Siliceous Hot Spring Deposits: Why They Remain Key Astrobiological Targets

For nearly 40 years, hydrothermal deposits have been recognized as potential paleobiological repositories for astrobiological exploration of Mars. Here, we summarize the motivation for this astrobiological search strategy as it pertains to our current understanding of silica-depositing hot spring ecosystems and terrestrial siliceous hot spring deposits. We also discuss the rover and orbital observations of recently discovered hydrothermal opaline silica deposits on Mars-interpreted as evidence of hot spring activity. The opaline silica digitate sinters near Columbia Hills represent the strongest evidence to date for potential fossilized biosignatures on Mars. The high habitability and preservation potentials of hot spring deposits on Earth, along with their ability to reveal insight into the metabolic evolution of life, strengthen the rationale for targeting siliceous hot spring deposits as high-priority astrobiology sites for future Mars missions.