Molecular Spectroscopy Symposium June 2008 HIGH RESOLUTION MOLECULAR SPECTROSCOPY FOR PLANETARY EXPLORATION John C. Pearson, Brian J. Drouin, Ken Cooper, Anders Skalare, Mark Allen and Christopher Webster Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109

2 Molecular Spectroscopy Symposium June 2008 NASA Planetary Science Goals Mars Science Goals, Objectives, Investigations. and Priorities: –Geological History of water ( 18 O: 16 O and H:D ratios) –Identify and characterize phases containing C, H, O, N, P and S –Carbon Cycling and 12 C: 13 C ratios –Identify complex organics –Atmospheric O 3, H 2 O 2, CO, OH, CH 4, SO 2 …. Astrobiology Road Map: –Water, atmospheric gas, organics on Mars –Origins and evolution of functional biomolecules –How to recognize signatures of life Solar System Exploration Road Map –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

3 Molecular Spectroscopy Symposium June 2008 Fundamental 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

4 Molecular Spectroscopy Symposium June 2008 Some 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 GHz heterodyne receiver Remote Observation –Radio Astronomy (Molecular Global Average & Line shape) –IR Astronomy (Molecular Global Average)  ISO  SWAS, ODIN

5 Molecular Spectroscopy Symposium June 2008 Tunable Laser Spectrometer (TLS) In Situ Science: CO 2 (with 12 C/ 13 C and 16 O/ 17 O/ 18 O ratios in CO 2 ) evolved from solids and in atmosphere; CH 4 abundance [w/SAM pre-conc.] 3 orders of magnitude better than current estimates of 10 ppb; 12 C/ 13 C ratio in methane. Technology: NIR laser – Nanoplus, Germany Interband Cascade (IC) Laser –JPL Manufactured Laser PI: Christopher Webster-JPL Mission Part of Sample Analysis at Mars (SAM) instrument (includes GCMS and sample handling) Mars Science Lander Launch 2009 NIR Laser IC Laser

6 Molecular Spectroscopy Symposium June 2008 TLS II Free running laser spectrometer 2 sealed reference cells for calibration 20cm base path Herriott cell 81 passes (16.8 m) on methane 2ppbv 43 passes (8.6 m) on CO 2 1ppmv 43 passes (8.6 m) on H 2 O 2ppmv Isotope ratios CH 4 and CO 2 3% at 30ppmv on 13 CH 4 2-5% at 3ppmv on 18 O/ 17 O/ 13 C CO 2 Optical demonstration of 6 channel Herriott Cell

7 Molecular Spectroscopy Symposium June 2008 TLS III 13 CH 4 H2OH2O CO 2 OC 18 O 13 CO 2 OC 17 0 CH 4 Test data from TLS: Both spectra are from Laboratory Air System records direct detector DC, 2f low gain, and 2f high gain Both reference and science channels are recorded 3.8 Kg, 42 Watts worst case power consumption First and so far only high resolution in situ spectrometer

8 Molecular Spectroscopy Symposium June 2008 Earth 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

9 Molecular Spectroscopy Symposium June 2008 Sensitivity Considerations for Active Instruments Long Ago Townes and Geschwind derived an upper limit for spectroscopic detection with an active instrument Where P rx 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

10 Molecular Spectroscopy Symposium June 2008 Radar 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 over relatively smooth surfaces Note: It is a relatively trivial addition to obtain brightness temperature (shown), to have a passive spectrometer or to do ranging

11 Molecular Spectroscopy Symposium June 2008 “Microwave” 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 atmosphere 5% CH 4 / 95% N 2 in cold DC discharge

12 Molecular Spectroscopy Symposium June 2008 Limb Sounders The MIRO instrument on Rosetta is the first planetary limb sounder –H 2 O, CH 3 OH, NH 3 in a comet encounter (in route now) Other limb sounders have been proposed –Marvel for Mars ( GHz) –Submillimeter Line Spectrometer (SLS) for Venus ( 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

13 Molecular Spectroscopy Symposium June 2008 Other 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

14 Molecular Spectroscopy Symposium June 2008 Acknowledgement This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration