Daniela Lazzaro

Distribution of taxonomic classes in the main belt of asteroids

Abstract In this work we analyze the bias-corrected taxonomic distribution of asteroids in the Main Belt based on the results of two large spectroscopic surveys with a total of 2026 objects. With the goal of minimizing selection effects that could affect our results, analyses were also performed on a sample from which the dynamical families and the small objects were removed. Our results differ significantly from the majority of previous work. The most notable difference concerns the distribution in semi-major axis of the S class (and its subtypes), found to compose a significant fraction of the asteroid population out to 3.0 AU. Also, we found differences in the distribution of the classes as we considered varying ranges of eccentricities and inclinations.

Search for relations among a sample of 460 asteroids with featureless spectra

Abstract We present an analysis of 460 featureless asteroid spectra in the range 0.5–0.92 μm obtained in the Small Solar System Objects Spectroscopic Survey. The spectra are described in terms of the continuum steepness ( cSlope ), its concavity ( RRE ), and the blue wing of drop in the UV reflectance ( BD ). Comparison with meteorite spectra confirms the link between CM meteorites and asteroids with asteroids with 0.7 μm band. Also, it is found that asteroids with extreme negative slope values may be related to CK chondrites and that asteroids with pronounced concave-down curvature are related to CO chondrites. An analysis of the distribution of the spectral parameters with semimajor axis, diameter, and albedo is performed.

V-type asteroids in the middle main belt

Abstract V-type asteroids are bodies whose surfaces are constituted of basalt. In the Main Asteroid Belt, most of these asteroids are assumed to come from the basaltic crust of Asteroid (4) Vesta. This idea is mainly supported by (i) the fact that almost all the known V-type asteroids are in the same region of the belt as (4) Vesta, i.e., the inner belt (semi-major axis 2.1 a 2.5 AU), (ii) the existence of a dynamical asteroid family associated to (4) Vesta, and (iii) the observational evidence of at least one large craterization event on Vestas surface. One V-type asteroid that is difficult to fit in this scenario is (1459) Magnya, located in the outer asteroid belt, i.e., too far away from (4) Vesta as to have a real possibility of coming from it. The recent discovery of the first V-type asteroid in the middle belt ( 2.5 a 2.8 AU), (21238) 1995WV7 [Binzel, R.P., Masi, G., Foglia, S., 2006. Bull. Am. Astron. Soc. 38, 627; Hammergren, M., Gyuk, G., Puckett, A., 2006. ArXiv e-print, astro-ph/0609420], located at ∼2.54 AU, raises the question of whether it came from (4) Vesta or not. In this paper, we present spectroscopic observations indicating the existence of another V-type asteroid at ∼2.53 AU, (40521) 1999RL95, and we investigate the possibility that these two asteroids evolved from the Vesta family to their present orbits by a semi-major axis drift due to the Yarkovsky effect. The main problem with this scenario is that the asteroids need to cross the 3/1 mean motion resonance with Jupiter, which is highly unstable. Combining N-body numerical simulations of the orbital evolution, that include the Yarkovsky effect, with Monte Carlo models, we compute the probability that an asteroid of a given diameter D evolves from the Vesta family and crosses over the 3/1 resonance, reaching a stable orbit in the middle belt. Our results indicate that an asteroid like (21238) 1995WV7 has a low probability (∼1%) of having evolved through this mechanism due to its large size ( D ∼ 5 km ), because the Yarkovsky effect is not sufficiently efficient for such large asteroids. However, the mechanism might explain the orbits of smaller bodies like (40521) 1999RL95 ( D ∼ 3 km ) with ∼ 70 – 100 % probability, provided that we assume that the Vesta family formed ≳ 3.5 Gy ago. We estimate the debiased population of V-type asteroids that might exist in the same region as (21238) and (40521) ( 2.5 a ≲ 2.62 AU ) and conclude that about 10 to 30% of the V-type bodies with D > 1 km may come from the Vesta family by crossing over the 3/1 resonance. The remaining 70–90% must have a different origin.

