Autor Thema: Entstehung von Chondren  (Gelesen 18579 mal)

Offline karmaka

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Re: Entstehung von Chondren
« Antwort #90 am: März 28, 2013, 23:21:48 nachm. »
Noch eine neue Theorie zur Chondrenbildung: Die Kurzschluss-Theorie

Chondrenbildung durch 'flache' elektrische Ströme ('current sheets'), hervorgerufen durch magnetische Turbulenzen

Erläuterung der Theorie

PAPER

MINERAL PROCESSING BY SHORT CIRCUITS IN PROTOPLANETARY DISKS

Colin P. McNally, Alexander Hubbard, Mordecai-Mark Mac Low, Denton S. Ebel, and Paola D'Alessio

The Astrophysical Journal Letters Volume 767 Number 1
Colin P. McNally et al. 2013 ApJ 767 L2 doi:10.1088/2041-8205/767/1/L2

Abstract

Zitat
Meteoritic chondrules were formed in the early solar system by brief heating of silicate dust to melting temperatures. Some highly refractory grains (Type B calcium-aluminum-rich inclusions, CAIs) also show signs of transient heating. A similar process may occur in other protoplanetary disks, as evidenced by observations of spectra characteristic of crystalline silicates. One possible environment for this process is the turbulent magnetohydrodynamic flow thought to drive accretion in these disks. Such flows generally form thin current sheets, which are sites of magnetic reconnection, and dissipate the magnetic fields amplified by a disk dynamo. We suggest that it is possible to heat precursor grains for chondrules and other high-temperature minerals in current sheets that have been concentrated by our recently described short-circuit instability. We extend our work on this process by including the effects of radiative cooling, taking into account the temperature dependence of the opacity; and by examining current sheet geometry in three-dimensional, global models of magnetorotational instability. We find that temperatures above 1600 K can be reached for favorable parameters that match the ideal global models. This mechanism could provide an efficient means of tapping the gravitational potential energy of the protoplanetary disk to heat grains strongly enough to form high-temperature minerals. The volume-filling nature of turbulent magnetic reconnection is compatible with constraints from chondrule-matrix complementarity, chondrule-chondrule complementarity, the occurrence of igneous rims, and compound chondrules. The same short-circuit mechanism may perform other high-temperature mineral processing in protoplanetary disks such as the production of crystalline silicates and CAIs.

Vielleicht liefert ALMA in Zukunft Antworten über Größe und Verteilung des Staubs.

Offline karmaka

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Re: Entstehung von Chondren
« Antwort #91 am: Juli 08, 2013, 19:29:02 nachm. »
Ein weiterer Bericht zum großen Thema:

Cosmochemist discovers potential solution to meteorite mystery

Chondrules may have formed from high-pressure collisions in early solar system


LINK

Vapor saturation of sodium: Key to unlocking the origin of chondrules

    Alexei V. Fedkin, Lawrence Grossman

    Dept. of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Ave., Chicago, IL 60637, United States

    http://dx.doi.org/10.1016/j.gca.2013.02.020

Zitat
Abstract

Sodium saturation of the vapor coexisting with chondrules at their liquidus temperatures implies that vapor-condensed phase equilibrium was reached at those temperatures for all elements more refractory than sodium. In order to investigate the possibility that chondrules formed in impact-generated plumes, equilibrium calculations were applied to droplets made from two different target compositions. Combinations of dust enrichment and Ptot were found that lead to sodium saturation, and the subsequent chemical and mineralogical evolution of the droplets was explored at those conditions. If an impact on a body of CI composition caused instantaneous heating, melting and devolatilization of the target rock and ejection of a plume of gaseous, liquid and solid matter that mixed with residual nebular gas at conditions where 50% or 90% of the sodium was retained by the resulting droplets at their liquidus temperature, their mineralogical and chemical properties would strongly resemble those of Type II chondrules. If the droplets cooled and equilibrated with the mixture of residual nebular gas and their devolatilized water, sulfur and alkalis, the fayalite content of the olivine and the chemical compositions of the bulk droplets and their glasses would closely resemble those of Types IIA and IIAB chondrules at CI dust enrichments between 400× and 800×. For 50% sodium retention, the corresponding values of Ptot are 2 bars (for 400×) and 1 bar (for 800×). For 90% retention, they are 25 and 10 bars, respectively. If, instead, the target has an anhydrous, ordinary chondrite-like composition, called H′, the ejected droplets are bathed in a gas mix consisting mostly of devolatilized sulfur and alkalis with residual nebular gas, a much more reducing plume. If the conditions were such that sodium were retained by the resulting droplets at their liquidus temperature, the fayalite contents of the olivine and the chemical compositions of the bulk droplets and their glasses would closely resemble those of Types IA and IAB chondrules at H′ dust enrichments between 103× and 4 × 103×. For 90% sodium retention, the corresponding values of Ptot are 15 bars (for 103×) and 2 bars (for 4 × 103×). For 50% retention, they are 2 and 8 × 10−2 bars, respectively.

