WatSen: searching for clues for water (and life) on Mars

Abstract

: There is plenty of evidence for fluid on Mars : large-scale (planet-wide) features have been captured over four decades by a procession of orbiting satellites equipped with cameras with increasingly higher spatial resolutions. Imagery of the surface shows channels, valleys, ice-caps, etc. Small-scale, more local evidence for fluid has come from images obtained by rovers on the Martian surface. Images that water produced many of the features are supported by spectroscopic measurements (again both planet-wide and local) over a range of wavelengths, which show the presence of minerals generally only produced in the presence of water (haemetite, jarosite, etc.). Results from meteorites continue this picture of fluid activity taking place over significant periods of Mars' history. Despite all these indicators of water, direct detection of water has never been performed. We have reviewed the evidence for water on Mars' surface, and have described WatSen, a combined humidity sensor and infrared IR detector, which can be employed to search for water at and below Mars' surface. WatSen is designed to be part of the suite of instruments on the mole that will be deployed as part of the Geophysics and Environment Package on ExoMars. The objectives of the package are as follows : (i) to detect water within Martian soil by measuring humidity and IR spectral characteristics of the substrate at surface and at depth ; (ii) to determine the mineralogy and mineral chemistry of surface soils (this measurement will provide the mineralogical context for the elemental results that come from other instruments mounted on the landing platform); (iii) to determine how mineralogy changes with depth. The utility of WatSen is that it will not only detect the presence of water, but will also be able to record which minerals are present and their chemistry ; it is also sensitive to many organic species. WatSen is a new instrument concept specifically designed to search for clues of the presence of water, and to look for evidence of life on Mars.

Mineralogy and chemistry of altered Icelandic basalts: Application to clay mineral detection and understanding aqueous environments on Mars

“…Our simple analysis of isolates from vesicle/fracture fills demonstrates that the ability to examine VNIR or TIR spectra from different portions of a rock at small scales (preferably non‐destructively, unlike this study) permits identification of a greater number of minerals relative to what is possible from whole‐rock spectra alone. This highlights the potential value of in situ instruments for small‐scale spectroscopy that would permit mineralogic identifications at spatial scales of hundreds of micrometers [e.g., Grady , 2006; Bibring and the Micromega Team , 2008]. Although this capability does not replace the capabilities of laboratory analyses, e.g., electron microprobe, it provides a means of rapid, non‐destructive analysis of the small‐scale textural relationships between mineral phases that may elucidate the style of alteration and changes in fluid composition with time.…”

“…In addition to orbital and outcrop‐scale measurements, microscopic IR instruments have been proposed for in situ investigation of aqueous processes on Mars [e.g., Grady , 2006; Bibring and the Micromega Team , 2008]. Here, we could not directly simulate these imaging microscopes over the desired wavelength range, so samples were extracted by hand from the bulk rock and individual vesicles and fractures and were measured separately.…”

WatSen: design and testing of a prototype mid-IR spectrometer and microscope package for Mars exploration

“…It was anticipated that by selecting an appropriate wavelength range for the detector, WatSen could also investigate the silicate mineralogy of the regolith, and identify the presence of secondary minerals including phyllosilicates and carbonates. Grady (2006) The main constraint on the physical size of the package was that it had to fit within the mole subsystem ( Figure 2) intended as a deployment mechanism for sensor packages. The mole was designed under ESA contract by DLR, Berlin (Gelmi et al, 2007).…”

“…The main objective of the WatSen instrument package would be to detect water adsorbed on the surface of soil grains (Grady, 2006). Liquid water will not be stable within the uppermost soil layers, the zone of sublimation.…”

“…2 Instrument Design 2.1 Design Specifications Grady (2006) outlined the required scientific specifications from ESA for WatSen to be considered viable for attachment to a mole in a future planetary exploration mission. The completed compact breadboard model surpasses ESA's original design specifications in terms of size, mass and power budgets (Table 1 and Figure 1).…”