# Hydrous Components of Dusty Surfaces Inferred From Zhurong In Situ Observations

Qing Zhang, Mathieu Vincendon, François Poulet, Maxime Pineau, John Carter, Lin Guo, Zhaopeng Chen, Dawei Liu, Bin Liu, Xin Ren, et al.

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Qing Zhang, Mathieu Vincendon, François Poulet, Maxime Pineau, John Carter, et al. Hydrous Components of Dusty Surfaces Inferred From Zhurong In Situ Observations. Geophysical Research Letters, 2025, 52 (18), 10.1029/2025GL115266. hal-05288532

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# Geophysical Research Letters®

## RESEARCH LETTER

10.1029/2025GL115266

**Special Collection:**

Dust-related processes on Mars:
Observations, Simulations, and
Experiments

**Key Points:**

* We find that previously identified hydration features are robust against instrumental biases and associated with dusty surfaces

* Comparison of in situ and orbital observations suggests that the 1.9 µm hydration feature may be relatively common for Mars dust

* The 2.2 µm feature may be attributed to hydrated silica with two possible origins: aeolian deposits and/or in situ aqueous alteration

**Supporting Information:**

Supporting Information may be found in
the online version of this article.

**Correspondence to:**

J. Liu,
liujj@nao.cas.cn

**Citation:**

Zhang, Q., Vincendon, M., Poulet, F., Pineau, M., Carter, J., Guo, L., et al. (2025). Hydrous components of dusty surfaces inferred from Zhurong in situ observations. *Geophysical Research Letters*, *52*, e2025GL115266. https://doi.org/10.1029/2025GL115266

Received 6 FEB 2025
Accepted 4 SEP 2025

## Hydrous Components of Dusty Surfaces Inferred From Zhurong In Situ Observations

<figure><img src="image_2.png" /></figure>

Qing Zhang¹,²,³,⁴ ID, Mathieu Vincendon², François Poulet², Maxime Pineau⁵,⁶ ID, John Carter²,⁵, Lin Guo¹,³ ID, Zhaopeng Chen¹,³ ID, Dawei Liu¹, Bin Liu¹ ID, Xin Ren¹,³ ID, Jean-Pierre Bibring², Chunlai Li¹,³ ID, and Jianjun Liu¹,³ ID

¹Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China, ²Institut d'Astrophysique Spatiale, CNRS, Université Paris-Saclay, Orsay, France, ³School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, China, ⁴Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, China, ⁵Aix-Marseille University, CNRS, CNES, LAM, Marseille, France, ⁶University Lyon 1, ENS de Lyon, CNRS, Laboratoire de Géologie de Lyon - Terre Planètes Environnement, UMR, Villeurbanne, France

**Abstract** The ubiquitous hydration features observed by Zhurong rover provided new insights into Mars aqueous paleoenvironments. However, the impact of the Martian dust was not previously discussed. Here, we conduct a joint analysis of the Multispectral Camera and Short-Wave Infrared data to constrain the surface composition. The results show that these hydration features are robust against instrumental biases and associated with dusty surfaces. The 1.9 µm feature is shared between Zhurong and Perseverance landing sites, suggesting that it may be relatively common for Mars dust. The discrepancy between in situ and orbital data could be mainly due to atmospheric effects. The 2.2 µm band is more specific to the Zhurong landing site, and spectrally consistent with hydrated silica regarding the band shape and position. We propose two possible processes for the origin of such hydrous components at Zhurong landing site, aeolian deposits from nearby cones and/or in situ aqueous alteration products.

**Plain Language Summary** The Zhurong rover landed in a dusty region, providing a unique opportunity to measure in situ spectral signature of surface dust. Using data from the Zhurong rover, we find that the dusty surfaces commonly exhibit two absorption bands at 1.9 and 2.2 µm related to hydration. This contrasts with previous knowledge from the orbiter that the dust is featureless in the near infrared. A comparable 1.9 µm band of dusty surfaces from Zhurong and Jezero Crater suggests that this feature may be relatively common for Martian dust. The 2.2 µm band observed at Zhurong landing site could be mainly attributed to hydrated silica by comparing observations with laboratory data. These results suggest that the identified hydrous components in dusty surfaces cannot directly point to the presence of aqueous activities at Zhurong landing site, which could also be aeolian deposits from nearby regions. These results have implications for understanding dust sources and/or surface aqueous processes on Mars.

