Magnetic reconnection flares in the photoplanetary nebula and the possible origin of meteorite chondrules

Levy, E. H.; Araki, Suguru

doi:10.1016/0019-1035(89)90126-7

Cited by 59 publications

(28 citation statements)

References 20 publications

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“…Furthermore, mechanisms that invoke intense electric currents such as magnetic reconnection 180 flares and current sheets predict strong fields in excess of 500 µT during chondrule heating (31). 181…”

Section: Mechanisms 52mentioning

confidence: 99%

Solar nebula magnetic fields recorded in the Semarkona meteorite

Weiss

Lima

et al. 2014

Science

159

223

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24 25 26Accepted Manuscript. This version has not undergone final editing. Please refer to the complete version of record at http://www.sciencemag.org/.2 Magnetic fields are proposed to have played a critical role in some of the most enigmatic 26 processes of planetary formation by mediating the rapid accretion of disk material onto the 27 central star and the formation of the first solids. However, there have been no direct 28 experimental constraints on these fields. Here we show that dusty olivine-bearing 29 chondrules from the Semarkona meteorite were magnetized in a nebular field of 54±21 µT. 30This intensity supports chondrule formation by nebular shocks or planetesimal collisions 31 rather than by electric currents, the x-wind, or other mechanisms near the sun. This 32 implies that background magnetic fields in the terrestrial planet-forming region were likely 33 5-54 µT, which is sufficient to account for measured rates of mass and angular momentum 34 transport in protoplanetary disks. 35 36Astronomical observations of young stellar objects indicate that early planetary systems 37 evolve through a protoplanetary disk phase in <5 million years (My) following the collapse of 38 their parent molecular clouds (1, 2). Disk evolution on such short timescales requires highly 39 efficient inward transport of mass accompanied by outward angular momentum transfer, which 40 allows disk material to accrete onto the central star while delivering angular momentum out of 41 the protoplanetary system. 42The mechanism of this rapid mass and angular momentum redistribution remains unknown. 43Several proposed processes invoke a central role for nebular magnetic fields. Among these, the 44 magnetorotational instability (MRI) and magnetic braking predict magnetic fields with intensities 45 of ~100 µT at 1 AU in the active layers of the disk (3, 4). Alternatively, transport by 46 magnetocentrifugal wind (MCW) requires large-scale, ordered magnetic fields stronger than ~10 47 µT at 1 AU. Finally, non-magnetic effects such as the baroclinic and Goldreich-Schubert-Fricke 48 instabilities may be the dominant mechanism of angular momentum transport in the absence of 49 sufficiently strong magnetic fields (5). Direct measurement of magnetic fields in the planet-50 forming regions of the disk can potentially distinguish among and constrain these hypothesized 51 mechanisms. 52Although current astronomical observations cannot directly measure magnetic fields in 53 planet-forming regions [(6); supplementary text], paleomagnetic experiments on meteoritic 54 materials can potentially constrain the strength of nebular magnetic fields. Chondrules are 55 millimeter-sized lithic constituents of primitive meteorites that formed in transient heating events 56 in the solar nebula. If a stable field was present during cooling, they should have acquired a 57 thermoremanent magnetization (TRM), which can be characterized via paleomagnetic 58 experiments. Besides assessing the role of magnetic fields in disk evolution, such paleomagnetic 59 measure...

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Section: Mechanisms 52mentioning

confidence: 99%

Solar nebula magnetic fields recorded in the Semarkona meteorite

Weiss

Lima

et al. 2014

Science

159

223

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“…Individual chondrules within meteorites appear to have been exposed to stronger Ðelds, 0.1È10 G (Levy 1988), but chondrules are believed to have formed under special, local "" Ñash-heating ÏÏ conditions such as magnetic Ñares (Levy & Araki 1989) or lightning (Desch & Cuzzi 2000), that may have involved strong magnetic Ðelds. If the remanent magnetization of meteorites in the solar system is due to a magnetic Ðeld that existed over the entire nebula, then these data provide an observational test of theories of star formation.…”

