Emily L. Schaller April 28, 2008 II. Volatile Ices on Outer Solar System Objects I. Seasonal Changes in Titan’s Cloud Activity

Titan Thick atmosphere surface pressure ~1.5 bar. 27 degree obliquity 16 day rotation period

Phase diagram of water T E

Phase diagram of methane T Gas Solid Liquid Credit: H. Roe

On the whiteboard in the interact room (circa December 2004)…..

Surface maps 90N 0 90S West Longitude 0180 Latitude Credit: NASA/JPL/Space Science Institute x

How long ago did it rain at the Huygens landing site? Or: How long ago was it cloudy?

Titan’s spectrum McKay et al., 2001

Narrowband imaging Methane transmission Adaptive optics at Keck 10-m Gemini 8-m

11/11/0311/12/03 11/13/0311/14/03 K’ Titan through different filters

South polar cloud locations

Why are clouds near the south pole?

Mean daily insolation on Titan

Temperature profile (1) temperature height dry adiabat surface temperature Stable

Temperature profile (2) temperature height dry adiabat surface temperature convection condensation buoyancy cloud tops wet adiabat

Tokano 2005 (Icarus)

Mean daily insolation on Titan

Large Cloud Outbursts (Schaller et al. Icarus 2006a)

Comparison to 1995 Event (Schaller et al. Icarus 2006a)

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 November 2004 Schaller et al. Icarus 2006b

Titan Images: December Present Schaller et al. Icarus 2006b

Mean daily insolation on Titan

Titan cloud latitudes Titan Southern Summer Solstice South Pole ceased to be area of maximum solar insolation South Pole ceased to be the area of maximum solar insolation Southern Summer Solstice Schaller et al. 2006b

Titan cloud latitudes Titan Southern Summer Solstice South Pole ceased to be area of maximum solar insolation Southern Summer Solstice South Pole ceased to be the area of maximum solar insolation Schaller et al. 2006b

Mitchell et al PNAS Models of Titan Cloud Activity with season (moist case (80% rh) (intermediate case (40% rh) Present

Models of Titan Cloud Activity with season Rannou et al Science Present

IRTF spectroscopic monitoring Disk integrated spectra of Titan covering microns with a resolution of 375 Data taken every night instrument is on the telescope (172 nights ) Disk integrated spectra: –total fractional cloud coverage –cloud altitudes –Interrupt at Gemini to determine latitudes These data can be compared with similar observations done in the 1990’s by Griffith et al.

IRTF Spectral Data (March-May, Oct 2006-June 2007) Spectra deviate at <2.12 microns indicating extremely low <0.15% tropospheric cloud activity in 95% of all nights

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)

2008-April April-15

II. Volatile Ices on Outer Solar System Objects

(Lewis 1995) Asteroid Belt Spectral Types

Classical KBOs Plutinos (3:2 resonance) Scattered Disk Objects Periodic comets Centaurs Jupiter Trojans The Outer Solar System

Brown 2000 Pluto

KBOs with featureless infrared spectra Relative Reflectance Wavelength (microns) 2003 VS AW UX TC302 (Barkume et al. 2008)

(Brown et al. 2007) Water ice model Relative Reflectance

Brown et al Eris

Kuiper Belt Near Infrared Spectra Methane-rich Water ice rich Featureless (e.g Pluto, Eris, 2005 FY9) (e.g. Orcus, 2003 EL61, 2003 AZ84) (e.g Huya, Varuna, 2003 VS2) Moderate Water ice Continuum?

Rock Water Ice Volatile ices (N 2, CH 4, CO)

Rock Water Ice Volatile ices (N 2, CH 4, CO)

Volatile escape model Assume all volatile ices are accessible to surface Assume surface radiative equilibrium temperature Calculate loss via thermal (Jeans) escape

Schaller & Brown ApJL (2007a) Temperature (K) Diameter (km)

` Schaller & Brown ApJL (2007a) Temperature (K) Diameter (km)

Schaller & Brown ApJL (2007a) Temperature (K) Diameter (km)

Schaller & Brown ApJL (2007a) Diameter (km)

Schaller & Brown ApJL (2007a) Diameter (km)

(Brown et al 2007)

2005 FY9

Schaller & Brown ApJL (2007a) Diameter (km)

Barkume, Brown & Schaller ApJL 2006 Strong Water ice spectra for 2003 EL61 and Satellite

2003 EL61 Density=2.7 g/cc

Schaller & Brown ApJL (2007a) Diameter (km)

Quaoar - Water ice spectrum (Jewitt & Luu 2004)

Quaoar Spectrum Schaller & Brown ApJL (2007b)

Quaoar Spectrum 40% crystalline water ice w/ 10 micron grains Schaller & Brown ApJL (2007b)

Quaoar with water ice + methane model Water ice Water ice+methane Schaller & Brown ApJL (2007b)

Quaoar Ethane model Schaller & Brown ApJL (2007b) Normalized Reflectance

Quaoar with full spectral model 35% crystalline water ice, 6% methane, 4% ethane, 55% dark continuum methane ethane Schaller & Brown ApJL (2007b)

Schaller & Brown ApJL 2007a

KBO Spectra –Methane –Moderate water ice -strong water ice –Featureless size Pluto, Eris, Triton 2005 FY9 Quaoar Orcus, 2003 AZ84 Varuna, 2003 EL61 Charon 2003 EL61 collisional family members (7 now known) most small KBOs

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

Schaller & Brown ApJL 2007a

2005 FY9 Methane model with 1 cm grains

2005 FY9 Residual with Ethane overlaid

2005 FY9 N 2 depleted by at least an order of magnitude compared with N 2 on Pluto Methane grains can grow large Growth of higher order hydrocarbons such as ethane, propane, etc.

Roe et al. 2005

Types of Clouds Small scale south polar ~1% coverage of Titan’s disk Consistently present from 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 Streaky, short lived Not evidence for seasonal change Likely tied to the surface