MARTE: A Mars Analog Drilling Project to Search for Subsurface Life at the Rio Tinto, Spain ABSTRACT The principal objective of the MARTE project is a field experiment program to search for a subsurface biosphere in the region of the Tinto River in southwestern Spain. The experiment has achieved new scientific results while also demonstrating the technology for searching for a subsurface biosphere on Mars. The Tinto river is in one of the largest deposits of sulfide minerals in the world. The surface (river) system is an acidic extreme environment produced and maintained by organisms that metabolize sulfide minerals and produce sulfuric acid as a byproduct. Evidence suggests that the river is a surface manifestation of an underground biochemical reactor. Organisms found in the river are capable of anaerobic autotrophic metabolism using sulfide and ferric iron mineral substrates found in the region, suggesting these organisms could thrive in the underground aquifer that underlies the region. The system is of great Astrobiological interest as an example of life sustained and controlled by inorganic compounds operating underground in anoxic conditions. The project includes the demonstration of the current state of component technologies required for planetary drilling in a realistic field setting. The central element is a dry- cutting, low-power coring drill system. Augmenting the drill are robotic systems for extracting the cores from the drill head and performing analysis using a suite of instruments to understand the composition, mineralogy, presence of organics, and search for life signatures in subsurface samples. A robotic system also characterizes borehole properties in situ. A Mars drilling mission simulation will be performed in 2005, including remote operation of the drilling, sample handling and instruments, as well as interpretation of results by a remote science team. Preparation for this simulated mission has included extensive work with conventional field and laboratory methods for aseptic drilling, sample handling, and sample analysis to fully document the subsurface and compare what can be learned with remote sensing instruments. A broad selection of scientists from the Mars and Astrobiology communities, as well as students, will be involved in the Mars mission simulation and ground truth analysis of samples.