Simone Marchi

The majority of basaltic asteroids are found in the inner main belt, although a few have also been observed in the outer main belt and near-Earth space. These asteroids -referred to as V-types- have surface compositions that resemble that of the 530km sized asteroid Vesta. Besides the compositional similarity, dynamical evidence also links many V-type asteroids to Vesta. Moreover, Vesta is one of the few asteroids to have been identified as source of specific classes of meteorites, the howardite, eucrite, diogenite achondrites (HEDs). Despite the general consensus on the outlined scenario, several questions remain unresolved. In particular, it is not clear if the observed spectral diversity among Vesta, V-types and HEDs is due to space weathering, as is thought to be the case for S-type asteroids. In this paper, SDSS photometry is used to address the question of whether the spectral diversity among candidate V-types and HEDs can be explained by space weathering. We show that visible spectral slopes of V-types are systematically redder with respect to HEDs, in a similar way to what is found for ordinary chondrite meteorites and S-types. On the assumption that space weathering is responsible for the slope mismatch, we estimated an upper limit for the reddening timescale of about 0.5Ga. Nevertheless, the observed slope mismatch between HEDs and V-types poses several puzzles to understanding its origin. The implication of our findings is also discussed in the light of Dawn mission to Vesta.

The cratering history of main belt asteroid (2867) Steins has been investigated using OSIRIS imagery acquired during the Rosetta flyby that took place on the 5th of September 2008. For this purpose, we applied current models describing the formation and evolution of main belt asteroids, that provide the rate and velocity distributions of impactors. These models coupled with appropriate crater scaling laws, allow the cratering history to be estimated. Hence, we derive Steins' cratering retention age, namely the time lapsed since its formation or global surface reset. We also investigate the influence of various factors -like bulk structure and crater erasing- on the estimated age, which spans from a few hundred Myrs to more than 1Gyr, depending on the adopted scaling law and asteroid physical parameters. Moreover, a marked lack of craters smaller than about 0.6km has been found and interpreted as a result of a peculiar evolution of Steins cratering record, possibly related either to the formation of the 2.1km wide impact crater near the south pole or to YORP reshaping.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

In this paper we present a new method for dating the surface of the Moon, obtained by modeling the incoming flux of impactors and converting it into a size distribution of resulting craters. We compare the results from this model with the standard chronology for the Moon showing their similarities and discrepancies. In particular, we find indications of a non-constant impactor flux in the last 500 Myr and also discuss the implications of our findings for the Late Heavy Bombardment hypothesis. We also show the potential of our model for accurate dating of other inner Solar System bodies, by applying it to Mercury.

The extrasolar planets (EPs) so far detected are very different to the planets in our own Solar System. Many of them have Jupiter-like masses and close-in orbits (the so-called hot planets, HPs), with orbital periods of only a few days. In this paper, we present a new statistical analysis of the observed EPs, focusing on the origin of the HPs. Among the several HP formation mechanisms proposed so far, the two main formation mechanisms are type II migration and scattering. In both cases, planets form beyond the so-called snow-line of the protoplanetary disk and then migrate inward due to angular momentum and energy exchange with either the protoplanetary disk or with companion planets. Although theoretical studies produce a range of observed features, no firm correspondence between the observed EPs and models has yet been established. In our analysis, by means of principal component analysis and hierarchical cluster analysis, we find convincing indications for the existence of two types of HPs, whose parameters reflect physical mechanisms of type II migration and scattering.

The discovery of an increasing number of extrasolar planets (EPs) prompts the development of a planetary taxonomy. Such analysis, as in many other fields of research, is useful to identify groups of objects sharing similar traits. When applied to extrasolar planets, the taxonomy may provide a valid support for disentangling the role of the several physical parameters (semimajor axis, metallicity etc.) involved in the planetary formation processes and subsequent evolution. We present the state-of-the-art for exoplanets taxonomy obtained with hierarchical algorithms and the definition of robust clusters of planets (this is an update of the taxonomy published in Marchi 2007). The physical relevance of the exoplanet clusters along with their implications for the formation theories are also discussed. Finally, we comment on the future improvements of such analysis taking into account new algorithms and new input variables.

In this paper we present the guidelines for an extrasolar planet taxonomy. The discovery of an increasing number of extrasolar planets showing a vast variety of planetary parameters, such as Keplerian orbital elements, and environmental parameters, such as stellar masses, spectral types, and metallicity, prompts the development of a planetary taxonomy. In this work, via principal component analysis followed by hierarchical clustering analysis, we report the definition of five robust groups of planets. We also discuss the physical relevance of such analysis, which may provide a valid basis for disentangling the role of the several physical parameters involved in the processes of planet formation and subsequent evolution. For instance, we were able to divide the hot Jupiters into two main groups on the basis of their stellar masses and metallicities. Moreover, for some groups, we find strong correlations among metallicity, semimajor axis, and eccentricity. The implications of these findings are discussed.

In this paper we present the guidelines for an extrasolar planet taxonomy. The discovery of an increasing number of extrasolar planets showing a vast variety of planetary parameters, like Keplerian orbital elements and environmental parameters, like stellar masses, spectral types, metallicity etc., prompts the development of a planetary taxonomy. In this work via principal component analysis followed by hierarchical clustering analysis, we report the definition of five robust groups of planets. We also discuss the physical relevance of such analysis, which may provide a valid basis for disentangling the role of the several physical parameters involved in the processes of planet formation and subsequent evolution. For instance, we were able to divide the hot Jupiters into two main groups on the basis of their stellar masses and metallicities. Moreover, for some groups, we find strong correlations between metallicity, semi-major axis and eccentricity. The implications of these findings are discussed.