32 research outputs found
Footprints of a possible Ceres asteroid paleo-family
Ceres is the largest and most massive body in the asteroid main belt.
Observational data from the Dawn spacecraft reveal the presence of at least two
impact craters about 280~km in diameter on the Ceres surface, that could have
expelled a significant number of fragments. Yet, standard techniques for
identifying dynamical asteroid families have not detected any Ceres family. In
this work, we argue that linear secular resonances with Ceres deplete the
population of objects near Ceres. Also, because of the high escape velocity
from Ceres, family members are expected to be very dispersed, with a
considerable fraction of km-sized fragments that should be able to reach the
pristine region of the main belt, the area between the 5J:-2A and 7J:-3A
mean-motion resonances, where the observed number of asteroids is low. Rather
than looking for possible Ceres family members near Ceres, here we propose to
search in the pristine region. We identified 156 asteroids whose taxonomy,
colors, albedo could be compatible with being fragments from Ceres. Remarkably,
most of these objects have inclinations near that of Ceres itself.Comment: 12 pages, 6 figures, 1 table. Accepted for publication in MNRA
On the oldest asteroid families in the main belt
Asteroid families are groups of minor bodies produced by high-velocity
collisions. After the initial dispersions of the parent bodies fragments, their
orbits evolve because of several gravitational and non-gravitational
effects,such as diffusion in mean-motion resonances, Yarkovsky and YORP
effects, close encounters of collisions, etc. The subsequent dynamical
evolution of asteroid family members may cause some of the original fragments
to travel beyond the conventional limits of the asteroid family. Eventually,
the whole family will dynamically disperse and no longer be recognizable.
A natural question that may arise concerns the timescales for dispersion of
large families. In particular, what is the oldest still recognizable family in
the main belt? Are there any families that may date from the late stages of the
Late Heavy Bombardment and that could provide clues on our understanding of the
primitive Solar System? In this work, we investigate the dynamical stability of
seven of the allegedly oldest families in the asteroid main belt. Our results
show that none of the seven studied families has a nominally mean estimated age
older than 2.7 Gyr, assuming standard values for the parameters describing the
strength of the Yarkovsky force. Most "paleo-families" that formed between 2.7
and 3.8 Gyr would be characterized by a very shallow size-frequency
distribution, and could be recognizable only if located in a dynamically less
active region (such as that of the Koronis family). V-type asteroids in the
central main belt could be compatible with a formation from a paleo-Eunomia
family.Comment: 9 pages, 5 figures, 5 tables. Accepted for publication in MNRA
The Rafita asteroid family
The Rafita asteroid family is an S-type group located in the middle main
belt, on the right side of the 3J:-1A mean-motion resonance. The proximity of
this resonance to the family left side in semi-major axis caused many former
family members to be lost. As a consequence, the family shape in the
domain is quite asymmetrical, with a preponderance of objects on the right side
of the distribution. The Rafita family is also characterized by a leptokurtic
distribution in inclination, which allows the use of methods of family age
estimation recently introduced for other leptokurtic families such as Astrid,
Hansa, Gallia, and Barcelona. In this work we propose a new method based on the
behavior of an asymmetry coefficient function of the distribution in the
plane to date incomplete asteroid families such as Rafita. By
monitoring the time behavior of this coefficient for asteroids simulating the
initial conditions at the time of the family formation, we were able to
estimate that the Rafita family should have an age of Myr, in good
agreement with results from independent methods such as Monte Carlo simulations
of Yarkovsky and Yorp dynamical induced evolution and the time behaviour of the
kurtosis of the distribution. Asteroids from the Rafita family can
reach orbits similar to 8\% of the currently known near Earth objects.
