molecular spectroscopy symposium 2008 16-20 june 2008 high resolution molecular spectroscopy for...

Molecular Spectroscopy Symposium 2008 16-20 June 2008

HIGH RESOLUTION MOLECULAR SPECTROSCOPY FOR PLANETARY EXPLORATION

John C. Pearson, Brian J. Drouin, Ken Cooper, Anders John C. Pearson, Brian J. Drouin, Ken Cooper, Anders Skalare, Mark Allen and Christopher Webster Skalare, Mark Allen and Christopher Webster

Jet Propulsion Laboratory, California Institute of Technology, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109Pasadena, CA 91109

2Molecular Spectroscopy Symposium 2008 16-20 June 2008

NASA Planetary Science GoalsNASA Planetary Science Goals

Mars Science Goals, Objectives, Investigations. and Priorities: 2006 http://mepag.jpl.nasa.gov/reports/MEPAG%20Goals_2-10-2006.pdf

– Geological History of water (18O:16O and H:D ratios)

– Identify and characterize phases containing C, H, O, N, P and S

– Carbon Cycling and 12C:13C ratios

– Identify complex organics

– Atmospheric O3, H2O2, CO, OH, CH4, SO2….

Astrobiology Road Map: 2008 http://astrobiology.arc.nasa.gov/roadmap/– Water, atmospheric gas, organics on Mars

– Origins and evolution of functional biomolecules

– How to recognize signatures of life

Solar System Exploration Road Map 2006 http://www.lpi.usra.edu/vexag/road_map_final.pdf

– Understand the original composition of solar system bodies

– Isotopic ratios yielding insight into time evolution

– Chemical and isotopic composition

– Study organics on Titan, Europa & Enceladus


Fundamental Instrument ConsiderationsFundamental Instrument Considerations

Instruments will always be too massive

– Few Kg is an upper limit

Instruments will always be too power hungry

– Few watts is an upper limit

Instruments will always have to be launched

– Lots of test and analysis is required

Instruments will always have to survive the space environment

– More tests, analysis and non-optimal electronic components

Corollary: Instruments will always be too expensive


Some Previous InstrumentsSome Previous Instruments

Major planetary instruments– Mass Spectrometers

Viking GCMS INMS Venus, Galileo, Cassini etc… Galileo Probe GCMS Huygens Probe GCMS

– Spectroscopy Low resolution UV and Visible (Mariner, Galileo, Cassini, …) Low resolution IR and Visible (Mariner, Galileo, Cassini,…)

Limb sounder (Comet only so far)– MIRO instrument on Rosetta has 550-600 GHz heterodyne receiver

Remote Observation– Radio Astronomy (Molecular Global Average & Line shape)

– IR Astronomy (Molecular Global Average) ISO SWAS, ODIN


Tunable Laser Spectrometer (TLS)Tunable Laser Spectrometer (TLS)

In Situ Science:

CO2 (with 12C/13C and 16O/17O/18O ratios in CO2) evolved from solids and in atmosphere;

CH4 abundance [w/SAM pre-conc.] 3 orders of magnitude better than current estimates of 10 ppb; 12C/13C ratio in methane.

Technology:NIR laser – Nanoplus, GermanyInterband Cascade (IC) Laser

– JPL Manufactured LaserPI:

Christopher Webster-JPLMission

Part of Sample Analysis at Mars (SAM) instrument (includes GCMS and sample handling)Mars Science Lander Launch 2009

NIR Laser IC Laser


TLS IITLS II

• Free running laser spectrometer2 sealed reference cells for calibration

• 20cm base path Herriott cell81 passes (16.8 m) on methane 2ppbv43 passes (8.6 m) on CO2 1ppmv43 passes (8.6 m) on H2O 2ppmv

• Isotope ratios CH4 and CO2

3% at 30ppmv on 13CH4

2-5% at 3ppmv on 18O/17O/13C CO2

Optical demonstration of 6 channel Herriott Cell


TLS IIITLS III

13CH4H2O CO2 OC18O

13CO2

OC170

CH4

Test data from TLS: Both spectra are from Laboratory AirSystem records direct detector DC, 2f low gain, and 2f high gainBoth reference and science channels are recorded3.8 Kg, 42 Watts worst case power consumption