## 1. Introduction

On 15 May 2021, the Zhurong rover landed in southern Utopia Planitia on Mars (109.925°E, 25.066°N) (J. Liu et al., 2022), where the surfaces are mantled by dust as inferred from the orbital visible/near infrared and thermal spectra (Ody et al., 2012; Ruff & Christensen, 2002). The ubiquitous Martian dust is considered as spectrally featureless in the near infrared (NIR) and would obscure the spectral signatures of underlying materials when their composition differs (Bibring et al., 2006; Mustard et al., 2005; Poulet et al., 2007). The presence of dust may limit our knowledge on the surface composition of Martian northern lowlands. Zhurong conducted in situ spectral observations with the Multispectral Camera (MSCam) and Short-Wave Infrared (SWIR) spectrometer to identify the surface mineralogy and reveal the geological history of landing site. Surprisingly, in situ observations show hydrous absorption bands at 1.9 and 2.2 µm observed on all kinds of surface targets along the traverse including rocks, soils and dunes. What causes the discrepancy between orbital and in situ observations remains unclear. These hydrous features were variously interpreted as gypsum, hydrated silica as well as allopheane or imogolite (Ju et al., 2024; C. Liu et al., 2022; Y. Liu et al., 2022; Liu et al., 2023; Qin et al., 2023; Zhao et al., 2023). The hypotheses proposed to explain the origins of such hydrated phases all suggest that they are the product of in situ

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aqueous alteration, either from groundwater (Y. Liu et al., 2022) or from as mineralized remnants of a frozen ocean (C. Liu et al., 2022).

However, the precise nature of the mineral mixture that could explain the observed spectral features remains subject to discussions, as well as the mechanisms for the aqueous alteration. Here, we conduct a joint analysis of in situ SWIR and MSCam data to provide additional clues about the Zhurong landing site mineralogy. First, we explore in detail potential instrumental or calibration biases that may affect the hydration features. Then, we analyze the impact of dust. Indeed, the links between dust and mineralogy inferred in the Zhurong area had not been previously discussed in detail. Dust is the finest grained (<10 µm), upper component of the soil and is rich in ferric oxides responsible for its red color and visible-range absorption feature. Dust is bright and its presence can substantially increase the surface albedo (Bell et al., 2000; Morris et al., 2006). Dust should be one key contribution to the Zhurong collected spectra, which are all acquired from the undisturbed red-toned and relatively bright surfaces. Actually, the MSCam calibration target observations show some dust deposition at the Zhurong landing site, without obvious dust cleaning events during the first 300 sols observations (Zhang et al., 2023). In this study, Zhurong visible and NIR data are notably compared with other observations from the Perseverance landing site and from orbit to assess the role of dust. Finally, we put these different constraints together to discuss the potential mineral phases and their possible formation pathway.

## 2. Data and Methods

### 2.1. Reflectance Spectra

The payload onboard Zhurong rover includes the MSCam and SWIR, which can acquire reflectance spectra ranging from the visible to the near-infrared. The MSCam uses a filter wheel to provide multiband images in the 0.48–1.0 µm range with bandwidths of tens of µm (Yang et al., 2022). These bands can be used to semi-quantitatively distinguish between nanophase ferric oxide (np-Ox) rich dust and less dust-coated surfaces (Bell et al., 2000). The SWIR point spectrometer adopts an acousto-optic tunable filter to disperse the light ranging from 0.85 to 2.4 µm with a spectral resolution of 3–12 nm, enabling the identification of a wide variety of minerals including primary and secondary minerals (Xu et al., 2021). The two data sets are thus highly complementary to investigate the mineralogical component of surface materials.

