Neutron emission on the surface of Mars

Abstract

The neutron emission of Mars is known to be produced due to the bombardment of Martian surface by Galactic Cosmic Rays (GCRs). As evidenced by numerical simulation, the intensity of neutron emission on the planetary surface is much larger than that of the neutron emission at the orbital altitude due to multiple reflections of the neutrons emitted from soil by the atmosphere. The code developed for simulations was validated using the experimental data of neutron emission acquired in the Gale crater by the RAD and DAN instruments aboard the NASA's Curiosity rover. Neutron emission was simulated for two Martian areas: the dry Solis Planum territory and the bottom of the Valles Marineris system of canyons, which is thought to be the most wet equatorial spot on Mars. For both areas a strong effect is found, showing a considerable difference between the neutron emission on the surface and at the altitude of a typical orbit. It was also shown that surface emission in these two areas is quite different due to the difference of mass fraction of water in the shallow subsurface. Finally, the seasonal variations of neutron emission in these areas due to the atmospheric seasonal changes are also estimated.