Surface and Downhole Prospecting Tools for Planetary Exploration: Tests of Neutron and Gamma Ray Probes

Abstract

The ability to locate and characterize icy deposits and other hydrogenous materials on the Moon and Mars will help us understand the distribution of water and, therefore, possible habitats at Mars, and may help us locate primitive prebiotic compounds at the Moon's poles. We have developed a rover-borne neutron probe that localizes a near-surface icy deposit and provides information about its burial depth and abundance. We have also developed a borehole neutron probe to determine the stratigraphy of hydrogenous subsurface layers while operating within a drill string segment. In our field tests, we have used a neutron source to "illuminate" surrounding materials and gauge the instruments' efficacy, and we can simulate accurately the observed instrument responses using a Monte Carlo nuclear transport code (MCNPX). An active neutron source would not be needed for lunar or martian near-surface exploration: cosmic-ray interactions provide sufficient neutron flux to depths of several meters and yield better depth and abundance sensitivity than an active source. However, for deep drilling (>or=10 m depth), a source is required. We also present initial tests of a borehole gamma ray lithodensity tool and demonstrate its utility in determining soil or rock densities and composition.

Footprint characteristics revised for field‐scale soil moisture monitoring with cosmic‐ray neutrons

“…[] and validated with measurements and hydrodynamic simulations. Further evidence for the correct performance of the URANOS model provides the comparison with measurement depths of 50–100 cm on the Moon or Mars missions, where cosmic‐ray neutrons penetrate dry ground of similar chemical composition [ Elphic et al ., ; McKinney et al ., ].…”

Farside explorer: unique science from a mission to the farside of the moon

“…In situ passive neutron/gamma-ray spectrometry [14] is here advocated as this instrument would benefit enormously from the long duration of the Farside Explorer mission. Though similar measurements have been made previously from orbit, the long accumulated measurement times for these surface measurements at a single locale would reduce the statistical uncertainties for elemental concentrations by orders of magnitude compared to those obtainable from orbit.…”

“…Neutron and gamma-ray spectrometers have flown previously on missions to the Moon, Mars, Mercury, and asteroids, and a miniaturized version of these orbital instruments has been proposed for in situ measurements on planetary surfaces [14]. The measurement technique uses neutrons and gamma-rays that are produced by galactic cosmic rays, and the returned data consists of energy pulse height spectra integrated over a commandable-length time cadence.…”

“…The neutron spectrometer itself could be built for ∼500 g [14], and the primary mass driver is the gamma-ray scintillator. The overall power utilized by the neutron gamma-ray spectrometer is less than 4 W, and since nighttime measurements are not required, the instrument would be turned off during the night to conserve power.…”

Astrobiology Special Collection: Instruments for In Situ Exploration of Planets

“…Pfiffner et al (2008) show how experience of deep-drill coring on Earth may be applied to Mars. Instruments that operate both on the surface and beneath it are described in the contribution from Elphic et al (2008), who consider neutron detectors for hydrogen (that might be water) and a gamma ray spectrometer for broad geochemical analysis. The DAME project, detailed by Glass et al (2008), describes a series of tests of automated drilling and their results at a number of Mars analog sites.…”