Rotational spectra of (162173) 1999 JU3, the target of the Hayabusa2 mission

Context. The Hayabusa2 mission, which will be launched by JAXA in 2014, will return samples from the C-type near-Earth asteroid (162173) 1999 JU3. To better plan the mission, it is important to obtain as many physical characteristics of the asteroid as possible from ground-based observations. Moreover, these can then be calibrated with the in-situ and laboratory studies and be used to better understand other similar objects. Regarding the surface composition of the target asteroid, previous spectroscopic studies in the visible provided conflicting results for the possible presence of a deep absorption band, which is usually related to aqueous alteration processes. Aims. Our goal is to better understand the surface composition of asteroid (162173) 1999 JU3, and how it relates to the spectral differences observed by diverse authors at different epochs and telescopes. Moreover, to support the JAXA mission planning, we aim to constrain the level of aqueous alteration and thermal activity undergone by the object. Methods. The adopted methodology was to observe different regions of the surface of the asteroid that rotates around its axis. Spectroscopic observations that cover about 70% of its surface were therefore obtained at the SOAR telescope in Chile on 2012 July 9−10. Results. Our results indicate that the surface of asteroid (162173) 1999 JU3 presents featureless spectra with very little variation. Conclusions. No sign of an absorption feature that could be related to aqueous alteration processes is detectable in the observed

Mineralogical characterization of Baptistina Asteroid Family: Implications for K/T impactor source

Abstract Bottke et al. [Bottke, W.F., Vokrouhlicky, D., Nesvorný, D., 2007. Nature 449, 48–53] linked the catastrophic formation of Baptistina Asteroid Family (BAF) to the K/T impact event. This linkage was based on dynamical and compositional evidence, which suggested the impactor had a composition similar to CM2 carbonaceous chondrites. However, our recent study [Reddy, V., Emery, J.P., Gaffey, M.J., Bottke, W.F., Cramer, A., Kelley, M.S., 2009. Meteorit. Planet. Sci. 44, 1917–1927] suggests that the composition of (298) Baptistina is similar to LL-type ordinary chondrites rather than CM2 carbonaceous chondrites. This rules out any possibility of it being related to the source of the K/T impactor, if the impactor was of CM-type composition. Mineralogical study of asteroids in the vicinity of BAF has revealed a plethora of compositional types suggesting a complex formation and evolution environment. A detailed compositional analysis of 16 asteroids suggests several distinct surface assemblages including ordinary chondrites (Gaffey SIV subtype), primitive achondrites (Gaffey SIII subtype), basaltic achondrites (Gaffey SVII subtype and V-type), and a carbonaceous chondrite. Based on our mineralogical analysis we conclude that (298) Baptistina is similar to ordinary chondrites (LL-type) based on olivine and pyroxene mineralogy and moderate albedo. S-type and V-type in and around the vicinity of BAF we characterized show mineralogical affinity to (8) Flora and (4) Vesta and could be part of their families. Smaller BAF asteroids with lower SNR spectra showing only a ‘single’ band are compositionally similar to (298) Baptistina and L/LL chondrites. It is unclear at this point why the silicate absorption bands in spectra of asteroids with formal family definition seem suppressed relative to background population, despite having similar mineralogy.

Photometric monitoring of 2060 Chiron's brightness at perihelion☆

Abstract The results of photometric and spectroscopic observations of comet/asteroid 2060 Chiron carried on at the Observatorio do Pico-dos-Dias (Brazil), at the European Southern Observatory (Chile) and at the Mauna Kea Observatory (Hawaii) during 1996 are presented. The analysis of the photometric data shows that even at a minimum of brightness 2060 Chiron presents some activity. The absolute magnitude, H v , varied from 6.79 in February to 6.22 in March. Therefore 2060 Chiron is still in a minimum of activity close to that of 1983–1985 and of 1994–1995.

Spectral characterization of V-type asteroids – II. A statistical analysis

In recent years several small basaltic V-type asteroids have been identified all around the main belt. Most of them are members of the Vesta dynamical family, but an increasingly large number appear to have no link with it. The question that arises is whether all these basaltic objects do indeed come from Vesta. To find the answer to the above questioning, we decided to perform a statistical analysis of the spectroscopic and mineralogical properties of a large sample of V-types, with the objective to highlight similarities and differences among them, and shed light on their unique, or not, origin. The analysis was performed using 190 visible and near-infrared spectra from the literature for 117 V-type asteroids. The asteroids were grouped according to their dynamical properties and their computed spectral parameters compared. Comparison was also performed with spectral parameters of a sample of HED meteorites and data of the surface of Vesta taken by the VIR instrument on board of the Dawn spacecraft. Our analysis shows that although most of the V-type asteroids in the inner main belt do have a surface composition compatible with an origin from Vesta, this seem not to be the case for V-types in the middle and outer main belt.

