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Measuring the Composition of a Cryogenic Sea · Measuring the Composition of a Cryogenic Sea ... 1...
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Measuring the Composition of a Cryogenic Sea Melissa G. Trainer 1 , Paul R. Mahaffy 1 , Ellen R. Stofan 2 , Jonathan I. Lunine 3 , and Ralph D. Lorenz 4 1 Code 699, NASA Goddard Space Flight Center, Greenbelt, MD 20771, [email protected]; 2 Proxemy Research; 3 Cornell University; 4 Applied Physics Lab, Johns Hopkins University Cryogenic Seas: Where and Why? The hydrocarbon lakes and seas of Titan • Only known extraterrestrial seas! • Polar lakes/seas at ~ 90 K • Composed primarily of ethane and methane A flash of sunlight reflected off of a northern lake on Titan as detected by Cassini VIMS, 2009 (NASA/JPL/UofA). From Hayes et al., GRL, 2008. Composition Titan Origins Prebiotic Chemistry Measurement Challenges Seas on Titan are part of a methane cycle that drives weather, climate, chemical, and geologic change on the moon. Estimates on polar lake composition from Cordier et al., ApJL, 2009 Evaporation and heat transfer CH 4 /C 2 H 6 /C 3 H 8 CH 4 outgassing Chemical transformation processes minor CxHyNz Extent of chemical processing HCN C 6 H 6 CH 3 CN CO 2 H 2 CO N 2 C 4 H 10 C 2 H 2 Noble gases, not detected in the atmosphere, may be stored in the sea liquid. Stable isotopes of CH 4 provide clues to its origin and evolution. Formation temperature Ar/Kr/Xe Origin of N 2 13/12 C CH 4 outgassing Organic chemistry in the atmosphere is known to produce high molecular weight species, which deposit on the surface in aerosol particles. • Trace CxHyNz molecules within the sea provide evidence of the extent of the atmosheric chemistry • Unexpected high molecular weight species, especially O-containing, give insight into the extent of prebiotic chemistry taking place in the sea liquid. Although rich with scientific opportunities, proper sampling of sea fluid and measurement of the composition is fraught with challenges: • Cold sea temperatures, ~ 90 K • Hot temperatures required to vaporize sample (for MS) • Uncertain composition, components with varying b.p.’s • Unknown particulate sizes/concentrations • Unknown viscosity, related to composition & particulates We have designed a robust sampling and measurement technique to address these challenges, as part of Titan Mare Explorer (TiME) Phase A study NASA/JPL/Space Science Institute Robust Sampling System is Critical NASA/JPL For compositional measurement, the highest-fidelity sample must be obtained from the sea: Sampling Requirement Avoid fractionation (ie preferential boiling) of sea components Retain sample during phase transitions Repeated sampling with consistent performace and sample quality System Requirement Sample capture must occur at sea temperature Sufficient sealing across broad temperature range Maintain full functionality after several exposures to sea (temperature, particulates, etc.) Particulate Testing Thermal End-to-End Testing Sampling System Concept Atmosphere Liquid Chamber sealed from liquid Allow fluid into reservoir Heater Vaporized Sample Gas Trap To MS Sample chamber is immersed in sea liquid to equilibrate to sea temperature; vent allows for gravity fill of sample Cryogenic valve design and materials accommodate temperature ramping from sea (90 K) to heating endpoint (~450 K), vaporizing major and minor components ‘Gas trap’ generated around sample chamber keeps power requirements down, reduces contact of valve to sea during heating Sample is transferred (volume expansion) to gas processing system (GPS) for mass spectrometer measurement (below) Sampling system brought to TRL 6 through testing program (right), including vibration Titan Hydrocarbon Sea Gas Processing System Expansion Volume V1 C1 V2 V3 Vent V4 FR Hydrocarbon Trap Capillary Leak Inlet To MS Vent A general concept for the gas processing system (GPS) linking the sampling inlet to the neutral mass spectrometer Earth Atm. Press. Titan Atm. Press. Titan Sea Temperature Liquid Nitrogen (LN 2 ) Ethane/Methane Mixture (75:25) Tetrafluoromethane (CF 4 ) Vapor Pressure Curves Boiling Points Cryogenic fluids were carefully chosen to provide most realistic test environment for inlet function: • LN 2 tests valve operation at low-temperature limit • CF 4 tests ingestion and heating of fluid with similar thermal properties to sea • CF 4 requires enclosed dewar for condensation of simulated sea A specialized