Synergistic Interactions Among Vacuum, Solar Heating, and UV Irradiation Enhance the Lethality of Interplanetary Space
A Planetary Atmospheric Chamber (PAC) was used to create simulations of interplanetary conditions to test the spore survival of three Bacillus spp. exposed to interacting conditions of vacuum (VAC), simulated solar heating (HEAT), and simulated solar ultraviolet irradiation (UV).
Synergism was observed among the experimental factors for all three Bacillus spp. tested that suggested the increased lethality of HEAT and UV when concomitantly exposed to VAC. The most aggressive biocidal effects were observed for assays with VAC + HEAT + UV conditions run simultaneously over short time-steps.
The results were used to predict the accumulation of extremely rapid Sterility Assurance Levels (SALs; def., −12 logs of bioburden reduction) measured in a few minutes to a few hours for external surfaces of interplanetary spacecraft.
Furthermore, the results were extrapolated to predict that approx. 1 × 104 SAL exposures might be accumulated for external surfaces on the Europa Clipper spacecraft during a 3.5-year transit time between Venus (0.7 AU) and Mars (1.5 AU) during a series of Venus–Earth–Earth gravity assists (VEEGA trajectory) to Jovian space.
The results are applicable to external spacecraft surfaces exposed to direct solar heating and UV irradiation during transits though the inner solar system.
Six cm water filter to remove thermal IR irradiation. (4) Agilent Turbo pump. (5) Roughing scroll pump for Mars surface conditions. (6) Roughing scroll pump for Agilent Turbo pump. (7) Tungsten-halogen lamp. (8) Front port composed of non-UV-transmitting borosilicate glass. (9) Lauda water chiller of the cryogenic cooling system for temperature control down to −10 °C (with yellow pipes). (10) Multi-port 6” CF flange with three 2.5” CF flanges. (11) Steel support structure for the UV-VIS illuminator. (12) Liquid nitrogen dewar for temperature control down to −100 °C. (13) All electrical power was located on the back wall. (14) Opto-22 data logging system. (15) Tanks of Mars gas located to the right of the PAC. (16) DC power supplies for internal PAC sensors.
Synergistic Interactions among Vacuum, Solar Heating, and UV Irradiation Enhance the Lethality of Interplanetary Space, Microorganisms via PubMed (open access)
Astrobiology,
