Institute
for Scientific Information
Dell'Oro A, Marzari F, Paolicchi P, Vanzani V:
Updated collisional probabilities of minor body populations
astronomy and astrophysics 366: (3) 1053-1060 FEB 2001
The
consistent increase in the discovery rate of new asteroids
and Trans Neptunian Objects (TNOs) in these last years has
urged an update of the values of intrinsic probability of
collision and impact Velocity for some minor body populations.
With the statistical method of Dell'Oro & Paolicchi
(1998) we have recomputed tl-le values of impact probability
and velocity for Hilda asteroids, for Trojans vs. Short
Period Comets (SPC), and for TNOs.
The
algorithm of Dell'Oro and Paolicchi is particularly suited
for the task since it can account for resonant behaviour
(Dell'Oro et al. 1998) and for the clustering of the perihelion
longitude of Main Belt asteroids and Hildas, caused by the
presence of a forced component in the eccentricity.
The
Hilda population turns out to be well sampled ill the orbital
parameter space since no significant changes are found for
the collision frequency among Hildas, and of Hildas with
Main Belt asteroids, although a much larger sample of orbits
has been used in our computations (232 objects) vs. the
smaller group used in previous computation by Dahlgren (1998)
(40 objects). We also computed the impact rate of SPCs vs.
Trojans that turned out to be an order of magnitude lower
respect to the Trojans vs. Trojans impact rate. The relative
velocity is instead about 30% higher.
Using
reasonable estimates of SPC and Trojan number densities,
we find that approximately 1 in every 100 collisions involving
Trojans may be with all SPC. In the case of TNOs there is
a consistent discrepancy between our values of the collision
probability and impact speed, and those computed by Davis
& Farinella (1997). The consistent increase in the number
of known TNOs (186 at present, only 16 at the time of the
Davis and Farinella's work) has led to a better knowledge
of their distribution in the phase space and, consequently,
to more reliable estimates of the collisional probability
and impact velocity.
Addresses:
Dell'Oro A, Univ Pisa, Dipartimento Fis, Piazza Torricelli
2, I-56127 Pisa, Italy. Univ Pisa, Dipartimento Fis, I-56127
Pisa, Italy. Univ Padua, Dipartimento Fis, I-35131 Padua,
Italy.
On the
Atmospheric Fragmentation of Small Asteroids Foschini L:
On the atmospheric fragmentation of small asteroids astronomy
and astrophysics 365: (3) 612-621 JAN 2001
It is
known, from observational data recorded from airbursts,
that small asteroids breakup at dynamical pressures lower
than their mechanical strength. This means that actual theoretical
models are inconsistent with observations. In this paper,
we present a detailed discussion about data recorded from
airbursts and about several theoretical models. We extend
and improve a theory previously outlined for the fragmentation
of small asteroids in the Earth atmosphere. The new condition
for fragmentation is given by the shock wave-turbulence
interaction, which results in sudden outburst of the dynamical
pressure.
Addresses:
Foschini L, CNR, Ins TeSRE, Via Gobetti 101, I-40129 Bologna,
Italy. CNR, Ins TeSRE, I-40129 Bologna, Italy.
Copyright
) 2001 Institute for Scientific Information
Mitch
Battros
Producer - Earth Changes TV
http://www.earthchangesTV.com
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