110 research outputs found
Differentiation signatures in the Flora region
Most asteroid families are very homogeneous in physical properties. Some show
greater diversity, however. The Flora family is the most intriguing of them.
The Flora family is spread widely in the inner main belt, has a rich
collisional history, and is one of the most taxonomically diverse regions in
the main belt. As a result of its proximity to the asteroid (4) Vesta (the only
currently known intact differentiated asteroid) and its family, migration
between the two regions is possible. This dynamical path is one of the counter
arguments to the hypothesis that there may be traces of a differentiated parent
body other than Vesta in the inner main belt region. We here investigate the
possibility that some of the V- and A- types (commonly interpreted as
basaltoids and dunites - parts of the mantle and crust of differentiated parent
bodies) in the Flora dynamical region are not dynamically connected to Vesta.Comment: accepted to AA (28 09 2015
Distribution of spin-axes longitudes and shape elongations of main-belt asteroids
Context: Large all-sky surveys provide us with a lot of photometric data that
are sparse in time (typically few measurements per night) and can be
potentially used for the determination of shapes and rotational states of
asteroids. The method which is generally used to derive these parameters is the
lightcurve inversion. However, for most asteroids their sparse data are not
accurate enough to derive a unique model and the lightcurve inversion method is
thus not very efficient.
Aims: To fully utilize photometry sparse in time, we developed a new
simplified model and applied it on the data from the Lowell photometric
database. Our aim was to derive spin axis orientations and shape elongations of
asteroids and to reconstruct distributions of these parameters for selected
subpopulations to find if there are some differences.
Methods: We model asteroids as geometrically scattering triaxial ellipsoids.
Observed values of mean brightness and the dispersion of brightness are
compared with computed values obtained from the parameters of the model --
ecliptical longitude and latitude of the pole and the ratios
, of axes of the ellipsoid. These parameters are optimized to get
the best agreement with the observation.
Results: We found that the distribution of for main-belt asteroids
is not uniform (in agreement with findings of Bowell et al., 2014, M&PS, 49,
95) and is dependent on the inclination of orbit. Surprisingly, the
non-uniformity of distribution is larger for asteroids residing on
low-inclination orbits. We also studied distributions of for several
groups of asteroids and found that small asteroids (km) are on average
more elongated than large ones.Comment: 10 pages; Accepted for publication in A&
Asteroid models from the Lowell Photometric Database
We use the lightcurve inversion method to derive new shape models and spin
states of asteroids from the sparse-in-time photometry compiled in the Lowell
Photometric Database. To speed up the time-consuming process of scanning the
period parameter space through the use of convex shape models, we use the
distributed computing project Asteroids@home, running on the Berkeley Open
Infrastructure for Network Computing (BOINC) platform. This way, the
period-search interval is divided into hundreds of smaller intervals. These
intervals are scanned separately by different volunteers and then joined
together. We also use an alternative, faster, approach when searching the
best-fit period by using a model of triaxial ellipsoid. By this, we can
independently confirm periods found with convex models and also find rotation
periods for some of those asteroids for which the convex-model approach gives
too many solutions. From the analysis of Lowell photometric data of the first
100,000 numbered asteroids, we derived 328 new models. This almost doubles the
number of available models. We tested the reliability of our results by
comparing models that were derived from purely Lowell data with those based on
dense lightcurves, and we found that the rate of false-positive solutions is
very low. We also present updated plots of the distribution of spin obliquities
and pole ecliptic longitudes that confirm previous findings about a non-uniform
distribution of spin axes. However, the models reconstructed from noisy sparse
data are heavily biased towards more elongated bodies with high lightcurve
amplitudes
Dynamical evolution of basaltic asteroids outside the Vesta family in the inner main belt
Basaltic V-type asteroids are leftovers from the formation and evolution of
differentiated planetesimals. They are thought to originate from mantles and
crusts of multiple different parent bodies. Identifying the links between
individual V-type asteroids and multiple planetesimals is challenging,
especially in the inner part of the main asteroid belt, where the majority of
V-type asteroids are expected to have originated from a single planetesimal,
namely, (4) Vesta.
In this work, we aim to trace the origin of a number of individual V-type
asteroids from the inner part of the main asteroid belt. The main goal is to
identify asteroids that may not be traced back to (4) Vesta and may therefore
originate from other differentiated planetesimals.
We performed a 2 Gy backward numerical integration of the orbits of the
selected V-type asteroids. For each asteroid, we used 1001 clones to map the
effect of orbital uncertainties. In the integration, we use information on
physical properties of the considered V-type asteroids such as pole
orientation, rotational period, and thermal parameters.
