Mineral identification and biosignature characterization in the field.
I am working with a group in the Electro-Optics Research Laboratory in the Electrical Engineering department at NMSU to identify biosignatures within geologic samples using an IR reflectance spectrometer. The spectrometer uses acousto-optic tunable filter (AOTF) technology to focus discrete frequencies of light onto a sample, which then reflects the light back onto a detector. By sweeping through a range of wavelengths (between 1.6 - 3.6 microns), we build a reflectance spectrum, which gives information on the absorption properties of the sample. Each mineral type has a unique spectral shape, which we use to determine the rough chemical composition of a sample.
In 2012, we paired an AOTF point spectrometer with a miniaturized laser desorption time-of-flight mass spectrometer (LD-TOF-MS) developed by collaborators at NASA's Goddard Space Flight Center (GSFC). The AOTF IR spectrometer can identify field markers indicating the presence of microorganisms, or evidence of local geologic anomalies consistent with the biologic origin of a field sample. These results can be used to inform other instruments, such as a mass spectrometer or a laser-induced breakdown spectroscopy system, of the most promising places to search for organics. This low-power prescreening method of life detection is especially useful on other planetary bodies where sample return is impractical and spacecraft resources need to be conserved.
The LD-TOF-MS and AOTF IR spectrometer share the same optical axis (as shown in the light path diagram), allowing for coincident IR spectroscopy and mass spectrometry measurements of a sample surface.
A schematic showing the optical path of the spectrometer. Light emerges from an IR source and passes through several optical components toward the AOTF crystal. The dispersion of light through the AOTF is dependent on the radio frequency supplied to the transducer. Light is then focused onto a sample and reflected off a pair of off-axis parabolic mirrors onto the detector.
A photograph of the optical head of PASA. PASA is approximately 2kg, operates in the 1.6 - 3.6 micron range, and requires 31W during operation. A single spectrum takes approximately 0.1s to acquire.
Following the AOTF IR spectrometer's integration with the LD-TOF-MS, we identified a need to collect measurements and identify biosignatures in the field. We developed the Portable AOTF Spectrometer for Astrobiology (PASA) to collect IR spectra of rock surfaces in cave environments. The optical design of PASA is similar to that of the original AOTF IR spectrometer, however, we have also included a visible camera oriented along the optical axis of PASA to collect context images of samples.
We have successfully demonstrated PASA on several field campaigns, and have identified a variety of minerals in the cave including sulfates, carbonates, metal oxides, and basalts. Spectra of samples measured in situ are distinct from those measured in the lab due to changes in humidity affecting the desorbed surface water content, necessitating measurements in the field to ensure spectra accurately represent the sample mineralogy. We have also demonstrated that PASA can be used to distinguish between biomineralized and geologically precipitated calcites in some cases.
We further improved PASA by increasing its focal length, increasing the broadband IR lamp brightness, reducing the mass, and moving the context camera off the optical axis of the IR spectrometer, which increases the IR signal by 20% by removing the need for a aperture bore-hole in one of the off-axis parabolic focusing mirrors. This new instrument, PASA-Lite, will be integrated onto a robotic platform to collect IR spectra within cave environments in locations inaccessible to human operators. We have successfully demonstrated PASA-Lite in two lava tubes (Four Windows and Big Skylight). We integrated PASA-Lite with LEMUR, a cave-climbing robot developed by colleagues at JPL, in Big Skylight Lava Tube and successfully measured the IR spectrum of a basalt surface. This expedition was documented by Air & Space/Smithsonian here.
A photograph of PASA-Lite mounted onto the LEMUR robotic platform.
N. J. Chanover, K. Uckert, D. G. Voelz, X. Xiao, R. Hull, P. J. Boston, A. Parness, N. Abcouwer, A. Willig. Near-IR Reflectance Spectra in a Lava Tube Cave from a Robotic Platform. 2nd International Planetary Caves Conference, Abstract #9032, Flagstaff, AZ, October 2015.
K. Uckert, N. J. Chanover, D. G. Voelz, X. Xiao, P. J. Boston, D. A. Glenar. Demonstration of a portable AOTF IR spectrometer for in situ exploration of planetary surfaces. Aerospace Conference, 2015 IEEE, pp 1-9, March 2015.
K. Uckert, S. A. Getty, N. Chanover, X. Li, W. B. Brinckerhoff, T. Cornish, D. Voelz, X. Xiao. IR Spectroscopy and Two-Step Laser Desorption/Ionization Time-of-Flight Mass Spectrometry as a Biosignature Identification Instrument Suite. Astrobiology Science Conference, Abstract #7607, Chicago, IL, June 2015.
