Assessment of microbial contamination probability for sample return from Martian moons Kosuke Kurosawa1, Kazuhisa, Fujita2, Hidenori Genda3, Ryuki Hyodo3, Takashi Mikouchi4 & Phobos/Deimos Microbial Contamination Assessment Team2 1Chiba Institute of Technology, 2JAXA, 3Tokyo Institute of Technology, 4The University of Tokyo 2018 9/19 Brief summary SterLim data Impact physics •Impact test Orbital dynamics •Heat test Stochastic analyses •Radiation test The spatial distribution The current microbe of microbes density on the moons ☆The total survived fraction of microbes at the present is only ~2 ppm on Phobos and ~50 ppm on Deimos. ☆Heterogeneous distribution of the microbes on the Martian moons ☆Microbe contamination probability of collected samples can be below 10-6 by appropriately choosing the sampling approaches. Each step considered in this study 5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch 1.Potential microbial living on Mars Each step considered in this study 5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch 1.Potential microbial living on Mars Each step considered in this study 5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch 1.Potential microbial living on Mars Each step considered in this study 5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch 1.Potential microbial living on Mars Each step considered in this study 5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch 1.Potential microbial living on Mars Each step considered in this study 5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch 1.Potential microbial living on Mars Each step considered in this study 5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch 1.Potential microbial living on Mars Each step considered in this study 5.Impact processes 7. The formation of radiation on the moon’s surface shield by natural meteoroids -Sterilization by shocks -Fragmentation -Mixing with the regolith 6. Sterilization -Dispersion by radiation 2.The launch of Mars 4.Sterilization by aerodynamic heating rocks due to impacts 3.Sterilization during the launch 1.Potential microbial living on Mars Difference from SterLim study SterLim view Our view Homogeneous deposition by averaging “Mars-rock bombardment” incoming flux to the uppermost layer & Impact physics Microbe distribution -Patchy in the horizontal direction -Depth-dependent Significant/Moderate/Minor effects SterLim Our work 1.Potential microbes Assuming same microbial Similar to SterLim, living on Mars density as Atacama Desert but a downward revision is introduced. Analytic model given by 3-D hydrodynamic simulations to obtain 2.The launch of Mars rocks the point-source theory appropriate initial conditions due to impacts (The same used by Melosh) for the trajectory analyses Sterilization during the launch based on 3.Sterilization during Not considered the data compilation of Martian meteorites the launch and recent finding on shock heating 4.Sterilization by Thermal analysis of Mars ejecta Not considered aerodynamic heating conducted along trajectories 5-1. Impact sterilization Microbe survival rate ~ 0.1 A revised-impact sterilization model on the moon’s surface regardless of impact velocity to treat vimp dependence Crater formation by Mars ejecta with 5-2. Impact processes Homogeneous deposition by retention & scattering of Mars ejecta on the moon’s surface averaging the incoming flux fragments taken into account Sterilization model Same as SterLim, but the effects 6. Sterilization by radiation constructed by experiments of the depth is also considered. 7. The formation of radiation Not considered A new stochastic model shield by natural meteoroids Outline 1. General assumptions 2. Transportation to the moons 3. Mars-rock bombardment on the moon 4. Background impact flux by natural meteoroids 5. The change in the microbe density with time 6. Microbe contamination risk assessment 7. Conclusions Outline 1. General assumptions 2. Transportation to the moons 3. Mars-rock bombardment on the moon 4. Background impact flux by natural meteoroids 5. The change in the microbe density with time 6. Microbe contamination risk assessment 7. Conclusions General assumptions - Potential microbe density on Mars - Supporting data (SterLim data) - Source crater Potential microbe density on Mars Terrestrial Mars analog Condition Location Microbe concentration 106 – 108 CFU/kg Yungay [Navarro-González+03; Maier+04] Hyperarid (Atacama Desert) 108 – 1010 cells equivalent/kg [Glavin+04; Drees+06; Lester+07; Connon+07] 6 7 Cold & Arid McMurdo Dry valley 10 – 10 cells equivalent/kg (Antarctic permafrost) [Goordial+16] 8 Initial microbe density nMars = 10 CFU/kg ※1 CFU/kg ~ 102 cells/kg Potential microbe density on Mars [Data are taken from Navarro-González+03] Not detected McMurdo Dry valley (Antarctic permafrost) [Goordial+16] ※1 CFU/kg ~ 102 cells/kg was assumed. Potential microbe density on Mars Terrestrial Mars analog Condition Location Microbe concentration 106 – 108 CFU/kg Yungay [Navarro-González+03; Maier+04] Hyperarid (Atacama Desert) 108 – 1010 cells equivalent/kg [Glavin+04; Drees+06; Lester+07; Connon+07] 6 7 Cold & Arid McMurdo Dry valley 10 – 10 cells equivalent/kg (Antarctic permafrost) [Goordial+16] 8 Initial microbe density nMars = 10 CFU/kg ※1 CFU/kg ~ 102 cells/kg Supporting data on sterilization The best systematic dataset to consider the case of Martian moons. SterLim impact test SterLim radiation test [Patel+18] [Patel+18] A different empirical model Time constant of MS2 was used based on the dataset was used. for conservative estimate. (Next slide) Impact survival rate The SterLim study assumed the survival rate is ~0.1. [Patel+18] Physical constraint: Survival rate must be decrease with increasing vimp because post shock temperature ∝ v2 An empirical model ± × −6 1.8 NΤN0 = exp − 9.5 4.3 10 Vimp Main source crater Zunil crater Diameter: 10.1 km Longitude: 166 deg. East Latitude: 7.7 deg. North (Near the equator) Impact direction: East-NorthEast [Preblich+07] Formation age: 0.1–1 Myr ago [Hartmann+10] [Preblich+07] The youngest-ray crater on Mars with a diameter of >10 km The other craters Transported mass to Phobos vs Formation age Transported mass Mtransported Age estimate Mojave (58 km) Hartmann+10 was estimated in this study. Hartmann+10 (discuss later) using Malin+06 data [Hyodo+, to be submitted] Golombek+14 Werner+14 Tooting (29 km) Mtransported strongly depends on Df. -> The smaller craters are McMurdo (23 km) not important. Zunil (10 km) Corinto (14 km) The other large craters are much older than Zunil. -> The microbes must be sterilized at the present. (Next slide) Required time treq for radiation sterilization N0 treq = TC(H)ln Nth For conservative estimate, Zunil 7 N0 = 10 (CFU/kg) -5 Nth = 10 (CFU/kg) (Req-10 for 100 g sampling) The others Target depth Depth (cm) treq(years) for sampling <0.04 2.0 x 103 1 4.4 x 105 10 1.7 x 106 30 2.0 x 106 The microbes from the other craters must be sterilized until now. Outline 1. General assumptions 2. Transportation to the moons 3. Mars-rock bombardment on the moon 4. Background impact flux by natural meteoroids 5. The change in the microbe density with time 6. Microbe contamination risk assessment 7. Conclusions Launch Difficulties in the estimation of the mass of high-speed ejecta High-speed ejection at velocities higher than ~20% of vimp cannot be treated by the widely-used point-source theory [Melosh84; Kurosawa&Takada19] <-Velocity-volume behavior in the point-source theory ※The previous studies used the point-source theory ? [Chappaz+13; SterLim study] [Housen & Holsapple11] Numerical simulations are necessary to address the total mass of high-speed ejecta Mej. 3-D SPH simulation A three-dimensional