2060 Chiron back to a minimum of brightness

The results of photometric observations of comet/asteroid 2060 Chiron at the Observatorio do Pico dos Dias (Brazil-OPD) and the Observatoire de Haute-Provence (France-OHP) during 1994 and 1995 are presented. The analysis of the data shows a decrease of 2060 Chiron brightness from its peak values of 1988–1991. The absolute magnitude, Hv, varies from a maximum of 6.6 in February 1994 up to a minimum of 6.8 in June 1995. Therefore 2060 Chiron is back to a minimum of activity close to that of 1983–1985. The slope parameter G is found to be G = 0.71 ± 0.15. It is suggested that the H-G magnitude system, generally adopted to present 2060 Chiron brightness, is not the most appropriate due to the cometary activity of this object.

Surface composition? and dynamical evolution of two retrograde objects in the outer solar system: 2008 YB3 and 2005 VD

Most of the objects in the trans-Neptunian belt (TNb) and related populations move in prograde orbits with low eccentricity and inclination. However, the list of icy minor bodies moving in orbits with an inclination above 40 has increased in recent years. The origin of these bodies, and in particular of those objects in retrograde orbits, is not well determined, and di erent scenarios are considered, depending on their inclination and perihelion. In this paper, we present new observational and dynamical data of two objects in retrograde orbits, 2008 YB3 and 2005 VD. We find that the surface of these extreme objects is depleted of ices and does not contain the ‘ultra-red’ matter typical of some Centaurs. Despite small di erences, these objects share common colors and spectral characteristics with the Trojans, comet nuclei, and the group of grey Centaurs. All of these populations are supposed to be covered by a mantle of dust responsible for their reddish- to neutral-color. To investigate if the surface properties and dynamical evolution of these bodies are related, we integrate their orbits for 10 8 years to the past. We find a remarkable di erence in their dynamical evolutions: 2005 VD’s evolution is dominated by a Kozai resonance with planet Jupiter while that of 2008 YB3 is dominated by close encounters with planets Jupiter and Saturn. Our models suggest that the immediate site of provenance of 2005 VD is the in the Oort cloud, whereas for 2008 YB3 it is in the trans-Neptunian region. Additionally, the study of their residence time shows that 2005 VD has spent a larger lapse of time moving in orbits in the region of the giant planets than 2008 YB3. Together with the small di erences in color between these two objects, with 2005 VD being more neutral than 2008 YB3, this fact suggests that the surface of 2005 VD has su ered a higher degree of processing, probably related to cometary activity episodes.

Re-assessing the ordinary chondrites paradox

Context. The so-called ordinary chondrite paradox has been a recurring topic in planetary science in the past twenty years. This paradox originated from the first comparisons between spectrophotometric measurements of meteorites and asteroids. Basically it is based on the lack of spectral analogs of the ordinay chondrites (OC) among the Main Belt asteroids, although present among the NEAs. Several hypothesis to account for the paradox have been published, all considering the effect of space weathering and different degrees of resurfacing on the asteroids surfaces. Aims. The aim of the present paper is to further investigate this intriguing problem considering that the small-sized population of Main Belt asteroids has not yet been analyzed. Methods. Spectroscopic observations of Main Belt asteroids with a size smaller than 5 km – similar to that of NEAs – were performed with the 8-m Gemini telescope. Furthermore, spectra obtained in large spectroscopic surveys were used to perform a statistical analysis of the fraction of spectral analogous to the OCs in the Main Belt and NEA populations. Results. The main result of this work is that the vast majority of the Main Belt Sk- and Sq-class asteroids can be matched to OC meteorites in the visible part of the spectrum. Conclusions. Our results suggest that a considerable fraction of the OC material in the Main Belt is presently unweathered enough to be comparable to meteorite laboratory spectra.