Exothermic chemical reactions can drive nonthermal crystallization of amorphous silicate grains

Chihiro Kaito, Yu Miyazaki, Akihito Kumamoto, Yuki Kimura

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


To explain how cometary silicates crystallize yet still preserve volatile interstellar ices in their parent comets, we experimentally demonstrate the possibility of chemical-reaction-driven crystallization, which is called non-thermal crystallization, using laboratory-synthesized amorphous Mg-bearing silicate grains. Analog silicate grains ∼50-100 nm in diameter covered with a carbonaceous layer consisting of amorphous carbon, CH 4, and other organics to a thickness of ∼10-30 nm were used as models. The analog silicate grains crystallized via the direct flow of surface reaction energy, which is produced by the graphitization of the carbonaceous layer due to oxidation at room temperature in air, into the silicates. The experimental results imply that amorphous silicates are transformed into crystalline silicates as the grains leave the comet's surface, rather than as the comet was accreted 4.5 billion years ago. Thus, primordial ices and amorphous silicate grains are predicted to reside in most comets until they approach the Sun.

Original languageEnglish
Pages (from-to)L57-L60
JournalAstrophysical Journal
Issue number1 PART 2
Publication statusPublished - 2007


  • Astrochemistry
  • Comets: General
  • Methods: Laboratory
  • Radiation mechanisms: Nonthermal

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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