*5.1.4 Lenticular and conical/tubular structures*

MAHLI images taken at Sol 869 show that the lenticular lozenge-shaped "rice grains" observed on brushed surfaces at Sols 809 and 880 (Mojave target), not only occur "on the surface" as harder and whitish structure, but massively affect the entire outcrop, covering about 50% of the lithological mass. Previously, these structures have been interpreted as mineral deposits, e.g. of Gypsum or Jarosite (NASA reports), but subsequently, due to the lack of sufficient amount of crystal, they were interpreted as pseudo-morphic crystals originating from amorphous substances.

In particular, the mineralogical composition of Mojave 2 (Sol 880) shows, in respect to the previous investigated rocks, a variation in mineral composition, exhibiting significant amounts of amorphous material (54%) and minor amount of Plagioclase (24%), Magnetite (4%), Hematite (4%), Jarosite (4%), Phyllosilicates (5%) and Fluorapatite (5%). Such data paradoxically suggest the coexistence of both oxidising (Hematite) and reducing (Magnetite) environments, as well as acidic (Jarosite) and neutral (Fluorapatite) components. Chemical data of this sample suggests the following composition: SiO2 (49%), FeO (16%), MgO (4%) CaO (4%) and Al2O3 (11%), together with other minor components, including Magnetite and Phosphorous [2].

Some of these minor components and minerals, such as Apatite, Magnetite, Ni, Zn and Br (from Curiosity APXS results; in [7]), found at Mojave target, on Earth are generally associated with microbial activity and stromatolites [50, 57] and suggested by AFL report as possible biosignature [58].

Given the lack of mineralogical (CheMin) or chemical (APXS) evidence for calcium sulphates in the Mojave 2 sample (Sol 880), it was assumed that these lenticular bodies represent, on the basis of their morphology, i.e., lenticular gypsum crystals laths, light color compared with the host rock, and penetration vertically into the bedrock, crystals laths that were formed syndepositionally with the Murray mudstone and were later re-dissolved by post depositional fluid flow, forming pseudo-morphic microcrystalline or amorphous substance of unknown composition [2, 7].

It should be noted that the occurrence of microbially precipitated fluorapatite is reported in Jurassic phosphate stromatolites by Sànchez [57] and it is also known that biomineralization processes could give Biologically Induced Mineralization (BIM) and Biologically Controlled Mineralization (BCM), where magnetite is one of major components [59]. Moreover, such structures were found in association with the previously described problematic diagenetic features [55, 60, 61], and hence, a number of controversial features are suggestive of possible biogenic shapes.

Morphological analysis of MAHLI images at sols 809 and 889 (at Mojave1 and Mojave2, respectively) reveal that the "lozenge-shaped sulphates" [51] show chaotic, mainly fusiform/filiform, septate, curved shape; some of which are in relief and resemble terrestrial microalgae (**Figures 8** and **9**).

In particular, considering their shape and dimension, we investigated the structural similarities with Dasycladales algae, giant filamentous Cyanobacteria or Euglenoids. This biological interpretation could be supported by the occurrence of two adjacent 'bright' bodies, present in the same image (Sol 880; **Figure 9**, features 3 and 4). Occurrence in the same target of spherical cross sections (having sharp inner surface and irregular outer edge), could be related to other cones, although less evident and in small amounts (**Figure 8**, Cn and R features). Another conical body, photographed by Opportunity at Meridiani Planum, shows a differentiated skeletal structure in transverse section (a conical thallus?), and possible regular radial laterals attached (of aspondyl type? **Figure 10**). In addition, images at Sol 1273 show transverse and oblique sections of a tube-like bodies associated with regularly jagged discontinuities of their shells (**Figure 11**; features 1–3). Hence, the variety of shapes, present which include septate filamentous structures, is of great biological interest and do not suggest crystal-type structures; and are worthy of morphometric investigation (**Table 2**, **Figure 12**), the results of which are reported in the following section.

