**4. Results and discussion**

Sodium ion and Chlorine are the most abundant species in the ocean of Enceladus. **Figure 4** shows the concentration of both species in mol per kg of H2O. The quantity of mol is calculated in function of the CO2 activity. Na<sup>þ</sup> is present in concentrations around 0.800 mol/kg while the concentrations of Cl� are constant, around 0.400 mol/ kg. **Figure 5** also shows that there are present some carbonates CO3 <sup>2</sup>�, bicarbonate HCO3 � and sulfate SO4 <sup>2</sup>�. CO3 <sup>2</sup>� has a concentration on average 0.075–0.030 mol/kg which tends to decrease with the activity of CO2. HCO3 � presents an increment from 0.020 to 0.070 mol/kg and SO4 <sup>2</sup>� has a concentration between 0.01 and 0.1 mol/kg.

The concentrations of salinity and chlorinity are relatively constant in the current terrestrial oceans. The average concentration from the seawater with a pH of 8.1 and temperature of 25°C are detailed in **Table 1**. Geological information extracted from sedimentary layers reveals that deep oceans were in a reduced state till the end of the Paleoproterozoic era. Iron and calcium sulfate probably played as reduced agents with the oxygen converting FeO into Fe2O3, and precipitating CaSO4. During the

#### **Figure 4.**

*Sodium ion and chlorine present in the ocean of Enceladus. The concentration of species are calculated in function of the* CO2 *activity.*

#### **Figure 5.**

*Some carbonates, bicarbonates, and sulfate present in the ocean of Enceladus. The concentration of species are calculated in function of the* CO2 *activity.*


#### **Table 2.**

*Concentration of species present in the seawater of the oceans on earth and in the ocean of Enceladus.*

Cryogenian era the concentration of sulphate could rise to levels similar to the recent ones, around 23 mol/kg of H2O [47].

**Table 2** shows few key species present in the ocean of Enceladus and in the seawater of the oceans on Earth. Sodium ion and Chlorine are the most abundant species in both oceans. The oceans on Earth are saltier with a pH of 8.1 on average, while the ocean of Enceladus is more basic, around pH 12.2. The ocean of Enceladus has more dissolved inorganic carbon than the ocean on Earth. On Enceladus, the predominant carbonate is CO3 <sup>2</sup>� while on Earth is the bicarbonateHCO3 �. The abundance of CO3 <sup>2</sup>�in the ocean of Enceladus could be due to the serpentinization of the molecular hydrogen. The concentration of sulfur in the ocean of Enceladus is variable compared to the one present on Earth.

Two scenarios can be considered to calculate the amount of sulphate that could be oxidized on the ocean of Enceladus. The lower concentration of SO4 <sup>2</sup>�, 0.01 g/kg, displayed in **Table 2**, takes place only in aqueous reductants environments where HS� reacts with the oxidants, while in the larger concentration 0.1 g/kg, some minerals are considered as a source for reductants. The concentration of sulphate in the ocean of Enceladus is below to the current amount of sulphate found on the oceans on Earth but, this concentration could have been smaller during the Snowball events, being close to the current quantities on the ocean of Enceladus.

The predominant concentration of inorganic carbonate species found in the ocean of Enceladus, set the ocean as not compatible with life except for the methane detected that can be a product of the methanogenesis of the carbon dioxide and the hydrogen. Would it be possible that the species detected in the ocean of Enceladus evolve to create the chains of life? how were the chemical conditions of the primitive terrestrial oceans before rising life? In order to figure out which similarities could be found between the terrestrial oceans and the ocean of Enceladus, it is necessary to understand the evolution of the ancient aqueous geochemistry of the oceans in the primitive Earth.

During the first stage of formation of Earth, it was bombarded by hydrous asteroids mainly type Cl chondrites bringing water, organic molecules, and chondritic minerals. Tectonic activity facilitated to diversity the mineralogy along the crust, increasing the mafic content of the top layers through the eruption of hot basaltic lavas. Chondritic material has been also detected in the plumes of Enceladus [14, 21], that is why, it could be possible to infer that this material can be settled in the seafloor of its ocean [48].