dewar was constructed to test the sampling system in a realistic fluid environment with appropriate thermal and mechanical interfaces Expansion pressures indicate that the sample chamber was completely filled (~2.5 cm 3 liquid) and that sample was captured, completely vaporized, and transferred to the Expansion Volume. Results show successful, repeated sample capture and processing in cryogenic fluid environment a From Tomasko et al., Planetary and Space Science, 56 (2008), 669-707. Diameter (μm) Titan Aerosol a Test Standards 0.01 0.1 1 10 Monomers formed at high altitudes Approximate Mesh Filter Size Fractal aggregates observed in stratosphere Condensed spheres in troposphere A mesh filter at the entrance to the sampling inlet could be used to protect valve from large particulates. Small particulates may also be present in the sea. The sampling inlet was tested against polystyrene particle standards across range of relevant sizes (left). Valve met leak rate requirements even at largest particle size Performance Requirement 2 1 A test was run using JSC-1a Mars Simulant dust, sieved to particle sizes ≤ 20 μm. This is a more extreme worst-case than will be encountered on Titan. 2 The range of acceptable leak rates was calculated to ensure good accuracy on NMS compositional measurements. This calculation accounted for possible sample fractionation and sample heating times. Neutral Mass Spectrometry for Versatile Compositional Analysis Appropriate sensitivity and versatility can be provided by a quadrupole mass spectrometer (QMS) similar to those on current missions: SAM Suite on MSL • LADEE • MAVEN SAM QMS CONTOUR NGIMS - model for LADEE/MAVEN MS Composition of Major and Minor Organic Species Wide mass range (to 550 Da) with unit resolution would allow for measurement of high molecular weight species present in sea, such as those predicted by atmospheric measurements and laboratory studies Noble Gases and Isotopes Trace noble gases and their isotope ratios are measured with static mass spectrometry Example from the calibration of the Mars Science Laboratory SAM mass spectrometer: The use of the hydrocarbon trap ( GPS figure, above) enables simple separations to achieve important compositional measurements: CH 4 /C 2 H 6 /C 3 H 8 High MW CxHyNz Molecules with different functionalities (ex// O-compounds groups) A getter in the pumping system removes all active gases from the manifold except CH 4 and the noble gases. Allows for quantification of noble gas ratios and isotopic measurements of more abundant (Argon/CH 4 ) species. (Mahaffy et al., SSR, 2012) Data for ratio plot (left) secured in ~ 30 sec during SAM QMS calibration for terrestrial Xe. Isotope ratios match terrestrial accuracy ~0.3%
Transcript of Measuring the Composition of a Cryogenic Sea · Measuring the Composition of a Cryogenic Sea ... 1...
Measuring the Composition of a Cryogenic SeaMelissa G. Trainer1, Paul R. Maha�y1, Ellen R. Stofan2, Jonathan I. Lunine3, and Ralph D. Lorenz4 1Code 699, NASA Goddard Space Flight Center, Greenbelt, MD 20771, [email protected]; 2Proxemy Research; 3Cornell University; 4Applied Physics Lab, Johns Hopkins University
Cryogenic Seas: Where and Why?The hydrocarbon lakes and seas of Titan • Only known extraterrestrial seas! • Polar lakes/seas at ~ 90 K • Composed primarily of ethane and methane
A �ash of sunlight re�ected o� of a northern lake on Titan as detected by Cassini VIMS, 2009 (NASA/JPL/UofA). From Hayes et al., GRL, 2008.
Composition Titan Origins Prebiotic Chemistry Measurement ChallengesSeas on Titan are part of a methane cycle that drives weather, climate, chemical, and geologic change on the moon.
Estimates on polar lake composition from Cordier et al., ApJL, 2009
Evaporation and heat transferCH4/C2H6/C3H8 CH4 outgassing Chemical transformation processes
minor CxHyNz Extent of chemical processing
HCN
C6H6
CH3CNCO2
H2CO
N2
C4H10
C2H2
Noble gases, not detected in the atmosphere, may be stored in the sea liquid. Stable isotopes of CH4 provide clues to its origin and evolution.
Formation temperatureAr/Kr/Xe Origin of N2
13/12 C CH4 outgassing
Organic chemistry in the atmosphere is known to produce high molecular weight species, which deposit on the surface in aerosol particles. • Trace CxHyNz molecules within the sea provide evidence of the extent of the atmosheric chemistry • Unexpected high molecular weight species, especially O-containing, give insight into the extent of prebiotic chemistry taking place in the sea liquid.