N. J. Chanover, K. Uckert, D. Voelz, X. Xiao, P. J. Boston. Near-IR Reflectance Spectroscopy of Biovermiculation Patterns in a Sulfuric Cave Environment. Astrobiology Science Conference, Abstract #7597, Chicago, IL, June 2015.
K. Uckert, N. J. Chanover, D. Voelz, X. Xiao, P. Boston. A Portable AOTF IR Reflectance Point Spectrometer for in situ Biosignature Detection. Lunar and Planetary Science Conference, Vol. 46, Abstract #2694, The Woodlands, TX, March, 2015.
N. J. Chanover, K. Uckert, D. Voelz, P. Boston. The Development and Field Testing of the Portable Acousto-optic Spectrometer for Astrobiology. The 46th Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society, Vol. 46, Abstract #214.22, Tucson, AZ, November, 2014.
N. J. Chanover, K. Uckert, D. Voelz, P. Boston. The Development and Field Testing of the Portable Acousto-optic Spectrometer for Astrobiology. International Workshop on Instrumentation for Planetary Missions, Abstract #1139, Greenbelt, MD, November, 2014.
K. Uckert, N. Chanover, D. Voelz, D. Glenar, W. Brinckerhoff, S. Getty, N. McMillan, P. Boston, X. Xiao, R. Tawalbeh, X. Li. Spectral mixture and chemometric algorithms applied to the identification of biosignatures on planetary surfaces. IEEE 5th Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing (WHISPERS), pp 1-4, June 2013.
N. Chanover, D. Voelz, D. Glenar, X. Xiao, R. Tawalbeh, K. Uckert, P. Boston, S. Getty, W. Brinckerhoff, P. Mahaffy, X. Li. Results from an integrated AOTF-LDTOF spectrometer suite for planetary surfaces. Aerospace Conference, 2013 IEEE, pp 1-14, March 2013.
N. J. Chanover, K. Uckert, D. Glenar, D. Voelz, X. Xiao, R. Tawalbeh, P. Boston, S. Getty, W. Brinckerhoff, P. Mahaffy. A miniature spectrometer for the detection of organics and identification of their mineral context. The 44th Annual Meeting of the Division for Planetary Sciences of the American Astronomical Society, Vol. 44, Abstract #215.21, Reno, NV, October, 2012.
N. J. Chanover, D. A. Glenar, K. Uckert, D. G. Voelz, X. Xiao, R. Tawalbeh, P. Boston, W. Brinckerhoff, S. Getty, P. Mahaffy. Miniature Spectrometer for Detection of Organics and Identification of their Mineral Context. International Workshop on Instrumentation for Planetary Missions, Vol. 1683, Abstract #1142, Greenbelt, MD, October, 2012.
N. Chanover, R. Tawalbeh, D. Glenar, D. Voelz, X. Xiao, K. Uckert, P. Boston, S. Getty, W. Brinckerhoff, P. Mahaffy, T. Cornish, and S. Ecelberger. Rapid assessment of high value samples: An AOTF-LDTOF spectrometer suite for planetary surfaces. Aerospace Conference, 2012 IEEE, pp 1-10, March 2012.
K. Uckert, N. J. Chanover, D. A. Glenar, D. G. Voelz, X. Xiao, R. Tawalbeh, P. Boston, W. Brinckerhoff, S. Getty, P. Mahaffy. A miniature AOTF-LDTOF spectrometer suite for the detection of biomarkers on planetary surfaces. Astrobiology Science Conference, Abstract #4442, Atlanta, GA, April 2012.
K. Uckert, N. J. Chanover, D. A. Glenar, D. G. Voelz, X. Xiao, R. Tawalbeh, P. Boston, W. Brinckerhoff, S. Getty, P. Mahaffy. A miniature AOTF-LDTOF spectrometer suite for the detection of biomarkers on planetary surfaces. Life Detection in Extraterrestrial Samples, Abstract #6042, San Diego, CA, February 2012.
N. J. Chanover, D. A. Glenar, D. G. Voelz, X. Xiao, R. Tawalbeh, K. Uckert, P. Boston, W. Brinckerhoff, S. Getty, P. Mahaffy. Rapid Assessment of High Value Samples: A Miniature AOTF-LDTOF Spectrometer Suite for Cave Environments. First International Planetary Cave Research Workshop, Abstract #8019, Carlsbad, NM, October 2011.