An Investigation of a Terrestrial Lava Tube with an Instrument Payload Integrated with the LEMUR Rock-Climbing Robot

Planetary caves are desirable destinations for future robotic astrobiology exploration missions due to their thermal stability and the protection these sites offer to microorganisms from solar radiation. A rock-climbing robot equipped with a suite of in situ instruments designed to identify biosignatures and characterize subsurface mineralogy is ideally suited to reveal the presence of extant or extinct microorganisms. We will present the characterization of several biologically interesting regions within Four Windows Lava Tube Cave in the El Malpais National Monument from a suite of instruments, including from measurements collected during a recent expedition to the cave with an astrobiologically-relevant instrument payload integrated with LEMUR. The LEMUR instrument payload consists of: 1) the Portable AOTF (acoutso-optic tunable filter) Spectrometer for Astrobiology (PASA), an infrared reflectance spectrometer; 2) the Advanced PIXL Experiment (APE), an X-ray fluorescence spectrometer; 3) the Green and UV Raman Imager with Laser-induced Autofluorescence (GURILA), a deep-UV Raman spectrometer. We consider Four Windows Cave to be a suitable analog to subsurface martian environments due to similar inferred morphology of observed skylights within basalt lava flows on Mars. We will present measurements of a variety of microbial mats in Four Windows Cave, including cyanobacteria and biovermiculation patterns, as well as biomineralized substrates. Additional laboratory measurements of returned samples and historical data collected during the last two decades reveal the distribution of water and organics within the cave and the deposition of biologically mediated carbonates and sulfates. We demonstrate the subsurface biosignature detection capabilities of the LEMUR science payload and describe the potential of this platform to acquire coincident hyperspectral maps of subsurface environments for future planetary missions.