Offline erich

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Re: Entstehung von Chondren
« Antwort #92 am: Juli 09, 2013, 09:09:29 vorm. »
Weiß nicht ob das schon hier diskuttiert wurde: http://news.uchicago.edu/article/2013/07/08/cosmochemist-discovers-potential-solution-meteorite-mystery  :gruebel:
Ich persönlich habe freilich noch eine etwas andere Theorie
<B>Rocks from beyond earth's gravity</B>

Offline karmaka

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Re: Entstehung von Chondren
« Antwort #93 am: August 17, 2014, 19:22:40 nachm. »
Neues zum Schockwellen-Modell der Entstehung von Chondren:

A critical analysis of shock models for chondrule formation

Sebastian M. Stammler, Cornelis P. Dullemond

Icarus, Volume 242, 1 November 2014, Pages 1–10, DOI: 10.1016/j.icarus.2014.07.024

LINK

Offline pema

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Re: Entstehung von Chondren
« Antwort #94 am: August 18, 2014, 11:24:13 vorm. »
Danke für den Link, Martin!

G. J. Taylor (Hawai'i Institute of Geophysics and Planetology) schrieb im Oktober 2005(!):

"Not everyone agrees with an origin by shock waves in the solar nebula, of course. Some meteoriticists think chondrules originated during impacts between solid or molten small bodies. Everyone agrees, however, that chondrules made their appearance early in the history of the solar system. Isotopic dating of chondrules shows that they formed within three million years of the formation of calcium-aluminum-rich inclusions (CAIs), the first solids to be produced in the solar nebula. This was a busy period. Most meteoriticists and astrophysicists believe that not only did shock waves create CAIs and normal chondrules from fluffy balls of dust, but chondrules and dust accreted into asteroid-sized planetesimals, some of which were melted by short-lived isotopes (mostly 26Al), forming metallic cores, mantles, and basaltic crusts. Other planetesimals were just heated a bit. All this in a period lasting only 3 million years. (Only geologists and astronomers attach the adjective "only" to 3 million years. But 3 million years is only 0.07% of the age of the Solar System.)"

 …der letzte Satz () des Zitats gefällt mir besonders gut!  :smile:

Gruss,
PeMa (Peter)

Offline karmaka

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Re: Entstehung von Chondren
« Antwort #95 am: August 29, 2014, 10:11:55 vorm. »
Kürzlich ist eine interessante kommentierte Zusammenfassung der Literatur
zum Thema Chondrengröße erschienen. Das PDF ist open access!  :smile:

Chondrule size and related physical properties: a compilation and evaluation of current data across all meteorite groups

Jon M. Friedrich, Michael K. Weisberg, Denton S. Ebel, Alison E. Biltz, Bernadette M. Corbett, Ivan V. Iotzov, Wajiha S. Khan, Matthew D. Wolman

invited review accepted for publication in Chemie der Erde
Earth and Planetary Astrophysics
arXiv:1408.6581
Submitted on 27 Aug 2014

PDF-LINK
« Letzte Änderung: August 29, 2014, 10:34:13 vorm. von karmaka »

Offline karmaka

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Re: Entstehung von Chondren
« Antwort #96 am: September 16, 2014, 15:42:51 nachm. »
Eine neue Lektüre zum Thema:

Semarkona: Lessons for chondrule and chondrite formation

Alexander Hubbard, Denton S. Ebel

PDF LINK (open access)

LINK

Zitat
We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona's parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.




Offline karmaka

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Re: Entstehung von Chondren
« Antwort #97 am: September 17, 2014, 14:45:50 nachm. »
Weiteres zum Thema:

Revisiting Jovian-Resonance Induced Chondrule Formation

M. Nagasawa, K. K. Tanaka, H. Tanaka, T. Nakamoto, H. Miura, T. Yamamoto

Submitted on 16 Sep 2014

PDF LINK (open access)

LINK

ABSTRACT:
Zitat
It is proposed that planetesimals perturbed by Jovian mean-motion resonances are the source of shock waves that form chondrules. It is considered that this shock-induced chondrule formation requires the velocity of the planetesimal relative to the gas disk to be on the order of > 7 km/s at 1 AU. In previous studies on planetesimal excitation, the effects of Jovian mean-motion resonance together with the gas drag were investigated, but the velocities obtained were at most 8 km/s in the asteroid belt, which is insufficient to account for the ubiquitous existence of chondrules. In this paper, we reexamine the effect of Jovian resonances and take into account the secular resonance in the asteroid belt caused by the gravity of the gas disk. We find that the velocities relative to the gas disk of planetesimals a few hundred kilometers in size exceed 12 km/s, and that this is achieved around the 3:1 mean-motion resonance. The heating region is restricted to a relatively narrow band between 1.5 AU and 3.5 AU. Our results suggest that chondrules were produced effectively in the asteroid region after Jovian formation. We also find that many planetesimals are scattered far beyond Neptune. Our findings can explain the presence of crystalline silicate in comets if the scattered planetesimals include silicate dust processed by shock heating.


