December 21, 2021. By Kolemann Lutz
The FREND neutron telescope onboard ExoMars Trace Gas Orbiter (TGO) collected 200km spot resolution imagery in Candor Chaos that suggests a very high mean water equivalent hydrogen (WEH) value as large as 40.3 wt% down to a 1-meter depth over a 41,000 square km surface area (size of Netherlands) inside Valles Marineris associated with geomorphological conditions.
European Space Agency’s ExoMars Trace Gas Orbiter (TGO), launched in 2016 as a joint mission between the European Space Agency and Roscosmos, orbits at 400km detected the water inside the Valles Marineris, a 3000-km-long canyon system on Mars. The water is located beneath the surface of the canyon system and was detected by the orbiter's FREND instrument, or Fine Resolution Epithermal Neutron Detector. With enhanced resolution of 60km satellite imagery from image reconstruction techniques, this instrument is able to map hydrogen in the top meter (3.28 feet) of Martian soil.
Valles Marineris (VM) experiences average highs of 0℃ (32F) and is believed to contain spring-like H2O reservoirs, which could be ripe location to search for astrobiology microbial life. A 2008 study with OMEGA data visible and near-IR mapping spectrometer on Mars Express orbiter detected water-altered minerals or hydrated sulfates covering over 13,000 km2 area of Valles Marineris.
"Neutrons are produced when highly energetic particles known as galactic cosmic rays' strike Mars; drier soils emit more neutrons than wetter ones," mentions study author Igor Mitrofanov, principal investigator of the FREND neutron telescope, and scientist from the Space Research Institute of the Russian Academy of Sciences. Galactic cosmic rays (GCR’s) penetrate down to the surface with very few interactions, most of which take place down to 1m depth.
Dry soil emits larger epithermal neutrons flux (neutron escapes surface) than wet soil. Epithermal neutron flux are thought to be one of the most accurate methods to estimate hydrogen content in Martian subsurface. The data suggests very high content of hydrogen in soil, mean water equivalent hydrogen value as large as 40.3 wt% associated with geomorphological conditions inside VM.
The 41,000 square km region studied is about the size of the Netherlands and is in close proximity to Candor Chaos region is situated in the northern canyon area, is part of a radial graben system in Valles Marineris. The local Area of Neutron Suppression (LANS-C) sub area (-72.5° E, -7 °S) is about 41,000 square km (240km x 360 km) with a mean value WEH of 40.3% wt, which could be explained by presence of highly hydrated minerals or water ice filling the porosity volume of regolith. Of the four detected hydrated mineral locations inside VM, detected water enhancement of 7-13 wt% was observed in external and middle sub-areas LANS-A and LANS-B.
Moreover, hydrated magnesium sulphate such as meridianiite(MgSO ₄·11H ₂O) or epsomite (MgSO4·7H2O) can contain substantial amounts of H2O (62 and 51 wt%, respectively) (Wang et al, 2013). The Valles Marineris canyon floor depth and higher atmospheric pressure and extra shadows created by walls could result in morphological conditions that result in water ice preservation (Schorghofer and Aharonson, 2005).
Mean elevations inside LANS-A, B, and C sub areas decrease toward the centre with increasing water quantities. With a -1455m mean elevation of entire LANS, one may postulate a correlation between high WEH and surface depth on the canyon floor. If such a water-rich region could be melted passively with waste heat, thermal mining, and/or SiO2 aerogel cyanobacteria sheets, further regolith heat simulations and data analysis will help emulate local minerals, environmental flow (EF) conditions, melting rate, remediation schemes, and soil parameters to form a self sustaining lake.
Candor Chaos, central part of Valles Marineris (VM), holds great potential to become a settlement site to support life and humans. Higher resolution spatial imagery enabled from orbiting satellites with larger antennas and next-gen neutron detectors hold the potential to improve the water detection, accuracy, and mineral quality/classification. Novel airborne, surface, and space-based architectures could yield higher resolution data mapping of the canyon system to help guide the growth of the settlement, plants, and life on the canyon surface.
I. Mitrofanov, et al, The evidence for unusually high hydrogen abundances in the central part of Valles Marineris on Mars, Icarus, Volume 374, 2022, 114805, ISSN 0019-1035,