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Muawia H. Shaddad - One of the best experts on this subject based on the ideXlab platform.
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A noble gas and cosmogenic radionuclide analysis of two ordinary chondrites from Almahata Sitta
Meteoritics & Planetary Science, 2012Co-Authors: Matthias M. M. Meier, Marc W Caffee, Kunihiko Nishiizumi, Peter Jenniskens, Muawia H. Shaddad, Kees C. Welten, Jon M. Friedrich, Rainer WielerAbstract:We present the results of a noble gas (He, Ne, Ar) and cosmogenic radionuclide (10Be, 26Al, 36Cl) analysis of two chondritic fragments (#A100, L4 and #25, H5) found in the Almahata Sitta strewn field in Sudan. We confirm their earlier attribution to the same fall as the Ureilites dominating the strewn field, based on the following findings: (1) both chondrite samples indicate a preatmospheric radius of approximately 300 g cm-2, consistent with the preatmospheric size of asteroid 2008 TC3 that produced the Almahata Sitta strewn field; (2) both have, within error, a 21Ne/26Al-based cosmic ray exposure age of approximately 20 Ma, identical to the reported ages of Almahata Sitta Ureilites; (3) both exhibit hints of ureilitic Ar in the trapped component. We discuss a possible earlier irradiation phase for the two fragments of approximately 1020 Ma, visible only in cosmogenic 38Ar. We also discuss the approximately 3.8 Ga (4He) and approximately 4.6 Ga (40Ar) gas retention ages, measured in both chondritic fragments. These imply that the two chondrite fragments were incorporated into the ureilite host early in solar system evolution, and that the parent asteroid from which 2008 TC3 is derived has not experienced a large break-up event in the last 3.8 Ga. (Less)
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A noble gas and cosmogenic radionuclide analysis of two ordinary chondrites from Almahata Sitta
2012Co-Authors: Matthias M. M. Meier, Marc W Caffee, Kunihiko Nishiizumi, Peter Jenniskens, Muawia H. Shaddad, Kees C. Welten, Jon M. Friedrich, Rainer WielerAbstract:Abstract – We present the results of a noble gas (He, Ne, Ar) and cosmogenic radionuclide (10Be, 26Al, 36Cl) analysis of two chondritic fragments (#A100, L4 and #25, H5) found in the Almahata Sitta strewn field in Sudan. We confirm their earlier attribution to the same fall as the Ureilites dominating the strewn field, based on the following findings: 1) both chondrite samples indicate a pre-atmospheric radius of ~300 g cm-2, consistent with the pre-atmospheric size of asteroid 2008 TC3 that produced the Almahata Sitta strewn field, 2) both have, within error, a 21Ne/26Al based cosmic ray exposure age of ~20 Ma, identical to the reported ages of Almahata Sitta Ureilites, 3) both exhibit hints of ureilitic Ar in the trapped component. We discuss a possible earlier irradiation phase for the two fragments of ~10-20 Ma, visible only in cosmogenic 38Ar. We also discuss the ~3.8 Ga (4He) and ~4.6 Ga (40Ar) gas retention ages, measured in both chondritic fragments. These imply that the two chondrite fragments were incorporated into the ureilite host early in solar system evolution, and that the parent asteroid from which 2008 TC3 is derived has not experienced a large break-up event in the last 3.8 Ga
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heterogeneous distributions of amino acids provide evidence of multiple sources within the almahata sitta parent body asteroid 2008 tc sub 3
Meteoritics & Planetary Science, 2011Co-Authors: Aaron S Burton, Peter Jenniskens, Daniel P Glavin, Michael P Callahan, Jason P Dworkin, Muawia H. ShaddadAbstract:Two new fragments of the Almahata Sitta meteorite and a sample of sand from the related strewn field in the Nubian Desert, Sudan, were analyzed for two to six carbon aliphatic primary amino acids by ultrahigh performance liquid chromatography with UV-fluorescence detection and time-of-flight mass spectrometry (LC-FT ⁄ ToF-MS). The distribution of amino acids in fragment #25, an H5 ordinary chondrite, and fragment #27, a polymict ureilite, were compared with results from the previously analyzed fragment #4, also a polymict ureilite. All three meteorite fragments contain 180-270 parts-per-billion (ppb) of amino acids, roughly 1000-fold lower than the total amino acid abundance of the Murchison carbonaceous chondrite. All of the Almahata Sitta fragments analyzed have amino acid distributions that differ from the Nubian Desert sand, which primarily contains l-a-amino acids. In addition, the meteorites contain several amino acids that were not detected in the sand, indicating that many of the amino acids are extraterrestrial in origin. Despite their petrological differences, meteorite fragments #25 and #27 contain similar amino acid compositions; however, the distribution of amino acids in fragment #27 was distinct from those in fragment #4, even though both are polymict Ureilites from the same parent body. Unlike in CM2 and CR2 ⁄ 3 meteorites, there are low relative abundances of a-amino acids in the Almahata Sitta meteorite fragments, which suggest that Strecker-type chemistry was not a significant amino acid formation mechanism. Given the high temperatures that asteroid 2008 TC3 appears to have experienced and lack of evidence for aqueous alteration on the asteroid, it is possible that the extraterrestrial amino acids detected in Almahata Sitta were formed by Fischer-Tropsch ⁄ Haber-Bosch type gas-grain reactions at elevated temperatures.
