# Hydration in the sulfate-bearing units, Gale crater, Mars

L. F. Lim, W. Rapin, Olivier Gasnault, S. Connell, R.C. Wiens, E. Dehouck,

P.-Y. Meslin, S. Schröder, R. Sheppard

► To cite this version:

L. F. Lim, W. Rapin, Olivier Gasnault, S. Connell, R.C. Wiens, et al.. Hydration in the sulfate-bearing units, Gale crater, Mars. Lunar and Planetary Science Conference, Lunar and Planetary Science Institute, Mar 2025, The Woodlands (Texas), United States. pp.1378. hal-05378346

HAL Id: hal-05378346

https://hal.science/hal-05378346v1

Submitted on 23 Nov 2025

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workspace average, leading to a median drillhole H₂O of 16 ± 7 wt%. Similarly, for Sequoia_drillhole (5 points), the median calculated H₂O wt% is 11 ± 1.5 wt%. However, we caution that these numbers are preliminary. The number of data points is relatively small and the abundances may be inflated by roughness.

Thus in both cases we see an H area enhancement of a factor of two in the drillhole LIBS spectra. Drill hole H signal has sometimes been found to exceed surface raster H signal in previous drill sites such as Cumberland (Schröder et al. 2015) in Yellowknife Bay or Rock Hall in the Murray formation, although not in Canaima. It has been proposed that changes due to dehydration in the Mars environment on a timescale of days may affect Perseverance abrasion patch samples (Connell et al., LPSC 2024) and fresh MSL drill holes might also be expected to expose higher hydration materials than long-exposed nearby surfaces. This is an area of active laboratory research (Connell et al., in review).

<figure><img src="image_2.png" /><figcaption>**Figure 3:** H₂O vs. MOC sum of oxides in the Sequoia workspace (no strong correlation)</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>**Figure 4:** H₂O vs. MOC MgO values in the Sequoia workspace</figcaption></figure>

*Hydration vs. MOC sum of oxides.* For the Sequoia workspace targets, the ChemCam MOC sum of oxides ranges from 81% to 93 wt%. The derived H₂O wt% values are not highly correlated with the sum of oxides on a point-by-point (R = -0.075) or a raster-by-raster (R = 0.25) basis (Fig. 3).

*Hydration vs. MOC MgO wt%:* In the Sequoia workspace, there is a positive correlation between the H₂O abundance and the ChemCam-derived MgO abundances from the same rasters (Fig. 4) consistent with much of the H₂O occurring in the Mg-sulfates.

**Future Work:** In addition to extending the LIBS hydration study to further ChemCam targets and pursuing laboratory investigations, we plan to look for correlations with orbital data. Spectral signatures of kieserite and polyhydrated sulfates (such as starkeyite) have previously been observed from orbit in certain locations in the layered sulfates in visible-near infrared reflectance by CRISM (e.g., Sheppard et al. 2021). Reflectance spectra such as those collected by CRISM are sensitive to bonding environments, meaning the hydration state of sulfate can be easily distinguished in laboratory quality data. We are investigating if the changes observed in the rover data can be distinguished within orbital data using characteristics such as width and depth of the hydration features in sulfate-bearing strata.

**Acknowledgments:** We gratefully acknowledge the MSL team and the MSL Participating Scientist Program for making this work possible.

**References:**

[1] Thomas, N. H., et al. (2020). *JGR Planets*, 125(9), e2019JE006289. [2] Chipera, S. J., *JGR Planets*, 128, e2023JE008041. [3] Rapin, W., Meslin, P-Y. (2017) *Spectrochimica Acta B*, 130, 82–100. [4] Maurice S. et al. (2016) *J. Anal. At. Spectrom.* 31, 863–889. [5] Tutolo et al., LPSC 2024 [6] Morrison et al., (2024) *Minerals*, 14, 773 [7] Pandey et al., (2025), this meeting [8] Rapin, W., Bousquet, B., et al. (2017). *Spectrochimica Acta B* 137, 13–22. [9] Schröder, S. et al. (2015) *Icarus* 249 [10] Connell S. et al. (2024), LPSC abstract #1773 [11] Connell S. et al. (2025), in review [12] Sheppard et al. (2021), *JGR* 126, e2020JE006372.