20101130 charm aharonson

8/13/2019 20101130 CHARM Aharonson

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Oded Aharonson (Caltech)Alex Hayes, Jonathan Lunine,Ralph Lorenz, Michael Allison,

Charles Elachi, Cassini RadarScience Team

Unveiling Titan:A World Strange and Familiar


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HST, Wide Field Camera 2


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Voyager 1 1980A Hazy world. Hemispheric Asymmetry,

Polar Collar/Hood

UV radiation and coronadischarge of N2/CH4mixtures

End product - tholin(from Greek muddy, viaCarl Sagan)

Image Credit: NASA/JPL/Caltech


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Titan: A New World


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Photo by K. Sturgill, Marion, Virginia


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The Magnificent Seven:


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Cassini VIMS: Titans spectral diversity

Based on Barnes et al., 2007


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Titans Dune1-2 km spacing

150 m characteristic heights


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Shuttle handheld digital cameraSTS107

Linear Dunes in the Namib Desert


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Titans Hydrologic Cycle


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Elivagar FluminaBraided, sinuous channels


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Analog Site - near Parker AZ(identified from airplane window, TUS-LAX circa 730am )


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Titans Odds @ Caltech


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The View from Huygens

Credit: ESA, NASA, Descent Imager/Spectral Radiometer Team (LPL)


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Image Credit: NASA/JPL


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0 375 750 1,125 1,500187.5km

n

Hayes et al. , 2008

m


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Courtesy NASA/JPL-Caltech


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Image Credit: NASA / JPL / University of Arizona / DLR


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Brown et al., Nature, 2008


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Current Radar Mapping

Aharonson et al. , 2009


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Polewards of 55, now >50%coverage in both hemispheres

North South

Filled 10%


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Zebker et al. , Science, 2009

Global Shape


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Mitchell et al. , 2008

GCM

2D GCM predicts:

Eevap. ~ 2 W/m2

i.e. 0.3 m/yr

Numerical Predictions

0 375 750 1 125 1 500187 5


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0 375 750 1,125 1,500187.5km

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Hayes et al. , 2008


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R. Lorenz (Pers. Comm.)

l l


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t=0,Ls,p=277.7, e=0.054

Solar Insolation

Peak South Polar Insolation:7.48 W/m2

Peak North Polar Insolation:6.04 W/m2haronson et al. , 2009

400


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-100 -80 -60 -40 -20 00

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Time Since Present (kyr)

Ls

ofPerihelion

-100 -80 -60 -40 -20 026

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Saturn'sObliq

uity()

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Saturn'sEccentricity()(%)

l l


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t=0,Ls,p=277.7, e=0.054 t=-31.5 kyr, Ls,p= 97.7, e=0.046

Solar Insolation

Aharonson et al. , 2009


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22-25

-0.7-0.04

0-6%

440-570 W/m2

O18

http://www.globalwarmingart.com/wiki/File:Milankovitch_Variations_png

Tit s Mil k it h P i ds


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~270 kyr ~45 kyr

Titans Milankovitch Periods


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MilutinMilankovi(1879 1958)

Ice Ages

JamesCroll

(1821-1890)

http://earth.rice.edu/mtpe/cryo/cryosphere/topics/ice_age.html


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11-20 km Putative Craters Sinlap, 80 km

Crater retention age:200 Myr (Wood et al., 2009) up to

1 Gyr crater retention age


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Putative Crater Distribution

Wood et al., 2009


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GCM Results

Graves, Schneider, et al.

Some Numbers


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Hypothesis consistent with

Hemispheric asymmetry in lakes Ontario Lake Ethane detection by VIMS

Insolation function energetics

Crater distribution latitudinal gradients

Some Numbers The differential heat flux can evaporate:

F~ 1.5 W/m2

L = 510 kJ/kg = 422 kg/m3

Ethane is significantly (x10,000) less volatile so is likelyto remain, and can retain residual methane in solution


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Schaller et al., 2009


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Hayes et al. , 201 0a in press)

A M d lD


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Hayes et al. , 201 0a in press)

A ModelData


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Hayes et al. , 201 0b in press)


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Ontario Reduction


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Ontario Reduction

Flux: 1.00.2 m/yrHayes et al. , 201 0b, in press)

Summary


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tan =(9.1+2.5)10-4

Possible to obtain firstextra-terrestrialbathymetry of near-shore

lake regions, correlate withgeology

Seasonal methane loss rate

from southern lakes Ontario: 1.00.2 m/yr

Smaller lakes: 1.070.23,1.100.23, 1.030.25,

1.090.34 m/yr

-2.0

Summary

Summary


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So far, no demonstrable lake

height changes have beenidentified in the North(Although several putative changes areseen, in part may be due to incidenceangle variations)

Climate models vary in theirpredictions, e.g. Newman etal., Graves et al., predict

peak summer evaporation,Tokano et al. predict peak inthe winter

Summary

Summary


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Summary Cassini revealed a statistically

significant asymmetry in lakedistribution

If the asymmetry is notinherent to the crust, we

propose it is due to anasymmetry in Titans seasonsforced by the orbit

The orbital parameters varywith 10s kyr periods,suggesting a dynamichydrologic methane cycle


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Thanks

20101130 charm aharonson

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