Titan: The Solar System s Abiotic Petroleum Factory

Transcription

1 Titan: The Solar System s Abiotic Petroleum Factory J. Hunter Waite, Ph.D. Institute Scientist Space Science & Engineering Division Southwest Research Institute

2 Titan: The Solar System s Abiotic Petroleum Factory Motivation for Titan Studies: Titan s atmosphere is similar to Earth s early atmosphere Titan may help us understand the origin of life in the solar system Titan may help us unlock the mysteries to organic formation in other regions of our galaxy and universe

3 Cassini Huygens Measurements

4 Orbiter In Situ Measurements

5 Mass Spectrometry

6 Mass Spectrometry

7 Cassini Huygens Measurements

8 Orbiter Remote Sensing Measurements

9 Infrared Spectrometry

10 Cassini Huygens Measurements

11 Probe Measurements

12 Cassini Huygens Measurements

13 Orbiter Radar Measurements

14 Methane Cycle

15 Possibilities for Titan Geology: What s Cryo-Volcanism? Large rocky core; layers of liquid, water ice Abundant ammonia; melting point of water ice lowered by ±100ºC Tectonism could breach crust; fluid could reach surface Ammonia-water cryo-lava would erupt as gelatinous mass A Model of Titan s s Interior

16 Cryo Volcanism

17 High Latitude Lakes

18 Methane Cycle

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20 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

21 Stratospheric Composition

22 Titan Dunes Namid Desert Arabian Desert

23 Descent Sequence

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25 Methane Cycle

26 Ion Neutral Mass Spectrometer About the mission and the instrument

27 Geometry of the T a, T b and T 5 trajectories: with respect to Titan

28 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 N 2 penetrating inside the closed source can be ionized and dissociated into N 2 and N and be observed in the detector on mass channels 28 and 14.

29 Atmospheric Structure Mass Spectrum recorded during T a N 2 CH 4 H 2

30 The Ion Neutral Mass Spectrometer produces ion and neutral mass spectra Ions Neutral Gases

31 Titan Neutral Species Density Profiles 1.E10 1.E09 density (cm^-3) 1.E08 1.E07 TA T5 T16 N 2 1.E06 CH 4 H 2 1.E altitude (km)

32 Titan Minor Neutral Species Density Profiles (All Flybys Co-added) 1.E07 density (cm^-3) 1.E06 1.E05 1.E04 C2H2 C2H4 C2H6 C3H4 C4H2 Ar C6H6 1.E altitude (km)

33 Relevance of INMS Observations Evolution of the atmosphere of Titan Outgassing of the interior Escape of gases from Titan Production of organic compounds Ion and neutral photochemsitry The role of the magnetospheric interacation

34 Evolution of the Atmosphere: Outgassing of the Interior The isotopes of Argon tell us about outgassing from the interior 40 Ar tells us how much of the volatile material has been outgassed from the interior 40 Ar = 0.8 ppm --> ~2% of interior volatiles are outgassed 40 Ar 36 Ar tells us how volatile materials like molecular nitrogen and methane were formed 36 Ar < 0.6 ppm --> most nitrogen is derived from ammonia 36 Ar

35 Evolution of the Atmosphere: Atmospheric Escape The isotopes of molecular nitrogen and methane tell us about escape of volatiles from the atmosphere The ratio of 14 N to 15 N in molecular 14 N 14 N nitrogen tells us how much of the atmosphere has escaped over 15 N 14 N geological time N The ratio of 12 C to 13 C in methane tells us about escape of methane and isotopic fractionation from photodissociation of methane 12 C H 4 13 C H 4

36 Evolution of the Atmosphere: Atmospheric Escape The isotopes of molecular nitrogen tell us about escape of nitrogen 14 N/ 15 N Isotopic Ratios by Flyby 300 The ratio of 14 N to 15 N in molecular nitrogen 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 isotopic ratio altitude (km) TA ingress TA egress T5 ingress T5 egress T16 ingress T16 egress

37 Evolution of the Atmosphere: Atmospheric Escape Methane isotopic ratios give us complimentary information 12 C/ 13 C Isotopic Ratios by Flyby isotopic ratio altitude (km) TA ingress TA egress T5 ingress T5 egress T16 ingress T16 egress

38 Evolution of the Atmosphere: Atmospheric Escape INMS also sees direct evidence of heating of the upper atmosphere of Titan by energetic particles from Saturn s magnetosphere Divergence between the thermal exospheric profiles and the INMS data (z>1600 km)

39 Evolution of the Atmosphere: Atmospheric Escape And these elevated coronal temperatures imply escape of nitrogen and methane

40 Evolution of the Atmosphere: Atmospheric Escape But not enough escape (10-4 ) to explain the implications of the measured isotopic ratio of molecular nitrogen Isotopic Ratio INMS value Terrestrial Reference 14 N/ 15 N C/ 13 C If we use the terrestrial 1 4 N/ 1 5 N as a reference this implies that over 70% of the Titan atmosphere has escaped over geological time, since the lighter isotope ( 1 4 N) escapes preferentially with regard to the heavier isotope, 1 5 N However, we note that in spite of the chemical loss of methane in the atmosphere and its escape from the atmosphere the value remains close to the terrestrial value implying resupply within the last 50 million years

41 Atmospheric Escape: Molecular Hydrogen from Methane Conversion Escapes H 2 ecapes three times faster than expected from Jean s escape Jean s escape Observed escape