Offline Morlok

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Re: Entstehung von Chondren
« Antwort #98 am: September 22, 2014, 17:24:15 nachm. »
10 Meteoritenforscher = 11-12 Theorien zur Chondrenbildung. Das Problem ist, dass man Silikate halt auf viele verschiedene Arten aufschmelzen kann. Wir haben z.B. Staub durch Plasmabögen rieseln lassen.

Ich wäre nicht überrascht, wenn die Chondrenbildung vielleicht gar kein großräumiger oder zentraler Vorgang im Sonnensystem war, und vielleicht nur ein regionales Zufallsereignis.

Offline lithoraptor

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Re: Entstehung von Chondren
« Antwort #99 am: September 22, 2014, 19:17:55 nachm. »
Moin!

Ich bin noch immer der Meinung, dass sich Chondren auf ganz unterschiedliche Weise gebildet haben können.

Was mich bei allen Theorien immer etwas stört ist das Faktum, dass sie immer irgendwie "absolutistisch" sind. Eben immer Beweise dafür gefunden werden, dass sich etwas nur so (und nicht anders) zugetragen haben kann. Könnte es nicht viel mehr doch so sein, dass sich Chondren auf ganz unterschiedliche Weise und zu ganz unterschiedlichen Zeiten gebildet haben können. Also durch Schockwellen, Nebelblitze und Kollisionen? Einen Wassertropfen kann ich auf der Erde ja auch nicht nur dadurch erzeugen, dass ich einen Stein ins Wasser klatsch. Warum muss es also immer ein entweder oder sein und nicht auch mal ein "auch".

Gruß

Ingo

Offline karmaka

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Re: Entstehung von Chondren
« Antwort #100 am: September 25, 2014, 21:59:27 nachm. »
10 Meteoritenforscher = 11-12 Theorien zur Chondrenbildung.

In diesem Sinne:

Forming Chondrules in Impact Splashes. I. Radiative Cooling Model

Cornelis Petrus Dullemond, Sebastian Markus Stammler, and Anders Johansen

The Astrophysical Journal Volume 794 Number 1
doi:10.1088/0004-637X/794/1/91
Published 25 September 2014.

LINK

Offline DCOM

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Re: Entstehung von Chondren
« Antwort #101 am: September 26, 2014, 08:52:45 vorm. »
Interessante Arbeit, danke!  :hut:

Auch die Isotopenverhältnisse in den Chondren von Bencubbin-Meteoriten scheinen für das Kollisionsmodell zu sprechen:

Olsen, M.B. et al. (2013) Magnesium isotope evidence for single stage formation of CB chondrules by colliding planetesimals. Astrophysical Journal Letters 776, L1 doi:10.1088/2041-8205/776/1/L1

Grüße, D.U.  :prostbier:

Offline karmaka

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Re: Entstehung von Chondren
« Antwort #102 am: Oktober 23, 2014, 11:28:12 vorm. »
Chondrule destruction in nebular shocks

Emmanuel Jacquet, Christopher Thompson

The Astrophysical Journal
arXiv:1410.6015
(Submitted on 22 Oct 2014)

LINK (abstract)
PDF-LINK

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Re: Entstehung von Chondren
« Antwort #103 am: November 13, 2014, 23:04:43 nachm. »
Solar nebula magnetic fields recorded in the Semarkona meteorite

Roger R. Fu, Benjamin P. Weiss, Eduardo A. Lima, Richard J. Harrison, Xue-Ning Bai, Steven J. Desch, Denton S. Ebel, Clement Suavet, Huapei Wang, David Glenn, David Le Sage, Takeshi Kasama, Ronald L. Walsworth, Aaron T. Kuan

Science DOI: 10.1126/science.1258022
Published Online November 13 2014

LINK

Materials/Methods, Supplementary Text, Tables, Figures, and/or References

Zitat
Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 μT. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the sun.

Offline karmaka

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Re: Entstehung von Chondren
« Antwort #104 am: Dezember 09, 2014, 23:07:58 nachm. »
Und wieder etwas Neues zum Thema:

The origin of chondrules: Constraints from matrix composition and matrix-chondrule complementarity

Herbert Palme, Dominik C. Hezel, Denton S. Ebel

Earth and Planetary Science Letters
Volume 411, 1 February 2015, Pages 11–19
doi:10.1016/j.epsl.2014.11.033

LINK

Zitat
Recent data confirm that matrix in carbonaceous chondrites has high Si/Mg and Fe/Mg ratios when compared to bulk carbonaceous chondrites with solar abundance ratios. Chondrules have the opposite signature, low Si/Mg and Fe/Mg ratios. In some carbonaceous chondrites chondrules have low Al/Ti ratios, matrix has the opposite signature and the bulk is chondritic. It is shown in detail that these complementary relationships cannot have evolved on the parent asteroid(s) of carbonaceous chondrites. They reflect preaccretionary processes. Both chondrules and matrix must have formed from a single, solar-like reservoir. Consequences of complementarity for chondrule formation models are discussed. An independent origin and/or random mixing of chondrules and matrix can be excluded. Hence, complementarity is a strong constraint for all astrophysical–cosmochemical models of chondrule formation. Although chondrules and matrix formed from a single reservoir, the chondrule-matrix system was open to the addition of oxygen and other gaseous components.

 

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