Autonomous Rover Detection and Response Applied to the Search for Life via Chloro- Phyll Fluorescence in the Atacama

Introduction: As planetary rovers travel longer distances in each command cycle, science conducted during traverse becomes a significant part of the overallmission. During traverse, the rover may pass an interesting feature never detected before (because it was not close enough) and never visited again (because continued progress was deemed more important than returning for further study). In this situation, we would like the rover to collect some information before it passes on. Like a good field scientist, it needs to detect interesting features and autonomously respond with followup observations [1,3]. This paper describes autonomous detection and response capabilities used to enhance a robotic search for life in the Atacama Desert of Chile, part of the NASA ASTEP Limits of Life in the Atacama campaign [4,5]. In the coastal desert region studied (site D, rh 10-80%), it was expected that sparse patches of lichens and cyanobacteria would be exposed on the surface. To study these organisms, our rover carried a fluorescence imager (FI), which could detect chlorophyll via its inherent fluorescence. It could detect other organic chemicals, such as DNA and proteins, after applying fluorescent marker dyes. The current design of the FI was optimized to study terrestrial life, but similar instruments could be deployed onMars or Europa, possibly focusing on a different set of biomarkers. Application of FI dyes was time-consuming and used up a limited supply of dye, so it was important to ensure each dye sample contained interesting data. Thus, we focused the dyes on samples where chlorophyll was autonomously detected. Autonomous chlorophyll detection and followup dye application was field tested in the Atacama. Samples autonomously chosen for dye followup were significantly more likely to contain photosynthetic organisms than samples chosen at random. Several of the autonomous followup images showed positive dye fluorescence. The new autonomy capabilities were successfully integrated into the operations scheme and saw continuing use by the remote team operating the rover. Fluorescence imager: The FI is a down-pointing camera mounted on the bottom of the Zoë rover (fig. 1). It has 10 cm field of view and resolution 180 μm. During autonomous response experiments, the sampling location under the FI was chosen by stopping the rover at fixed distances along its traverse, and the camera was deployed and auto-focused using z-axis motion. The sample under study was not moved. The FI could be used to detect either the reflectance or fluorescence of a sample in various channels. A xenon flashlamp provided illumination. Six optical interference filters could be automatically switched into the excitation path between the flashlamp and sample, and another ten filters could be switched into the detection path between the sample and CCD. The FI captured reflectance under a combination of sunlight and flashlamp illumination with no excitation filter. Separate images with red, green, and blue emission filters were combined to form a visual color image. In fluorescencemode it captured a black and white intensity image, with excitation and Figure 1: The FI deployed and spraying underneath the robot Zoë in the Atacama Desert of Chile with an overlay of Zoë in the desert.