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 $\lambda$ and latitude $\beta$ of the pole and the ratios $a/b$, $b/c$ of axes of the ellipsoid. These parameters are optimized to get the best agreement with the observation. Results: We found that the distribution of $\lambda$ 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 $\lambda$ distribution is larger for asteroids residing on low-inclination orbits. We also studied distributions of $a/b$ for several groups of asteroids and found that small asteroids ($D<25\,$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$_{5}$, 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

Editorial: Asteroid modeling: Processing and combining diverse datasets

Non peer reviewe

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