1\% of the simulated objects are present in NEO-space during the final
10 Myr of the simulation, and thus would be comparable to objects in the
present-day NEO population.Comment: Accepted 2017 January 19. Received 2017 January 17; in original form
2016 September
Accurate free and forced rotational motions of rigid Venus
% context :The precise and accurate modelling of a terrestrial planet like
Venus is an exciting and challenging topic, all the more interesting since it
can be compared with that of the Earth for which such a modelling has already
been achieved at the milliarcsecond level % aims: We want to complete a
previous study (Cottereau and Souchay, 2009), by determining at the
milliarcsecond level the polhody, i.e. the torque-free motion of the axis of
angular momentum of a rigid Venus in a body-fixed frame, as well as the
nutation of its third axis of figure in space, which is fundamental from an
observational point of view. results :In a first part we have computed the
polhody, i.e. the respective free rotational motion of the axis of angular
momentum of Venus with respect to a body-fixed frame. We have shown that this
motion is highly elliptical, with a very long period of 525 cy to be compared
with 430 d for the Earth. This is due to the very small dynamical flattening of
Venus in comparison with our planet. In a second part we have computed
precisely the Oppolzer terms which allow to represent the motion in space of
the third Venus figure axis with respect to Venus angular momentum axis, under
the influence of the solar gravitational torque. We have determined the
corresponding tables of coefficients of nutation of the third figure axis both
in longitude and in obliquity due to the Sun, which are of the same order of
amplitude as for the Earth. We have shown that the coefficients of nutation for
the third figure axis are significantly different from those of the angular
momentum axis on the contrary of the Earth. Our analytical results have been
validated by a numerical integration which revealed the indirect planetary
effects.Comment: 14 pages, 11 figures, accepted for publication in section 11.
Celestial mechanics and astrometry of Astronomy and Astrophysics (27/02/2010
Machine learning to predict the solar flux and geomagnetic indices to model density and Drag in Satellites
In recent years (2000-2021), human-space activities have been increasing
faster than ever. More than 36000 Earth' orbiting objects, all larger than 10
cm, in orbit around the Earth, are currently tracked by the European Space
Agency (ESA). Around 70\% of all cataloged objects are in Low-Earth Orbit
(LEO). Aerodynamic drag provides one of the main sources of perturbations in
this population, gradually decreasing the semi-major axis and period of the LEO
satellites. Usually, an empirical atmosphere model as a function of solar radio
flux and geomagnetic data is used to calculate the orbital decay and lifetimes
of LEO satellites. In this respect, a good forecast for the space weather data
could be a key tool to improve the model of drag. In this work, we propose
using Time Series Forecasting Model to predict the future behavior of the solar
flux and to calculate the atmospheric density, to improve the analytical models
and reduce the drag uncertainty
Dynamics Around an Asteroid Modeled as a Mass Tripole
The orbital dynamics of a spacecraft orbiting around irregular small
celestial bodies is a challenging problem. Difficulties to model the gravity
field of these bodies arise from the poor knowledge of the exact shape as
observed from the Earth. In order to understand the complex dynamical
environment in the vicinity of irregular asteroids, several studies have been
conducted using simplified models. In this work, we investigate the qualitative
dynamics in the vicinity of an asteroid with an arched shape using a tripole
model based on the existence of three mass points linked to each other by rods
with given lengths and negligible masses. We applied our results to some real
systems, namely, asteroids 8567, 243 Ida and 433 Eros and also Phobos, one of
the natural satellites of Mars
Numerical investigations of the orbital dynamics around a synchronous binary system of asteroids
In this article, equilibrium points and families of periodic orbits in the
vicinity of the collinear equilibrium points of a binary asteroid system are
investigated with respect to the angular velocity of the secondary body, the
mass ratio of the system and the size of the secondary. We assume that the
gravitational fields of the bodies are modeled assuming the primary as a mass
point and the secondary as a rotating mass dipole. This model allows to compute
families of planar and halo periodic orbits that emanate from the equilibrium
points and . The stability and bifurcations of these families are
analyzed and the results are compared with the results obtained with the
Restricted Three-Body Problem (RTBP). The results provide an overview of the
dynamical behavior in the vicinity of a binary asteroid system