Organisms cannot devise chemical processes by themselves, they must copy natural reactions, adapt them, and optimize them through time. Phosphorylation is the addition of a phosphate group into a protein, being the main mechanism of

#### *Is the Ocean of Enceladus in a Primitive Evolutionary Stage? DOI: http://dx.doi.org/10.5772/intechopen.104862*

biochemistry. This mechanism participates in some proteins regulation like ATP formation, fatty acids metabolization, and citric acid cycle. Prebiotic phosphorylation of biological molecules is a reaction that represent a challenge for the study of the origin of life. It has been proven that using diamidophosphate (DAP) instead of phosphates, thermodynamic barriers decreased for this reaction in water, and different organic building blocks were able to be assembled [49]. Based on that analysis, it was demonstrated that is possible to generate DAP and other amino - phosphor compounds when P-bearing molecules are mixed with aqueous ammonia solutions. The sources of phosphor could come from iron P-bearing minerals, condensed phosphates which contain salts and metals, or reduced phosphorus compounds. Those reactions probably took place in the aqueous conditions of the early Earth. If the concentration of ammonia in the hydrothermal vents of Enceladus would be similar to the prebiotic oceans on Earth, that phosphate reaction could happen in the ocean of Enceladus.

Although the currents anaerobic sulfur-reducing hyperthermophiles are associated to the first forms of life on Earth, the supply of sulfur in early times is supposed to have been more limited than now. However, due to geochemical evidence, it was proposed that iron could has been the first external electron acceptor in microbial metabolism [50]. **Table 2** shows a low concentration of sulfur in the ocean of Enceladus, and for this reason, the hydrothermal activity inferred by the molecular hydrogen detected from the plumes suggests that the iron could play a similar role in the geochemical reactions in the ocean of Enceladus.

Life not only came from hydrothermal vents but also, it could have risen on freshwater accumulations from geysers, precipitations, and hot spots, which could have linked to hydration-dehydration cycles. In hydrothermal vents, the thermal gradient allows for the concentration of solutes in the vents through the polymerization of minerals and sources of chemical energy like serpentinization. In the second system, the extreme concentration of chemical species took place due to the wetting-drying cycles, and the energy derived from evaporation provided the conditions of polymerization [51].

Enceladus looks like a potentially habitable world due to the similar current concentration of some key species present in the ocean to the ones that were present in the seawater of the oceans on Earth. There were detected traces of organic elements that could come from the water-rock interaction which can be also filled by minerals like iron, sodium, potassium, and calcium. There have been also detected the presence of biological consumable energy that on Earth, this energy is supplied by photosynthetic organisms like chemoautotrophs from a methanogenesis activity.

The environmental condition into the ocean of Enceladus could be in accord with life due to similarities with the oceans on Earth (pressures from 0.5 to 600 bar, which can be also found in some terrestrial environments [52], temperatures of 0–90°C, salinity calculated from the plumes between 0.5 and 2%. These values are lower than the ones on Earth which salinity is 3.5%). According to Porco et al. [53], the concentration of biological compounds could be potentially higher in the plume than in the seawater if the bubble scrubbing were allowed. These structures rise through the fluid while the organic material is attached to the water-gas interface until the eruption of the bubble through the jets. The addition of these organic compounds depends on their solubility and the surface activity. Surfactants like amphiphilic molecules would be instantly attached to the interface as they are able to reduce the surface tension, then the hydrophobic compounds would also be quickly attached.

Measurements in situ will be necessary to probe the feasibility of the ocean of Enceladus to harbor life. The information taken from the plumes by the Cassini

mission provided data about the composition of the material expelled by the jets. The possibility to analyze samples from the plumes could bring a better understanding in how to make a characterization of the seawater and also, distinguish if there are residual elements that come from the interaction between living organisms and the environment.
