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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

Cumulative CH3Cl production when supplemented with NaCl or Mg(ClO4)2.(A) Murchison and (B) terrestrial soil; both non-supplemented and when supplemented with sodium chloride or magnesium perchlorate. Experimental protocol is given in Fig. 1 and text. Error bars indicate SD of mean values from independent samples (n = 3–4).
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f2: Cumulative CH3Cl production when supplemented with NaCl or Mg(ClO4)2.(A) Murchison and (B) terrestrial soil; both non-supplemented and when supplemented with sodium chloride or magnesium perchlorate. Experimental protocol is given in Fig. 1 and text. Error bars indicate SD of mean values from independent samples (n = 3–4).

Mentions: The effect of supplementation of Murchison and Hawaiian soil samples with Cl− or ClO4− was then investigated. An intimate mixture of supplement and sample was achieved by addition as an aqueous solution followed by lyophilization. When the Murchison sample with 10% NaCl (6.1% Cl−) was heated to 400°C, CH3Cl emissions were some 13 fold higher than those of the non-supplemented sample (Fig. 2A). No other chlorinated compounds such as CH2Cl2 and CHCl3 were detected. In view of the suggestion that heating of Martian soil with ClO4− could lead to formation of CH3Cl45 supplementation of Murchison at 1 and 10% magnesium perchlorate (0.32 and 3.2% on a Cl basis, respectively) was examined. At the 1% supplementation level CH3Cl emissions were approximately 40 fold higher than for the non-supplemented material and increased a further 2 fold at the 10% level. No significant difference was noted on overall emissions whether powdered magnesium perchlorate was ground with the sample or added as an aqueous solution and lyophilized prior to pyrolysis. Interestingly, CH2Cl2 and traces of CHCl3 were detected at the 1% supplementation level although total emissions of CH2Cl2 were over two orders of magnitudes less than those of CH3Cl, but increased markedly at higher perchlorate concentrations (Table 1). The Hawaiian soil sample displayed similar CH3Cl release patterns to those of Murchison when either Cl− or ClO4− was added (Fig. 2B). Chloromethane release increased by factors of approximately 250 and 1300 on supplementation with Cl− or ClO4−, respectively. As with Murchison when supplemented with ClO4−, CH3Cl release ceased at 400°C. The greatly increased emissions observed from the fortified Hawaiian soil relative to the fortified Murchison sample can as with the non-supplemented samples be attributed to the much higher methoxyl content. Again maximum CH3Cl emissions occurred at temperatures above 250°C in contrast with Murchison where emissions mainly occurred between 200 and 300°C with maximum release at 250°C. Maximum conversion of methoxyl groups to CH3Cl from Murchison and Hawaiian soil samples were ~25 and 60%, respectively when 10% magnesium perchlorate were added. These conversion rates are in line with those previously reported for terrestrial biological material under similar temperatures regimes111215. The lower conversion rates observed for Murchison is presumably due to its more complex mineralogical composition. No CH2Cl2 or CHCl3 emissions were detected from Cl− supplemented soil samples but ClO4− supplementation again resulted in release of traces of these compounds (Table 1).


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)

Cumulative CH3Cl production when supplemented with NaCl or Mg(ClO4)2.(A) Murchison and (B) terrestrial soil; both non-supplemented and when supplemented with sodium chloride or magnesium perchlorate. Experimental protocol is given in Fig. 1 and text. Error bars indicate SD of mean values from independent samples (n = 3–4).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Cumulative CH3Cl production when supplemented with NaCl or Mg(ClO4)2.(A) Murchison and (B) terrestrial soil; both non-supplemented and when supplemented with sodium chloride or magnesium perchlorate. Experimental protocol is given in Fig. 1 and text. Error bars indicate SD of mean values from independent samples (n = 3–4).
Mentions: The effect of supplementation of Murchison and Hawaiian soil samples with Cl− or ClO4− was then investigated. An intimate mixture of supplement and sample was achieved by addition as an aqueous solution followed by lyophilization. When the Murchison sample with 10% NaCl (6.1% Cl−) was heated to 400°C, CH3Cl emissions were some 13 fold higher than those of the non-supplemented sample (Fig. 2A). No other chlorinated compounds such as CH2Cl2 and CHCl3 were detected. In view of the suggestion that heating of Martian soil with ClO4− could lead to formation of CH3Cl45 supplementation of Murchison at 1 and 10% magnesium perchlorate (0.32 and 3.2% on a Cl basis, respectively) was examined. At the 1% supplementation level CH3Cl emissions were approximately 40 fold higher than for the non-supplemented material and increased a further 2 fold at the 10% level. No significant difference was noted on overall emissions whether powdered magnesium perchlorate was ground with the sample or added as an aqueous solution and lyophilized prior to pyrolysis. Interestingly, CH2Cl2 and traces of CHCl3 were detected at the 1% supplementation level although total emissions of CH2Cl2 were over two orders of magnitudes less than those of CH3Cl, but increased markedly at higher perchlorate concentrations (Table 1). The Hawaiian soil sample displayed similar CH3Cl release patterns to those of Murchison when either Cl− or ClO4− was added (Fig. 2B). Chloromethane release increased by factors of approximately 250 and 1300 on supplementation with Cl− or ClO4−, respectively. As with Murchison when supplemented with ClO4−, CH3Cl release ceased at 400°C. The greatly increased emissions observed from the fortified Hawaiian soil relative to the fortified Murchison sample can as with the non-supplemented samples be attributed to the much higher methoxyl content. Again maximum CH3Cl emissions occurred at temperatures above 250°C in contrast with Murchison where emissions mainly occurred between 200 and 300°C with maximum release at 250°C. Maximum conversion of methoxyl groups to CH3Cl from Murchison and Hawaiian soil samples were ~25 and 60%, respectively when 10% magnesium perchlorate were added. These conversion rates are in line with those previously reported for terrestrial biological material under similar temperatures regimes111215. The lower conversion rates observed for Murchison is presumably due to its more complex mineralogical composition. No CH2Cl2 or CHCl3 emissions were detected from Cl− supplemented soil samples but ClO4− supplementation again resulted in release of traces of these compounds (Table 1).

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