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Chloromethane release from carbonaceous meteorite affords new insight into Mars lander findings.

Keppler F, Harper DB, Greule M, Ott U, Sattler T, Schöler HF, Hamilton JT - Sci Rep (2014)

Bottom Line: Controversy continues as to whether chloromethane (CH3Cl) detected during pyrolysis of Martian soils by the Viking and Curiosity Mars landers is indicative of organic matter indigenous to Mars.Thus CH3Cl emissions recorded by Mars lander experiments may be attributed to methoxyl groups in undegraded organic matter in meteoritic debris reaching the Martian surface being converted to CH3Cl with perchlorate or chloride in Martian soil.However we cannot discount emissions arising additionally from organic matter of indigenous origin.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Earth Sciences, University of Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany [2] Max-Planck-Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany.

ABSTRACT
Controversy continues as to whether chloromethane (CH3Cl) detected during pyrolysis of Martian soils by the Viking and Curiosity Mars landers is indicative of organic matter indigenous to Mars. Here we demonstrate CH3Cl release (up to 8 μg/g) during low temperature (150-400°C) pyrolysis of the carbonaceous chondrite Murchison with chloride or perchlorate as chlorine source and confirm unequivocally by stable isotope analysis the extraterrestrial origin of the methyl group (δ(2)H +800 to +1100‰, δ(13)C -19.2 to +10‰,). In the terrestrial environment CH3Cl released during pyrolysis of organic matter derives from the methoxyl pool. The methoxyl pool in Murchison is consistent both in magnitude (0.044%) and isotope signature (δ(2)H +1054 ± 626‰, δ(13)C +43.2 ± 38.8‰,) with that of the CH3Cl released on pyrolysis. Thus CH3Cl emissions recorded by Mars lander experiments may be attributed to methoxyl groups in undegraded organic matter in meteoritic debris reaching the Martian surface being converted to CH3Cl with perchlorate or chloride in Martian soil. However we cannot discount emissions arising additionally from organic matter of indigenous origin. The stable isotope signatures of CH3Cl detected on Mars could potentially be utilized to determine its origin by distinguishing between terrestrial contamination, meteoritic infall and indigenous Martian sources.

No MeSH data available.


Related in: MedlinePlus

Stable hydrogen isotope composition of chloromethane.δ2H values of CH3Cl released during pyrolysis of Murchison and terrestrial soil. Grey shaded areas indicate the δ2H of the organic matter methoxyl pool (mean ± SD, n = 5–10). The black and blue vertical bars indicate the ranges of δ2H for extracted organic matter and volatiles from Murchison243435 and terrestrial organic matter36, respectively. Error bars indicate SD of mean values from independent samples (n = 3–4). SDs for soil sample were in the range of 1 to 30‰ and thus too small to be displayed.
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f4: Stable hydrogen isotope composition of chloromethane.δ2H values of CH3Cl released during pyrolysis of Murchison and terrestrial soil. Grey shaded areas indicate the δ2H of the organic matter methoxyl pool (mean ± SD, n = 5–10). The black and blue vertical bars indicate the ranges of δ2H for extracted organic matter and volatiles from Murchison243435 and terrestrial organic matter36, respectively. Error bars indicate SD of mean values from independent samples (n = 3–4). SDs for soil sample were in the range of 1 to 30‰ and thus too small to be displayed.

Mentions: Measurements of the stable hydrogen and carbon isotope values (δ2H, δ13C) of CH3Cl using an automated purification and preconcentration procedure21 were conducted where concentrations permitted at various stages during pyrolysis of the Murchison and Hawaiian soil samples (Fig. 3). Mean δ2H of CH3Cl emissions from Murchison ranged from roughly +800 to +1100 per mil (‰) and unequivocally confirm the extraterrestrial origin of the methyl group. The values are in the same range as those measured for the methoxyl pool (+1054 ± 626‰) in Murchison and are quite different from those of hydrogen in organic matter on Earth. They are within the range of values reported for various types of organic compounds in Murchison (+188 to +2980‰) thus excluding terrestrial contamination as the methoxyl source (Fig. 4). In contrast mean δ2H for CH3Cl from −192 to −149‰ for emissions by terrestrial soil are within the expected range for terrestrial organic matter and similar to those measured for the methoxyl pool (−184 ± 10‰) of such matter. These values are also consistent with the predicted values of CH3Cl when derived from ether and ester methoxyl groups2122 of organic matter derived from vegetation in Hawaii which indicate a mean isotope fractionation of −178 ± 34‰ relative to the modelled precipitation values of Hawaii. Thus thermal treatment of Murchison and Hawaiian soil samples causes no significant fractionation between the precursor methyl group and the CH3Cl emitted, a finding in accord with previous observations of CH3Cl release from terrestrial samples during thermal conversion212223.


Chloromethane release from carbonaceous meteorite affords new insight into Mars lander findings.