First and so far only high resolution in situ spectrometer


Earth Observing InstrumentsEarth Observing Instruments

Some Moderate to high resolution Spectrometers

– Atmospheric Trace Molecule Spectroscopic Experiment (ATMOS)

– Cryogenic Infrared Spectrometer and Telescope for the Atmosphere (CRISTA)

– Atmospheric Infrared Sounder (AIRS)

– Tropospheric Emission Spectrometer (TES)

– Atmospheric Chemistry Experiment (ACE)

Microwave Instruments

– UARS Microwave Limb Sounder

– EOS Microwave Limb Sounder

– ODIN in Limb Sounder Mode

Long History of increasingly sophisticated spectroscopic instruments

– Technology has not yet made it to the other planets


Sensitivity Considerations for Active InstrumentsSensitivity Considerations for Active Instruments

Long Ago Townes and Geschwind derived an upper limit for spectroscopic detection with an active instrument

Where Prx is the received power and is the post detection bandwidth

Real systems rarely achieve this source noise dominated limit

The signal to noise ratio of real Heterodyne detectors is

The signal to noise ratio of a direct detector is

Where is the quantum efficiency, f is the detected bandwidth, is the frequency and NEP is the intrinsic noise equivalent power. If hv>kT first term dominates otherwise the second dominates

Note that NEP is likely to be strongly affected by the total input power level

rxvPkTP 22min

rxsys

rxrx

vPkT

P

P

PSNR

22min

vNEPvhvPfvkTvPkT

P

P

PSNR

rxrx

rxrx

22min )(22


Radar SpectroscopyRadar Spectroscopy

Requires a thin atmosphere or exosphere

Transmit signal in at least 3 closely spaced tones

Detect in as narrow bandwidth as possible (1/pulse time)

Ratio to detect absorption

Noise is source noise + speckle noise (proportional to surface relief and spacecraft velocity)

Strong lines can be detected at a few ppm in a column of 1016 over relatively smooth surfaces

2 2

3 44t

r

PGP

R

Note: It is a relatively trivial addition toobtain brightness temperature (shown), to have a passive spectrometer or to do ranging


““Microwave” SpectrometersMicrowave” Spectrometers

All polar molecules have rotational band making millimeter/submillimeter systems ideal for detecting a wide range of molecules

This potential for microwave spectrometers as gas analyzers was recognized long ago

– Requires low power consumption All solid state is necessary

– Requires wide electronic tuning range Synthesized or calibrated free running

– Requires high sensitivity without cryogenics Ambient temperature detection

Microwave electronics can also survive a wide range of environments (20K-380K)

– Ideal for in situ studies with access to surface or atmosphere

– Can be made work with >10% tuning range to >1 THz

Limit of detection in ideal cases ~1 part per trillion in the volume

Spectrum of simulated Titan atmosphere5% CH4 / 95% N2 in cold DC discharge


Limb SoundersLimb Sounders

The MIRO instrument on Rosetta is the first planetary limb sounder

– H2O, CH3OH, NH3 in a comet encounter (in route now)

Other limb sounders have been proposed– Marvel for Mars (540-600 GHz)

– Submillimeter Line Spectrometer (SLS) for Venus (540-620 GHz)

– Titan/Jupiter concepts under development Several bands including 1200 GHz on Titan for CH4 & NH3

– Bandwidth, Mass, Power and $$$ are the big challenges

Potentially useful with very tenuous atmospheres– Better in case where more gas is present

Can also be done at shorter wavelengths or with occultation


Other ChallengesOther Challenges

Several key spectroscopic challenges exist

– Remote observation of solid material content Preferable imaging with no moving parts Parts per million sensitivity is needed

– Improved resolution IR-UV spectrometers Preferably imaging with no moving parts Small and low power

– Theoretical limited sensitivity

Spectroscopic instruments all require laboratory measurements

– Supporting the development, calibration and data reduction for these and similar instruments is a major opportunity for spectroscopists


AcknowledgementAcknowledgement

This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration

molecular spectroscopy symposium 2008 16-20 june 2008 high resolution molecular spectroscopy for...

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