Although rich with scientific opportunities, proper sampling of sea �uid and measurement of the composition is fraught with challenges:
• Cold sea temperatures, ~ 90 K • Hot temperatures required to vaporize sample (for MS) • Uncertain composition, components with varying b.p.’s • Unknown particulate sizes/concentrations • Unknown viscosity, related to composition & particulates
We have designed a robust sampling and measurement technique to address these challenges, as part of Titan Mare Explorer (TiME) Phase A studyNASA/JPL/Space Science Institute
Robust Sampling System is Critical
NASA/JPL
For compositional measurement, the highest-fidelity sample must be obtained from the sea:
Sampling Requirement
Avoid fractionation (ie preferential boiling) of sea components
Retain sample during phase transitions
Repeated sampling with consistent performace and sample quality
System Requirement
Sample capture must occur at sea temperature
Su�cient sealing across broad temperature range
Maintain full functionality after several exposures to sea (temperature, particulates, etc.)
Particulate TestingThermal End-to-End TestingSampling System ConceptAtmosphere
Liquid
Chamber sealed from
liquid
Allow �uid into reservoir
Heater
Vaporized SampleGas
Trap
To MS
Sample chamber is immersed in sea liquid to equilibrate to sea temperature; vent allows for gravity fill of sampleCryogenic valve design and materials accommodate temperature ramping from sea (90 K) to heating endpoint (~450 K), vaporizing major and minor components‘Gas trap’ generated around sample chamber keeps power requirements down, reduces contact of valve to sea during heatingSample is transferred (volume expansion) to gas processing system (GPS) for mass spectrometer measurement (below)Sampling system brought to TRL 6 through testing program (right), including vibration
Titan Hydrocarbon SeaGas Processing System
Expansion VolumeV1
C1
V2 V3
Vent
V4FR
Hydrocarbon Trap
Capillary Leak Inlet
To MS
VentA general concept for the gas processing system (GPS) linking the sampling inlet to the neutral mass spectrometer
Earth Atm. Press.Titan Atm. Press.
Tita
n Se
a Te
mpe
ratu
re
Liquid Nitrogen (LN2)
Ethane/Methane Mixture(75:25)
Tetra�uoromethane (CF4)
Vapor Pressure CurvesBoiling Points
Cryogenic fluids were carefully chosen to provide most realistic test environment for inlet function: • LN2 tests valve operation at low-temperature limit • CF4 tests ingestion and heating of fluid with similar thermal properties to sea • CF4 requires enclosed dewar for condensation of simulated sea
A specialized dewar was constructed to test the sampling system in a realistic fluid environment with appropriate thermal and mechanical interfaces
Expansion pressures indicate that the sample chamber was completely filled (~2.5 cm3 liquid) and that sample was captured, completely vaporized, and transferred to the Expansion Volume.
Results show successful, repeated sample capture and
processing in cryogenic �uid environment
a From Tomasko et al., Planetary and Space Science, 56 (2008), 669-707.
Diameter (μm)
Titan Aerosol a
Test Standards
0.01 0.1 1 10
Monomers formed at high altitudes
Appr
oxim
ate
Mes
h Fi
lter S
ize
Fractal aggregates observed in stratosphere
Condensed spheres in troposphere
A mesh filter at the entrance to the sampling inlet could be used to protect valve from large particulates. Small particulates may also be present in the sea.The sampling inlet was tested against polystyrene particle standards across range of relevant sizes (left).
Valve met leak rate requirements even at largest particle size
Performance Requirement 2
1 A test was run using JSC-1a Mars Simulant dust, sieved to particle sizes ≤ 20 μm. This is a more extreme worst-case than will be encountered on Titan. 2 The range of acceptable leak rates was calculated to ensure good accuracy on NMS compositional measurements. This calculation accounted for possible sample fractionation and sample heating times.
Neutral Mass Spectrometry for Versatile Compositional AnalysisAppropriate sensitivity and versatility can be provided by a quadrupole mass spectrometer (QMS) similar to those on current missions:SAM Suite on MSL • LADEE • MAVEN
SAM QMS
CONTOUR NGIMS - model for LADEE/MAVEN MS
Composition of Major and Minor Organic Species
Wide mass range (to 550 Da) with unit resolution would allow for measurement of high molecular weight species present in sea, such as those predicted by atmospheric measurements and laboratory studies
Noble Gases and IsotopesTrace noble gases and their isotope ratios are measured with static mass spectrometryExample from the calibration of the Mars Science Laboratory SAM mass spectrometer:
The use of the hydrocarbon trap ( GPS figure, above) enables simple separations to achieve important compositional measurements: CH4/C2H6/C3H8
High MW CxHyNz
Molecules with di�erent functionalities (ex// O-compounds groups)
A getter in the pumping system removes all active gases from the manifold except CH4 and the noble gases. Allows for quantification of noble gas ratios and isotopic measurements of more abundant (Argon/CH4) species.
(Maha�y et al., SSR, 2012)
Data for ratio plot (left) secured in ~ 30 sec during SAM QMS calibration for terrestrial Xe.Isotope ratios match terrestrial accuracy ~0.3%