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magnetism and mineralogy of almahata sitta polymict ureilite asteroid 2008 tc 3 implications for the ureilite parent body magnetic field
Meteoritics & Planetary Science, 2011Co-Authors: Viktor Hoffmann, Rupert Hochleitner, Masayuki Torii, Minoru Funaki, Takashi Mikouchi, Melanie Kaliwoda, Peter Jenniskens, Muawia H. ShaddadAbstract:The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC 3 consortium were investigating Almahata Sitta’s (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on Ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low-Ni kamacites with large grain sizes. Additional contributions come from micron-sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon-rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I-IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II-IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009).
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Magnetism and mineralogy of Almahata Sitta polymict ureilite (= asteroid 2008 TC 3 ): Implications for the ureilite parent body magnetic field
Meteoritics & Planetary Science, 2011Co-Authors: Viktor Hoffmann, Rupert Hochleitner, Masayuki Torii, Minoru Funaki, Takashi Mikouchi, Melanie Kaliwoda, Peter Jenniskens, Muawia H. ShaddadAbstract:The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC 3 consortium were investigating Almahata Sitta’s (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on Ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low-Ni kamacites with large grain sizes. Additional contributions come from micron-sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon-rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I-IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II-IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009).
Peter Jenniskens - One of the best experts on this subject based on the ideXlab platform.
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A noble gas and cosmogenic radionuclide analysis of two ordinary chondrites from Almahata Sitta
Meteoritics & Planetary Science, 2012Co-Authors: Matthias M. M. Meier, Marc W Caffee, Kunihiko Nishiizumi, Peter Jenniskens, Muawia H. Shaddad, Kees C. Welten, Jon M. Friedrich, Rainer WielerAbstract:We present the results of a noble gas (He, Ne, Ar) and cosmogenic radionuclide (10Be, 26Al, 36Cl) analysis of two chondritic fragments (#A100, L4 and #25, H5) found in the Almahata Sitta strewn field in Sudan. We confirm their earlier attribution to the same fall as the Ureilites dominating the strewn field, based on the following findings: (1) both chondrite samples indicate a preatmospheric radius of approximately 300 g cm-2, consistent with the preatmospheric size of asteroid 2008 TC3 that produced the Almahata Sitta strewn field; (2) both have, within error, a 21Ne/26Al-based cosmic ray exposure age of approximately 20 Ma, identical to the reported ages of Almahata Sitta Ureilites; (3) both exhibit hints of ureilitic Ar in the trapped component. We discuss a possible earlier irradiation phase for the two fragments of approximately 1020 Ma, visible only in cosmogenic 38Ar. We also discuss the approximately 3.8 Ga (4He) and approximately 4.6 Ga (40Ar) gas retention ages, measured in both chondritic fragments. These imply that the two chondrite fragments were incorporated into the ureilite host early in solar system evolution, and that the parent asteroid from which 2008 TC3 is derived has not experienced a large break-up event in the last 3.8 Ga. (Less)
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A noble gas and cosmogenic radionuclide analysis of two ordinary chondrites from Almahata Sitta
2012Co-Authors: Matthias M. M. Meier, Marc W Caffee, Kunihiko Nishiizumi, Peter Jenniskens, Muawia H. Shaddad, Kees C. Welten, Jon M. Friedrich, Rainer WielerAbstract:Abstract – We present the results of a noble gas (He, Ne, Ar) and cosmogenic radionuclide (10Be, 26Al, 36Cl) analysis of two chondritic fragments (#A100, L4 and #25, H5) found in the Almahata Sitta strewn field in Sudan. We confirm their earlier attribution to the same fall as the Ureilites dominating the strewn field, based on the following findings: 1) both chondrite samples indicate a pre-atmospheric radius of ~300 g cm-2, consistent with the pre-atmospheric size of asteroid 2008 TC3 that produced the Almahata Sitta strewn field, 2) both have, within error, a 21Ne/26Al based cosmic ray exposure age of ~20 Ma, identical to the reported ages of Almahata Sitta Ureilites, 3) both exhibit hints of ureilitic Ar in the trapped component. We discuss a possible earlier irradiation phase for the two fragments of ~10-20 Ma, visible only in cosmogenic 38Ar. We also discuss the ~3.8 Ga (4He) and ~4.6 Ga (40Ar) gas retention ages, measured in both chondritic fragments. These imply that the two chondrite fragments were incorporated into the ureilite host early in solar system evolution, and that the parent asteroid from which 2008 TC3 is derived has not experienced a large break-up event in the last 3.8 Ga
