Summary

The exploration of Mars has long been one of the most tantalizing forefronts of scientific endeavor and represents a key pillar in astrobiology research. Through remote imaging and in-situ robotic missions, a great deal has been learned about the environment of Earth’s planetary neighbor, yet the unknown secrets of the Red Planet still capture the imagination as much as ever: Is the planet geologically active? How much water is present? How fertile are the soils? Could Mars theoretically sustain life even if it is in fact sterile today? The examination of atmospheric composition, the analysis of soil makeup and chemistry, the search for liquid water, the assessments of geological activity, and the monitoring of weather conditions on Mars by robotic missions over the decades all bring one closer to understanding the habitability—or lack thereof—of Mars throughout history. Thus far, missions to Mars have observed an extremely thin atmosphere, an absence of liquid water at the surface, freezing surface temperatures, a soil chemistry which is damaging to organic molecules, and a lack of protection from space weather such as solar UV radiation. Beginning with the Mars Science Laboratory (MSL) Curiosity mission in 2011, Mars surface missions were designed to probe environments besides the hostile surface itself, such as close-up examinations of surface rocks to unravel their mineral compositions (MSL Curiosity rover, Perseverance rover), investigating potential geologic activity in an attempt to deduce the nature of the Martian core (InSight lander), digging down to recover soil and rock samples to examine for traces of molecular fossils (ExoMars Franklin rover), and the detection of underground ice deposits and subsurface mineral composition (Perseverance and Zhurong rovers). The history of human exploration of Mars follows a timeline of unexpected findings, the challenges of verifying data, adaptations to the engineering challenges of delayed response operation under difficult physical conditions, and the logistical challenges of ever more complex missions.