Evidence for carbonates on
Mars was first discovered in 2008. Carbonates were formed in the early history of Mars. Evidence shows Mars was once warmer and wet about 4 billion years ago, that is about 560 million years after the
formation of Mars. [1][2] At this time span, the water on early Mars reacted with Mars'
carbon dioxide, this reaction formed
carbonic acid.[3] The carbonic acid joined into the
water cycle on early Mars.[4] The carbonic acid in the water cycle produced carbonates. The
carbonates removed (leached)
greenhouse gases,
water vapor, and carbon dioxide from Mars' atmosphere.[5][6][7]
Mars probes
Previously, most
remote sensing instruments such as
OMEGA and
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]
Though ubiquitous, a 2003 study of carbonates on Mars showed that they are dominated by
magnesite (MgCO3) in Martian dust, had mass fractions less than 5%, and could have formed under current atmospheric conditions.[10] Furthermore, with the exception of the surface dust component, by 2007
carbonates had not been detected by any in situ mission, even though mineralogic modeling did not preclude small amounts of calcium carbonate in Independence class rocks of
Husband Hill in
Gusev crater.[11][12] (note: An
IAU naming convention within Gusev is not yet established).
Remote sensing data
The first successful identification of a strong infrared spectral signature from
surficialcarbonate minerals of local scale (< 10 km2) was made by the
MRO-
CRISM team in 2008.[13] Spectral modeling in 2007 identified a key deposit in
Nili Fossae dominated by a single mineral phase that was spatially associated with
olivine outcrops. The dominant mineral appeared to be
magnesite, while morphology inferred with
HiRISE and thermal properties suggested that the deposit was lithic. Stratigraphically, this layer appeared between
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.
when the
Thermal and Evolved Gas Analyzer (TEGA) and
WCL experiments on the 2009
Phoenix Mars lander found between 3–5wt% calcite (CaCO3) and an alkaline soil.[17] In 2010 analyses by the Mars Exploration Rover Spirit, identified outcrops rich in magnesium-iron carbonate (16–34 wt%) in the Columbia Hills of Gusev crater, most likely precipitated from carbonate-bearing solutions under hydrothermal conditions at near-neutral pH in association with volcanic activity during the Noachian era.[18]
After
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]
Carbonates found on Mars
Name
Mission
MgCO3
magnesite
remote sensing, MRO-CRISM
2008
MgCO3
magnesite
remote sensing Mars Express-PFS
2009
CaCO3
calcite
Phoenix
2009
FeCO3
siderite
Curiosity
2020
Gallery
Huygens Crater - circle shows location of carbonate deposit - representing a time when Mars had abundant liquid water on its surface (Scale bar = 259 km).
Nili Fossae on Mars - largest known carbonate deposit.
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