Astronomy & Astrophysics 473, 661–672 (2007)
DOI: 10.1051/0004-6361:20078131
Atmospheric deceleration and light curves of Draconid meteors
and implications for the structure of cometary dust
J. Borovicka, P. Spurny, and P. Koten
Astronomical Institute of the Academy of
Sciences, Fricova 298, 25165 Ondrejov Observatory, Czech Republic
Abstract. The observation of Draconid meteors was used to
infer information on the structure, porosity, strength, and composition
of the dust of comet 21P/Giacobini-Zinner. Stereoscopic video and
photographic observations of six faint and one bright Draconid meteors
provided meteor morphologies, heights, light curves, and atmospheric
decelerations. The spectrum of the bright meteor was also obtained. We
developed a simple model of meteoroid ablation and fragmentation. The
model assumes that cometary meteoroids are composed of constituent
grains. By fitting the observed decelerations and light curves, we have
found that the grain mass range was relatively narrow in all meteoroids
but differed from case to case. Some meteoroids were coarse grained
with grain masses 10−9 to 10−10 kg, others were
fine grained with grain masses one order of magnitude lower. Individual
mm-sized meteoroids contained tens of thousands to almost a million
grains (assuming grain density close to 3000 kg m−3). The
meteoroids were porous aggregates of grains, having porosities of about
90% and bulk densities of 300 kg m−3. Grain separation
started after the surface of the meteoroid received energy of 106
J m−2. The separation continued during the first half of
meteor trajectories. We call this phase erosion. The energy needed for
grain erosion was 15−30× lower than the energy of vaporization.
However, 30% of the largest meteoroid was resistant to thermal erosion;
this part disrupted later mechanically under a very low dynamic
pressure of 5 kPa. The relative abundances of Na, Mg, and Fe were
nearly chondritic, but differential ablation caused preferential loss
of sodium at the beginning of the trajectory.
Keywords: meteors, meteoroids – comets: individual:
21P/Giacobini-Zinner
______________________________
back to the list of publications
next abstract
previous abstract