titan: the solar system’s abiotic petroleum factory€¦ · cassini huygens measurements . probe...

Titan: The Solar System’s AbioticPetroleum Factory

J. Hunter Waite, Ph.D.J. Hunter Waite, Ph.D.Institute ScientistInstitute Scientist

Space Science & Engineering DivisionSpace Science & Engineering DivisionSouthwest Research InstituteSouthwest Research Institute®®

Titan: The Solar System’s AbioticPetroleum Factory

Motivation for Titan Studies:

n Titan’s atmosphere is similar to Earth’s early atmosphere

n Titan may help us understand the origin of life in the solar system

n Titan may help us unlock the mysteries to organic formation in other regions of our galaxy and universe

Cassini Huygens Measurements

Orbiter In Situ Measurements

Mass Spectrometry

Mass Spectrometry

Cassini Huygens Measurements

Orbiter Remote Sensing Measurements

Infrared Spectrometry

Cassini Huygens Measurements

Probe Measurements

Cassini Huygens Measurements

Orbiter Radar Measurements

Methane Cycle

Possibilities for Titan Geology:What’s Cryo-Volcanism?

n Large rocky core; layers of liquid,water ice

n Abundant ammonia; melting pointof water ice lowered by ±100ºC

n Tectonism could breach crust; fluidcould reach surface

n Ammonia-water “cryo-lava” would erupt as gelatinous mass

A Model ofA Model ofTitanTitan’’s Interiors Interior

Cryo Volcanism

High Latitude Lakes

Methane Cycle

Interstellar Clouds

Organic Molecules in the Interstellar Medium, Comets and Meteorites: A Voyage from Dark Clouds to the Early Earth,Pascale Ehrenfreund & Steven B. Charnley, Annual Review of Astronomy & Astrophysics, 38:427-83, 2000

Stratospheric Composition

Dunes

Namid Desert Arabian Desert

Titan

Descent Sequence

Methane Cycle

Ion Neutral Mass Spectrometer

About the mission and the instrument

Geometry of the Ta, Tb and T5 trajectories: with respect to Titan

r

1on 4.

The Ion Neutral Mass Spectrometer The 2 INMS sources

In this presentation:

- Neutral densities from closed source

- Ion densities from open source

Note:

A molecule of N2 penetrating inside the closed source can be ionized and dissociatedinto N +

2 and N+ and beobserved in the detectomass channels 28 and

Atmospheric Structure Mass Spectrum recorded during Ta

N2 ‡

CH4 ‡

H2 ‡

The Ion Neutral Mass Spectrometer produces ion and neutral mass spectra

Neutral GasesIIoonnss

Titan Neutral Species Density Profiles

1.E+05

1.E+06

1.E+07

1.E+08

1.E+09

1.E+10

900 1000 1100 1200 1300 1400 1500 1600 1700

altitude (km)

dens

ity (c

m^-

3)

TA

T5T16

N2

CH4

H2

Titan Minor Neutral Species Density Profiles(All Flybys Co-added)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

900 1000 1100 1200 1300 1400

altitude (km)

dens

ity (c

m^-

3)

C2H2C2H4C2H6C3H4C4H2ArC6H6

Relevance of INMS Observations

nEvolution of the atmosphere of Titan –Outgassing of the interior –Escape of gases from Titan

nProduction of organic compounds –Ion and neutral photochemsitry –The role of the magnetospheric interacation

Evolution of the Atmosphere:Outgassing of the Interior

n The isotopes of Argon tell usabout outgassing from the interior

– 40Ar tells us how much of the volatile material has been outgassed from the interior 4040ArAr

• 40Ar = 0.8 ppm --> ~2% ofinterior volatiles areoutgassed

– 36Ar tells us how volatile materials like molecular nitrogen and methane were formed

• 36Ar < 0.6 ppm --> mostnitrogen is derived fromammonia

3636ArAr

Evolution of the Atmosphere:Atmospheric Escape

n The isotopes of molecular nitrogen and methane tell us about escape of volatiles from the atmosphere

– The ratio of 14N to 15N in molecular 1414NN 1414NNnitrogen tells us how much of theatmosphere has escaped over 1515NN 1414NNgeological time

– The ratio of 12C to 13C in methanetells us about escape of methaneand isotopic fractionation from

1212C HC H44photodissociation of methane

1313C HC H44

Evolution of the Atmosphere: Atmospheric Escape

n The isotopes of molecular nitrogen tell us about escapof nitrogen

e

– The ratio of 14N to 15N in molecularnitrogen tells us how much of the atmosphere has escaped over geological time