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heterogeneous distributions of amino acids provide evidence of multiple sources within the almahata sitta parent body asteroid 2008 tc sub 3
Meteoritics & Planetary Science, 2011Co-Authors: Aaron S Burton, Peter Jenniskens, Daniel P Glavin, Michael P Callahan, Jason P Dworkin, Muawia H. ShaddadAbstract:Two new fragments of the Almahata Sitta meteorite and a sample of sand from the related strewn field in the Nubian Desert, Sudan, were analyzed for two to six carbon aliphatic primary amino acids by ultrahigh performance liquid chromatography with UV-fluorescence detection and time-of-flight mass spectrometry (LC-FT ⁄ ToF-MS). The distribution of amino acids in fragment #25, an H5 ordinary chondrite, and fragment #27, a polymict ureilite, were compared with results from the previously analyzed fragment #4, also a polymict ureilite. All three meteorite fragments contain 180-270 parts-per-billion (ppb) of amino acids, roughly 1000-fold lower than the total amino acid abundance of the Murchison carbonaceous chondrite. All of the Almahata Sitta fragments analyzed have amino acid distributions that differ from the Nubian Desert sand, which primarily contains l-a-amino acids. In addition, the meteorites contain several amino acids that were not detected in the sand, indicating that many of the amino acids are extraterrestrial in origin. Despite their petrological differences, meteorite fragments #25 and #27 contain similar amino acid compositions; however, the distribution of amino acids in fragment #27 was distinct from those in fragment #4, even though both are polymict Ureilites from the same parent body. Unlike in CM2 and CR2 ⁄ 3 meteorites, there are low relative abundances of a-amino acids in the Almahata Sitta meteorite fragments, which suggest that Strecker-type chemistry was not a significant amino acid formation mechanism. Given the high temperatures that asteroid 2008 TC3 appears to have experienced and lack of evidence for aqueous alteration on the asteroid, it is possible that the extraterrestrial amino acids detected in Almahata Sitta were formed by Fischer-Tropsch ⁄ Haber-Bosch type gas-grain reactions at elevated temperatures.
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magnetism and mineralogy of almahata sitta polymict ureilite asteroid 2008 tc 3 implications for the ureilite parent body magnetic field
Meteoritics & Planetary Science, 2011Co-Authors: Viktor Hoffmann, Rupert Hochleitner, Masayuki Torii, Minoru Funaki, Takashi Mikouchi, Melanie Kaliwoda, Peter Jenniskens, Muawia H. ShaddadAbstract:The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC 3 consortium were investigating Almahata Sitta’s (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on Ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low-Ni kamacites with large grain sizes. Additional contributions come from micron-sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon-rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I-IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II-IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009).
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Magnetism and mineralogy of Almahata Sitta polymict ureilite (= asteroid 2008 TC 3 ): Implications for the ureilite parent body magnetic field
Meteoritics & Planetary Science, 2011Co-Authors: Viktor Hoffmann, Rupert Hochleitner, Masayuki Torii, Minoru Funaki, Takashi Mikouchi, Melanie Kaliwoda, Peter Jenniskens, Muawia H. ShaddadAbstract:The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC 3 consortium were investigating Almahata Sitta’s (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on Ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low-Ni kamacites with large grain sizes. Additional contributions come from micron-sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon-rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I-IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II-IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009).
Viktor Hoffmann - One of the best experts on this subject based on the ideXlab platform.
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magnetism and mineralogy of almahata sitta polymict ureilite asteroid 2008 tc 3 implications for the ureilite parent body magnetic field
Meteoritics & Planetary Science, 2011Co-Authors: Viktor Hoffmann, Rupert Hochleitner, Masayuki Torii, Minoru Funaki, Takashi Mikouchi, Melanie Kaliwoda, Peter Jenniskens, Muawia H. ShaddadAbstract:The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC 3 consortium were investigating Almahata Sitta’s (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on Ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low-Ni kamacites with large grain sizes. Additional contributions come from micron-sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon-rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I-IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II-IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009).
