Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences最新文献

{"title":"Interstellar and circumstellar grain formation and survival","authors":"A. Jones","doi":"10.1098/rsta.2001.0890","DOIUrl":"https://doi.org/10.1098/rsta.2001.0890","url":null,"abstract":"Dust formation is primarily associated with stars in their dying throes, e.g. when low–mass stars reach the red–giant or asymptotic–giant branch (AGB) phase of their evolution, or when massive stars explode as supernovae (SNe). While the contribution of AGB stars to the galactic dust budget is significant, both in terms of variety and quantity, that due to SNe is not yet clear. AGB stardust formation includes grains of amorphous and crystalline silicates, hydrogenated carbons, silicon carbide and graphite. However, not all of these materials have yet been detected in circumstellar regions or in the interstellar medium (ISM). The derived lifetimes for these materials in the ISM appear to be short compared with the time–scale for the formation of new dust. Thus a grain lifetime and propagation problem is posed. Apparently, it is also necessary to reform and grow grains in the ISM, through accretion and coagulation processes, in order to explain interstellar dust observations. This paper discusses dust formation in circumstellar and interstellar environments, dust sources and their contributions to the galactic dust budget, and dust survival and propagation in the ISM.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"135 1","pages":"1961 - 1972"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78030376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unresolved questions regarding the origins of Solar System solids","authors":"P. Cassen","doi":"10.1098/rsta.2001.0888","DOIUrl":"https://doi.org/10.1098/rsta.2001.0888","url":null,"abstract":"It is remarkable that we possess samples of Solar System solids which have retained a record of galactic and stellar events that occurred well before the birth of the Sun, as well as samples which contain evidence of Solar System processes that occurred during the earliest stages of planet building. The signatures of such processes are most commonly recognized in isotopic anomalies, identifiable against a pervasive background of isotopic homogeneity, and systematic trends in the elemental abundance patterns of primitive meteoritic materials. Although the significance of these anomalies and patterns is unmistakable, their interpretation in terms of specific processes is problematic. Central to such interpretations are questions of spatial scale: do cosmogonically significant isotopic and elemental compositions reflect processes that occurred on the grand scale of the proto–solar cloud, or do they result from many localized events within a nebular or planetary environment? The question is fundamental to our understanding of the formation of solid objects in the Solar System. This question will be examined here, with specific reference to theoretical models of nebular evolution and planet building, and evidence regarding the survival of presolar signatures, the origin of short–lived radionuclides and oxygen isotopic systematics.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"36 1","pages":"1935 - 1947"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84663971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The rates of accretion, core formation and volatile loss in the early Solar System","authors":"A. Halliday, Der-Chuen Lee, D. Porcelli, U. Wiechert, M. Schönbächler, M. Rehkämper","doi":"10.1098/rsta.2001.0901","DOIUrl":"https://doi.org/10.1098/rsta.2001.0901","url":null,"abstract":"Nuclides with half–lives of 105–108 yr permit the elucidation of nebula time–scales and the rates of accretion of planetesimals. However, the 182Hf–182W system with a half–life of 9_2 Myr also provides new and very useful constraints on the formation of the terrestrial planets. This technique allows one to address the timing of metal–silicate equilibration in objects as different as chondrites and the Earth. With improvements in sensitivity and precision, very small time differences in metal segregation in asteroids should be resolvable from measuring iron meteorites. It is already clear that the formation and differentiation of some asteroidal–sized objects was completed in less than 10 Myr. Accretion and core formation were protracted in the case of the Earth (greater than 50 Myr) relative to Mars (probably less than 20 Myr). Indeed, the Martian mantle appears to retain both chemical and isotopic heterogeneities that are residual from the process of core formation. Such early features appear to have been eliminated from the Earth's mantle presumably because of 4.5 Gyr of relatively efficient convective mixing. Tungsten isotope data provide compelling support for the ‘giant impact’ theory of lunar origin. The Moon is a high Hf/W object that contains a major component of chondritic W. This is consistent with a time of formation of greater than 50 Myr after the start of the Solar System. New highly precise oxygen isotope data are unable to resolve any difference between the source of components in the Earth and Moon. Therefore, the giant impact itself may have produced some of the differences in moderately volatile element budgets between these objects. This finds support in precise Sr isotopic data for early lunar samples. The data are consistent with the proto–Earth and Theia (the impactor) having Rb/Sr ratios that were not very different from that of present day Mars. Therefore, the extended history of accretion, rather than nebular phenomena, may be responsible for some of the major differences between the terrestrial planets.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"11 1","pages":"2111 - 2135"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88683239","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Physical conditions of protosolar matter","authors":"L. Hartmann","doi":"10.1098/rsta.2001.0896","DOIUrl":"https://doi.org/10.1098/rsta.2001.0896","url":null,"abstract":"I review a few astronomical constraints concerning physical conditions in and evolutionary time–scales of protoplanetary discs. Some revisions are suggested to the scenario by which short–lived radioactive species would enter the protosolar cloud. The increasing evidence for substantial grain growth in discs at ages of 1 Myr is also outlined. Protoplanetary discs are accretion discs; when (inner) dust emission decreases strongly, accretion stops, demonstrating a relationship between the disappearance of infrared excess emission and accretable gas. The time–scale for disc ‘clearing’ is ca. 3–10 Myr, with a large range for individual systems. If disc masses estimated from dust emission are at all accurate, then the amount of material accreted onto the central star during the T Tauri phase is a substantial fraction of the total disc mass available at 1 Myr; and this in turn implies substantial radial motion of the accreting material during disc evolution. It may be that the formation of planets is the primary mechanism resulting in the cessation of accretion; certainly it is difficult to see how gas can be removed from T Tauri discs on 10 Myr time–scales.