Main Characteristics of Space Radiation
Solar Particle Events
Galactic Cosmic Rays
There have been several solar system measurements of the GCR at distances at and beyond Mars, providing confidence in extrapolations of more detailed GCR measures taken near Earth. There have also been limited radiation measurements taken from satellites in orbit around Mars (relevant instruments on Mars Odyssey include the Mars Radiation Environment Experiment [MARIE], the High Energy Neutron Detector, and neutron information from the Gamma Ray Spectrometer; there have also been indirect measurements using instruments on Mars Global Surveyor). Use of these data for estimates of the surface radiation environment requires transport code estimates of particles created in or scattered from the martian atmosphere and calculations of particle transport from the surface through the atmosphere.
The Radiation Assessment Detector (RAD) on the 2009 Mars Science Laboratory will characterize the broad spectrum of radiation at the martian surface. RAD will measure high-energy charged particles coming through the martian atmosphere. In addition to identifying neutrons, gamma rays, protons, and alpha particles, RAD will measure galactic cosmic ray heavy ions up to iron on the periodic table.
Finding 2-1. Current knowledge of the radiation environment on the Moon. Data from many satellites have enabled the characterization of GCR and SPEs near Earth, and these results serve to characterize the radiation incident on the surface of the Moon. Knowledge of the secondary radiation, which is produced by galactic cosmic rays and SPEs interacting with material on the lunar surface, is currently based on data from Apollo, Lunar Prospector, and Clementine and on calculations.
Finding 2-2. Current knowledge of the radiation environment on Mars. The radial extrapolation of the GCR environment from Earth to Mars is well understood, based on measurements made by numerous scientific satellites as they traveled outward through the solar system. To within a few percent or so, the GCR environment at the top of the martian atmosphere is expected to be the same as that near Earth. There are very few simultaneous measurements of SPEs at Earth and at Mars, and current models are inadequate to extrapolate near-Earth measurements of SPEs to Mars. Knowledge of the secondary radiation environment on the surface of Mars is currently based on calculations and measurements taken by spacecraft in Mars orbit.