# Presentation: 208090

## Prediction of Martian Surface Neutron Environment

**Prediction of Martian Surface Neutron Environment**

**M. S. Clowdsley****1****, G. DeAngelis****2****, J. W. Wilson****1****, F. F. Badavi****3****, and R. C. Singleterry****1**

- 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

## 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!!!**

## Planetary Surface Material and Atmosphere 

- (Simonsen et al.)

- Mars Induced Fields

- GCR ion

- Diffuse
- neutrons

- High energy
- particles

## GCR Environments

- 1977 Solar Minimum (solid)
- 1990 Solar Maximum (dashed)

- Martian Surface

- Free Space

## Mars Surface Neutrons

## Mars Surface “Worst Case SPE” Environment

- “Worst Case SPE” = 4 X proton component of
-                                    Sept. ’89 Event
- Exploration Design Basis SPE as yet undefined

- Martian Surface

- Free Space

## Dose Equivalent on Mars Surface Due to GCR

## Mars Surface Mapping

- Charged Ions – 1977 Solar Minimum

- from Space Ionizing Radiation Environment and Shielding Tools (SIREST) web site
- http://sirest.larc.nasa.gov

## Mars Surface Mapping

- Neutrons – 1977 Solar Minimum

- from Space Ionizing Radiation Environment and Shielding Tools (SIREST) web site
- http://sirest.larc.nasa.gov

## 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

## Mars Surface Environment

## 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:

-                   **CO****2****           %      95.32**
**       ****N****2****             %      02.70**
**      ****Ar             %      01.60**
**       ****O****2****            %      00.13**
**      ****CO            %      00.08**
-                    **      **

## 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.

## Model for Mars Surface

- The adopted Mars surface chemical composition:

-                    **SiO****2****          %      44.2**
**      ****Fe****2****O****3****        %      16.8**
**      ****Al****2****O****3****        %      08.8**
**      ****CaO          %      06.6**
**      ****MgO         %      06.2**
**       ****SO****3****          %      05.5**
**     ****Na****2****O         %      02.5**
**      ****TiO****2****         %      01.0**
**     **

## Model for Mars Surface

- The composition, different with respect to the regolith (**e.g. CO****2**** ice, H****2****O 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**

## Conclusions

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