1,406 research outputs found
Tidal interactions - crude body model in dynamical investigations
The paper presents results of investigations of small bodies dynamics in a
vicinity of giant planets. We used the most simple body model: gravitationally
bounded, rotating contact binary affected by the tidal force acting from a
planet. Spin variations of such binaries were extensively studied during
planetary close encounters. Two main types of dynamical behaviour were
observed: (i) huge but interim fluctuations of the angular velocity and (ii)
permanent changes of a rotation during a close approach. The first type is
observed mainly for fast rotators, while the second one was encountered in a
population of slowly spinning objects with periods longer than 12 hours.
Conclusions on usability of such crude physical body models in dynamical
investigations and a comparison to previous results were attached. The results
allow us to formulate a thesis explaining the phenomenon of creation of the
extremely slow rotators and an observational excess of such type of objects
Did the Hilda collisional family form during the late heavy bombardment?
We model the long-term evolution of the Hilda collisional family located in
the 3/2 mean-motion resonance with Jupiter. Its eccentricity distribution
evolves mostly due to the Yarkovsky/YORP effect and assuming that: (i) impact
disruption was isotropic, and (ii) albedo distribution of small asteroids is
the same as for large ones, we can estimate the age of the Hilda family to be
. We also calculate collisional activity in the J3/2
region. Our results indicate that current collisional rates are very low for a
200\,km parent body such that the number of expected events over Gyrs is much
smaller than one.
The large age and the low probability of the collisional disruption lead us
to the conclusion that the Hilda family might have been created during the Late
Heavy Bombardment when the collisions were much more frequent. The Hilda family
may thus serve as a test of orbital behavior of planets during the LHB. We
tested the influence of the giant-planet migration on the distribution of the
family members. The scenarios that are consistent with the observed Hilda
family are those with fast migration time scales to
, because longer time scales produce a family that is depleted
and too much spread in eccentricity. Moreover, there is an indication that
Jupiter and Saturn were no longer in a compact configuration (with period ratio
) at the time when the Hilda family was created
Identifying Near Earth Object Families
The study of asteroid families has provided tremendous insight into the
forces that sculpted the main belt and continue to drive the collisional and
dynamical evolution of asteroids. The identification of asteroid families
within the NEO population could provide a similar boon to studies of their
formation and interiors. In this study we examine the purported identification
of NEO families by Drummond (2000) and conclude that it is unlikely that they
are anything more than random fluctuations in the distribution of NEO
osculating orbital elements. We arrive at this conclusion after examining the
expected formation rate of NEO families, the identification of NEO groups in
synthetic populations that contain no genetically related NEOs, the orbital
evolution of the largest association identified by Drummond (2000), and the
decoherence of synthetic NEO families intended to reproduce the observed
members of the same association. These studies allowed us to identify a new
criterion that can be used to select real NEO families for further study in
future analyses, based on the ratio of the number of pairs and the size of
strings to the number of objects in an identified association.Comment: Accepted for publication in Icarus. 19 pages including 11 figure
Towards Initial Mass Functions for Asteroids and Kuiper Belt Objects
Our goal is to understand primary accretion of the first planetesimals. The
primitive meteorite record suggests that sizeable planetesimals formed in the
asteroid belt over a period longer than a million years, each composed entirely
of an unusual, but homogeneous, mixture of mm-size particles. We sketch a
scenario in which primary accretion of 10-100km size planetesimals proceeds
directly, if sporadically, from aerodynamically-sorted mm-size particles
(generically "chondrules"). These planetesimal sizes are in general agreement
with the currently observed asteroid mass peak near 100km diameter, which has
been identified as a "fossil" property of the pre-erosion, pre-depletion
population. We extend our primary accretion theory to make predictions for
outer solar system planetesimals, which may also have a preferred size in the
100km diameter range. We estimate formation rates of planetesimals and assess
the conditions needed to match estimates of both asteroid and Kuiper Belt
Object (KBO) formation rates. For nebula parameters that satisfy observed mass
accretion rates of Myr-old protoplanetary nebulae, the scenario is roughly
consistent with not only the "fossil" sizes of the asteroids, and their
estimated production rates, but also with the observed spread in formation ages
of chondrules in a given chondrite, and with a tolerably small radial diffusive
mixing during this time between formation and accretion (the model naturally
helps explain the peculiar size distribution of chondrules within such
objects). The scenario also produces 10-100km diameter primary KBOs. The
optimum range of parameters, however, represents a higher gas density and
fractional abundance of solids, and a smaller difference between keplerian and
pressure-supported orbital velocities, than "canonical" models of the solar
nebula. We discuss several potential explanations for these differences.Comment: Icarus, in pres
Origin and Sustainability of The Population of Asteroids Captured in the Exterior Resonance 1:2 with Mars
At present, approximately 1500 asteroids are known to evolve inside or
sticked to the exterior 1:2 resonance with Mars at a = 2.418 AU, being (142)
Polana the largest member of this group. The effect of the forced secular modes
superposed to the resonance gives rise to a complex dynamical evolution.
