I. Seasonal Changes in Titan’s Cloud Activity

Emily L. Schaller

April 28, 2008

II. Volatile Ices on Outer Solar System Objects

I. Seasonal Changes in Titan’s Cloud Activity

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

http://www.lsbu.ac.uk/water/phase.html

TE

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

Latit

ude

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 transmissionAdaptive optics atKeck 10-mGemini 8-m

11/11/03 11/12/03 11/13/03 11/14/03

K’

2.12

2.17

Titan through different filters

South polar cloud locations

Why are clouds near the south pole?

Mean daily insolation on Titan

Temperature profile (1)

temperature

heig

ht

dry adiabat

surface temperature

Stable

Temperature profile (2)

temperature

heig

ht

dry adiabat

surface temperature

convection

condensation

buoyancy

cloud tops

wet adiabat

Tokano 2005 (Icarus)


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 2001- November 2004

Schaller et al. Icarus 2006b

Titan Images:December 2004 - Present

Schaller et al. Icarus 2006b


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. 2006 PNAS

Models of Titan Cloud Activity with season

(moist case (80% rh) (intermediate case (40% rh)

Present Present

Models of Titan Cloud Activity with season

Rannou et al. 2006 Science

Present

IRTF spectroscopic monitoring• Disk integrated spectra of Titan covering 0.8-2.4

microns with a resolution of 375• Data taken every night instrument is on the

telescope (172 nights 2006-2008)• 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 deviateat <2.12 micronsindicating extremely low <0.15% tropospheric cloud activity in 95% of all nights

1995-1999

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)

QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.

QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.

2008-April-14

2008-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 spectraR

ela

tive R

eflect

an

ce

Wavelength (microns)

2003 VS2

2002 AW197

2002 UX25

2002 TC302

(Barkume et al. 2008)

QuickTime™ and aTIFF (LZW) decompressor


(Brown et al. 2007)

Water ice model

Rel

ativ

e R

efle

ctan

ce

http://en.wikipedia.org/wiki/Image:EightTNOs.png

Brown et al. 2005

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 (N2, CH4, CO)

Rock

Water Ice

Volatile ices (N2, CH4, 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)

Te

mp

era

ture

(K

)

Diameter (km)

`


Te

mp

era

ture

(K

)

Diameter (km)


Te

mp

era

ture

(K

)

Diameter (km)

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


(Brown et al 2007)

2005 FY9


Barkume, Brown & Schaller ApJL 2006

Strong Water ice spectra for 2003 EL61 and Satellite

2003 EL61

Density=2.7 g/cc


Quaoar - Water ice spectrum

(Jewitt & Luu 2004)

Quaoar Spectrum

Schaller & Brown ApJL (2007b)

Quaoar Spectrum40% crystalline water ice w/ 10 micron grains


Quaoar with water ice + methane model

Water ice

Water ice+methane


Quaoar

Ethane model


Nor

mal

ized

Ref

lect

ance

Quaoar with full spectral model

35% crystalline water ice, 6% methane, 4% ethane, 55% dark continuum

methane methane methaneethane


Schaller & Brown ApJL 2007a

KBO Spectra

– Methane

– Moderate water ice -strong water ice

– Featureless

size

Pluto, Eris, Triton2005 FY9

Quaoar

Orcus, 2003 AZ84Varuna,

2003 EL61

Charon

2003 EL61 collisionalfamily 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

• 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.

Roe et al. 2005

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• Streaky, short lived• Not evidence for seasonal change• Likely tied to the surface

Documents

I. Seasonal Changes in Titan’s Cloud Activity