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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 from Murchison and terrestrial soil.The sample was heated in a glass vessel (under N2) for 15 min at 150°C then heating was programmed to increase at 50°C min−1 to 200°C, at which temperature the sample was held for 15 min. This programming in 50°C increments continued to a maximum temperature of 400°C. The amount of CH3Cl was measured at the end of the hold period at each temperature by gas chromatography–mass spectrometry10. After this the vessel was opened and flushed with N2 before resealing for the next heating step. The arrows indicate the temperature ranges where methyl ester and ether groups are converted to CH3Cl.
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f1: Cumulative CH3Cl production from Murchison and terrestrial soil.The sample was heated in a glass vessel (under N2) for 15 min at 150°C then heating was programmed to increase at 50°C min−1 to 200°C, at which temperature the sample was held for 15 min. This programming in 50°C increments continued to a maximum temperature of 400°C. The amount of CH3Cl was measured at the end of the hold period at each temperature by gas chromatography–mass spectrometry10. After this the vessel was opened and flushed with N2 before resealing for the next heating step. The arrows indicate the temperature ranges where methyl ester and ether groups are converted to CH3Cl.

Mentions: Firstly we examined ground samples of Murchison and Hawaiian soil for their potential to form CH3Cl during thermal conversion at low temperatures. Significant CH3Cl release from Murchison was observed at temperatures between 200 and 400°C (Fig. 1). However the Hawaiian soil sample showed 28 fold greater CH3Cl release over the heating cycle. The much lower emissions from Murchison are explained not only by the lower organic matter content but also more importantly by the much reduced methoxyl content of the Murchison organic matter. Methoxyl content of Hawaiian soil organic matter determined using hydrogen iodide (HI)20 was 1.55 ± 0.66%. Determination of the methoxyl content of the organic component in Murchison proved more difficult presumably because the physical nature of the meteoritic material rendered the methoxyl groups less accessible. Successive treatments with HI yielded a methoxyl content of 0.044 ± 0.025%. Release of CH3Cl from Hawaiian soil organic matter attains a maximum at 300–350°C as would be predicted since it contains a substantial proportion of methyl ether groups (lignin type)1115 whereas the temperature profile of Murchison emissions is more linear indicating that methyl ester groups, which release CH3Cl at lower temperatures, may also be of significance.


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 from Murchison and terrestrial soil.The sample was heated in a glass vessel (under N2) for 15 min at 150°C then heating was programmed to increase at 50°C min−1 to 200°C, at which temperature the sample was held for 15 min. This programming in 50°C increments continued to a maximum temperature of 400°C. The amount of CH3Cl was measured at the end of the hold period at each temperature by gas chromatography–mass spectrometry10. After this the vessel was opened and flushed with N2 before resealing for the next heating step. The arrows indicate the temperature ranges where methyl ester and ether groups are converted to CH3Cl.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Cumulative CH3Cl production from Murchison and terrestrial soil.The sample was heated in a glass vessel (under N2) for 15 min at 150°C then heating was programmed to increase at 50°C min−1 to 200°C, at which temperature the sample was held for 15 min. This programming in 50°C increments continued to a maximum temperature of 400°C. The amount of CH3Cl was measured at the end of the hold period at each temperature by gas chromatography–mass spectrometry10. After this the vessel was opened and flushed with N2 before resealing for the next heating step. The arrows indicate the temperature ranges where methyl ester and ether groups are converted to CH3Cl.
Mentions: Firstly we examined ground samples of Murchison and Hawaiian soil for their potential to form CH3Cl during thermal conversion at low temperatures. Significant CH3Cl release from Murchison was observed at temperatures between 200 and 400°C (Fig. 1). However the Hawaiian soil sample showed 28 fold greater CH3Cl release over the heating cycle. The much lower emissions from Murchison are explained not only by the lower organic matter content but also more importantly by the much reduced methoxyl content of the Murchison organic matter. Methoxyl content of Hawaiian soil organic matter determined using hydrogen iodide (HI)20 was 1.55 ± 0.66%. Determination of the methoxyl content of the organic component in Murchison proved more difficult presumably because the physical nature of the meteoritic material rendered the methoxyl groups less accessible. Successive treatments with HI yielded a methoxyl content of 0.044 ± 0.025%. Release of CH3Cl from Hawaiian soil organic matter attains a maximum at 300–350°C as would be predicted since it contains a substantial proportion of methyl ether groups (lignin type)1115 whereas the temperature profile of Murchison emissions is more linear indicating that methyl ester groups, which release CH3Cl at lower temperatures, may also be of significance.

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