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Magnetism and mineralogy of Almahata Sitta polymict ureilite (= asteroid 2008 TC 3 ): Implications for the ureilite parent body magnetic field
Meteoritics & Planetary Science, 2011Co-Authors: Viktor Hoffmann, Rupert Hochleitner, Masayuki Torii, Minoru Funaki, Takashi Mikouchi, Melanie Kaliwoda, Peter Jenniskens, Muawia H. ShaddadAbstract:The Almahata Sitta meteorite is the first case of recovered extraterrestrial material originating from an asteroid that was detected in near Earth space shortly before entering and exploding in the high atmosphere. The aims of our project within the 2008 TC 3 consortium were investigating Almahata Sitta’s (AS) magnetic signature, phase composition and mineralogy, focussing on the opaque minerals, and gaining new insights into the magnetism of the ureilite parent body (UPB). We report on the general magnetic properties and behavior of Almahata Sitta and try to place the results in context with the existing data set on Ureilites and ureilite parent body models. The magnetic signature of AS is dominated by a set of low-Ni kamacites with large grain sizes. Additional contributions come from micron-sized kamacites, suessite, (Cr) troilite, and daubreelite, mainly found in the olivine grains adjacent to carbon-rich veins. Our results show that the paleomagnetic signal is of extraterrestrial origin as can be seen by comparing with laboratory produced magnetic records (IRM). Four types of kamacite (I-IV) have been recognized in the sample. The elemental composition of the ureilite vein metal Kamacite I (particularly Co) clearly differs from the other kamacites (II-IV), which are considered to be indigenous. Element ratios of kamacite I indicate that it was introduced into the UPB by an impactor, supporting the conclusions of Gabriel and Pack (2009).
Patrick Michel - One of the best experts on this subject based on the ideXlab platform.
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origin and history of ureilitic material in the solar system the view from asteroid 2008 tc3 and the almahata sitta meteorite
Meteoritics & Planetary Science, 2015Co-Authors: C A Goodrich, Lionel Wilson, Patrick Michel, William K Hartmann, D P Obrien, Stuart J Weidenschilling, Martin JutziAbstract:Asteroid 2008 TC3 (approximately 4 m diameter) was tracked and studied in space for approximately 19 h before it impacted Earth’s atmosphere, shattering at 44–36 km altitude. The recovered samples (>680 individual rocks) comprise the meteorite Almahata Sitta (AhS). Approximately 50–70% of these are Ureilites (ultramafic achondrites). The rest are chondrites, mainly enstatite, ordinary, and Rumuruti types. The goal of this work is to understand how fragments of so many different types of parent bodies became mixed in the same asteroid. Almahata Sitta has been classified as a polymict ureilite with an anomalously high component of foreign clasts. However, we calculate that the mass of fallen material was ≤0.1% of the pre-atmospheric mass of the asteroid. Based on published data for the reflectance spectrum of the asteroid and laboratory spectra of the samples, we infer that the lost material was mostly ureilitic. Therefore, 2008 TC3 probably contained only a few percent nonureilitic materials, similar to other polymict Ureilites except less well consolidated. From available data for the AhS meteorite fragments, we conclude that 2008 TC3 samples essentially the same range of types of ureilitic and nonureilitic materials as other polymict Ureilites. We therefore suggest that the immediate parent of 2008 TC3 was the immediate parent of all ureilitic material sampled on Earth. We trace critical stages in the evolution of that material through solar system history. Based on various types of new modeling and re-evaluation of published data, we propose the following scenario. (1) The ureilite parent body (UPB) accreted 0.5–0.6 Ma after formation of calcium-aluminum-rich inclusions (CAI), beyond the ice line (outer asteroid belt). Differentiation began approximately 1 Ma after CAI. (2) The UPB was catastrophically disrupted by a major impact approximately 5 Ma after CAI, with selective subsets of the fragments reassembling into daughter bodies. (3) Either the UPB (before breakup), or one of its daughters (after breakup), migrated to the inner belt due to scattering by massive embryos. (4) One daughter (after forming in or migrating to the inner belt) became the parent of 2008 TC3. It developed a regolith, mostly ≥3.8 Ga ago. Clasts of enstatite, ordinary, and Rumuruti-type chondrites were implanted by low-velocity collisions. (5) Recently, the daughter was disrupted. Fragments were injected or drifted into Earth-crossing orbits. 2008 TC3 comes from outer layers of regolith, other polymict Ureilites from deeper regolith, and main group Ureilites from the interior of this body. In contrast to other models that have been proposed, this model invokes a stochastic history to explain the unique diversity of foreign materials in 2008 TC3 and other polymict Ureilites.
