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Sulfate minerals: a problem for the detection of organic compounds on Mars?

Lewis JM, Watson JS, Najorka J, Luong D, Sephton MA - Astrobiology (2015)

Bottom Line: Perchlorates are recognized as confounding minerals for thermal degradation studies.A laboratory standard of ferric sulfate hydrate released sulfur dioxide from 550 °C, and an oxygen peak was detected in the products.Calcium sulfate did not decompose below 1000 °C.

View Article: PubMed Central - PubMed

Affiliation: 1 Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London , London, United Kingdom .

ABSTRACT
The search for in situ organic matter on Mars involves encounters with minerals and requires an understanding of their influence on lander and rover experiments. Inorganic host materials can be helpful by aiding the preservation of organic compounds or unhelpful by causing the destruction of organic matter during thermal extraction steps. Perchlorates are recognized as confounding minerals for thermal degradation studies. On heating, perchlorates can decompose to produce oxygen, which then oxidizes organic matter. Other common minerals on Mars, such as sulfates, may also produce oxygen upon thermal decay, presenting an additional complication. Different sulfate species decompose within a large range of temperatures. We performed a series of experiments on a sample containing the ferric sulfate jarosite. The sulfate ions within jarosite break down from 500 °C. Carbon dioxide detected during heating of the sample was attributed to oxidation of organic matter. A laboratory standard of ferric sulfate hydrate released sulfur dioxide from 550 °C, and an oxygen peak was detected in the products. Calcium sulfate did not decompose below 1000 °C. Oxygen released from sulfate minerals may have already affected organic compound detection during in situ thermal experiments on Mars missions. A combination of preliminary mineralogical analyses and suitably selected pyrolysis temperatures may increase future success in the search for past or present life on Mars.

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Related in: MedlinePlus

Total ion current chromatograms of the gaseous products during individual heating experiments of lab standards representing the non-sulfate mineralogy of the natural jarosite clay sample. All chromatograms are presented at the same scale.
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f2: Total ion current chromatograms of the gaseous products during individual heating experiments of lab standards representing the non-sulfate mineralogy of the natural jarosite clay sample. All chromatograms are presented at the same scale.

Mentions: The major gases released by the natural jarosite clay at 600°C and 1000°C were carbon dioxide, water, and sulfur dioxide (Fig. 1). A minor peak of mass-to-charge ratio (m/z) 28 was also detected at both temperatures, which could be either nitrogen or carbon monoxide, as both species have the same mass and retention time. We infer that this species is more likely to be carbon monoxide, as it is an expected product of partial combustion, the peak area increased with temperature, and no m/z 28 peak was seen in any other sample apart from siderite (Figs. 2 and 3). Oxygen was not detected at any temperature step for the natural jarosite clay.


Sulfate minerals: a problem for the detection of organic compounds on Mars?

Lewis JM, Watson JS, Najorka J, Luong D, Sephton MA - Astrobiology (2015)

Total ion current chromatograms of the gaseous products during individual heating experiments of lab standards representing the non-sulfate mineralogy of the natural jarosite clay sample. All chromatograms are presented at the same scale.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4363818&req=5

f2: Total ion current chromatograms of the gaseous products during individual heating experiments of lab standards representing the non-sulfate mineralogy of the natural jarosite clay sample. All chromatograms are presented at the same scale.
Mentions: The major gases released by the natural jarosite clay at 600°C and 1000°C were carbon dioxide, water, and sulfur dioxide (Fig. 1). A minor peak of mass-to-charge ratio (m/z) 28 was also detected at both temperatures, which could be either nitrogen or carbon monoxide, as both species have the same mass and retention time. We infer that this species is more likely to be carbon monoxide, as it is an expected product of partial combustion, the peak area increased with temperature, and no m/z 28 peak was seen in any other sample apart from siderite (Figs. 2 and 3). Oxygen was not detected at any temperature step for the natural jarosite clay.

Bottom Line: Perchlorates are recognized as confounding minerals for thermal degradation studies.A laboratory standard of ferric sulfate hydrate released sulfur dioxide from 550 °C, and an oxygen peak was detected in the products.Calcium sulfate did not decompose below 1000 °C.

View Article: PubMed Central - PubMed

Affiliation: 1 Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London , London, United Kingdom .

ABSTRACT
The search for in situ organic matter on Mars involves encounters with minerals and requires an understanding of their influence on lander and rover experiments. Inorganic host materials can be helpful by aiding the preservation of organic compounds or unhelpful by causing the destruction of organic matter during thermal extraction steps. Perchlorates are recognized as confounding minerals for thermal degradation studies. On heating, perchlorates can decompose to produce oxygen, which then oxidizes organic matter. Other common minerals on Mars, such as sulfates, may also produce oxygen upon thermal decay, presenting an additional complication. Different sulfate species decompose within a large range of temperatures. We performed a series of experiments on a sample containing the ferric sulfate jarosite. The sulfate ions within jarosite break down from 500 °C. Carbon dioxide detected during heating of the sample was attributed to oxidation of organic matter. A laboratory standard of ferric sulfate hydrate released sulfur dioxide from 550 °C, and an oxygen peak was detected in the products. Calcium sulfate did not decompose below 1000 °C. Oxygen released from sulfate minerals may have already affected organic compound detection during in situ thermal experiments on Mars missions. A combination of preliminary mineralogical analyses and suitably selected pyrolysis temperatures may increase future success in the search for past or present life on Mars.

Show MeSH
Related in: MedlinePlus