User:Dannajaimes01/Carbonates on Mars

The formation of carbonates on Mars have been suggested based on evidence of the presence of liquid water and atmospheric carbon dioxide in the planet's early stages. Moreover, due to their utility in registering changes in environmental conditions such as pH, temperature, fluid composition, carbonates have been considered as a primary target for planetary scientists' research. However, since their first detection in 2008, the large deposits of carbonates that were one expected on Mars have not been found , leading to multiple potential explanations that can explain why carbonates did not form massively on the planet.

Absence of carbonates on Mars
Geological and geomorphological evidence has reinforced the idea of the presence of liquid water on early Mars. Therefore, abundant precipitation of carbonates from atmospheric and water reactions is expected. However, spectral imaging has revealed only small amounts of carbonates, generating doubts about humans' understanding of geological processes on Mars. To overcome this problem, scientists have proposed explanations that reconcile the absence of carbonates with the presence of a CO2-rich atmosphere and liquid water.

Cold and Dry Early Mars Environments
According to this explanation, the early Martian conditions are similar to those at present. Essentially, it suggests that carbonates are absent because the planet never experienced conditions that included the presence of liquid water and a CO2-rich thick atmosphere. Even if this explanation provides an insight in the reasons why carbonates are not present, it is in disagreement with the geomorphological and mineralogical evidence supporting the existence of liquid water on Mars' surface.

Inability of Detection with Current Technology
This hypothesis establishes that the Thermal Emission Spectrometer (TES) aboard the Mars Global Surveyor spacecraft and the Thermal Emission Imaging System (THEMIS) on board the Mars Odyssey spacecraft are unable to detect carbonates. According to this notion, the carbonates indeed formed and are still exist on Mars, but they remain undetected due to the limited sensitivity of the current tools used for mineralogical detection on the planet.

Secondary Chemical Alteration
This concept involves the potential for secondary chemical alteration of ancient carbonates on Mars, due to the formation of acid rain resulting from the combination of water vapor and sulfates. The consequence of this process implies the chemical decomposition of superficial carbonates layers, as carbonates are not resistant to acidic pH conditions; acid-fog weathering; and photo-decomposition.

Hidden Carbonate Deposits
According to this perspective, massive carbonates deposits formed but are hidden beneath several layers of secondary alteration rocks, preventing their identification on the surface. Other alternatives to this hypothesis include: Masking of carbonates as a consequence of the abundant soils on Mars; and resurfacing processes that have covered carbonate deposits, such as eolian deposition and late sedimentation processes.

Inhibition due to Acidic Conditions
Finally, this hypothesis defends the idea that carbonates never precipitated because the pH conditions of the environment were too acidic to allow carbonates to precipitate, or at least siderite, which is the primary carbonate mineral expected to precipitate first. The acidic conditions are derived from the high partial pressures of atmospheric carbon dioxide, as well as a persistent sulfate and iron enrichment that affect the optimal conditions for carbonates to precipitate.