– The change in the ratio as a function of altitude is due to diffusive separation in the presence of gravity

14N/15N Isotopic Ratios by Flyby

50

100

150

200

250

900 1000 1100 1200 1300 1400 1500 1600 1700altitude (km)

isot

opic

ratio

TA ingress TA egress T5 ingress T5 egress T16 ingress T16 egress

300

Evolution of the Atmosphere: Atmospheric Escape

n Methane isotopic ratios give us complimentary information 12C/13C Isotopic Ratios by Flyby

0

20

40

60

80

100

120

140

900 1000 1100 1200 1300 1400 1500 1600 1700altitude (km)

isot

opic

ratio

TA ingress TA egress T5 ingress T5 egress T16 ingress T16 egress

160

Evolution of the Atmosphere:Atmospheric Escape

n INMS also sees direct evidence of heating ofthe upper atmosphereof Titan by energeticparticles fromSaturn’s magnetosphere

Divergence betweenthe thermal exospheric

profiles and the INMS data(z>1600 km)

Evolution of the Atmosphere: Atmospheric Escape

nAnd these elevated coronal temperatures implyescape of nitrogen and methane

Evolution of the Atmosphere: Atmospheric Escape

n But not enough escape (10-4) to explain the implications of the measured isotopic ratio of molecular nitrogen

Isotopic Ratio INMS

value Terrestrial Reference

14N/15N 155 215 12C/13C 96 93.8

nnIIff wwee uussee tthhee tteerrrreessttrriiaall 1144NN//1155NN aass aa rreeffeerreennccee tthhiiss iimmpplliieess tthhaatt oovveerr 7700%%

ooff tthhee TTiittaann aattmmoosspphheerree hhaass eessccaappeedd oovveerr ggeeoollooggiiccaall ttiimmee,, ssiinnccee tthhee

lliigghhtteerr iissoottooppee ((1144NN)) eessccaappeess pprreeffeerreennttiiaallllyy wwiitthh rreeggaarrdd ttoo tthhee hheeaavviieerr

iissoottooppee,, 1155NN

nnHHoowweevveerr,, wwee nnoottee tthhaatt iinn ssppiittee ooff tthhee cchheemmiiccaall lloossss ooff mmeetthhaannee iinn tthhee

aattmmoosspphheerree aanndd iittss eessccaappee ffrroomm tthhee aattmmoosspphheerree tthhee vvaalluuee rreemmaaiinnss

cclloossee ttoo tthhee tteerrrreessttrriiaall vvaalluuee iimmppllyyiinngg rreessuuppppllyy wwiitthhiinn tthhee llaasstt

5500 mmiilllliioonn yyeeaarrss

JeanJean’’ss

escapeescape

ObservedObserved

escapeescape

AAttmmoosspphheerriicc EEssccaappee::

MMoolleeccuullaarr HHyyddrrooggeenn ffrroomm MMeetthhaannee CCoonnvveerrssiioonn EEssccaappeess

HH22 eeccaappeess

tthhrreeee ttiimmeess

ffaasstteerr tthhaann

eexxppeecctteedd

ffrroomm JJeeaann’’ss

eessccaappee

Ion Neutral Mass Spectrometer

Production of Complex Organics at High Altitude

via Ion Neutral Chemistry

Complex Carbon Nitrile Chemistry

n The neutral composition at 1200 kmin addition to the primaryconstituents N2, CH4, and H2 includes a host of hydrocarbons:C2H2, C2H2, C2H6,C3H4, C3H8, C4H2, HCN, HC3N, C2N2, and C6H6.

==> TITAN”S UPPER ATMOSPHERE IS A KEY SOURCE of CARBON NITRILE COMPOUNDS

n Correspondingly, the ionosphericcomposition has a complexhydrocarbon/nitrile chemistry thatincludes almost all possiblehydrocarbon and nitrile species through C7.

