Investigation on the Absorption Bands Around 3.3 μm in CRISM Data

While analyzing NIR-IR CRISM data on a site in Oxia Planum area, in the view of the ExoMars2022 mission, absorptions around 3.3 µm were noted in some pixel spectra. Absorptions in the range 3.1–3.6 mm are under the spotlight in planetary contexts since hydrocarbons molecules show bands in this range. Consequently, we started to search eventual hydrocarbon compounds on Mars surface, using CRISM data in the range 3.2–3.4 mm. To date, methane has been the unique hydrocarbon detected on Mars. Like other hydrocarbons, methane shows absorptions around 3.3 mm. Hence, we begun the investigation on CRISM data, on that locations where methane was detected and where it could form on the basis of the mineralogy of the specific site. The datasets chosen for this study include some sites of observations in Oxia Planum area, Gale Crater and Nili Fossae area. Beside the study of CRISM IR data, in the event that some observed absorptions were related to methane, we tried to calculate a theoretical lower limit of detection for each observation in CRISM data. This was performed using the Planetary Spectrum Generator, simulating the CRISM spectra of the different sites, with the diverse concentrations of CH4. These simulations served to establish the relation between concentration and methane band depths, as seen by CRISM spectrometer. Then, mapping the Modified Gaussian Model (MGM) fit on CRISM data, we extracted the band parameters of the absorptions in the 3.3 µm spectral region. Aside rare, suspected absorptions, an artifact was highlighted. Therefore, we took measures to avoid, as more as possible, this artifact from the interpretation of the 3.3 mm absorptions: distribution of clusters of pixels not vertically stacked and a rather conservative threshold on depth value. As result, we found interesting clusters of pixels which spectra overcome the imposed threshold. Furthermore, the threshold value varies from one observation to another, in a range between 0.0136–0.0237, that would correspond to a range of theoretical lower limits of concentration between 180 and 600 ppbv. Despite all the precautions, we consider that part of these absorptions could still be an artifact. Nevertheless, the aim of this paper is to show that CRISM data can show theoretically absorptions of hydrocarbons, and methane, in such quantities that in some observations are compatible with the order of the methane spikes effectively detected on Mars. Even if this work does not confirm nor deny the occurrences of methane seepages or hydrocarbons in the investigated images, it shows a possible method for searching hydrocarbons in CRISM data and for assessing a confidence limit in the detection methane band in CRISM data.

Investigation on the Absorption Bands Around 3.3 μm in CRISM Data

Recently, the methane seepage detected by Mars Sample Laboratory (MSL) in the Gale crater area during 2013 was confirmed by methane detection by the Planetary Fourier Spectrometer (PFS). While analyzing NIR-IR CRISM data on a site in Oxia Planum area, in the view of a future comparison with data that will be collected by the Rosalind Franklin rover onboard the ExoMars2022 mission, a 3.3 μm absorption was noted in some pixel spectra. Since methane, like other hydrocarbons, shows absorptions in the range 3.1-3.6 μm, we begun to study this band in CRISM data to explore the possibility to look for seepages on Mars surface. The datasets chosen for this study, aside the site in Oxia Planum area, include some sites of observations on Gale Crater and other sites in Nili Fossae area. We used the Planetary Spectrum Generator to simulate CRISM spectra of the different sites, with the diverse concentrations of CH4 spikes. These simulations served to establish the relation between concentration and methane band depths, as seen by CRISM spectrometer. Then, mapping the Modified Gaussian Model fit on CRISM data, we extracted the band parameters of the absorptions in the 3.3 μm spectral region. Aside rare, suspected absorptions, an artifact was highlighted. Therefore, we have set a threshold on the depth to consider as depth of potential true absorptions, on the basis of the standard deviation (s) of absorption depth map. Finally, we concluded to favor as potential absorptions: distribution of clusters of pixels in the band mapping not vertically stacked and a threshold value >μ (average)+5σ (standard deviation) of the depth map. These threshold values set the lower limit for each observation on the methane concentration potentially detectable by CRISM. The threshold value varies from one observation to another, in a range between 0.0136-0.0237, that would correspond in a range of lower limit concentrations of 180 and 600 ppbv. We found interesting cluster of pixels which spectra overcome the imposed threshold. We still consider that part of them could still be a kind of unknown artifact. Nevertheless, the aim of this paper is to show that CRISM data can show potential absorptions of methane in such quantities that in some observations are compatible with the order of the methane spikes effectively detected in literature. Even if this work does not confirm nor deny the occurrences of methane seepages in the investigated images it shows a possible method for assessing a confidence limit in the detection of this band in CRISM data.

Extraction of aqueous minerals on Mars using CRISM based Targeted Reduced Data Records

Many scientific studies have been carried out to extract the aqueous mineral signatures on the surface of Mars, which has a record of all minerals such as silicates form by magmatic processes and aqueous minerals in the presence of watery environment. To observe these watery conditions, a visible/shortwave infrared mineral mapping camera on Mars Reconnaissance Orbiter (MRO) called Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is used. The aim of this research is to extract the aqueous minerals on Mars using CRISM sensor. Gale Crater is selected for this study because of its past liquid water history.Gale is ~154 km in diameter and centered near 5.3&deg; S, 138&deg; E. Gale Crater has an interior mound named as "<i>Aeolis Mons</i>", which is nearly 100 km wide and 5 km high, consisting of layered sulfates and phyllosilicates. The CRISM reflectance (I/F) targeted reduced data records data of Gale crater, FRT000233AC, centred at 4&deg;25' S and 137&deg;20' E with high spatial (18 m, 35 m / pixel) and spectral resolution (362&ndash;1020 nm (VNIR), 1002&ndash;3920 nm (IR), 655 nm / channel) with 545 bands is acquired for this study. The detection and quantification of minerals has been carried out by using a model called modified Gaussian model (MGM). MGM is an approach that uses modified Gaussians in wave number space to model absorption shapes and fits them to a reflectance spectrum.