Follow the Water... on Mars

Mars shows evidence of having had watercourses, lakes and even possibly an ocean in its Northern Hemisphere (Ocean Borealis). What happened to cause the strong depletion of its atmosphere and the disappearance of its interior magnetic field? Recent observations show that there is still much to learn about the history of water on Mars. Water ice was detected in mid-latitudes, which is unexpected according to current models. Another unusual piece of evidence was the recent detection of large quantities of hydrated silicates (such as opals) in regions at low latitudes. Some selected fluvial-marine environments and ancient coastal regions were the subject of our study, particularly the mineralogical component.

Two indicators are the morphological evidence that reveals an active hydrosphere with liquid water flow and the probable existence of an ocean. The deltaic lobes record possible interactions between watercourses and a potential giant water body on Mars. Satellite imagery of Mars showing desiccated river channels and ancient crater lake beds insinuate that the planet was warmer, wetter, and more dynamic in its ancient past than it is today. However, we have little idea how much water there was on Mars, what was its chemistry and how long it persisted. Multiple ocean shorelines have been proposed that encircle the northern plains of Mars (Carr+2003; Dickeson+2020). Past oceans would imply many constraints on the climate, habitability and hydrological planetary evolution. Recent detections of water ice at the Martian low latitudes (Xiaoguang+2023) and also of an important amount of highly hydrated minerals (like opals) at low latitudes (Sun+2003) , clearly show that the history of water on Mars must be re-addressed.

Space-based datasets were crucial to reach the goals of this present study. This relevance was two-fold: the exploration of the selected fluvial-marine environments and the ancient shorelines of Borealis Ocean in great detail, for what we used datasets of high-resolution cameras (HRSC from Mars Express, CaSSIS from ExoMars, CTX and Hirise from MRO) and hyper spectral instruments as OMEGA from MEX and CRISM from MRO in order to perform reflectance studies.

The datasets from OMEGA/MEX and CRISM/MRO enabled us to capture the known spectral diversity of the surface, and allowed us to successfully highlight and differentiate between locations with differing spectral signatures.

Recent visible to short wavelength infrared (VSWIR) orbital observations of Mars revealed widespread and diverse minerals present on the surface that record a complex history of changing geologic processes and climatic conditions. Spectral signatures indicate a wide range of primary and alteration minerals that have been detected in the analyses of data from OMEGA (Bibring+2004) instrument onboard Mars Express and CRISM (Murchie+2007) instrument on board the Mars Reconnaissance Orbiter (MRO) (Zurek&Smrekar,+2007).

Constraining the nature and distribution of both primary and secondary mineralogy on the surface of Mars is central to understanding igneous processes that formed the crust, and subsequent alteration of it by liquid water on the surface or in the subsurface and by impacts and exposure to the low pressure atmosphere of Mars. OMEGA and CRISM measure the VSWIR to mid-infrared portions of the spectrum (0.35–5.2 μm and 0.362–3.92 μm, respectively).

The OMEGA instrument has a spatial sampling ranging from 350 to 10,000 m/pixel depending on the orbital altitude and a set of 352 bands or 400 bands (sampled at 7.5 nm from 0.35 to 1.05 μm,14 nm from 0.94 to 2.70 μm, and ~21 nm from 2.65 to 5.2 μm). CRISM can be targeted with a high spatial sampling of 18-36m/pixel, or a survey mode at 100 or 200m/pixel. CRISM targeted observations have hyper spectral resolution (544 bands, sampled at 6.55 nm), while survey mode spectral resolution can range from 72 to 261 bands depending on the observation mode, with sampling density varying from 53.4 nm between channels at sparsely sampled wavelengths to contiguous sampling at 6.55 nm/channel.

In the framework of the present study we searched for serpentines, olivine, clays and hydrated silicate mineral deposits in some selected fluvial-marine Martian environments and old shorelines from ocean Borealis, water ice-deposits in some designated shield volcanoes edifications and craters.

The areas of interest covered in this study are: the deltaic fan of Isara Valles in the region of Menmonia- -5.31755°, Lon: -146.15593; Mars Vallis- 14.31227°, Lon: -177.22114; the deltaic fan of the Camichel crater- Lat: 2. 3152°, Lon: -51.62544°; the deltaic fans of the semi-confined basin in the northern region of Elysium Mons- Lat: 32.50897°, Lon: 148.99952°; the deltaic fan in the crater near the dichotomous line of Isidis Basin- Lat: 26.94654°, Lon: 76. 05766°; the large crater located in Syrtis Major to the southwest of Isidis Basin- Lat: 21.00273°, Lon: 63.01488° and the progressive delta in the Margaritifer Sinus region- Lat: -23.4507°, Lon: -12. 20301°. These regions were chosen on the basis of their possible genesis (fluvial-marine or lacustrine) represented by their deltaic, fluvial and lacustrine alluvial morphology which can be identified using Digital Elevation Models (DEM), and by the presence of hydrated minerals detected by surface reflectance analysis.

Our work in short:

• We Identified and characterized morphological evidence associated with fluvial-marine environments on Mars and their relevance to constrain and characterize possible Martian old shorelines of Ocean Borealis
• We used OMEGA spectra datasets from Mars Express and CRISM/MRO as well, to detect and characterize specific minerals in old fluvial-marine systems on Mars surface. The methodology used was based in the diverse reflectance properties of the minerals we intended to study
• We used Exomars/TGO CaSSIS instrument to perform detailed geologic studies of minerals on Mars. A late-stage formation of hydrated minerals on hydrothermal sites has the potential to rewrite the history of water on the planet (Jakosky+2021). Also, the geochemical study of volcanic edifications in their regional context is particularly relevant for the reconstruction of paleo climate.

• We built several maps, DTM and mineralogical maps (Jaumann et al., 2007, Carter et al., 2023) of the selected regions on the ancient sea shorelines and surface water flows using high-definition images from HRSC, OMEGA, CaSSIS and MRO/CRISM, performing identification and interpretation of morphological evidence associated with fluvial-marine environments (Bhardwaj+2021).