### **5.2 Morphometric results**

#### *5.2.1 Euclidean morphometry*

The metric data for each image is summarized in the upper section of **Figure 13**. There was considerable variation in all metrics among images with the exception of the fit of lengths to a log-normal distribution, the KS tests suggesting that this distribution fitted the objects of interest in all images. V/M ratio varied from a maximum value of 1.08 (Jar-1) indicating a random distribution of profiles, to a minimum of 0.32 (Euglena) suggesting the majority of profiles exhibit a degree of uniformity in their distribution. Variation in length and width also varied among images being least in the Martian sample and Terrestrial Euglena and greatest in the alga Gymnocodium. Length/width ratios were greatest for Gymnocodium and least for the three gypsum

**117**

**Figure 10.**

*cracked cone is littler bigger and show a collar.*

crystal samples. Significant departures from a rectangular distribution, suggesting orientation specificity, were observed in the Mars sample and also by the stromatolite algal filaments, Gymnocodium, Jarosite and feldspar phenocrysts. The percentage

*Different conical bodies, detected at Meridiani Planum by Opportunity; possible biological remnant of fossils "incertae sedis". These microscopic cones have littler bigger dimension. On the top (frames A, B) the cone has similar size and shows an internal zoned structure of a possible algal stem (C), having a number of lateral structures (arrows), resembling (far, not confirmed) terrestrial Dasycladales laterals side. Below (D, E) the* 

*Life on Mars: Clues, Evidence or Proof? DOI: http://dx.doi.org/10.5772/intechopen.95531*

#### **Figure 10.**

*Different conical bodies, detected at Meridiani Planum by Opportunity; possible biological remnant of fossils "incertae sedis". These microscopic cones have littler bigger dimension. On the top (frames A, B) the cone has similar size and shows an internal zoned structure of a possible algal stem (C), having a number of lateral structures (arrows), resembling (far, not confirmed) terrestrial Dasycladales laterals side. Below (D, E) the cracked cone is littler bigger and show a collar.*

crystal samples. Significant departures from a rectangular distribution, suggesting orientation specificity, were observed in the Mars sample and also by the stromatolite algal filaments, Gymnocodium, Jarosite and feldspar phenocrysts. The percentage

#### **Figure 11.**

*Comparison of a Dasycladales limestone (b/n pictures) to Martian putative fossils, at Sols 880 (frames O-R) and 1273 (frames D-F, H,I,M). Resembling (far, not confirmed) features of terrestrial Dasycladales include millimetric dimensions, a calcareous (conical or tube-like) stem, occasionally having regular discontinuity (frame G; from [62]), as are undulation or fissures. Such structures are visible on the above b/n pictures, as well on putative Martian fossils where regular transversal lines (arrow 1) or tube-like structures and their transversal sections (arrows 2 and 3) are visible. Careful observation shows knurled shells (for algal laterals). Similar structures appear to be seen in the rover's images (see the arrows), including the knurled shells.*

**119**

*Life on Mars: Clues, Evidence or Proof? DOI: http://dx.doi.org/10.5772/intechopen.95531*

and least for the mineral deposits.

*from Mineralienatlas.de., authorized).*

**Figure 12.**

other terrestrial microalgae.

of profiles exhibiting a fusiform shape or a degree of curvature also varied among images being generally greatest for the Mars sample and the terrestrial microalgae

*Fossil and living terrestrial algae together with mineral crystals used to compare with the "rice grains" in Figure 2: (1) Population of fossil stromatolite algal filaments (From: [63], their Figure 5); (2) Population of fossil algae (Gymnocodium group, possibly a red or green alga) (From: [41], Plate 57 7/8); (3) Sample image of living* Euglena viridis*; (4) Gypsum crystals (Gesso-2), (5) Jarosite crystals (jarosite 4138d, www. dakotamatrix.com), (6) crystals of feldspar (phenocrysts) (1200px-Montblanc-granite-phenocrysts. Mineral* 