The radiance data measured by the two spectrometers were calibrated to reflectance factor with their calibration targets (Liu et al., 2023; Zhang et al., 2022). The widespread hydration features from the SWIR observations have not been measured by orbital spectroscopy in the region where Zhurong landed (Ody et al., 2012; Wu et al., 2021). Besides, the SWIR calibration targets also have some subtle absorptions in the longer wavelengths (Figure S1 in Supporting Information S1). Thus, we first assess whether these ubiquitous hydration features are caused or modified by instrumental and/or calibration artifacts (Text S1 and Figure S1 in Supporting Information S1). A detailed analysis of assumptions regarding the use of calibration targets does not reveal any related spectral artifacts. We find that while the 1.9 µm absorption band is influenced by instrumental temperature, it appears to reach a robust value at low temperature. We do not observe such an instrumental effect on the 2.2 µm band, which appears to be insensitive to the instrumental temperature.

The collected SWIR spectra are expected to result from surface mixtures due to the relatively wide field-of-view (FOV) of 36.5 mrad (spot size of ~10 cm at the typical 3 m imaging distance), which is far wider than Laser Induced Breakdown Spectroscopy (LIBS) ablation region with sub-millimeter scale spot (Qin et al., 2023; Xu et al., 2021) (Figure S2 in Supporting Information S1). The spatial resolution of MSCam acquired images is 0.45 mm/pixel at 3 m distance (Yang et al., 2022). The two instruments sometimes conducted conjoint observations of the same surface targets (Figures 1b–1d). For these co-observations, the Micro-Imager (MI) image is first co-registered with the MSCam image based on the surface context. Then, the FOV of SWIR in the MSCam image can be estimated giving the facts that the SWIR and MI share the same optical axis and the FOV of SWIR is 5 times larger than that of MI (Xu et al., 2021). We calculated the mean spectrum of the MSCam measurement within the FOV of SWIR and merged the two spectra (Table S2). The absolute reflectance discrepancies between the two data sets were normalized with the overlapping bands in the 850–950 nm wavelength range (Figure 1a). Data description and selection can refer to the Text S2 in Supporting Information S1.
<figure><img src="image_3.png" /><figcaption>**Figure 1.** Conjoint analysis of Short-Wave Infrared (SWIR) and Multispectral Camera (MSCam). (a) Examples of SWIR and MSCam co-observation merged spectra of (b) dune, (c) and (d) rocks and soils. Low opacity envelopes around each spectrum represent standard deviations of MSCam data within the FOV of SWIR. Red circle illustrates the SWIR FOV, overlain on MSCam RGB color restoration image. Panels (e) and (g) are 1.9 and 2.2 µm absorption bands, respectively. The smoothed spectrum (blue line) overlays on unsmoothed raw spectrum (gray line). The gray dashed line is the continuum calculated by a linear regression from the absorption shoulders marked with red crosses. Panels (f) and (h) are two-Gaussian fit for the 1.9 and 2.2 µm absorption bands, respectively. The correlation coefficient of each Gaussian deconvolution is noted.</figcaption></figure>

## 2.2. Absorption Bands Characterization

The 1.9 and 2.2 µm absorption bands were observed from all kinds of surface targets (C. Liu et al., 2022; Y. Liu et al., 2022; Qin et al., 2023). Before characterizing the hydrated absorption bands, all the SWIR spectra were processed by the following steps. First, spikes in the original spectra were corrected using a method described in Carter et al. (2013) and then the de-spiked spectra were slightly smoothed by the wavelet denoising filter (Figures 1e and 1g). Then, the continuum was removed by dividing a linear line, which was defined as a linear regression from both sides of the absorption bands (Le Pivert-Jolivet et al., 2023). Finally, we adapted a two-Gaussian model to better fit a given absorption band and characterize the band asymmetry (Figures 1f and 1h). Given the low signal-to-noise ratio, we only fitted part of the 1.9 and 2.2 µm absorption bands (1.89–1.98 µm for the 1.9 µm band and 2.15–2.28 µm for the 2.2 µm band) to obtain a band minimum as robust as possible. To eliminate the influence of noise, only data with fit correlation coefficients greater than 90% and band depth of each Gaussian function greater than 0.01 were used to measure the spectral parameters (Figure S3 in Supporting Information S1).

