Cratering rate on Pluto produced by the inner trans-Neptunian population

Aims. The aim of this work is to obtain the cratering rate on Pluto and to estimate the size distribution of the population in the inner trans-Neptunian region. Methods. We find the intrinsic collisional probability and the mean collision velocity for the interaction between Pluto and the projectile population crossing its orbit, using the L7 Synthetic Model from the CFEPS Project. The size distribution of this population is found using the smallest satellite of Pluto, Styx, as a constraint, because it survives the collisional process for the solar system age. Results. We find that the mean intrinsic collisional probability and mean collision velocity between Pluto and the projectile population are (Pi) = 1.3098 × 10-22 km-2 yr-1 and (Vcol) = 2.005 ± 0.822 km s-1. If the projectile sample is separated between Plutinos and non-Plutinos and the intrinsic collisional probability of these sub-populations are taken into account, we find a ratio of approximately 20:1 in favor of non-Plutinos resulting in the greatest contribution to the cratering rate on Pluto. The projectile population for the inner trans-Neptunian belt is characterized using a double power-law mean-size distribution with exponents qA = 3.5 and qB = 5.14 for the small and large size end of the population, respectively, and break radius at rb = 11.86 km or 7.25 km for mean densities of the projectiles ρ1 = 1.85 g cm-3 and ρ2 = 1 g cm-3. With this mean-size distribution we find that an object with radius of ~28 km produces a crater in Pluto with a diameter of ~250 km in a time larger than the solar system age, indicating that this kind of large structure has a very low probability of occurrence.Fil: Calandra, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "el Leoncito". Casleo Sede San Juan | Universidad Nacional de San Juan. Complejo Astronómico "el Leoncito". Casleo Sede San Juan | Universidad Nacional de la Plata. Complejo Astronómico "el Leoncito". Casleo Sede San Juan | Universidad Nacional de Córdoba. Complejo Astronómico "el Leoncito". Casleo Sede San Juan; ArgentinaFil: Gil Hutton, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "el Leoncito". Casleo Sede San Juan | Universidad Nacional de San Juan. Complejo Astronómico "el Leoncito". Casleo Sede San Juan | Universidad Nacional de la Plata. Complejo Astronómico "el Leoncito". Casleo Sede San Juan | Universidad Nacional de Córdoba. Complejo Astronómico "el Leoncito". Casleo Sede San Juan; Argentina. Universidad Nacional de San Juan; Argentin

On the calibration of the relation between geometric albedo and polarimetric properties for the asteroids

We present a new extensive analysis of the old problem of finding a satisfactory calibration of the relation between the geometric albedo and some measurable polarization properties of the asteroids. To achieve our goals, we use all polarimetric data at our disposal. For the purposes of calibration, we use a limited sample of objects for which we can be confident to know the albedo with good accuracy, according to previous investigations of other authors. We find a new set of updated calibration coefficients for the classical slope - albedo relation, but we generalize our analysis and we consider also alternative possibilities, including the use of other polarimetric parameters, one being proposed here for the first time, and the possibility to exclude from best-fit analyzes the asteroids having low albedos. We also consider a possible parabolic fit of the whole set of data.Comment: Accepted by MNRA

Infrared spectroscopy of the largest known trans-neptunian object 2001 KX76

We report complete near-infrared (0.9-2.4 $\mu$m) spectral observations of the largest know trans-neptunian objects (TNO) 28976 = 2001 KX$_{76}$ taken in two different nights using the new Near Infrared Camera Spectrometer (NICS) attached to the 3.56m Telescopio Nazionale Galileo (TNG). The spectra are featureless and correspond to a neutral colored object. Our observations indicate that the surface of 2001 KX$_{76}$ is probably highly evolved due to long term irradiation, and that collisional resurfacing processes have not played an important role in its evolution.Comment: 1 Latex file, 2 postscript files. A&A in pres

Polarimetric survey of main-belt asteroids: IV New results from the first epoch of the CASLEO survey