A PCA of the data resulted in the extraction of two Principal Components (PC's) accounting for 96% of the total variance (PC1 = 77%, PC2 = 19%) indicating that separation of images along PC1 is more significant than along PC2. A plot of the 10 images in relation to PC1 and PC2 is shown in **Figure 13** with significant correlations between the factor loadings of the images on the PC and the various metrics. **Figure 13** shows: (1) that the three images of gypsum crystals (G1–3) have very similar metrics and form a distinct cluster not closely related to the Mars sample or to any of the investigated algae, (2) neither feldspar phenocrysts nor jarosite crystals are closely related to the Mars sample (3) Gymnocodium (Gym) and the Stromatolite Algal filaments (SA) are more closely related to the gypsum crystals in their metrics than Euglena (Eug) and (4) of the studied microalgae. Correlations between factor loadings and the various metrics suggest, the proportion of profiles with a fusiform shape, the proportion of curved profiles and the degree of variation in profile widths are all significantly correlated with PC1 and PC2 and, therefore, are the most important of the metrics distinguishing among images, the Martian sample and terrestrial Euglena displaying the most consistent widths and having a greater proportion of fusiform and curved profiles than the mineral deposits and

#### **Figure 12.**

*Fossil and living terrestrial algae together with mineral crystals used to compare with the "rice grains" in Figure 2: (1) Population of fossil stromatolite algal filaments (From: [63], their Figure 5); (2) Population of fossil algae (Gymnocodium group, possibly a red or green alga) (From: [41], Plate 57 7/8); (3) Sample image of living* Euglena viridis*; (4) Gypsum crystals (Gesso-2), (5) Jarosite crystals (jarosite 4138d, www. dakotamatrix.com), (6) crystals of feldspar (phenocrysts) (1200px-Montblanc-granite-phenocrysts. Mineral from Mineralienatlas.de., authorized).*

of profiles exhibiting a fusiform shape or a degree of curvature also varied among images being generally greatest for the Mars sample and the terrestrial microalgae and least for the mineral deposits.

A PCA of the data resulted in the extraction of two Principal Components (PC's) accounting for 96% of the total variance (PC1 = 77%, PC2 = 19%) indicating that separation of images along PC1 is more significant than along PC2. A plot of the 10 images in relation to PC1 and PC2 is shown in **Figure 13** with significant correlations between the factor loadings of the images on the PC and the various metrics. **Figure 13** shows: (1) that the three images of gypsum crystals (G1–3) have very similar metrics and form a distinct cluster not closely related to the Mars sample or to any of the investigated algae, (2) neither feldspar phenocrysts nor jarosite crystals are closely related to the Mars sample (3) Gymnocodium (Gym) and the Stromatolite Algal filaments (SA) are more closely related to the gypsum crystals in their metrics than Euglena (Eug) and (4) of the studied microalgae. Correlations between factor loadings and the various metrics suggest, the proportion of profiles with a fusiform shape, the proportion of curved profiles and the degree of variation in profile widths are all significantly correlated with PC1 and PC2 and, therefore, are the most important of the metrics distinguishing among images, the Martian sample and terrestrial Euglena displaying the most consistent widths and having a greater proportion of fusiform and curved profiles than the mineral deposits and other terrestrial microalgae.

#### **Figure 13.**

*Results of Euclidean morphometric investigation on "rice grains". On the top (A) the plot shows results of Euclidean morphometry analysis, differences and similarities, between the 10 images analyzed: PC1 against PC2 (Eug = Euglena, Gyp 1–3 Images of gypsum crystals, FD = Feldspar phenocrysts, Gym = Gymnocodium, Jar1 - Jar2 = Jarosite crystals, SA = Stromatolite algal filaments). Below (B), comparison of fractal dimension values (Mars, "rice grains" vs. Gypsum (P < 0.01) and vs. Euglena viridis (P = n.s.)). Its fractal dimension permit to distinguish them from the mineral negative control, while it is not possible to distinguish the Martian features from the biologic control, perfectly superimposable among them.*

### *5.2.2 Fractal morphometry*

Fractal analysis data are summarized in **Figure 13**, bottom, B. Fractal dimension of the Martian "rice grains" is lower than the one of the negative control, gypsum, with high statistical significance (p < 0.01). Vice versa, fractal dimension of the Martian "rice grains" overlaps the one of the unicellular alga *Euglena viridis*, positive control (D = 1.570 + 0.047 vs. 1.581 + 0.055, mean + SD, n = 30 per each sample).
