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


  • 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


  • 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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