Aims: We present results of a polarimetric survey of main-belt asteroids at Complejo Astronómico El Leoncito (CASLEO), San Juan, Argentina. The aims of this survey are to increase the database of asteroid polarimetry, to estimate diversity in polarimetric properties of asteroids that belong to different taxonomic classes, and to search for objects that exhibit anomalous polarimetric properties. Methods: The data were obtained using the Torino and CASPROF polarimeters at the 2.15 m telescope. The Torino polarimeter is an instrument that allows simultaneous measurement of polarization in five different bands, and the CASPROF polarimeter is a two-hole aperture polarimeter with rapid modulation. Results: The survey began in 1995, and until 2012 data on a large sample of asteroids were obtained. We here present and analyze the unpublished results for 129 asteroids of different taxonomic types, 56 which were polarimetrically observed for the first time. We find that the asteroids (402) Chloe and (729) Watsonia are Barbarians, and asteroid (269) Justitia shows a phase – polarization curve that seems to have a small inversion angle. Data obtained in UBVRI colors allow us to sketch an analysis of the wavelength dependence of the degree of linear polarization for 31 asteroids, in spite of some large error bars in some cases.Fil: Gil Hutton, Ricardo Alfredo. Consejo Nacional de Investigaciones Cientí­ficas y Técnicas. Centro Cientí­fico Tecnológico San Juan. Complejo Astronómico "El Leoncito"; Argentina. Universidad Nacional de San Juan; ArgentinaFil: Cellino, A.. Osservatorio Astrofisico di Torino; ItaliaFil: Bendjoya, Ph.. Université de Nice Sophia Antipolis. Observatoire de la Côte d’Azur; Franci

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.Fil: Tabaré Gallardo, Carlos. Universidad de la República; UruguayFil: Venturini, Julia. Universidad de la República; UruguayFil: Roig, Fernando Virgilio. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Gil Hutton, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "el Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico ; Argentin

Taxonomy of asteroid families among the Jupiter Trojans: Comparison between spectroscopic data and the Sloan Digital Sky Survey colors

We present a comparative analysis of the spectral slope and color distributions of Jupiter Trojans, with particular attention to asteroid families. We use a sample of data from the Moving Object Catalogue of the Sloan Digital Sky Survey, together with spectra obtained from several surveys. A first sample of 349 observations, corresponding to 250 Trojan asteroids, were extracted from the Sloan Digital Sky Survey, and we also extracted from the literature a second sample of 91 spectra, corresponding to 71 Trojans. The spectral slopes were computed by means of a least-squares fit to a straight line of the fluxes obtained from the Sloan observations in the first sample, and of the rebinned spectra in the second sample. In both cases the reflectance fluxes/spectra were renormalized to 1 at 6230 $\textrm{\AA}$. We found that the distribution of spectral slopes among Trojan asteroids shows a bimodality. About 2/3 of the objects have reddish slopes compatible with D-type asteroids, while the remaining bodies show less reddish colors compatible with the P-type and C-type classifications. The members of asteroid families also show a bimodal distribution with a very slight predominance of D-type asteroids, but the background is clearly dominated by the D-types. The L4 and L5 swarms show different distributions of spectral slopes, and bimodality is only observed in L4. These differences can be attributed to the asteroid families since the backgraound asteroids show the same slope distribtuions in both swarms. The analysis of individual families indicates that the families in L5 are taxonomically homogeneous, but in L4 they show a mixture of taxonomic types. We discuss a few scenarios that might help to interpret these results.Comment: 20 pages, 15 figures, 2 table

On the genesis of the Haumea system

The scenarios proposed in the literature for the genesis of the system formed by the dwarf planet 136108 Haumea, its two satellites and a group of some 10 bodies (the family) with semimajor axes, eccentricities and inclinations close to Haumea's values, are analysed against collisional, physical, dynamical and statistical arguments in order to assess their likelihood. All scenarios based on collisional events are reviewed under physical arguments and the corresponding formation probabilities in a collisional environment are evaluated according to the collisional evolution model alicandep. An alternative mechanism is proposed based on the potential possibility of (quasi-) independent origin of the family with respect to Haumea and its satellites. As a general conclusion the formation of the Haumea system is a low-probability event in the currently assumed frame for the evolution of the outer Solar system. However, it is possible that current knowledge is missing some key element in the whole story that may contribute to increase the odds for the formation of such a system.This research was partially supported by Spanish grants AYA2011-06202-C02-01 (JLO) and AYA2011-06202-C02-02 (ACB). RGH gratefully acknowledges financial support by CONICET through PIP 114-201101-00358 and Junta de Andalucia 2012-FQM1776

