Prediction of Martian Surface Neutron Environment

1. Prediction of Martian Surface Neutron Environment M. S. Clowdsley1, G. DeAngelis2, J. W. Wilson1, F. F. Badavi3, and R. C. Singleterry1 1 NASA Langley Research Center, Hampton, VA 2Old Dominion University, Norfolk, VA 3Christopher Newport University, Newport News, VA Solar and Space Physics and the Vision for Space Exploration Meeting Wintergreen, Virginia October 16-20, 2005

2. Radiation Transport Codes • Monte Carlo Codes: MCNPX, HETC, FLUKA, TIGRE • Accurately model the transport of neutrons, protons, and other light ions (and electrons in the case of TIGRE) • GCR ions being added • Require large amounts of computer time • Deterministic Codes: HZETRN, GRNTRN • Accurately model the transport of neutrons, protons, light ions, and GCR • Provide rapid transport calculations HZETRN used in following calculations!!!

3. Mars Induced Fields Planetary Surface Material and Atmosphere GCR ion High energy particles Diffuse neutrons (Simonsen et al.)

4. GCR Environments Free Space Martian Surface 1977 Solar Minimum (solid) 1990 Solar Maximum (dashed)

5. Mars Surface Neutrons

6. Mars Surface “Worst Case SPE” Environment Free Space Martian Surface “Worst Case SPE” = 4 X proton component of Sept. ’89 Event Exploration Design Basis SPE as yet undefined

7. Dose Equivalent on Mars Surface Due to GCR

8. Mars Surface Mapping Charged Ions – 1977 Solar Minimum from Space Ionizing Radiation Environment and Shielding Tools (SIREST) web site http://sirest.larc.nasa.gov

9. Mars Surface Mapping Neutrons – 1977 Solar Minimum from Space Ionizing Radiation Environment and Shielding Tools (SIREST) web site http://sirest.larc.nasa.gov

10. Mars Surface Mapping Low Energy Neutrons – 1977 Solar Minimum from Space Ionizing Radiation Environment and Shielding Tools (SIREST) web site http://sirest.larc.nasa.gov

11. Mars Surface Environment

12. Model for Mars Atmosphere • Atmospheric chemical and isotopic composition modeled using results from in-situ Viking 1 & 2 Landers measurements for both major and minor components: CO2 % 95.32 N2 % 02.70 Ar % 01.60 O2 % 00.13 CO % 00.08

13. Model for Mars Surface • The surface altitude, or better the atmospheric depth for incoming particles, determined using a model for the Martian topography based on the data provided by the Mars Orbiter Laser Altimeter (MOLA) instrument on board the Mars Global Surveyor (MGS) spacecraft. • The Mars surface chemical composition model based on an averaging process over the measurements obtained from orbiting spacecraft, namely the Mars 5 with gamma-ray spectroscopy, and from landers at the various landing sites, namely Viking Lander 1, Viling Lander 2, Phobos 2 and Mars Pathfinder missions.

14. Model for Mars Surface SiO2 % 44.2 Fe2O3 % 16.8 Al2O3 % 08.8 CaO % 06.6 MgO % 06.2 SO3 % 05.5 Na2O % 02.5 TiO2 % 01.0 • The adopted Mars surface chemical composition:

15. Model for Mars Surface • The composition, different with respect to the regolith (e.g. CO2 ice, H2O ice), of seasonal and perennial polar caps has been taken into account by modeling the deposition of the possible volatile inventory over the residual caps, along with its geographical variations all throughout the Martian year, for both the Mars North Pole and South Pole, from results from imaging data of orbiter spacecraft and from groundbased observations • No 3D time dependent models for the Martians polar caps was previously available for radiation studies

16. Conclusions • The Martian surface environment including albedo neutrons can be calculated using existing transport codes • These codes must be validated with detector data!!!!!!