21 August 2018
Curiosity is probing the subsurface today with its Dynamic Albedo of Neutrons (DAN) instrument. At three different times, Curiosity will use DAN in its ‘active’ mode for 20 minutes, sending pulses of neutrons into the ground beneath the rover, and then listening for the neutrons that are scattered back to the instrument. Hydrogen atoms in water will reduce the energy of the neutrons, so the scattered signal that DAN receives will tell us about how much water might be present in the form of hydrated minerals and amorphous phases, to a depth of 1 m beneath the surface. Curiosity is using DAN multiple times today because the neutron output from the DAN Pulsing Neutron Generator (PNG) has decreased over time (though it is well beyond its expected life), and we hope that integrating over multiple intervals will give the same signal-to-noise ratio that DAN observations had at the start of Curiosity’s mission.
In addition, Curiosity is performing more analyses of the ‘Stoer’ sample and continues to characterize the region around the drill site. A major activity today is a second X-Ray Diffraction (XRD) analysis by the CheMin instrument, which will provide more detailed information about the mineralogy. Curiosity will also be firing up the ChemCam laser to examine two rock targets near the drill hole: ‘Mainland,’ which is 30 cm from the Stoer hole and will tell us about bedrock chemistry variations; and ‘Doonie_Point,’ which is about 1 m from the Stoer hole and might be a concretion in the bedrock.
Written by Melissa Rice, Planetary Geologist at Western Washington University