Calcium-aluminum-rich inclusion found in the Ivuna CI chondrite: Are CI chondrites a good proxy for the bulk composition of the solar system?     

David R. Frank  Gary R. Huss  Michael E. Zolensky  Kazuhide Nagashima  Loan Le 《Meteoritics & planetary science》2023,58(10):1495-1511

Cosmochemists have relied on CI carbonaceous chondrites as proxies for chemical composition of the non-volatile elements in the solar system because these meteorites are fine-grained, chemically homogeneous, and have well-determined bulk compositions that agree with that of the solar photosphere, within uncertainties. Here we report the discovery of a calcium-aluminum-rich inclusion (CAI) in the Ivuna CI chondrite. CAIs are chemically highly fractionated compared to CI composition, consisting of refractory elements and having textures that either reflect condensation from nebular gas or melting in a nebular environment. The CAI we found is a compact type A CAI with typical ¹⁶O-rich oxygen. However, it shows no evidence of ²⁶Al, which was present when most CAIs formed. Finding a CAI in a CI chondrite raises serious questions about whether CI chondrites are a reliable proxy for the bulk composition of the solar system. Too much CAI material would show up as mismatches between the CI composition and the composition of the solar photosphere. Although small amounts of refractory material have previously been identified in CI chondrites, this material is not abundant enough to significantly perturb the bulk compositions of CI chondrites. The agreement between the composition of the solar photosphere and CI chondrites allows no more than ~0.5 atom% of CAI-like material to have been added to CI chondrites. As the compositions of CI chondrites, carbonaceous asteroids, and the solar photosphere are better determined, we will be able to reduce the uncertainties in our estimates of the composition of the solar system.  相似文献   

Mineralogy,petrology, and oxygen isotopic compositions of chondritic and achondritic lithologies in the anomalous CB carbonaceous chondrites Sierra Gorda 013 and Fountain Hills     

Alexander N. Krot  Kazuhide Nagashima  Marina A. Ivanova  Dante Lauretta  Guy Libourel  Brandon C. Johnson  Frank E. Brenker  Viktoria Hoffman  Martin Bizzarro 《Meteoritics & planetary science》2024,59(4):754-777

The CB (Bencubbin-like) metal-rich carbonaceous chondrites are subdivided into the CB_a and CB_b subgroups. The CB_a chondrites are composed predominantly of ~cm-sized skeletal olivine chondrules and unzoned Fe,Ni-metal ± troilite nodules. The CB_b chondrites are finer grained than the CB_as and consist of chemically zoned and unzoned Fe,Ni-metal grains, Fe,Ni-metal ± troilite nodules, cryptocrystalline and skeletal olivine chondrules, and rare refractory inclusions. Both subgroups contain exceptionally rare porphyritic chondrules and no interchondrule fine-grained matrix, and are interpreted as the products of a gas–melt impact plume formed by a high-velocity collision between differentiated planetesimals about 4562 Ma. The anomalous metal-rich carbonaceous chondrites, Fountain Hills and Sierra Gorda 013 (SG 013), have bulk oxygen isotopic compositions similar to those of other CBs but contain coarse-grained igneous clasts/porphyritic chondrule-like objects composed of olivine, low-Ca-pyroxene, and minor plagioclase and high-Ca pyroxene as well as barred olivine and skeletal olivine chondrules. Cryptocrystalline chondrules, zoned Fe,Ni-metal grains, and interchondrule fine-grained matrix are absent. In SG 013, Fe,Ni-metal (~80 vol%) occurs as several mm-sized nodules; magnesiochromite (Mg-chromite) is accessory; daubréelite and schreibersite are minor; troilite is absent. In Fountain Hills, Fe,Ni-metal (~25 vol%) is dispersed between chondrules and silicate clasts; chromite and sulfides are absent. In addition to a dominant chondritic lithology, SG 013 contains a chondrule-free lithology composed of Fe,Ni-metal nodules (~25 vol%), coarse-grained olivine and low-Ca pyroxene, interstitial high-Ca pyroxene and anorthitic plagioclase, and Mg-chromite. Here, we report on oxygen isotopic compositions of olivine, low-Ca pyroxene, and ±Mg-chromite in Fountain Hills and both lithologies of SG 013 measured in situ using an ion microprobe. Oxygen isotope compositions of olivine, low-Ca pyroxene, and Mg-chromite in these meteorites are similar to those of magnesian non-porphyritic chondrules in CB_a and CB_b chondrites: on a three-isotope oxygen diagram (δ¹⁷O vs. δ¹⁸O), they plot close to a slope-1 (primitive chondrule mineral) line and have a very narrow range of Δ¹⁷O (=δ¹⁷O–0.52 × δ¹⁸O) values, −2.5 ± 0.9‰ (avr ± 2SD). No isotopically distinct relict grains have been identified in porphyritic chondrule-like objects. We suggest that magnesian non-porphyritic (barred olivine, skeletal olivine, cryptocrystalline) chondrules in the CB_as, CB_bs, and porphyritic chondrule-like objects in SG 013 and Fountain Hills formed in different zones of the CB impact plume characterized by variable pressure, temperature, cooling rates, and redox conditions. The achondritic lithology in SG 013 represents fragments of one of the colliding bodies and therefore one of the CB chondrule precursors. Fountain Hills was subsequently modified by impact melting; Fe,Ni-metal and sulfides were partially lost during this process.  相似文献   