The majority of V-types in the inner main belt outside the Vesta family are
clearly Vesta fugitives. Two objects, namely, (3307) Athabasca and (17028) 1999
FJ, show no clear dynamical link to (4) Vesta. Together with (809) Lundia
(from our previous work), these objects could represent the parent bodies of
anomalous HED meteorites such as the Banbura Rockhole. Furthermore, some
objects of the low-inclination population cannot be traced back to (4) Vesta
within the 2 Gy integration
Observations of "Fresh" and Weathered Surfaces on Asteroid Pairs and Their Implications on the Rotational-Fission Mechanism
The rotational-fission of a rubble-pile asteroid can result in an "asteroid
pair", two un-bound asteroids sharing similar orbits. This mechanism might
exposes material that previously had never have been exposed to the weathering
conditions of space. Therefore, the surfaces of asteroid pairs offer the
opportunity to observe non-weathered fresh spectra. We report near-IR
spectroscopic observations of 31 asteroids in pairs. We analyze their spectral
slopes, 1 {\mu}m absorption band, taxonomy, and estimate the time elapsed since
their separation. Analyzing the 19 S-complex objects in our sample, we find two
fresh Q-type asteroids that are the first of their kind to be observed in the
main-belt over the full visible and near-IR range. This solidly demonstrates
that Q-type objects are not limited to the NEA population. The pairs in our
sample present a range of fresh and weathered surfaces with no clear evidence
for a correlation with the ages of the pairs. However, our sample includes old
pairs (1 to 2 My) that present low spectral slopes. This illustrates a
timescale of at least ~2 My before an object develops high spectral slope that
is typical for S-type asteroids.
We discuss mechanisms that explain the existence of weathered pairs with
young dynamical ages and find that the "secondary fission" model (Jacobson &
Scheeres 2011) is the most robust with our observations since: 1) the secondary
members in our sample present fresh parameters that tend to be fresher than
their weathered primaries; 2) most of the fresh pairs in our sample have low
size ratios between the secondary and the primary; 3) 33% of the primaries in
our sample are fresh, similar to the prediction set by this model; 4) known
satellites orbit two of the pairs in our sample with low size ratio and fresh
surface; 5) there is no correlation between the weathering state and the
primary shape as predicted by other models.Comment: 19 pages, 17 figures, 4 tables. Accepted to Icaru
Selecting asteroids for a targeted spectroscopic survey
Asteroid spectroscopy reflects surface mineralogy. There are few thousand
asteroids whose surfaces have been observed spectrally. Determining the surface
properties of those objects is important for many practical and scientific
applications, such as for example developing impact deflection strategies or
studying history and evolution of the Solar System and planet formation.
The aim of this study is to develop a pre-selection method that can be
utilized in searching for asteroids of any taxonomic complex. The method could
then be utilized im multiple applications such as searching for the missing
V-types or looking for primitive asteroids.
We used the Bayes Naive Classifier combined with observations obtained in the
course of the Sloan Digital Sky Survey and the Wide-field Infrared Survey
Explorer surveys as well as a database of asteroid phase curves for asteroids
with known taxonomic type. Using the new classification method we have selected
a number of possible V-type candidates. Some of the candidates were than
spectrally observed at the Nordic Optical Telescope and South African Large
Telescope.
We have developed and tested the new pre-selection method. We found three
asteroids in the mid/outer Main Belt that are likely of differentiated type.
Near-Infrared are still required to confirm this discovery. Similarly to other
studies we found that V-type candidates cluster around the Vesta family and are
rare in the mid/oter Main Belt.
The new method shows that even largely explored large databases combined
together could still be further exploited in for example solving the missing
dunite problem.Comment: accepted to A
Asteroid astrometric and photometric studies using Markov-chain Monte Carlo methods
Planetary Science belongs to the so-called fundamental sciences, which do not have to have immediate practical applications or implications. The recent decades have however shown that the study of asteroids may have direct implications on our life. Studies of asteroid dynamics have shown that some of those objects can collide with the Earth. Studies of asteroid mineralogy suggest that some of them contain minerals and elements important for industry. For both of those topics, determining physical and dynamical properties is crucial.
Markov-chain Monte Carlo methods and algorithms such as the Metropolis-Hastings algorithm are growing in popularity and becoming important tools in deriving model parameters in many branches of science today. In this thesis, Bayesian statistics along with the above-mentioned numerical methods have been used to infer dynamical and physical properties of asteroids.