For each absorption band, we measured the band position, band depth and band depth ratio. Band position and depth are the position and depth of minimum reflectance, respectively. Band depth ratio can be used to quantify the asymmetry of the absorption band, which is measured by the band depth ratio of the two Gaussian functions
<figure><img src="image_4.png" /><figcaption>**Figure 2.** (a) Mean spectrum of all the Multispectral Camera and Short-Wave Infrared (low temperature observations) co-observations is shown in red, with the light red envelope representing the standard deviations of all the data. The four vertical lines illustrate the typical absorption features in merged spectra. For comparison, two available OMEGA orbital observations from the Zhurong landing site are shown in grayscale lines (black line is ORB0368_5 at $L_s = 29^\circ$ and gray line is ORB6612_5 at $L_s = 216.5^\circ$). The ORB0368_5 observation is obtained while atmospheric dust opacity is low but it shows a faint water ice signature at 1.5 µm. The ORB6612_5 observation is obtained during the dusty season and with a lower spectral sampling due to the aging of the detector, but it does not contain detectable water ice signature. The blue spectrum is SuperCam Infrared Spectrometer observation of a highly dusty surface target Naltsos in Jezero Crater (Mandon et al., 2023). (b), (c), (d) and (e) are continuum removed absorption bands of 0.53, 0.95, 1.9 and 2.2 µm, respectively.</figcaption></figure>

used to represent a given band (Figures 1f and 1h). These parameters were plotted against each other and compared to the same parameters from spectral library minerals. Specifically, we focused on the minerals that have a 2.2–2.25 µm absorption band, including hydrated silica, montmorillonite, gypsum, jarosite, allophane (Figure S4 in Supporting Information S1). The various crystallinities of hydrated silica and measurements in different environments are from Chauviré et al. (2017, 2021) and Pineau et al. (2020). Other spectra are available via the USGS (Kokaly et al., 2017) and RELAB spectral library. The detailed sample IDs are given in Supporting Information S1 (Table S3). These library spectra were first resampled into SWIR bands and then added the same level of noise as SWIR. The noisy library spectra were processed in the same steps as done with SWIR.

# 3. Results and Discussion

## 3.1. Spectral Characteristics: Description and Comparison With Other Observations

The in situ collected spectra are characterized by a red slope in the visible, a clear (>10%) absorption feature at ~0.53 µm, and three faint (a few %) absorption bands at ~0.95, ~1.9 and ~2.2 µm (Figure 2). The 1.4 µm hydroxyl- and H₂O-related absorption is too weak to be identified. The red visible slope and the deep 0.53 µm absorption band are mainly due to nanop phase ferric oxides, suggesting the presence of dust (Bell et al., 2000), which is consistent with orbital observations and the bright and red-hued surfaces in color composite images (Figure 1). Given that the left and right shoulders of 0.95 µm absorption band are anchored at ~0.8 and 1.2 µm, respectively, the 0.95 µm absorption feature is possibly attributed to the presence of ferric bearing materials, rather than ferrous bearings which generally exhibits the wider 1 µm and 2 µm band (Dehouck et al., 2017; Viviano-Beck et al., 2014). The presence of ferrihydrite in dust was suggested by Valantinas et al. (2025). The faint absorptions at ~1.9 and 2.2 µm with band depth less than 4% are attributed to some water/hydroxyl-bearing mineral phases.