Oxygen isotopic composition of an enstatite ribbon of probable cometary origin     

Ryan C. Ogliore  Donald E. Brownlee  Kazuhide Nagashima  David J. Joswiak  Josiah B. Lewis  Alexander N. Krot  Kainen L. Utt  Gary R. Huss 《Meteoritics & planetary science》2020,55(6):1371-1381

Filamentary enstatite crystals are found in interplanetary dust particles (IDPs) of likely cometary origin but are very rare or absent in meteorites. Crystallographic characteristics of filamentary enstatites indicate that they condensed directly from vapor. We measured the O isotopic composition of an enstatite ribbon from a giant cluster IDP to be δ¹⁸O = 25 ± 55, δ¹⁷O = ?19 ± 129, ?¹⁷O = ?32 ± 134 (2σ errors), which is inconsistent at the 2σ level with the composition of the Sun inferred from the Genesis solar wind measurements. The particle's O isotopic composition, consistent with the terrestrial composition, implies that it condensed from a gas of nonsolar O isotopic composition, possibly as a result of vaporization of disk region enriched in ¹⁶O‐depleted solids. The relative scarcity of filamentary enstatite in asteroids compared to comets implies either that this crystal condensed from dust vaporized in situ in the outer solar system where comets formed or it condensed in the inner solar system and was subsequently transported outward to the comet‐forming region.  相似文献   

A Transit of Venus Possibly Misinterpreted as an Unaided-Eye Sunspot Observation in China on 9 December 1874     

Hayakawa  Hisashi  Sôma  Mitsuru  Tanikawa  Kiyotaka  Willis  David M.  Wild  Matthew N.  Macdonald  Lee T.  Imada  Shinsuke  Hattori  Kentaro  Richard Stephenson  F. 《Solar physics》2019,294(9):1-13

Solar Physics - Large sunspots can be observed with the unaided eye under suitable atmospheric seeing conditions. Such observations are of particular value because the frequency of their appearance...  相似文献   

日本琵琶湖中微囊藻水华形成机理的再认识     

Antonio Quesa  Jean-Jacques Frenette  早川和秀  熊谷道夫 《湖泊科学》1998,10(S1):341-345

Blooms of cyanobacteria are responsible for many problems in freshwater ecosystems. The massive growth of these microorganisms may limit the utilization of freshwater for human requirements since, apart from other problems, the production of toxic substances has been found to occur frequently during blooming periods. Ecologically, cyanobacterial blooms can modify dramatically the ecosystem through their low edibility within the food web and the huge primary production. Thus, saprobic processes are stimulated and the characteristics related to anaerobic conditions are also more extreme.Cyanobacterial blooms are many times explained as the consequence of the eutrophication of waterbodies. However, factors promoting bloom formation and ecological succession of cyanobacteria are not well understood yet.  相似文献   

Historical Auroras in the 990s: Evidence of Great Magnetic Storms     

Hisashi Hayakawa  Harufumi Tamazawa  Yurina Uchiyama  Yusuke Ebihara  Hiroko Miyahara  Shunsuke Kosaka  Kiyomi Iwahashi  Hiroaki Isobe 《Solar physics》2017,292(1):12

A significant carbon-14 enhancement has recently been found in tree rings for the year 994, suggesting an extremely strong and brief cosmic ray flux event. The origin of this particular cosmic ray event has not been confirmed, but one possibility is that it might be of solar origin. Contemporary historical records of low-latitude auroras can be used as supporting evidence of intense solar activity around that time. We investigate previously reported as well as new records that have been found in contemporary observations from the 990s to determine potential auroras. Records of potential red auroras in late 992 and early 993 were found around the world, i.e. in the Korean Peninsula, Saxonian cities in modern Germany, and the Island of Ireland, suggesting the occurrence of an intense geomagnetic storm driven by solar activity.  相似文献