Keppler F, Harper DB, Greule M, Ott U, Sattler T, Schöler HF, Hamilton JT - Sci Rep (2014)

Stable hydrogen isotope composition of chloromethane.δ2H values of CH3Cl released during pyrolysis of Murchison and terrestrial soil. Grey shaded areas indicate the δ2H of the organic matter methoxyl pool (mean ± SD, n = 5–10). The black and blue vertical bars indicate the ranges of δ2H for extracted organic matter and volatiles from Murchison243435 and terrestrial organic matter36, respectively. Error bars indicate SD of mean values from independent samples (n = 3–4). SDs for soil sample were in the range of 1 to 30‰ and thus too small to be displayed.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230006&req=5

f4: Stable hydrogen isotope composition of chloromethane.δ2H values of CH3Cl released during pyrolysis of Murchison and terrestrial soil. Grey shaded areas indicate the δ2H of the organic matter methoxyl pool (mean ± SD, n = 5–10). The black and blue vertical bars indicate the ranges of δ2H for extracted organic matter and volatiles from Murchison243435 and terrestrial organic matter36, respectively. Error bars indicate SD of mean values from independent samples (n = 3–4). SDs for soil sample were in the range of 1 to 30‰ and thus too small to be displayed.
Mentions: Measurements of the stable hydrogen and carbon isotope values (δ2H, δ13C) of CH3Cl using an automated purification and preconcentration procedure21 were conducted where concentrations permitted at various stages during pyrolysis of the Murchison and Hawaiian soil samples (Fig. 3). Mean δ2H of CH3Cl emissions from Murchison ranged from roughly +800 to +1100 per mil (‰) and unequivocally confirm the extraterrestrial origin of the methyl group. The values are in the same range as those measured for the methoxyl pool (+1054 ± 626‰) in Murchison and are quite different from those of hydrogen in organic matter on Earth. They are within the range of values reported for various types of organic compounds in Murchison (+188 to +2980‰) thus excluding terrestrial contamination as the methoxyl source (Fig. 4). In contrast mean δ2H for CH3Cl from −192 to −149‰ for emissions by terrestrial soil are within the expected range for terrestrial organic matter and similar to those measured for the methoxyl pool (−184 ± 10‰) of such matter. These values are also consistent with the predicted values of CH3Cl when derived from ether and ester methoxyl groups2122 of organic matter derived from vegetation in Hawaii which indicate a mean isotope fractionation of −178 ± 34‰ relative to the modelled precipitation values of Hawaii. Thus thermal treatment of Murchison and Hawaiian soil samples causes no significant fractionation between the precursor methyl group and the CH3Cl emitted, a finding in accord with previous observations of CH3Cl release from terrestrial samples during thermal conversion212223.

Bottom Line: Controversy continues as to whether chloromethane (CH3Cl) detected during pyrolysis of Martian soils by the Viking and Curiosity Mars landers is indicative of organic matter indigenous to Mars.Thus CH3Cl emissions recorded by Mars lander experiments may be attributed to methoxyl groups in undegraded organic matter in meteoritic debris reaching the Martian surface being converted to CH3Cl with perchlorate or chloride in Martian soil.However we cannot discount emissions arising additionally from organic matter of indigenous origin.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Earth Sciences, University of Heidelberg, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany [2] Max-Planck-Institute for Chemistry, Hahn-Meitner-Weg 1, 55128 Mainz, Germany.

ABSTRACT
Controversy continues as to whether chloromethane (CH3Cl) detected during pyrolysis of Martian soils by the Viking and Curiosity Mars landers is indicative of organic matter indigenous to Mars. Here we demonstrate CH3Cl release (up to 8 μg/g) during low temperature (150-400°C) pyrolysis of the carbonaceous chondrite Murchison with chloride or perchlorate as chlorine source and confirm unequivocally by stable isotope analysis the extraterrestrial origin of the methyl group (δ(2)H +800 to +1100‰, δ(13)C -19.2 to +10‰,). In the terrestrial environment CH3Cl released during pyrolysis of organic matter derives from the methoxyl pool. The methoxyl pool in Murchison is consistent both in magnitude (0.044%) and isotope signature (δ(2)H +1054 ± 626‰, δ(13)C +43.2 ± 38.8‰,) with that of the CH3Cl released on pyrolysis. Thus CH3Cl emissions recorded by Mars lander experiments may be attributed to methoxyl groups in undegraded organic matter in meteoritic debris reaching the Martian surface being converted to CH3Cl with perchlorate or chloride in Martian soil. However we cannot discount emissions arising additionally from organic matter of indigenous origin. The stable isotope signatures of CH3Cl detected on Mars could potentially be utilized to determine its origin by distinguishing between terrestrial contamination, meteoritic infall and indigenous Martian sources.

No MeSH data available.


Related in: MedlinePlus