The Zhurong-collected spectra share some similar spectral features with orbital observations of the landing area by OMEGA/Mars Express: both exhibit a red slope in the visible and absorption bands at ~0.53 and 0.95 µm (Figures 2b and 2c). Subtle differences are noted in the NIR range where in situ SWIR observations exhibit faint absorption bands at ~1.9 and 2.2 µm, while the orbital data have not captured these signatures (Figures 2d and 2e). The difference may be due to the influence of the atmosphere on several levels. First, artifacts introduced by the
empirical volcano-scan atmospheric correction of the wide 2 µm CO₂ band (Langevin et al., 2006; Wiseman et al., 2016) may prevent identification of shallow bands in that range. Second, we note that the presence of water ice clouds during the Aphelion Cloud Belt season (Smith, 2008) may also interfere with the 1.9 µm feature of surfaces regarding the latitude of Zhurong landing site. Third, faint surface signature may also be more difficult to identify from orbit due to contrast decrease related to atmospheric aerosols scattering (Vincendon et al., 2007). Similarly, atmospheric effects may also explain discrepancies between orbital and in situ data at 1.9 µm at the Perseverance landing site (Mandon et al., 2023). Actually, the in situ 1.9 µm band of dusty surfaces observed by the SuperCam Infrared Spectrometer (IRS) observations is strikingly similar to that observed by the Zhurong rover (Figure 2d).

The slightly fainter 2.2 µm absorption band is absent in orbital data, nor in Perseverance observation of a dust covered target (Figure 2e). In that wavelength range a contrast decrease due to atmospheric scattering is the most plausible atmospheric explanation to the difference between orbital and in situ data. However, the difference between landing sites suggests the presence of some different water-bearing minerals in the dusty surfaces of these two regions. This suggests that the hydrated phases responsible for the 2.2 µm feature specific to the Zhurong landing area are not a component of the globally well-mixed dust. It could be either physical weathering products derived from local/regional hydrated outcrops or formed by different post-depositional aqueous alteration such as induration processes. One the other hand, the in situ SWIR and SuperCam IRS observations of a comparable 1.9 µm band (Figure 2d) not detected from orbit suggest that this feature may be relatively common for Mars dust and may also be present elsewhere where orbital data do not show such a feature. Additional evidence for a widespread presence of hydration in dust is found in Curiosity observations obtained at Gale crater (Meslin et al., 2013). Whether this hydration feature is contained within the highly mobile global dust, or is caused by some more local indurated dust, is however not yet known without ambiguity from available data. Perseverance observations notably show that the magnetic component of the dust deposited from the atmosphere does not contain a detectable 1.9 µm feature (Mandon et al., 2023). The 1.9 µm band is a combination of bending and stretching modes of H₂O and its possible widespread presence within dust may have some implications on the interpretation of the ubiquitous 3 µm hydration feature of the Martian surface (Audouard et al., 2014), that has been attributed to OH-bearing material in the absence of 1.9 µm signature (Beck et al., 2015).

## 3.2. Potential Hydrated Phases in Dusty Surfaces

Due to some uncertainties regarding the reliability of the 1.9 µm band depth as discussed in Supporting Information S1 (Text S1), and the fact that this band may be relatively ubiquitous (see previous section), we mainly used the 2.2 µm feature to discriminate the potential hydrated phases specific to the Zhurong area. The 2.2 µm absorption band is a diagnostic feature, attributed to the Si-OH or Al-OH vibrations and H₂O combinations and overtones in some sulfates (Clark et al., 1990). To further discriminate the different phases, we evaluated the shape of 2.2 µm absorption band with band minimum position and band asymmetry parameter. In this parameter space, different mineral phases can be better separated from each other (Figure 3). Most of SWIR observations exhibit the 2.2 µm band minimum position ranging from 2.23 to 2.25 µm and relatively symmetric absorptions, and generally fall in the range of hydrated silica, suggesting that the observed 2.2 µm absorption features could be possibly mainly attributed to hydrated silica. However, the Zhurong LIBS does not provide any favorable information. We note that the collected LIBS spectrum of each target is the average value of 60 single-shot spectra (Luo et al., 2024), which makes it difficult to tell whether the collected spectrum represents the outer dusty layer and/or underlying rock layer. The soil and dune targets representing the aeolian materials do not show an apparent increase in Si compared to the rock targets (Figure S5 in Supporting Information S1). This discrepancy may be due to the presence of silica-enriched rinds on rocks (Q. Zhang et al., 2024).

