“…However, high above Earth’s surface in the stratosphere (∼15–50 km), another Mars analog environment exists, presenting a unique combination of environmental insults that more closely resemble conditions on the Red Planet. In the middle stratosphere during daytime hours, the following Mars-like factors are simultaneously present: intense, full spectrum ultraviolet (UV) radiation, high energy ionizing radiation (including secondary scattering), desiccation, hypoxia, and ultralow temperatures and pressures ( Clark and McCoy, 1965 ; Potemra and Zmuda, 1970 ; Vampola and Gorney, 1983 ; Keating et al, 1987 ; Clancy and Muhleman, 1993 ; Von Engeln et al, 1998 ; Seele and Hartogh, 1999 ; Shepherd, 2000 ; Lambert et al, 2007 ; Mertens et al, 2016 ; Caro et al, 2019 ). Taken together, these combined conditions cannot be found naturally anywhere on the surface of the Earth and would be challenging to easily reproduce in laboratory-based experiments.…”