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

Johansen, Anders LU and Okuzumi, Satoshi (2018) In Astronomy and Astrophysics 609.
Abstract

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... (More)

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.

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organization
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type
Contribution to journal
publication status
published
subject
keywords
Meteorites, meteors, meteoroids, Minor planets, asteroids: general, Planets and satellites: formation, Protoplanetary disks
in
Astronomy and Astrophysics
volume
609
publisher
EDP Sciences
external identifiers
  • scopus:85039951412
ISSN
0004-6361
DOI
language
English
LU publication?
yes
id
1413b6d5-7c01-40fa-b905-0577a695e39c
date added to LUP
2018-01-11 07:38:41
date last changed
2018-05-29 09:47:25
@article{1413b6d5-7c01-40fa-b905-0577a695e39c,
  abstract     = {<p>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 <sup>26</sup>Al 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 <sup>26</sup>Al 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.</p>},
  articleno    = {A31},
  author       = {Johansen, Anders and Okuzumi, Satoshi},
  issn         = {0004-6361},
  keyword      = {Meteorites, meteors, meteoroids,Minor planets, asteroids: general,Planets and satellites: formation,Protoplanetary disks},
  language     = {eng},
  month        = {01},
  publisher    = {EDP Sciences},
  series       = {Astronomy and Astrophysics},
  title        = {Harvesting the decay energy of <sup>26</sup> Al to drive lightning discharge in protoplanetary discs},
  url          = {http://dx.doi.org/},
  volume       = {609},
  year         = {2018},
}