Average Mass1100 - 1300 km

0.001

0.01

0.1

1

10

100

1000

5 13 18 23 28 33 38 43 48 53 58 63 68 73 78 83 88 93 98Mass Number

Den

sity

(cm

-3)

N2 CH4 H2

C6H6

C3H4

C4H2

C7s

C6s C5s

C4s

C3s

HCNH+

CHCH55++

IV.2 The Composition: photo- and electron impact ionization and dissociations

n Nitrogen

n Methane

n Acetylene

n Ethylene

n Ethane

n H, H2, N, HCN, HC3N, C N2 2

IV.3 The Composition:the main ion-neutral scheme

n The chemical scheme starts from the photo- and electronimpact dissociation and ionization of Nitrogen and Methane

– Creation of the first key neutrals: C2H4 and HCN – Production of the major ions: H2CN+, C2H +

5 , CH + 3

IV.4 The Composition: the main ion-neutral scheme – production rates

fl Local time dependent

production rates

for C2H4

Local time dependentproduction rates ‡

for H2CN+

IV.5 The Composition: subsequent production of key hydrocarbons

n Production of hydrocarbons:

– C2H2 – CH3 – C2H6 – C4H2 – C3H8 ,…

Local time dependent ‡

production rates

for C2H6

INMS: Neutrals (~ 1200 km)

Species INMS (TA)

CH4 3.3 x 10-2

C2H2 2.8 x 10-4

C2H6 1.2 x 10-4

C3H4 4.0 x 10-6

C3H8 2.3 x 10-6

Waite et al. 2005

IV.6 The Composition: production of heavy hydrocarbons and key ions

Local time dependentproduction rates

for c-C6H6

‡

n Production of Hydro- Key

carbons: ions: – C H +

3 3 – CH5 – C3H4 – C2H +

3 – C6H6 – C3H +

5 – C6H +

7

IV.8 The Composition: neutral results – local time dependent density profiles (1)

N2 CH4

C2H2 C2H4

IV.10 The Composition: ion results – local time dependent density profiles (1)

Electron density

Density ofH2CN+

IV.11 The Composition: ion results – local time dependent density profiles (2)

C2H5 + C3H5

+

Ion Neutral Mass Spectrometer

An Increased Role for the Magnetospheric Interaction

and Nitrile Ion Chemistry

Solar Radiation

INMS: Ions (1100 - 1300 km)

IONOSPHERIC ALTITUDE PROFILES INMS T5 outbound

0.1

1

10

100

1000

10000

1000 1100 1200 1300 1400 1500 1600 1700Altitude (km)

Den

sity

(cm

-3)

172829415179TOT18Ne

TOTAL

HCNH+ C2H5+

C3H5+

C4H3+

C5H5N+, C6H7+

CH5+

ALT (km)SZA (deg) 135 138 140 141 142 143 143TIME from CA (s) 126 193 245 287 324 359 393

Electron Density

NH4+?

N2 N2+ CH3

+ C2H5+hv, e HCNH+

N2H+

H2

CH5+CH4 CH4

+

H2

hv, e

N+

hv, e

HCN+

C2H4+

C3H3+

C3H5+

C2H2+

C2H3+

C2H4+

C5H7+

hv, e

C5H9+

C5H5+

C3H2N+

C5H5N+

C2H4+

C4H5+ C6H5

+

C4H2

C4H3+

C2H2+

C2H3+

CnHm+

C7H7+

C11H9+

C4H2

C9H9+

C6H7+

C3H4

Black = CH4 Red = C2H2 Blue = C2H4Turquise = C2H6 Orange = C3H4Plum = N Green = proton transfer

Keller et al. model flowchart

n CxHy+H+

odd mass

n CxHyN+H+

even mass

INMS / Keller et al. model

Missing masses:

18, 30, 42, 54, 56

INMS / new Vuitton and Yelle model

New model flowchart

Ion Neutral Mass Spectrometer

Ultimate Fate of Complex Organics

Minor species determined from the mass spectral deconvolution with one sigma error.

Species INMS-Derived Values Stratospheric Values (1)

CH4 2.19 ±0.002 x 10-2 2.2 x 10-2

H2 4.05 ±0.03 x 10-3 1.1 x 10-3 C2H2 1.89 ±0.05 x 10-4 2.2 x 10-6 C2H4 2.59 ±0.70 x 10-4 – 5.26 ±0.08 x 10-4 9.0 x 10-8 C2H6 1.21 ±0.06 x 10-4 9.4 x 10-6 C3H4 3.86 ±0.22 x 10-6 4.4 x 10-9

C2H4 value depends on the value adopted for HCN.

Atmospheric Composition: Molar fractions estimated at 1174 km from the Ta data

(Closed source)

Stratospheric Composition

Cat Scratches

Acknowledgements

n National Aeronautics and Space Administration

n European Space Agency

n Jet Propulsion Laboratory

n Cassini-Huygens Science Teams

n Visual Infrared Mapping Spectrometer Team

n Radar Team

n Imaging Science Team

n Ion Neutral Mass Spectrometer Team

n Composite InfraredSpectrometer Team

n Gas Chromatograph MassSpectrometer Team

n SwRI Communications Department

Southwest Research Institute®