I. Seasonal Changes in Titan’s Cloud Activity Emily L. Schaller



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I. Seasonal Changes in Titan’s Cloud Activity

  • Emily L. Schaller

  • April 28, 2008




Titan

  • Thick atmosphere surface pressure ~1.5 bar.

  • 27 degree obliquity

  • 16 day rotation period



















Titan through different filters



South polar cloud locations



Why are clouds near the south pole?



Mean daily insolation on Titan



Temperature profile (1)



Temperature profile (2)





Mean daily insolation on Titan



Large Cloud Outbursts



Comparison to 1995 Event



What causes large cloud outbursts?

  • Surface heating?

  • Increased condensation nucleii?

  • Increased methane humidity

      • Injected somewhere else and brought to the pole?


Typical Titan images: November 2001- November 2004



Titan Images: December 2004 - Present



Mean daily insolation on Titan











IRTF spectroscopic monitoring







I. Conclusions:

  • Seasonally varying insolation and uplift from the general circulation appears to control the location of clouds on Titan.

  • The dissipation in Titan’s south polar clouds is the first indication of seasonal change in Titan’s weather.

  • Large cloud events occur in different seasons of Titan’s year and may be caused by increased methane humidity, CCN or other factors.

  • The near lack of cloud activity in IRTF observations (February) contrasts sharply with similar observations of Griffith et al. (2000) around autumnal equinox (Sept, Oct)







II. Volatile Ices on Outer Solar System Objects









KBOs with featureless infrared spectra















Volatile escape model

  • Assume all volatile ices are accessible to surface

  • Assume surface radiative equilibrium temperature

  • Calculate loss via thermal (Jeans) escape





`











2005 FY9











Quaoar - Water ice spectrum





Quaoar Spectrum



Quaoar Spectrum















KBO Spectra

  • KBO Spectra

    • Methane
    • Moderate water ice -strong water ice
    • Featureless


Conclusions

  • Spectra of KBOs depend on object size, temperature, and collisional history

  • Thermal escape explains range of spectra seen on KBOs

  • Quaoar is a transition object between volatile rich and volatile poor.

  • Crystalline water ice is present on all water ice-rich objects and likely does not indicate cryovolcanism





2005 FY9



2005 FY9



2005 FY9

  • N2 depleted by at least an order of magnitude compared with N2 on Pluto

  • Methane grains can grow large

  • Growth of higher order hydrocarbons such as ethane, propane, etc.





Types of Clouds

  • Small scale south polar

      • ~1% coverage of Titan’s disk
      • Consistently present from 2001-2004
  • Large cloud outbursts

      • Clouds increase in brightness by ~15 times over typical levels
      • Last for ~1 month
      • Observed in two different seasons
  • Midlatitude (40S) clouds



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