Carbonates on Mars

THEMIS—sensitive to infrared emissivity spectral features of carbonates—had not suggested the presence of carbonate outcrops,^[8] at least at the 100 m or coarser spatial scales available from the returned data.^[9]

Gusev crater.^[11][12] (note: An IAU

phyllosilicates below and mafic cap rocks above, temporally between the Noachian and Hesperian eras. Even though infrared spectra are representative of minerals to less than ≈0.1 mm depths^[14] (in contrast to gamma spectra which are sensitive to tens of cm depths),^[15] stratigraphic,^{[clarification needed]} morphologic,^{[clarification needed]} and thermal properties are consistent with the existence of the carbonate as outcrop rather than alteration rinds.^{[clarification needed]} Nevertheless, the morphology was distinct from typical terrestrial sedimentary carbonate layers suggesting formation from local aqueous alteration of olivine and other igneous minerals. However, key implications were that the alteration would have occurred under moderate pH and that the resulting carbonates were not exposed to sustained low pH aqueous conditions even as recently as the Hesperian

Spirit Rover stopped working scientists studied old data from the Miniature Thermal Emission Spectrometer, or Mini-TES and confirmed the presence of large amounts of carbonate-rich rocks, which means that regions of the planet may have once harbored water. The carbonates were discovered in an outcrop of rocks called "Comanche."^[19][18]

Carbonates (calcium or iron carbonates) were discovered in a crater on the rim of Huygens Crater, located in the Iapygia quadrangle. The impact on the rim exposed material that had been dug up from the impact that created Huygens. These minerals represent evidence that Mars once had a thicker carbon dioxide atmosphere with abundant moisture. These kind of carbonates only form when there is a lot of water. They were found with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter. Earlier, the instrument had detected clay minerals. The carbonates were found near the clay minerals. Both of these minerals form in wet environments. It is supposed that billions of years age Mars was much warmer and wetter. At that time, carbonates would have formed from water and the carbon dioxide-rich atmosphere. Later the deposits of carbonate would have been buried. The double impact has now exposed the minerals. Earth has vast carbonate deposits in the form of limestone.^[20]