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Comment on “Parent body depth-pressure-temperature relationships and the style of the ureilite anatexis” by P. H. Warren (MAPS 47:209–227)
Meteoritics & Planetary Science, 2013Co-Authors: Cyrena Anne Goodrich, James A. Van Orman, Lionel Wilson, Patrick MichelAbstract:Ureilites are carbon-rich ultramafic (olivine + dominantly low-Ca pyroxene) achondrites with poorly understood petrogenesis. One major problem concerns the origin of extensive variation in FeO content (olivine core Fo values ranging from approximately 75 to 95) among the individual Ureilites. The two main competing hypotheses to explain this variation are: (1) equilibrium smelting, in which ureilite Fo values were established by pressure-dependent (depth-linked) carbon redox reactions on the ureilite parent body during partial melting; or (2) nebular inheritance, in which the variation in FeO contents was derived from ureilite precursors and was preserved during partial melting. The paper “Parent body depth-pressure-temperature relationships and the style of the ureilite anatexis” by Warren (2012) discusses a series of topics related to ureilite petrogenesis. In each case, an argument is presented within the context of smelting versus nonsmelting models. Collectively, these arguments create the impression that there are many valid arguments against smelting. The purpose of this comment is to point out flaws in some of these arguments, and/or to show that the issues they address are independent of smelting versus nonsmelting models. Both equilibrium smelting and nebular inheritance (simple anatexis) models face challenges in explaining all the properties of Ureilites, but both remain viable.
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comment on parent body depth pressure temperature relationships and the style of the ureilite anatexis by p h warren maps 47 209 227
Meteoritics & Planetary Science, 2013Co-Authors: Cyrena Anne Goodrich, James A. Van Orman, Lionel Wilson, Patrick MichelAbstract:Ureilites are carbon-rich ultramafic (olivine + dominantly low-Ca pyroxene) achondrites with poorly understood petrogenesis. One major problem concerns the origin of extensive variation in FeO content (olivine core Fo values ranging from approximately 75 to 95) among the individual Ureilites. The two main competing hypotheses to explain this variation are: (1) equilibrium smelting, in which ureilite Fo values were established by pressure-dependent (depth-linked) carbon redox reactions on the ureilite parent body during partial melting; or (2) nebular inheritance, in which the variation in FeO contents was derived from ureilite precursors and was preserved during partial melting. The paper “Parent body depth-pressure-temperature relationships and the style of the ureilite anatexis” by Warren (2012) discusses a series of topics related to ureilite petrogenesis. In each case, an argument is presented within the context of smelting versus nonsmelting models. Collectively, these arguments create the impression that there are many valid arguments against smelting. The purpose of this comment is to point out flaws in some of these arguments, and/or to show that the issues they address are independent of smelting versus nonsmelting models. Both equilibrium smelting and nebular inheritance (simple anatexis) models face challenges in explaining all the properties of Ureilites, but both remain viable.
S Marchi - One of the best experts on this subject based on the ideXlab platform.
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on the origin of the almahata sitta meteorite and 2008 tc3 asteroid
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Julie Gayonmarkt, Alessandro Morbidelli, M Delbo, S MarchiAbstract:Asteroid 2008 TC3 was a near-Earth asteroid that impacted the Earth on 2008 October 7. Meteorites were produced by the break-up of 2008 TC3 in the high atmosphere and at present, about 600 meteorites – called Almahata Sitta – coming from 2008 TC3 have been recovered. A mineralogical study of Almahata Sitta fragments shows that the asteroid 2008 TC3 was made of meteorites of different types (Ureilites, H, L and E chondrites). Understanding the origin of this body and how it was put together remain a challenge. Here we perform a detailed spectroscopical and dynamical investigation to show that the most likely source region of 2008 TC3 is in the inner main belt at low inclination (i < 8 ◦ ). We show that asteroids with spectroscopic classes that can be associated with the different meteorite types of Almahata Sitta are present in the region of the main belt that includes the Nysa-Polana family and objects of the background at low inclination. Searching for a possible scenario of formation for 2008 TC3, we show that there is little chance that 2008 TC3 was formed by low-velocity collisions between asteroids of different mineralogies, in the current asteroid belt. It seems more likely that the heterogeneous composition of 2008 TC3 was inherited from a time when the asteroid belt was in a different dynamical state, most likely in the very early Solar system. Because Ureilites are fragments of a large, thermally metamorphosed asteroid, this suggests that the phases of collisional erosion (the break-up of the ureilite parent body) and collisional accretion (the formation of the parent body of 2008 TC3) overlapped for some time in the primordial asteroid belt.