It is challenging to infer whether other hydrated phases are also present from the SWIR spectra alone. The sulfur signal detected from LIBS in soils and dunes and their strong correlation with calcium suggests the presence of calcium sulfates (Y. Zhang et al., 2024). Further north at higher latitudes (>1500 km distance), orbital evidence for the presence of calcium sulfates has also been suggested (Carter, Riu, et al., 2023; Stcherbinine et al., 2021). We have performed a linear mixing of hydrated silica and gypsum. The results show that mix of the hydrated silica with a few to tens of percents of gypsum may remain compatible with observed spectral signature (orange three-pointed star in Figure 3). Note also that sulfates and hydrated silica are the two most commonly found hydrated phases in the northern plains from orbital studies, sometimes at close proximity or as mineral mixtures (e.g., Pineau et al., 2024). Other hydrated phases may thus also participate to the observed 2.2 µm band with minor
<figure><img src="image_5.png" /><figcaption>**Figure 3.** Diagram of the 2.2 µm band minimum position as a function of the 2.2 µm band depth ratio to differentiate the minerals. Different colors and shapes denote different phases. Linear mixtures of hydrated silica and gypsum in this parameter space are plotted for comparison with a step of 10% increasing of gypsum. The error bars correspond to the uncertainty determined with shifting the continuum anchor points with two spectels.</figcaption></figure>

proportions. There are a few outliers in the SWIR data set with their band center shifting to the shorter wavelength, suggesting that other phases in these surface targets may have a relatively higher proportion. Collectively, for most surface targets, the observed 2.2 µm absorption bands are however primarily consistent with hydrated silica.

### 3.3. Origin of Hydrous Components

The origin of hydrated minerals observed at the Zhurong landing site is ambiguous as the collected spectra are mainly from the undisturbed dusty coverings, that do not seem to be associated with underlying rocks. Thus, the origin of the hydrated mineral phases could be either detrital or authigenic. The surface albedo of Zhurong landing area is brighter than the less dust-coated dark regions but darker than the same dust-coated regions like Tharsis (Putzig et al., 2005; Vincendon et al., 2015). Albedo variations indicate that the upper surface of Zhurong landing site may be a mixture of globally well-mixed fine dust and regional and/or local materials. In line with this hypothesis, the spectral data collected by Zhurong rover reveal the simultaneous presence of a 1.9 µm band that may be associated with well-mixed dust and a 2.2 µm band that may correspond to more regional/local properties. Our analysis suggests that this local component of the dusty surfaces may be rich in hydrated silica mixed with some calcium sulfates. Martian atmospheric dust has been known to be enriched in sulfur and chlorine based on orbital and in situ observations from different sites (Berger et al., 2016; Bish et al., 2013; Yen et al., 2005). The deposited well-mixed fine dust could be one potential source for sulfates that may be present in the dusty surfaces.

There are a few potential scenarios that can be proposed to explain the presence of hydrated silica: detrital and/or authigenic materials. Both scenarios were also proposed to explain the presence of hydrated silica in the aeolian sediments globally around Mars (Sun & Milliken, 2018).

In one possible scenario, the occurrence of hydrated silica at the Zhurong landing site is associated with aeolian silica deposits from nearby regional sources. Hydrated silica has been identified from northern plains typically associated with cones (Carter, Pineau, et al., 2023), which have been interpreted as mud volcanism from the morphological perspective (Broz et al., 2023; Ivanov et al., 2014). The cone is one of the most typical landforms around the Zhurong landing site. The morphological characteristics of cones around the landing site also suggest the nature of mud volcanism (Huang et al., 2022; Ye et al., 2021; J. Zhang et al., 2024). The observed hydrated
silica feature along the traverse may thus be physically weathered and transported from nearby cones, where the nearest cone is just about 6 km away from the landing site. No high-resolution CRISM data is available however to confirm the existence of alteration in these cones. In this context, the observed hydration features are not necessarily indicative of aqueous alteration occurred at the Zhurong landing site but provide insights into the dust source in these regions.