First, a new Markov-chain Monte Carlo ranging method is developed for computing asteroid orbits. The method is applicable for asteroids with short observational time intervals and/or small number of observations. The method is particularly useful in deriving orbits for new asteroid discoveries and computing collision probabilities for such objects. The Markov-chain Monte Carlo ranging method is applied to a number of asteroids including a recent Earth impactor - asteroid 2008 TC3. Markov-chain Monte Carlo ranging is available through the open-source orbit-computation package called OpenOrb and is implemented into the Gaia satellite data processing pipeline, where it will be heavily used in the daily data processing.
Second, Markov-chain Monte Carlo and Monte Carlo methods are used to assess phase curve photometric parameters and their uncertainties. Absolute magnitudes and photometric parameters are derived for half a million asteroids by fitting phase curves to the Lowell Observatory photometric database. Asteroid phase curves depend on physical properties of regolith and absolute magnitudes are useful in computing sizes and albedos. Fitting the phase functions to a large number of asteroid families suggests homogeneity of photometric parameters in asteroid families. The derived photometric parameters are also found to correspond to asteroid taxonomic complexes and colors
Asteroid taxonomic signatures from photometric phase curves
We explore the correlation between an asteroid's taxonomy and photometric
phase curve using the H, G12 photometric phase function, with the shape of the
phase function described by the single parameter G12. We explore the usability
of G12 in taxonomic classification for individual objects, asteroid families,
and dynamical groups. We conclude that the mean values of G12 for the
considered taxonomic complexes are statistically different, and also discuss
the overall shape of the G12 distribution for each taxonomic complex. Based on
the values of G12 for about half a million asteroids, we compute the
probabilities of C, S, and X complex membership for each asteroid. For an
individual asteroid, these probabilities are rather evenly distributed over all
of the complexes, thus preventing meaningful classification. We then present
and discuss the G12 distributions for asteroid families, and predict the
taxonomic complex preponderance for asteroid families given the distribution of
G12 in each family. For certain asteroid families, the probabilistic prediction
of taxonomic complex preponderance can clearly be made. The Nysa-Polana family
shows two distinct regions in the proper element space with different G12
values dominating in each region. We conclude that the G12-based probabilistic
distribution of taxonomic complexes through the main belt agrees with the
general view of C complex asteroid proportion increasing towards the outer
belt. We conclude that the G12 photometric parameter cannot be used in
determining taxonomic complex for individual asteroids, but it can be utilized
in the statistical treatment of asteroid families and different regions of the
main asteroid belt.Comment: submitted to Icaru
Asteroids seen by JWST-MIRI: Radiometric Size, Distance and Orbit Constraints
Infrared measurements of asteroids are crucial for the determination of
physical and thermal properties of individual objects, and for the
understanding of the small-body populations in the solar system as a whole. But
standard radiometric methods can only be applied if the orbit of an object is
known, hence its position at the time of the observation. We present MIRI
observations of the outer-belt asteroid 10920 and an unknown object, detected
in all 9 MIRI bands in close proximity to 10920. We developed a new method
"STM-ORBIT" to interpret the multi-band measurements without knowing the
object's true location. The method leads to a confirmation of radiometric
size-albedo solution for 10920 and puts constraints on the asteroid's location
and orbit in agreement with its true orbit. Groundbased lightcurve observations
of 10920, combined with Gaia data, indicate a very elongated object (a/b >=
1.5), with a spin-pole at (l, b) = (178{\deg}, 81{\deg}), and a rotation period
of 4.861191 h. A thermophysical study leads to a size of 14.5 - 16.5 km, a
geometric albedo between 0.05 and 0.10, and a thermal inertia in the range 9 to
35 Jm-2s-0.5K-1. For the newly discovered MIRI object, the STM-ORBIT method
revealed a size of 100-230 m. The new asteroid must be on a very
low-inclination orbit and it was located in the inner main-belt region during
JWST observations. A beaming parameter {\eta} larger than 1.0 would push the
size even below 100 meter, a main-belt regime which escaped IR detections so
far. These kind of MIRI observations can therefore contribute to formation and
evolution studies via classical size-frequency studies which are currently
limited to objects larger than about one kilometer in size. We estimate that
MIRI frames with pointings close to the ecliptic and only short integration
times of a few seconds will always include a few asteroids, most of them will
be unknown objects.Comment: 17 pages, 10 figures, 4 tables, accepted for A&A publication on Nov
22, 202
- …