To address the growing need for in situ molecular analysis of Mars samples at fine spatial scales, NASA is developing the miniature LITMS instrument, which combines a laser and gas chromatograph mass spectrometer with a precision subsampling system. LITMS executes a powerful search for biosignatures and geochemical gradients in a rock sample’s individual layers where such features are most distinct.
Mars continues to entrance and challenge us as a world at once strikingly Earth-like, and yet clearly alien upon closer investigation. Tantalizing evidence of an early water-rich era and the potential for subsurface preservation have made the prospect of detecting ancient or even modern signs of life a central focus of Mars exploration. A series of powerful orbiting and surface missions over the past few decades has greatly enriched our understanding of Mars as a complex, dynamic planet, with select regions exhibiting evidence of having been habitable in the past.
These missions have culminated most recently in the arrival of the Perseverance rover, which is both exploring for potential signatures of past life and collecting high-value samples for later analysis in Earth labs via Mars Sample Return (MSR). The MSR samples will bring unprecedented depth to our investigation of the geochemistry, habitability, and possibly the biology of Mars, enabled by the ultra-sensitive and micron-scale probes afforded by terrestrial laboratories. Along with new knowledge, MSR will also inevitably invite new questions and motivate continued future exploration, likely with a finer scientific focus.
Future robotic missions to examine potential niches for the preservation of biosignatures will undoubtedly call for more intensive study of the molecular composition of samples at fine spatial scales. Martian rock samples are heterogeneous on millimeter and submillimeter scales, reflecting the merging of various mineral phases of differing origins during rock formation or the deposition of thin sedimentary layers. Furthermore, organic compounds that may only occur in trace amounts in the bulk rock, and thus are hard to detect in the presence of high background noise, may be found at much higher concentrations in isolated phases or layers. As on Earth, such layers would be most evident in a drill core sample, where even “short” (few-cm) intact cores can record dramatic chemical variations with depth.
Instruments that perform fine (submillimeter) scale analysis of rock samples are presently deployed on the Perseverance rover. These key investigations enable in situ science as well as identify samples for return to Earth. Looking forward, the need for detailed molecular characterization at such scales, with the full analytical toolkit of a multi-source mass spectrometer, will grow. Scientists will want to distinguish potential biosignatures such as complex organic compounds or homochirality – life’s preference for using only right- or left-handed forms of certain chiral molecules. To this end, an SMD-sponsored team based at Goddard Space Flight Center has been developing the Linear Ion Trap Mass Spectrometer (LITMS) instrument for precision molecular analysis on a future Mars astrobiology lander or rover.