Polarization of asteroid (387) Aquitania: the newest member of a class of large inversion angle asteroids

We present new imaging polarimetric observations of two Main Belt asteroids, (234) Barbara and (387) Aquitania, taken in the first half of 2008 using the Dual-Beam Imaging Polarimeter on the University of Hawaii 2.2 meter telescope, located on Mauna Kea, Hawaii. Barbara had been previously shown to exhibit a very unusual polarization-phase curve by Cellino, et al. (2006). Our observations confirm this result and add Aquitania to the growing class of large inversion angle objects. Interestingly, these asteroids show spinel features in their IR spectra suggesting a mineralogical origin to the phase angle-dependent polarimetric features. As spinel is associated with calcium-aluminum-rich inclusions and carbonaceous chondrites, these large inversion angle asteroids may represent some of the oldest surfaces in the solar system. Circular as well as linear polarization measurements were obtained but circular polarization was not detected.Comment: 12 pages, 2 figures, accepted to Icaru

The first confirmation of V-type asteroids among the Mars crosser population

The Mars crossing region constitutes a path to deliver asteroids from the Inner Main Belt to the Earth crossing space. While both the Inner Main Belt and the population of Earth crossing asteroids contains a significant fraction of asteroids belonging to the V taxonomic class, only two of such V-type asteroids has been detected in the Mars crossing region up to now. In this work, we searched for asteroids belonging to the V class among the population of Mars crossing asteroids, in order to support alternative paths to the delivery of this bodies into the Earth crossing region. We selected 18 candidate V-type asteroids in the Mars crossing region using observations contained in the Sloan Digital Sky Survey Moving Objects Catalog. Then, we observed 4 of these candidates to take their visible spectra using the Southern Astrophysical Research Telescope (SOAR). We also performed the numerical simulation of the orbital evolution of the observed asteroids. We confirmed that 3 of the observed asteroids belong to the V class, and one of these may follow a path that drives it to an Earth collision in some tens of million years

Neptune Trojans and Plutinos: colors, sizes, dynamics, and their possible collisions

Neptune Trojans and Plutinos are two subpopulations of trans-Neptunian objects located in the 1:1 and the 3:2 mean motion resonances with Neptune, respectively, and therefore protected from close encounters with the planet. However, the orbits of these two kinds of objects may cross very often, allowing a higher collisional rate between them than with other kinds of trans-Neptunian objects, and a consequent size distribution modification of the two subpopulations. Observational colors and absolute magnitudes of Neptune Trojans and Plutinos show that i) there are no intrinsically bright (large) Plutinos at small inclinations, ii) there is an apparent excess of blue and intrinsically faint (small) Plutinos, and iii) Neptune Trojans possess the same blue colors as Plutinos within the same (estimated) size range do. For the present subpopulations we analyzed the most favorable conditions for close encounters/collisions and address any link there could be between those encounters and the sizes and/or colors of Plutinos and Neptune Trojans. We also performed a simultaneous numerical simulation of the outer Solar System over 1 Gyr for all these bodies in order to estimate their collisional rate. We conclude that orbital overlap between Neptune Trojans and Plutinos is favored for Plutinos with large libration amplitudes, high eccentricities, and small inclinations. Additionally, with the assumption that the collisions can be disruptive creating smaller objects not necessarily with similar colors, the present high concentration of small Plutinos with small inclinations can thus be a consequence of a collisional interaction with Neptune Trojans and such hypothesis should be further analyzed.Comment: 15 pages, 9 figures, 6 tables, accepted for publication in A&