I. Seasonal Changes in Titan’s Cloud Activity
II. Volatile Ices on Outer Solar System Objects
Emily L. Schaller
April 28, 2008
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
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E
http://www.lsbu.ac.uk/water/phase.html
Phase diagram of methane
Liquid
Solid
T
Gas
Credit: H. Roe
On the whiteboard in the interact room (circa December 2004)…..
Latitude
90N
0
x
90S
180
0
West Longitude
Credit: NASA/JPL/Space Science Institute
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
Methane transmission
Adaptive optics at
Keck 10-m
Gemini 8-m
Titan through different filters
K’
2.12
2.17
11/11/03
11/12/03
11/13/03
11/14/03
South polar cloud locations
Why are clouds near the south
pole?
Mean daily insolation on Titan
Temperature profile (1)
Stable
dry adiabat
temperature
surface temperature
cloud tops
Temperature profile (2)
buoyancy
wet adiabat
condensation
convection
dry adiabat
temperature
surface temperature
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 2001- November 2004
Schaller et al. Icarus 2006b
Titan Images:
December 2004 - Present
Schaller et al. Icarus 2006b
Mean daily insolation on Titan
Titan cloud latitudes
Southern Summer
Solstice
Titan Southern
Summer Solstice
Schaller et al. 2006b
South
Pole
ceasedtotobe the area
South
Pole
ceased
be area of maximum
of maximum
solar insolation
solar insolation
Titan cloud latitudes
Southern Summer
Solstice
Titan Southern
Summer Solstice
Schaller et al. 2006b
South
ceasedtoto be the area
SouthPole
Pole ceased
ofbe
maximum
solar insolation
area of maximum
solar insolation
Models of Titan Cloud Activity with season
Present
Present
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(moist case (80% rh)
Mitchell et al. 2006 PNAS
(intermediate case (40% rh)
Models of Titan Cloud Activity with season
Present
Rannou et al. 2006 Science
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 deviate
at <2.12 microns
indicating 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)
Quic kT i me™ and a
T IFF (LZW) dec om pres s or
are needed t o s ee thi s pi c ture.
2008-April-14
2008-April-15
Quic kT i me™ and a
T IFF (LZW) dec om pres s or
are needed t o s ee thi s pi c ture.
II. Volatile Ices on Outer Solar
System Objects
Asteroid Belt Spectral Types
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(Lewis 1995)
The Outer Solar System
Classical KBOs
Plutinos (3:2 resonance)
Scattered Disk Objects
Periodic comets
Centaurs
Jupiter Trojans
Pluto
Brown 2000
KBOs with featureless infrared spectra
2002 TC302
Relative Reflectance
2002 UX25
(Barkume et al. 2008)
2002 AW197
2003 VS2
Wavelength (microns)
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Water ice model
(Brown et al. 2007)
http://en.wikipedia.org/wiki/Image:EightTNOs.png
Eris
Brown et al. 2005
Kuiper Belt Near Infrared Spectra
Continuum?
Methane-rich
(e.g Pluto, Eris,
2005 FY9)
Water ice rich
(e.g. Orcus, 2003 EL61,
2003 AZ84)
Moderate Water ice
Featureless
(e.g Huya, Varuna,
2003 VS2)
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
Temperature (K)
Schaller & Brown ApJL (2007a)
Diameter (km)
Temperature (K)
`
Schaller & Brown ApJL (2007a)
Diameter (km)
Temperature (K)
Schaller & Brown ApJL (2007a)
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)
Strong Water ice spectra for 2003 EL61 and Satellite
Barkume, Brown & Schaller ApJL 2006
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)
Normalized Reflectance
Quaoar
Schaller & Brown ApJL (2007b)
Ethane model
Quaoar with full spectral model
methane
ethane
methane
methane
35% crystalline water ice, 6% methane, 4% ethane, 55% dark continuum
Schaller & Brown ApJL (2007b)
Schaller & Brown ApJL 2007a
KBO Spectra
size
– Methane
Pluto, Eris, Triton
2005 FY9
2003 EL61
Quaoar
Charon
– Moderate water ice
Orcus, 2003 AZ84
Varuna,
– Featureless
most small KBOs
-strong water ice
2003 EL61 collisional
family members
(7 now known)
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