Limits...
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

Release of chloromethane, trans-2-butene and cis-2-butene from Murchison.(A) Murchison without supplementation, (B) with added Mg(ClO4)2 (10%) and (C) with added with NaCl (10%) over the temperature range 150 to 400°C (50°C steps); amounts produced at each temperature step.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4230006&req=5

f3: Release of chloromethane, trans-2-butene and cis-2-butene from Murchison.(A) Murchison without supplementation, (B) with added Mg(ClO4)2 (10%) and (C) with added with NaCl (10%) over the temperature range 150 to 400°C (50°C steps); amounts produced at each temperature step.

Mentions: Non-chlorinated volatile organic compounds (VOCs) were also observed during thermal treatment of Murchison and Hawaiian soil samples. Interestingly the formation and release of the VOCs were very different from those for CH3Cl. Figure 3 shows the release of CH3Cl and two non-chlorinated compounds, trans-2-butene and cis-2-butene, from Murchison with and without ClO4− supplementation. When Murchison was heated without ClO4−, the non-chlorinated compounds were much more abundant than CH3Cl (Fig. 3A, Supplementary Table 2). However, upon addition of ClO4− the non-chlorinated VOCs were only observed at temperatures below 200°C (Fig. 3B, Supplementary Table 2) whereas maximum CH3Cl formation was at 250°C. Moreover CH3Cl release dramatically increased, by two to three orders of magnitude, upon supplementation. This might indicate that during decomposition of ClO4− the organic matter giving rise to the VOCs was effectively oxidized and thus explains why they are not formed at measureable levels. However because CH3Cl is preferentially formed, when chlorine is available, from methoxyl groups which are not as prone to such oxidation processes at lower temperatures its formation is enhanced. In addition other chlorinated methanes, such as CH2Cl2 and CHCl3, which were not detected in Murchison and soil without added ClO4−, were clearly identified in the samples that contained ClO4−. These chlorinated compounds were not observed when chloride (NaCl) was added to Murchison. Thus, after low temperature pyrolysis (150 to 300°C) of Murchison in the presence of ClO4−, chlorohydrocarbons were by far the most abundant organic compounds detected by the analytical procedures employed in this study. Interestingly the temperature profile for CH3Cl release from Murchison with added ClO4− showing maximum formation at around 250°C (Fig. 3B) is remarkably similar to that recently reported for CH3Cl release from heated samples of Martian fines at Rocknest6 and a mudstone at Yellowknife Bay10 whereas Murchison without supplementation or with added NaCl showed a different pattern of CH3Cl formation over this temperature range (Fig. 3C).


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)

Release of chloromethane, trans-2-butene and cis-2-butene from Murchison.(A) Murchison without supplementation, (B) with added Mg(ClO4)2 (10%) and (C) with added with NaCl (10%) over the temperature range 150 to 400°C (50°C steps); amounts produced at each temperature step.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Release of chloromethane, trans-2-butene and cis-2-butene from Murchison.(A) Murchison without supplementation, (B) with added Mg(ClO4)2 (10%) and (C) with added with NaCl (10%) over the temperature range 150 to 400°C (50°C steps); amounts produced at each temperature step.
Mentions: Non-chlorinated volatile organic compounds (VOCs) were also observed during thermal treatment of Murchison and Hawaiian soil samples. Interestingly the formation and release of the VOCs were very different from those for CH3Cl. Figure 3 shows the release of CH3Cl and two non-chlorinated compounds, trans-2-butene and cis-2-butene, from Murchison with and without ClO4− supplementation. When Murchison was heated without ClO4−, the non-chlorinated compounds were much more abundant than CH3Cl (Fig. 3A, Supplementary Table 2). However, upon addition of ClO4− the non-chlorinated VOCs were only observed at temperatures below 200°C (Fig. 3B, Supplementary Table 2) whereas maximum CH3Cl formation was at 250°C. Moreover CH3Cl release dramatically increased, by two to three orders of magnitude, upon supplementation. This might indicate that during decomposition of ClO4− the organic matter giving rise to the VOCs was effectively oxidized and thus explains why they are not formed at measureable levels. However because CH3Cl is preferentially formed, when chlorine is available, from methoxyl groups which are not as prone to such oxidation processes at lower temperatures its formation is enhanced. In addition other chlorinated methanes, such as CH2Cl2 and CHCl3, which were not detected in Murchison and soil without added ClO4−, were clearly identified in the samples that contained ClO4−. These chlorinated compounds were not observed when chloride (NaCl) was added to Murchison. Thus, after low temperature pyrolysis (150 to 300°C) of Murchison in the presence of ClO4−, chlorohydrocarbons were by far the most abundant organic compounds detected by the analytical procedures employed in this study. Interestingly the temperature profile for CH3Cl release from Murchison with added ClO4− showing maximum formation at around 250°C (Fig. 3B) is remarkably similar to that recently reported for CH3Cl release from heated samples of Martian fines at Rocknest6 and a mudstone at Yellowknife Bay10 whereas Murchison without supplementation or with added NaCl showed a different pattern of CH3Cl formation over this temperature range (Fig. 3C).

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