365 research outputs found
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
Heating of near-Earth objects and meteoroids due to close approaches to the Sun
It is known that near-Earth objects (NEOs) during their orbital evolution may
often undergo close approaches to the Sun. Indeed it is estimated that up to
~70% of them end their orbital evolution colliding with the Sun. Starting from
the present orbital properties, it is possible to compute the most likely past
evolution for every NEO, and to trace its distance from the Sun. We find that a
large fraction of the population may have experienced in the past frequent
close approaches, and thus, as a consequence, a considerable Sun-driven
heating, not trivially correlated to the present orbits. The detailed dynamical
behaviour, the rotational and the thermal properties of NEOs determine the
exact amount of the resulting heating due to the Sun. In the present paper we
discuss the general features of the process, providing estimates of the surface
temperature reached by NEOs during their evolution. Moreover, we investigate
the effects of this process on meteor-size bodies, analyzing possible
differences with the NEO population. We also discuss some possible effects of
the heating which can be observed through remote sensing by ground-based
surveys or space missions.Comment: 8 pages, 5 figures, accepted by MNRA
Small crater populations on Vesta
The NASA Dawn mission has extensively examined the surface of asteroid Vesta,
the second most massive body in the main belt. The high quality of the gathered
data provides us with an unique opportunity to determine the surface and
internal properties of one of the most important and intriguing main belt
asteroids (MBAs). In this paper, we focus on the size frequency distributions
(SFDs) of sub-kilometer impact craters observed at high spatial resolution on
several selected young terrains on Vesta. These small crater populations offer
an excellent opportunity to determine the nature of their asteroidal precursors
(namely MBAs) at sizes that are not directly observable from ground-based
telescopes (i.e., below ~100 m diameter). Moreover, unlike many other MBA
surfaces observed by spacecraft thus far, the young terrains examined had
crater spatial densities that were far from empirical saturation. Overall, we
find that the cumulative power-law index (slope) of small crater SFDs on Vesta
is fairly consistent with predictions derived from current collisional and
dynamical models down to a projectile size of ~10 m diameter (Bottke et al.,
2005a,b). The shape of the impactor SFD for small projectile sizes does not
appear to have changed over the last several billions of years, and an argument
can be made that the absolute number of small MBAs has remained roughly
constant (within a factor of 2) over the same time period. The apparent steady
state nature of the main belt population potentially provides us with a set of
intriguing constraints that can be used to glean insights into the physical
evolution of individual MBAs as well as the main belt as an ensemble.Comment: Accepted by PSS, to appear on Vesta cratering special issu
Spitzer Observations of Spacecraft Target 162173 (1999 JU3)
Near-Earth asteroid 162173 (1999 JU3) is the primary target of the Hayabusa-2
sample return mission, and a potential target of the Marco Polo sample return
mission. Earth-based studies of this object are fundamental to these missions.
We present a mid-infrared spectrum (5-38 microns) of 1999 JU3 obtained with
NASA's Spitzer Space Telescope in May 2008. These observations place new
constraints on the surface properties of this asteroid. To fit our spectrum we
used the near-Earth asteroid thermal model (NEATM) and the more complex
thermophysical model (TPM). However, the position of the spin-pole, which is
uncertain, is a crucial input parameter for constraining the thermal inertia
with the TPM; hence, we consider two pole orientations. In the extreme case of
an equatorial retrograde geometry we derive a lower limit to the thermal
inertia of 150 J/m^2/K/s^0.5. If we adopt the pole orientation of Abe et al.
(2008a) our best-fit thermal model yields a value for the thermal inertia of
700+/-200 J/m^2/K/s^0.5 and even higher values are allowed by the uncertainty
in the spectral shape due to the absolute flux calibration. The lower limit to
the thermal inertia, which is unlikely but possible, would be consistent with a
fine regolith similar to wthat is found for asteroid 433 Eros. However, the
thermal inertia is expected to be higher, possibly similar to or greater than
that on asteroid 25143 Itokawa. Accurately determining the spin-pole of
asteroid 162173 will narrow the range of possible values for its thermal
inertia.Comment: 4 pages, 2 figures; to be published as a Letter in Astronomy and
Astrophysic
The Cratering History of Asteroid (2867) Steins
The cratering history of main belt asteroid (2867) Steins has been
investigated using OSIRIS imagery acquired during the Rosetta flyby that took
place on the 5th of September 2008. For this purpose, we applied current models
describing the formation and evolution of main belt asteroids, that provide the
rate and velocity distributions of impactors. These models coupled with
appropriate crater scaling laws, allow the cratering history to be estimated.
Hence, we derive Steins' cratering retention age, namely the time lapsed since
its formation or global surface reset. We also investigate the influence of
various factors -like bulk structure and crater erasing- on the estimated age,
which spans from a few hundred Myrs to more than 1Gyr, depending on the adopted
scaling law and asteroid physical parameters. Moreover, a marked lack of
craters smaller than about 0.6km has been found and interpreted as a result of
a peculiar evolution of Steins cratering record, possibly related either to the
formation of the 2.1km wide impact crater near the south pole or to YORP
reshaping.Comment: Accepted by Planetary and Space Scienc
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