On the probability of extant endolithic life on Mars

Mars was previously deemed too cold and too dry to support endolithic life. The argument was based on field observations that in the Antarctic dry valleys, the coldest endolithic microbial ecosystem known, there are many apparently suitable but uncolonized sandstone rocks. It was thought that these particular rocks do not receive sufficient insolation during the summer to be warm enough for biological activity. New observations contradict this conventional wisdom. The uncolonized rocks appear to be under too thick a snow cover. While snow, the sole source for moisture, is essential to survival, too much snow blocks sunlight from the photosynthetic organisms below. These observations suggest that endolithic life could exist in a still colder and drier climate. This insight, together with the evidence from the Phoenix Lander that ice is present in the surface soil on Mars, indicates that a Martian biota living in or under rocks is a distinct possibility. Sanstone boulders in the Antarctic dry valleys. Variability in surface weathering, previously considered a sign of temperature stress for life below, is an indicator of robustness and adaptability.