20/11/2024 Des veines d’eau liquide sur le planète Mars ?

Jusqu’ici, les rovers qui avaient exploré la planète Mard n’y avaient pas trouve d’eau, que ce soit dans la faibe atmosphère qui l’entoure, en surface ou à quelques décimètres de profondeur.

Meme si dans les millénaires précédent, elle avait et couverte d’eau, identifiable par les traces qu’elle avait laissé sur le relief, il n’en était rien resté, ne fut-ce pour entretenir une vie microbienne simple.

Les hydrographes qui étudient la plaète pensent que certans échantillons de sol martien, rapportés par les rovers, montrent que des sillons détectés à la surfe avaient pu contenir assez d’humidité pour y entretenir des microbes, dans des températures compatibles avec la vie. Les prochaines expéditions sur Marsas seront particulièrement chargées d’y rechercher, sinon encore des microbes, du du moins de l’eau fut-ce sous forme de traces.

Référence

Liquid Vein networks as habitats in ice-cemented ground on Earth and Mars: Effects of soil geometry and salts☆

H.G. Sizemore ^a, M.T. Mellon ^b and others

https://doi.org/10.1016/j.icarus.2025.116828Get rights and content

Highlights

• •We developed new SFCs describing the residual liquid in example“Martian” and “Antarctic” soils below T = 0 °C.
• •We calculated total liquid fraction, S_l, and refugia diameter, d_r, under Martian and Antarctic environmental conditions.
• •We defined new habitability thresholds based on these parameters: S_l > 5 % and (2) d_r > 1 mm.
• •Salts are likely the dominant factor controlling liquid availability in the icy permafrost of Mars and in Beacon Valley.
• •Phoenix-like soils poleward of 50°N with 1 wt% Mg(ClO₄)₂ produce S_l ∼ 6 % and d_r > 5 mm in the current Martian climate.

Abstract

We have carried out simulations of permafrost liquid fraction to investigate the historical habitability of Martian and Antarctic ground ice. These simulations are based on the development of new soil freezing curves (SFCs) for example Martian and Antarctic soils, and expand upon our previous investigation of the temperature history of shallow Martian ice (Mellon et al., 2024). We considered the effects of salt doping on both soil types, using magnesium perchlorate, Mg(ClO₄)₂, as an endmember low-eutectic-temperature solute representative of Mars, and NaCl as a high-eutectic-temperature endmember, approximately representative of solutes in the Dry Valleys of Antarctica. We applied our SFCs to calculate the total liquid fraction, S_l, and maximum liquid vein diameter (or refugia diameter), d_r, in the icy permafrost under relevant Martian and Antarctic environmental conditions, building on previous work that considered habitability limits in the context of temperature, T, and water activity, a_w, only. We defined habitability thresholds of S_l ≥ 5 % and d_r ≥ 1 μm, then examined which of four habitability metrics (T, a_w, S_l, d_r) presents the dominant limitation to shallow ice habitability in the Martian icy-permafrost environment and in the perennially sub-freezing environments of the Antarctic Dry Valleys. We also re-evaluated optimal landing site selection for Mars life and habitability exploration missions in this context.

We find that, without salts, neither of the examined soils produce habitable values of S_l or d_r below ∼ − 3 °C based on pore-confinement effects alone. The addition of 1 dry wt% NaCl extends the occurrence of habitable values of S_l and d_r to the eutectic temperature of −21 °C; the addition of 1 dry wt% Mg(ClO₄)₂ extends the occurrence of habitable values of S_l and d_r to the magnesium perchlorate eutectic temperature of −64 °C, well below the previously defined extreme metabolic limit of T = −40 °C. In both the Antarctic Dry Valley and Martian environments solute concentration is spatially variable and can occur locally at more or less than the 1 wt% scenarios we investigated. In the case of localized solute deficits, habitable S_l and d_r may not be achieved, even during summertime and high-obliquity temperature excursions. However, meeting the requirement of d_r > 1 μm and S_l > 5 % is surprisingly easy for silty to sandy soils with plausible salt doping in both the Martian and Antarctic summertime environments. Further, our simulations indicate that for soils found at the Phoenix landing site, 1 wt% Mg(ClO₄)₂ produces S_l ∼ 6 % and d_r > 5 μm poleward of ∼50°N in the current Martian climate.

Our new results re-enforce our previous landing site recommendations for Mars habitability missions (Mellon et al., 2024), indicating that progressively higher northern latitudes offer progressively better opportunities to sample “warmer” ice, which has met or exceeded multiple habitability metrics for extended time periods.