An alternative explanation for the presence of hydrated silica is that the dusty covering materials have experienced chemical weathering locally. Hydrated silica is a common alteration product of basaltic rocks under a wide variety of temperature, pressure and fluid conditions. The silicates release silica when they are subjected to even minor degrees of aqueous alteration. Silica then precipitates from an oversaturated solution (Horgan et al., 2017; McLennan, 2003; Pan et al., 2021; Pineau et al., 2020; Smith et al., 2013). The deposited dust provides silicate materials and only minimal water is needed for triggering the chemical reactions. The presence of transient liquid surface fluids at the Zhurong landing site is also supported by the surface morphological properties of dunes, which exhibit cemented crusts, cracks, aggregates and polygonal ridges. The water may form as temperature decreases in the atmosphere a thin transient water film on the deposited dust materials that enable chemical weathering (Liu et al., 2023; Qin et al., 2023). Such an interpretation may have the implication for the late-stage aqueous conditions. While the presence of water only suggests that the surface condition is favorable for the formation of hydrated silica, current data do not enable to further distinguish among these scenarios, whether the putative hydrated silica is formed by in situ aqueous alteration at the Zhurong landing site or from aeolian deposit or a combination of both processes.

## 4. Conclusions

In this work, we conduct a joint analysis of SWIR and MSCam observations to investigate the surface composition of the Zhurong landing site. The results show that the widespread hydration-related absorption bands at 1.9 and 2.2 µm are robust against instrumental biases. In more detail, the 2.2 µm band is found to be insensitive to instrumental temperature, while the 1.9 µm band is influenced by instrumental temperature but appears to be robust at low temperature. The visible and NIR spectra show that these hydration features are ubiquitously associated with dusty surfaces. The 1.9 µm feature is comparable in terms of band depth and shape with that observed by SuperCam IRS over dusty surfaces, suggesting that this feature may be relatively common for the Martian dust despite the fact that it is not commonly detected from orbit. The discrepancy between in situ and orbital observations may be mainly caused by atmospheric effects. The 2.2 µm absorption band is more specific to the Zhurong landing site and suggests a local component to dusty surfaces. For most observations, the shape of this 2.2 µm band is mostly consistent with hydrated silica by comparison with laboratory spectra. Other phases may also be present notably at a low abundance. Given the hydration features in the dusty surfaces, we propose two potential processes to explain the presence of hydrated silica at the Zhurong landing site, either aeolian detrital deposits derived from nearby cones' materials or in situ aqueous alteration products. This work may provide important clues to the dust source of Zhurong landing site and/or late-stage aqueous alteration environment.

## Data Availability Statement

All Zhurong MSCam and SWIR data used in this work are available at https://moon.bao.ac.cn/web/enmanager/mars1. A table of the observations used and details for accessing the data are provided in Supporting Information S1 (Text S2) and Tables S1 and S2.

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## Acknowledgments

The authors would like to thank the editor Kevin Lewis, reviewer Melissa Rice and one anonymous reviewer for their thoughtful and constructive reviews that significantly improved the manuscript. We would like to thank the Tianwen-1 payload team for mission operations and China National Space Administration for providing the Tianwen-1 data that made this study possible. The data used in this work are processed and produced by Ground Research and Application System (GRAS) of China's Lunar and Planetary Exploration Program. This research utilizes spectra acquired by John F. Mustard and Janice L. Bishop with the NASA RELAB facility at Brown University and USGS spectral library. This study is funded by the National Key R&D Program of China (2022YFF0503204) and two co-authors are funded under the Agence Nationale de la Recherche (ANR, France) (Grant PALEOSILICA ANR-20-CE49-0013). Q.Z. is also supported by International Cooperation Training Program from the University of Chinese Academy of Sciences.
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