Oxygen-Nitrogen
        • Silicates and other minerals, similar to what is found in chondrites
    • Visible due to interaction with the Sun
    • Comet sources today include two main reservoirs: the Kuiper Belt and the Oort Cloud
      • Kuiper Belt:
        • Source of short-period comets; influenced by Jupiter’s gravity, aka “Jupiter Family Comets” (JFCs)
        • In the plane of the solar system; 30-50 AU
      • Oort Cloud:
        • Source of long-period comets
        • Spherical, loose cloud of icy bodies; 10,000 to 100,000 AU
    • Significance:
      • Comets preserve the best, most accessible record of the temperature, pressure and molecular composition of the solar nebular disk
      • Formed in the outer Solar System at 4.57Ga
      • Have existed at cryogenic temperatures since formation (preserve volatile compunds)

  • List the main discoveries about comets from the Rosetta mission to comet 67P

    • Comets have geology
      • Overall shape
      • Complex topography
      • Water stored in the interior
    • Comets contain organic molecules
      • glycine, hydrogen sulfide, ammonia, hydrogen cyanide, and many others

  • Explain how all the objects discussed in this lecture may be related

Extra-solar Planets: #

Learning Outcomes:

  • Consider and apply different definitions for “planet”
    • Any body in the solar system that is more massive than the total mass of all of the other bodies in a similar orbit– Ceres?–Pluto?
      • Ceres, Pluto are still not planets
    • Geophysical Definition: “a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape…regardless of its orbital parameters” (Runyon et al. 2017*)– Ceres?–Pluto?– Large KBOs?
      • Too many planets?
  • Define exoplanet(or ‘extrasolar planet’) and explain why it is difficult to find them
    • Planets orbiting other Stars.
    • Difficulties:
      • Planets don’t produce light of their own
      • They are very far away
      • They are lost in the blinding glare of the star
  • Describe some of the ways exoplanets are discovered
    • Radial velocity (Swaying of star due to planet)
    • Astrometric measurement (Wobble of star)
    • Transit (planet crosses in front of star)
    • Direct imaging
    • Gravitational lensing
  • List three missions that have contributed to finding exoplanets
    • The MOST mission
    • The Kepler mission
    • The TESS mission

  • Describe some of the diversity of exoplanets, as they compare to our own solar system #

The Big Picture: Comparative Planetology #

Learning Outcomes:

  • Explain the diversity of planetary bodies in our solar system through the interaction of planetary matter and planetary energy

    • Planetary Matter:
      • Chemical composition (refractory vs. volatile)
      • Size/mass (how much accreted)
    • Planetary Energy:
      • Amount (how much originally, and since)
      • Type (accretion, radiogenic, core formation, tidal, solar, impacts and local energy during crater formation)
    • Thermal Evolution (Geologic Evolution)
      • Loss of heat depends on:
        • Size (surface area/mass)
        • Composition
        • Energy content (how much it had began with, continues to have)
        • Heat transfer

  • Place various planetary bodies in our solar system on a “cube” whose axes are composition, size and thermal evolution

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  • Consider how the Earth is ‘just right’ for life, and where else in the solar system you would prioritize to look for life (as we know it)

    • Size and composition
      • Plate tectonics (recycles crust, regulates carbon cycle)
      • Silicates + water
      • Differentiation from atmosphere through degassing
      • Gravity to hold gases
    • Distance from Sun
      • Hydrologic cycle
    • Life as we know it requires water, energy, access to organic materials, and time
    • Consider earth not just in terms of a hydrologic cycle
    • Moon formed by giant impact
      • stabilized earth’s tilt (obliquity)
      • created ocean tides
    • Plate tectonics
      • regulation of carbon cycle (CO2 in atmosphere)
    • Presence of gas giants
      • protection against disruption/impacts?

The Search for Life on Mars #

Learning Outcomes:

  • Summarize the results from the biology experiment on the Viking mission to Mars, and explain why it did not show evidence for life
    • Incubated samples of surface under different conditions
      • Results were positive, but heat sterilized control sample was also positive
    • Soil is highly chemically reactive, containing an oxidant.
    • No organic molecules detected
    • Conclusion: no evidence of life
  • State the main implication for the exploration of Mars of the supposed evidence for fossil life in the ALH 84001 martian meteorite
    • The evidence presented by McKay et al. (1996) is not widely accepted as firm evidence for past life by the scientific community
    • The identification of life in a martian meteorite requires multiple lines of positive evidence
    • Must not rely on morphology (of bacteria-like structures, mineral grains) alone
    • NASA’s “Follow the Water”
  • Explain the importance of sample return in the exploration of Mars
    • Analyses on Earth are much more advanced, providing information that cannot be obtained from rovers or orbiters
      • Detection of life/biomarkers, geochronology, etc.
      • Samples remain available for future generations, as technology advances
    • Samples from locations where context is known are much more valuable than random samples