Section: Magnetic Field Of the Protoplanetary Diskmentioning

confidence: 99%

The Magnetic Decoupling Stage of Star Formation

Desch

Mouschovias

2001

ApJ

105

131

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We present the results of the Ðrst numerical calculations to model magnetic decoupling in a collapsing molecular cloud core. Magnetic decoupling is the stage during which the motion of the neutrals ceases to signiÐcantly a †ect the magnetic Ðeld strength and the magnetic Ðeld ceases to signiÐcantly a †ect this motion. We have analyzed the resistivity of a weakly ionized, magnetic gas, and we have separated the contributions of ohmic dissipation and ambipolar di †usion. The chemical model used to determine the abundances of ionized particles accounts for, among other things, a distribution of grain radii. The evolution of an axisymmetric, magnetic molecular cloud core is followed from central densities of 300 to 2 ] 1012 cm~3. Typically, magnetic decoupling begins at a central density of 3 ] 1010 cm~3 and is complete by a density of 2 ] 1012 cm~3. We Ðnd that the mechanism responsible for magnetic decoupling is ambipolar di †usion, not ohmic dissipation, and that decoupling precedes the formation of a central stellar object. When the central density is a few times 1012 cm~3, a nearly uniform magnetic Ðeld of G extends over a region B20 AU in radius that contains a mass B0.01 This value of B dec B 0.1 M _ . is consistent with measurements of remanent magnetization in meteorites. Magnetic decoupling at B dec this stage is not accompanied by hydromagnetic shocks. We estimate that the "" magnetic Ñux problem ÏÏ of star formation is resolved by ambipolar di †usion before the magnetic Ðeld is refrozen in the matter because of thermal ionization.

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“…The latter process may have been a critical source of turbulent viscosity that in turn is likely required for mass and momentum transfer in the disk and, ultimately, the formation of the Sun and planets. Stellar and MRI-generated fields, as well as residual fields from the parent molecular cloud and transient fields from possible nebular lightning-and impact-generated plasmas, may have also been intimately involved in the formation and/or magnetization of the earliest solar system macroscopic solids, inclusions and chondrules in chondrites (Levy and Araki 1989;Shu et al 1996Shu et al , 1997Crawford and Schultz 1999;Desch and Cuzzi 2000;Desch and Connolly 2002;Joung et al 2004). Despite their great importance in planet formation, there has been as yet no unambiguous evidence of any of these field sources in meteorites.…”

Section: Introductionmentioning

confidence: 99%

Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation

et al. 2009

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The large-scale compositional structures of planets are primarily established during early global differentiation. Advances in analytical geochemistry, the increasing diversity of extraterrestrial samples, and new paleomagnetic data are driving major changes in our understanding of the nature and timing of these early melting processes. In particular, paleomagnetic studies of chondritic and small-body achondritic meteorites have revealed a diversity of magnetic field records. New, more sensitive and highly automated paleomagnetic instrumentation and an improved understanding of meteorite magnetic properties and the effects of shock, weathering, and other secondary processes are permitting primary and secondary magnetization components to be distinguished with increasing confidence. New constraints on the post-accretional histories of meteorite parent bodies now suggest that, contrary to early expectations, few if any meteorites have been definitively shown to retain records of early solar and protoplanetary nebula magnetic fields. However, recent studies of pristine samples coupled with new theoretical insights into the possibility of dynamo generation on small bodies indicate that some meteorites retain records of internally generated fields. These results indicate that some planetesimals formed metallic cores and early dynamos within just a few million years of solar system formation.

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Magnetic reconnection flares in the photoplanetary nebula and the possible origin of meteorite chondrules

Cited by 59 publications

References 20 publications

Solar nebula magnetic fields recorded in the Semarkona meteorite

Solar nebula magnetic fields recorded in the Semarkona meteorite

The Magnetic Decoupling Stage of Star Formation

Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation

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