Cave Biosignatures

Identifying Life in the Subsurface using a Suite of Instruments

Cave Biosignatures

The search for life and habitable environments on other solar system bodies is one of the basic motivators for planetary exploration. Due to the difficultly and significance of detecting extant or extinct extraterrestrial life in situ, several independent measurements from multiple instrument techniques are necessary to support such a claim. We demonstrate the unambiguous detection of biosignatures using a suite of instrument techniques including IR reflectance spectroscopy, laser desorption/ionization mass spectrometry, laser induced breakdown spectroscopy, X-ray diffraction / X-ray fluorescence, and scanning electron microscopy / energy dispersive X-Ray spectroscopy. We focus our measurements on subterranean field samples, whose primitive biosignatures are analogous to those expected on high-interest astrobiology targets.

Fort Stanton Cave

We have participated in several expeditions to Fort Stanton Cave, an extensive limestone cavern in central New Mexico with a diverse assortment of speleothems and cave decorations. We primarily measured calcium carbonates, gypsum, and manganese oxide samples with each of the aforementioned instruments.

Using laser-induced breakdown spectroscopy (LBS) and IR spectroscopy, we were able to distinguish biologically precipitated carbonates from samples that were precipitated abiotically. Samples that underwent biomineralization processes form irregular crystal structures (primarily due to microorganisms entombing themselves in carbonate waste, acting as nucleation sites), which show distinct IR spectral features. Trace elements associated with microbiologic activity is also present in these samples, as identified by LIBS.

Mass spectrometry measurements of manganese oxide samples collected from Fort Stanton Cave show evidence for biologic activity through the detection of insoluble manganese oxides, indicating a biologic formation mechanism.



Operating PASA in Fort Stanton Cave. Photo credit: Wayne Walker

El Malpais Lava Tubes

Dr. Penny Boston pointing out actinobacteria in Four Windows Cave. Photo credit: Bob Hull



Lava tubes are the most likely type of cave to exist on other planetary surfaces, and are therefore an important place to perform analog studies. We have participated in expeditions to the "Big Tubes" (Big Skylight Cave and Four Windows Cave) in the El Malpais National monument to identify the presence of biologic activity on the surface of the basaltic cave wall.

Within Four Windows Cave, we have identified the presence of primitive microorganisms, primarily actinobacteria, which extract metal ions from the volcanic rock to oxidize, providing energy for growth and reproduction. In many cases, the bacteria communities arrange themselves in biovermiculation patterns - maze-like biomats arranged such that nutrient extraction from the rock is optimized by the community.

We have also participated in an expedition to Big Skylight Cave to integrate our PASA-Lite IR reflectance spectrometer with a rock-climbing robot, LEMUR. LEMUR is able to access regions of the cave unaccessible to human operators, allowing PASA-Lite to acquire IR spectra of exposed rock surfaces. We have successfully measured the IR reflectance spectrum of a basalt wall with PASA-Lite mounted on LEMUR, but have not yet attempted to measure biologically active regions of the lava tube system. Future measurements of microbially active basalt with PASA-Lite mounted on a robotic platform will demonstrate the potential biosignature detection capabilities of an IR spectrometer within caves on other planetary surfaces.

Cueva de Villa Luz

Cueva de Villa Luz is a unique, relatively young, hypogenic cave undergoing active formation through sulfuric acid dissolution. The extreme cave environment supports a diverse microbial ecosystem, which is responsible for the formation of several unique speleothems including snottites (tenuous mucousy formations hanging from the cave ceiling) and biovermiculations (acidic biofilms coating a host rock in an irregular pattern, shown in the figure). Many of these formations are sensitive to the low-pH environment, and therefore ideally studied in situ.

We collected several measurements of these formations with PASA and identified IR spectral features consistent with sulfur-bearing species, hydration absorption features, and spectral absorption features associated with each distinct region of the biovermiculation pattern. This expedition was documented by National Geographic here.



Operating PASA in Cueva de Villa Luz. Photo credit: Val Hildreth-Werker

Relevant Publications

A complete publication list is available in my CV and Google Scholar profile.

K. Uckert, N. J. Chanover, S. Getty, D. G. Voelz, W. B. Brinckerhoff, N. McMillan, X. Xiao, P. J. Boston, X. Li, A. McAdam, D. A. Glenar, A. Chavez. The Characterization of Biosignatures in Cave Samples using a suite of in situ Instrument Techniques I: Calcium Carbonate. In Preparation.

K. Uckert, N. J. Chanover, S. Getty, D. G. Voelz, W. B. Brinckerhoff, N. McMillan, X. Xiao, P. J. Boston, X. Li, A. McAdam, D. A. Glenar, A. Chavez. The Characterization of Biosignatures in Cave Samples using a suite of in situ Instrument Techniques II: Gypsum, Mn Oxide, & Sulfur. In Preparation.

K. Uckert, N. J. Chanover, S. Getty, D. G. Voelz, W. B. Brinckerhoff, N. McMillan, X. Xiao, P. J. Boston, X. Li, A. McAdam, D. A. Glenar. The Characterization of Biosignatures in Caves using a Suite of Instruments. 2nd International Planetary Caves Conference, Abstract #9023, Flagstaff, AZ, October 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. McMillan, A. Chavez, N. Chanover, D. Voelz, K. Uckert, R. Tawalbeh, J. Gariano, I. Dragulin, X. Xiao, R. Hull. Rapid and Portable Methods for Identification of Bacterially Influenced Calcite: Application of Laser-Induced Breakdown Spectroscopy and AOTF Reflectance Spectroscopy, Fort Stanton Cave, New Mexico. American Geophysical Union Fall Meeting, Abstract #B33B-0171, San Fransisco, CA, December, 2014.

K. Uckert, N. J. Chanover, S. Getty, W. B. Brinckerhoff, D. G. Volez, N. McMillan, X. Xiao, X. Li, M. Floyd, P. J. Boston. The Identification of Biosignatures on Planetary Surfaces from in situ Techniques, Including Miniaturized Mass Spectroscopy. 62rd American Society for Mass Spectrometry (ASMS) Conference on Mass Spectrometry and Allied Topics, Baltimore, MD, June 2014.

K. Uckert, N. J. Chanover, S. Getty, W. B. Brinckerhoff, X. Li, M. Floyd, D. G. Voelz, X. Xifeng, R. Tawalbeh, N. McMillan, A. Chavez, P. J. Boston, D. A. Glenar, S. Ecelberger, and T. Cornish. A comparative study of in situ biosignature detection spectroscopy techniques on planetary surfaces. Aerospace Conference, 2014 IEEE, pp 1-12, March 2014.

A. Chavez, K. Uckert, N. J. McMillan, N. Chanover, D. G. Voelz. Using Laser Induced Breakdown Spectroscopy (LIBS), Scanning Electron Microscopy (SEM), and Acousto-Optic Tunable Filter Spectroscopy (AOTF) to Distinguish Between Bacterially and Non-bacterially Influenced Calcite And Gypsum, Fort Stanton Cave, NM. Geological Society of America Annual Meeting, Vol 45(7), pp 777, Denver, CO, October 2013.

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. 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.