15 research outputs found
Collisional Velocities and Rates in Resonant Planetesimal Belts
We consider a belt of small bodies around a star, captured in one of the
external or 1:1 mean-motion resonances with a massive perturber. The objects in
the belt collide with each other. Combining methods of celestial mechanics and
statistical physics, we calculate mean collisional velocities and collisional
rates, averaged over the belt. The results are compared to collisional
velocities and rates in a similar, but non-resonant belt, as predicted by the
particle-in-a-box method. It is found that the effect of the resonant lock on
the velocities is rather small, while on the rates more substantial. The
collisional rates between objects in an external resonance are by about a
factor of two higher than those in a similar belt of objects not locked in a
resonance. For Trojans under the same conditions, the collisional rates may be
enhanced by up to an order of magnitude. Our results imply, in particular,
shorter collisional lifetimes of resonant Kuiper belt objects in the solar
system and higher efficiency of dust production by resonant planetesimals in
debris disks around other stars.Comment: 31 pages, 11 figures (some of them heavily compressed to fit into
arxiv-maximum filesize), accepted for publication at "Celestial Mechanics and
Dynamical Astronomy
A Dust Cloud of Ganymede Maintained by Hypervelocity Impacts of Interplanetary Micrometeoroids
A dust cloud of Ganymede has been detected by in-situ measurements with the
dust detector onboard the Galileo spacecraft. The dust grains have been sensed
at altitudes below five Ganymede radii (Ganymede radius = ). Our
analysis identifies the particles in the dust cloud surrounding Ganymede by
their impact direction, impact velocity, and mass distribution and implies that
they have been kicked up by hypervelocity impacts of micrometeoroids onto the
satellite's surface. We calculate the radial density profile of the particles
ejected from the satellite by interplanetary dust grains. We assume the yields,
mass and velocity distributions of the ejecta obtained from laboratory impact
experiments onto icy targets and consider the dynamics of the ejected grains in
ballistic and escaping trajectories near Ganymede. The spatial dust density
profile calculated with interplanetary particles as impactors is consistent
with the profile derived from the Galileo measurements. The contribution of
interstellar grains as projectiles is negligible. Dust measurements in the
vicinities of satellites by spacecraft detectors are suggested as a beneficial
tool to obtain more knowledge about the satellite surfaces, as well as dusty
planetary rings maintained by satellites through the impact ejecta mechanism.Comment: 31 pages, 10 figures, accepted for Planetary and Space Scienc
Debris disk size distributions: steady state collisional evolution with P-R drag and other loss processes
We present a new scheme for determining the shape of the size distribution,
and its evolution, for collisional cascades of planetesimals undergoing
destructive collisions and loss processes like Poynting-Robertson drag. The
scheme treats the steady state portion of the cascade by equating mass loss and
gain in each size bin; the smallest particles are expected to reach steady
state on their collision timescale, while larger particles retain their
primordial distribution. For collision-dominated disks, steady state means that
mass loss rates in logarithmic size bins are independent of size. This
prescription reproduces the expected two phase size distribution, with ripples
above the blow-out size, and above the transition to gravity-dominated
planetesimal strength. The scheme also reproduces the expected evolution of
disk mass, and of dust mass, but is computationally much faster than evolving
distributions forward in time. For low-mass disks, P-R drag causes a turnover
at small sizes to a size distribution that is set by the redistribution
function (the mass distribution of fragments produced in collisions). Thus
information about the redistribution function may be recovered by measuring the
size distribution of particles undergoing loss by P-R drag, such as that traced
by particles accreted onto Earth. Although cross-sectional area drops with
1/age^2 in the PR-dominated regime, dust mass falls as 1/age^2.8, underlining
the importance of understanding which particle sizes contribute to an
observation when considering how disk detectability evolves. Other loss
processes are readily incorporated; we also discuss generalised power law loss
rates, dynamical depletion, realistic radiation forces and stellar wind drag.Comment: Accepted for publication by Celestial Mechanics and Dynamical
Astronomy (special issue on EXOPLANETS
Impact-generated dust clouds around planetary satellites: spherically symmetric case
An analytic model of an impact-generated, steady-state, spherically symmetric dust cloud around an atmosphereless planetary satellite (or planet-Mercury, Pluto) is constructed. The projectiles are assumed to be interplanetary micrometeoroids. The model provides the expected mass, density, and velocity distributions of dust in the vicinities of parent bodies. Applications are made to Jupiter's moon Ganymede and six outer satellites of Saturn. In the former case, the model is shown to be consistent with the measurements of the dust detector system onboard the Galileo spacecraft. In the latter case, estimates are given and recommendations are made for the planned experiment with the Cassini cosmic dust analyzer (CDA) during targeted flybys of the spacecraft with the moons. The best CDA pointing to maximize the number of detections is in the ram direction. With this pointing, measurements are possible within a few to about 20min from the closest approach, with maximum minute impact rates ranging from about 1 for Phoebe and Hyperion to thousands for Enceladus. Detections of the ejecta clouds will still be likely if CDA's angular offset from the ram direction does not exceed /45°. The same model can be applied to dust measurements by other space missions, like New Horizons to Pluto or BepiColombo to Mercury
The Study of the Effects of Surface Dielectric Barrier Discharge Low Temperature Plasma Products on Spring and Winter Wheat Germination
The use of ion-plasma technologies for treatment of seeds of different crop plants is particularly important for regions that exist in environment of risk farming. This is due to the lack of supplies in the treatment, durability, reliability and performance of these technologies. However, the mixed results of studies obtained for different species and varieties of seeds, make it necessary to detail compare the effects of the low-temperature plasma products for different cultures. This paper presents the results of experimental studies of the effects of plasma products of surface dielectric barrier discharge on the germination of spring and winter wheat. It has been shown that irrespective of time and the exposure intensity laboratory germination of spring wheat seeds reduced of 74% in the control group to 52% of the treated seeds, while the germination of wheat seeds is not reduced even at a relatively long exposure (20 min). The modes of treatment (3 min, 2.1-2.4 kV) at which germination of winter wheat seeds increase from 81% in the control group to 87% of the treated seeds have been selected. Resistance of winter wheat seed germination to the product of the discharge plasma can be used to form the conditions for safe suppression of a variety of pathogenic organisms on the surface of seeds
DUNES survey observational results
VizieR online Data Catalogue associated with article published in journal Astronomy & Astrophysics with title 'DUst around NEarby Stars. The survey observational results.' (bibcode: 2013A&A...555A..11E