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Anders Johansen. Profile picture.

Anders Johansen

Professor

Anders Johansen. Profile picture.

Harvesting the decay energy of 26 Al to drive lightning discharge in protoplanetary discs

Author

  • Anders Johansen
  • Satoshi Okuzumi

Summary, in English

Chondrules in primitive meteorites likely formed by recrystallisation of dust aggregates that were flash-heated to nearly complete melting. Chondrules may represent the building blocks of rocky planetesimals and protoplanets in the inner regions of protoplanetary discs, but the source of ubiquitous thermal processing of their dust aggregate precursors remains elusive. Here we demonstrate that escape of positrons released in the decay of the short-lived radionuclide 26Al leads to a large-scale charging of dense pebble structures, resulting in neutralisation by lightning discharge and flash-heating of dust and pebbles. This charging mechanism is similar to a nuclear battery where a radioactive source charges a capacitor. We show that the nuclear battery effect operates in circumplanetesimal pebble discs. The extremely high pebble densities in such discs are consistent with conditions during chondrule heating inferred from the high abundance of sodium within chondrules. The sedimented mid-plane layer of the protoplanetary disc may also be prone to charging by the emission of positrons, if the mass density of small dust there is at least an order of magnitude above the gas density. Our results imply that the decay energy of 26Al can be harvested to drive intense lightning activity in protoplanetary discs. The total energy stored in positron emission is comparable to the energy needed to melt all solids in the protoplanetary disc. The efficiency of transferring the positron energy to the electric field nevertheless depends on the relatively unknown distribution and scale-dependence of pebble density gradients in circumplanetesimal pebble discs and in the protoplanetary disc mid-plane layer.

Department/s

  • Lund Observatory
  • eSSENCE: The e-Science Collaboration

Publishing year

2018-01-01

Language

English

Publication/Series

Astronomy and Astrophysics

Volume

609

Document type

Journal article

Publisher

EDP Sciences

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • Meteorites, meteors, meteoroids
  • Minor planets, asteroids: general
  • Planets and satellites: formation
  • Protoplanetary disks

Status

Published

ISBN/ISSN/Other

  • ISSN: 0004-6361