42 Ion Neutral Mass Spectrometer Production of Complex Organics at High Altitude via Ion Neutral Chemistry

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44 Complex Carbon Nitrile Chemistry Density (cm -3 ) CH CH 4 H 2 CH 5 C 6 H 6 C 3 H 4 C 4 H 2 HCNH N 2 Average Mass km C3s C4s Mass Number C6s C5s C7s The neutral composition at 1200 km in addition to the primary constituents N 2, CH 4, and H 2 includes a host of hydrocarbons: C 2 H 2, C 2 H 2, C 2 H 6,C 3 H 4, C 3 H 8, C 4 H 2, HCN, HC 3 N, C 2 N 2, and C 6 H 6. ==> TITAN S UPPER ATMOSPHERE IS A KEY SOURCE of CARBON NITRILE COMPOUNDS Correspondingly, the ionospheric composition has a complex hydrocarbon/nitrile chemistry that includes almost all possible hydrocarbon and nitrile species through C7.

45 IV.2 The Composition: photo- and electron impact ionization and dissociations Nitrogen Acetylene Ethylene Methane Ethane H, H 2, N, HCN, HC 3 N, C N 2 2

46 IV.3 The Composition: the main ion-neutral scheme The chemical scheme starts from the photo- and electron impact dissociation and ionization of Nitrogen and Methane Creation of the first key neutrals: C 2 H 4 and HCN Production of the major ions: H 2 CN, C 2 H 5, CH 3

47 IV.4 The Composition: the main ion-neutral scheme production rates Local time dependent production rates for C 2 H 4 Local time dependent production rates for H 2 CN

48 IV.5 The Composition: subsequent production of key hydrocarbons Production of hydrocarbons: C 2 H 2 CH 3 C 2 H 6 C 4 H 2 C 3 H 8, Local time dependent production rates for C 2 H 6

49 INMS: Neutrals (~ 1200 km) Species INMS (TA) CH x 10-2 C 2 H x 10-4 C 2 H x 10-4 C 3 H x 10-6 C 3 H x 10-6 Waite et al. 2005

50 IV.6 The Composition: production of heavy hydrocarbons and key ions Production of Hydro- Key carbons: ions: C3H 3 CH 5 C 3 H 4 C 2 H 3 C 6 H 6 C 3 H 5 C 6 H 7 Local time dependent production rates for c-c 6 H 6

51 IV.8 The Composition: neutral results local time dependent density profiles (1) N 2 CH 4 C 2 H 2 C 2 H 4

52 IV.10 The Composition: ion results local time dependent density profiles (1) Electron density Density of H 2 CN

53 IV.11 The Composition: ion results local time dependent density profiles (2) C 2 H 5 C 3 H 5

54 Ion Neutral Mass Spectrometer An Increased Role for the Magnetospheric Interaction and Nitrile Ion Chemistry

55 Solar Radiation

56 INMS: Ions ( km)

57 10000 IONOSPHERIC ALTITUDE PROFILES INMS T5 outbound 1000 HCNH C 2 H TOTAL 10 CH 5 NH 4? 1 C 4 H 3 C 5 H 5 N, C 6 H 7 C 3 H ALT (km) SZA (deg) Altitude 140 (km) TIME from CA (s) Density (cm -3 ) Electron Density TOT 18 Ne

58 Keller et al. model flowchart N 2 H hv, CH 4 CH CH e 4 5 H 2 hv, e H 2 C 5 H 5 N C 3 H 2 N N 2 hv, e N 2 hv, e N C x H y H odd mass C x H y NH even mass HCN CH 3 C 2 H 4 C 3 H 3 C 2 H 2 C 2 H 3 C 2 H 4 C 2 H 5 C 3 H 5 C 2 H 4 C 4 H 5 C 5 H 7 C 5 H 9 C 5 H 5 Black = CH 4 Red = C 2 H 2 Blue = C 2 H 4 Turquise = C 2 H 6 Orange = C 3 H 4 Plum = N Green = proton transfer HCNH C 6 H 5 C 4 H 3 C 4 H 2 C 7 H 7 C n H m C 6 H 7 C 3 H 4 C 11 H 9 C 2 H 2 C 2 H 3 C 9 H 9 C 4 H 2

59 INMS / Keller et al. model Missing masses: 18, 30, 42, 54, 56

60 INMS / new Vuitton and Yelle model

61 New model flowchart

62 Ion Neutral Mass Spectrometer Ultimate Fate of Complex Organics

63 Atmospheric Composition: Molar fractions estimated at 1174 km from the T a data (Closed source) Minor species determined from the mass spectral deconvolution with one sigma error. Species INMS-Derived Values Stratospheric Values (1) CH ±0.002 x x 10-2 H ±0.03 x x 10-3 C 2 H ±0.05 x x 10-6 C 2 H ±0.70 x ±0.08 x x 10-8 C 2 H ±0.06 x x 10-6 C 3 H ±0.22 x x 10-9 C 2 H 4 value depends on the value adopted for HCN.

64 Stratospheric Composition

65 Cat Scratches

66 Acknowledgements National Aeronautics and Space Administration European Space Agency Jet Propulsion Laboratory Cassini-Huygens Science Teams Visual Infrared Mapping Spectrometer Team Imaging Science Team Ion Neutral Mass Spectrometer Team Composite Infrared Spectrometer Team Gas Chromatograph Mass Spectrometer Team SwRI Communications Department Radar Team

67 Southwest Research Institute