Chaotic diffusion, collisions, close encounters with massive asteroids and
mainly orbital migration due to the Yarkovsky effect generate continuous
captures to and losses from the resonance, with a fraction of asteroids
remaining captured over long time scales and generating a concentration in the
semimajor axis distribution that exceeds by 20% the population of background
asteroids. The Yarkovsky effect induces different dynamics according to the
asteroid size, producing an excess of small asteroids inside the resonance. The
evolution in the resonance generates a signature on the orbits, mainly in
eccentricity, that depends on the time the asteroid remains captured inside the
resonance and on the magnitude of the Yarkovsky effect. The greater the
asteroids, the larger the time they remain captured in the resonance, allowing
greater diffusion in eccentricity and inclination. The resonance generates a
discontinuity and mixing in the space of proper elements producing
misidentification of dynamical family members, mainly for Vesta and Nysa-Polana
families. The half-life of resonant asteroids large enough for not being
affected by the Yarkovsky effect is about 1 Gyr. From the point of view of
taxonomic classes, the resonant population does not differ from the background
population and the excess of small asteroids is confirmed.Comment: Accepted for publication in Icaru
Tidal disruption of NEAs - a case of P\v{r}\'ibram
This work studies the dynamical evolution of a possible meteor stream along
the orbit of the P\v{r}\'{i}bram meteorite, which originated in the tidal
disruption of the putative rubble-pile-like parent body during a close approach
to the Earth. We assumed the disruption at the time when the ascending or
descending node of the parent orbit was close to the Earth's orbit. In the last
5000 years, the P\v{r}\'{i}bram orbit has crossed the Earth orbit twice. It
happened about 4200 years and 3300 years ago. In both cases, we modeled the
release of particles from the simplified model of rotating asteroid, and traced
their individual orbital evolution to the current date. It takes several
hundred years to spread released meteoroids along the entire orbit of the
parent body. Even today, the stream would be relatively narrow.
Considering a model parent body with physical parameters of the asteroid
Itokawa, the complete disintegration of the object produced 3.8
meteoroid particles with diameter 1\,cm. The meteor activity observed
from the Earth is revealed and justification of follow-up observation during
suggested activity of the shower in the first two weeks of April is discussed.
The Earth's tidal forces would disintegrate a fraction of NEA population into
smaller objects. We evaluate the upper limit of mass of disintegrated asteroids
within the mean NEA lifetime and the contribution of disrupted matter to the
size distribution of the NEA.Comment: 8 pages, 10 figure
Impactor flux and cratering on Ceres and Vesta: Implications for the early Solar System
We study the impactor flux and cratering on Ceres and Vesta caused by the
collisional and dynamical evolution of the asteroid Main Belt. We develop a
statistical code based on a well-tested model for the simultaneous evolution of
the Main Belt and NEA size distributions. This code includes catastrophic
collisions and noncollisional removal processes such as the Yarkovsky effect
and the orbital resonances. The model assumes that the dynamical depletion of
the early Main Belt was very strong, and owing to that, most Main Belt
comminution occurred when its dynamical structure was similar to the present
one. Our results indicate that the number of D > 1 km Main Belt asteroids
striking Ceres and Vesta over the Solar System history are approximately 4 600
and 1 100 respectively. The largest Main Belt asteroids expected to have
impacted Ceres and Vesta had diameters of 71.7 km and 21.1 km. The number of D
> 0.1 km craters on Ceres is \sim 3.4 \times 10^8 and 6.2 \times 10^7 on Vesta.
The number of craters with D > 100 km are 47 on Ceres and 8 on Vesta. Our study
indicates that the D = 460 km crater observed on Vesta had to be formed by the
impact of a D \sim 66.2 km projectile, which has a probability of occurr \sim
30% over the Solar System history. If significant discrepancies between our
results about the cratering on Ceres and Vesta and data obtained from the Dawn
Mission were found, they should be linked to a higher degree of collisional
evolution during the early Main Belt and/or the existence of the late heavy
bombardment. An increase in the collisional activity in the early phase may be
provided for an initial configuration of the giant planets consistent with, for
example, the Nice model. From this, the Dawn Mission would be able to give us
clues about the initial configuration of the early Solar System and its
subsequent dynamical evolution.Comment: Accepted for publication in Astronomy and Astrophysic
The effects of the target material properties and layering on the crater chronology: the case of Raditladi and Rachmaninoff basins on Mercury
In this paper we present a crater age determination of several terrains
associated with the Raditladi and Rachmaninoff basins. These basins were
discovered during the first and third MESSENGER flybys of Mercury,
respectively. One of the most interesting features of both basins is their
relatively fresh appearance. The young age of both basins is confirmed by our
analysis on the basis of age determination via crater chronology. The derived
Rachmaninoff and Raditladi basin model ages are about 3.6 Ga and 1.1 Ga,
respectively. Moreover, we also constrain the age of the smooth plains within
the basins' floors. This analysis shows that Mercury had volcanic activity
until recent time, possibly to about 1 Ga or less. We find that some of the
crater size-frequency distributions investigated suggest the presence of a
layered target. Therefore, within this work we address the importance of
considering terrain parameters, as geo-mechanical properties and layering, into
the process of age determination. We also comment on the likelihood of the
availability of impactors able to form basins with the sizes of Rachmaninoff
and Raditladi in relatively recent times.Comment: Accepted by PSS, to appear on MESSENGER Flybys special issu
- …