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"3 45 1","pages":"2049 - 2060"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86266091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The hydrology of carbonaceous chondrite parent bodies and the evolution of planet progenitors","authors":"E. Young","doi":"10.1098/rsta.2001.0900","DOIUrl":"https://doi.org/10.1098/rsta.2001.0900","url":null,"abstract":"Oxygen isotope ratio data from carbonaceous chondrites are explained if aqueous fluids flowed from high to low temperatures within the parent objects of these primitive meteorites. Recognition of ancient hydrological activity on primitive asteroid precursors affords a new class of constraints on the heat sources (ages?) and sizes of planet precursors in the early Solar System based on the geological evolution of planetesimals.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"1 1","pages":"2095 - 2110"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77160055","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The chemical composition of the interstellar medium","authors":"A. Witt","doi":"10.1098/rsta.2001.0889","DOIUrl":"https://doi.org/10.1098/rsta.2001.0889","url":null,"abstract":"Our knowledge of the abundances of heavy elements with nuclear charge Z > 2 in the interstellar medium is surprisingly incomplete. Several factors contribute to this state of affairs. A substantial but unknown fraction of heavy elements is locked up in interstellar dust, but the total mass of interstellar grains, as well as their size distribution and exact composition, are still uncertain. The use of the chemical compositions of stellar atmospheres as a reference for the interstellar medium has become questionable, as the range in stellar compositions is becoming more fully known. The study of the stellar nucleosynthetic sources of heavy elements also provides only uncertain constraints, given that many different types of processes have contributed to the enrichment of the interstellar medium. The solution to the present dilemma may reside in the in situ detection and chemical characterization of interstellar grains themselves, which could be accomplished in the near future.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"43 1","pages":"1949 - 1959"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87147640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Condensed matter astrophysics: constraints and questions on the early development of the Solar System","authors":"C. Allègre","doi":"10.1098/rsta.2001.0902","DOIUrl":"https://doi.org/10.1098/rsta.2001.0902","url":null,"abstract":"We discuss the following fundamental problems of early Solar System history. (i) Fine chronology, using long–lived U–Pb as well as the different extinct radionuclides. (ii) The nature of the solid material from which the planets were made. (iii) The immediate prehistory of the formation of the Solar System including the question of a possible supernova trigger. (iv) The origin of anomalies in oxygen isotopes. In each case, an effort has been made to distinguish what we know from what we need to learn.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"65 1","pages":"2137 - 2155"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88960364","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chemical and isotopic heterogeneity in protosolar matter","authors":"H. Palme","doi":"10.1098/rsta.2001.0897","DOIUrl":"https://doi.org/10.1098/rsta.2001.0897","url":null,"abstract":"It is argued that the inner Solar System is chemically fractionated with regard to the bulk Solar System. It is enriched in refractory and depleted in volatile elements. Carbonaceous chondrites reflect the major fractionation trends of the present inner Solar System material. Other groups of meteorites are indicative of processes in more local environments. Although the element pattern of material in the inner Solar System bears some resemblance to that in grains of the interstellar medium (ISM), Solar System materials have, with few exceptions, no memory of their ISM origin. After decoupling of the Solar System from ISM, isotopic and elemental remixing occurred followed by metal, forsterite and volatile element fractionations.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"4 1","pages":"2061 - 2075"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75194765","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Origin of short–lived radionuclides","authors":"S. Russell, M. Gounelle, R. Hutchison","doi":"10.1098/rsta.2001.0893","DOIUrl":"https://doi.org/10.1098/rsta.2001.0893","url":null,"abstract":"This paper reviews the evidence for short–lived radionuclides in the early Solar System and critically evaluates models for their origin. Radionuclides with half–lives of less than 50 Myr for which firm and consistent evidence has been found are 10Be, 26Al, 41Ca, 53Mn, 60Fe, 107Pd, 129I and 182Hf. The oldest Solar System objects, calcium–aluminium–rich inclusions (CAIs), contained 10Be, 26Al, 41Ca and 53Mn on formation. We discuss whether a spallation or stellar origin for the radionuclides is more likely, and conclude that the initial presence of short–lived radionuclides in CAIs can be most easily explained if these formed by spallation reactions close to the protosun.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"19 1","pages":"1991 - 2004"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84741799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Theories of planetary formation: constraints from the study of meteorites","authors":"R. Hutchison, I. Williams, S. Russell","doi":"10.1098/rsta.2001.0898","DOIUrl":"https://doi.org/10.1098/rsta.2001.0898","url":null,"abstract":"Compositional variations between chondrite groups and the inventory of short–lived nuclides once present in them are consistent with an origin in the accretion disc of a T Tauri protosun. T Tauri outbursts reprocessed infalling matter, part of which was recycled back into the disc. Chondrites and rapidly cooled igneous meteorites together form the basis of a chronology of events over the first 50 Myr of Solar System history. Chondrites contain evidence of hypervelocity impact within 2 Myr of the formation of the Solar System. This requires the local presence of a Jupiter–massed object to pump up relative velocities. Capture of an interstellar cloudlet, which subsequently underwent gravitational collapse, or of an unbound planet is implied. Capture at a low inclination and high eccentricity would have stirred the matter in the accretion disc, triggered planetesimal formation and growth, stabilized the orbit of the proto–Jupiter, and ended the T Tauri phase of the protosun.","PeriodicalId":20023,"journal":{"name":"Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences","volume":"4 1","pages":"2077 - 2093"},"PeriodicalIF":0.0,"publicationDate":"2001-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84117939","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}