Search

Abstract: The sizes, shapes, and surface or subsurface properties of Near Earth Objects (mostly asteroids, also inactive comet nuclei) are still poorly known, since any accurate determination requires in situ missions. It may nevertheless be estimated that the sizes of these irregular bodies range from a few tens of kilometres to a few tens of meters, with possibly about 1000 NEOs with sizes greater than 1 km. Their surfaces are estimated to be quite rough, and at least partially covered with regolith. To cite this article: A.C. Levasseur-Regourd et al., C. R. Physique 6 (2005). [Copyright &y& Elsevier]

Abstract: A short overview of main characteristics of the impactor population from which major terrestrial impacts originated is given. This population includes the objects that may hit the Earth in the future (potentially hazardous asteroids, PHAs). An impact frequency (a way of measuring the probability of a given collision) versus impact energy (an index of the impact consequences) relationship is described on the basis of this analysis. The current state of actions started planetwide by the most developed countries to face the threat represented by an asteroid collision with the Earth is summarized. The ‘Torino scale’, which assesses the risks connected with a discovery of a PHA in a simple and clear way is finally described. To cite this article: M. Fulchignoni, M.A. Barucci, C. R. Physique 6 (2005). [Copyright &y& Elsevier]

Ten years after the discovery of the first object entirely outside the orbit of Neptune, the number of detected Edgeworth-Kuiper Belt objects (EKBO) is close to 800: after the discovery of the asteroid 1 Ceres, it took 115 years to discover the same number of asteroids. These large comets dressed as asteroids are very elusive objects, challenging the observers with their faintness. As well as the comets and the asteroids, this group of objects represent a valuable source of information on the physical and chemical environment of the Solar System at the epoch of planet growth. In this paper we summarize the results of the first statistical studies of the bulk physical and chemical properties of EKBO, based on broad band photometry data. To cite this article: M. Fulchignoni, A.C. Delsanti, C. R. Physique 4 (2003). [Copyright &y& Elsevier]

Abstract: The petrologic diversity of meteorites demonstrates that planetesimals ranged from unmelted, variably metamorphosed aggregates to fully molten, differentiated bodies. However, partially differentiated bodies have not been unambiguously identified in the asteroid belt. New constraints on the density, composition, and morphology of 21 Lutetia from the Rosetta spacecraft indicate that the asteroid''s high bulk density exceeds that of most known chondritic meteorite groups, yet its surface properties resemble those of some carbonaceous and enstatite chondrite groups. This indicates that Lutetia likely experienced early compaction processes like metamorphic sintering. It may have also partially differentiated, forming a metallic core overlain by a primitive chondritic crust. [Copyright &y& Elsevier]

Abstract: Ground-based high angular-resolution images of asteroid (2) Pallas at near-infrared wavelengths have been used to determine its physical properties (shape, dimensions, spatial orientation and albedo distribution). We acquired and analyzed adaptive optics (AO) J/H/K-band observations from Keck II and the Very Large Telescope taken during four Pallas oppositions between 2003 and 2007, with spatial resolution spanning 32–88km (image scales 13–20km/pixel). We improve our determination of the size, shape, and pole by a novel method that combines our AO data with 51 visual light-curves spanning 34 years of observations as well as archived occultation data. The shape model of Pallas derived here reproduces well both the projected shape of Pallas on the sky (average deviation of edge profile of 0.4pixel) and light-curve behavior (average deviation of 0.019 mag) at all the epochs considered. We resolved the pole ambiguity and found the spin-vector coordinates to be within 5° of [longitude, latitude]=[30°, −16°] in the Ecliptic J2000.0 reference frame, indicating a high obliquity of about 84°, leading to high seasonal contrast. The best triaxial-ellipsoid fit returns ellipsoidal radii of , and . From the mass of Pallas determined by gravitational perturbation on other minor bodies , [Michalak, G., 2000. Astron. Astrophys. 360, 363–374], we derive a density of significantly different from the density of C-type (1) Ceres of [Carry, B., Dumas, C., Fulchignoni, M., Merline, W.J., Berthier, J., Hestroffer, D., Fusco, T., Tamblyn, P., 2008. Astron. Astrophys. 478 (4), 235–244]. Considering the spectral similarities of Pallas and Ceres at visible and near-infrared wavelengths, this may point to fundamental differences in the interior composition or structure of these two bodies. We define a planetocentric longitude system for Pallas, following IAU guidelines. We also present the first albedo maps of Pallas covering ∼80% of the surface in K-band. These maps reveal features with diameters in the 70–180km range and an albedo contrast of about 6% with respect to the mean surface albedo. [Copyright &y& Elsevier]

Abstract: 832 Karin is the largest member of the young Karin cluster that formed ago in the outer main belt. Surprisingly, recent near-IR spectroscopy measurements [Sasaki, T., Sasaki, S., Watanabe, J., Sekiguchi, T., Yoshida, F., Kawakita, H., Fuse, T., Takato, N., Dermawan, B., Ito, T., 2004. Astrophys. J. 615 (2), L161–L164] revealed that Karin''s surface shows different colors as a function of rotational phase. It was interpreted that 832 Karin shows us the reddish space-weathered exterior surface of the parent body as well as an interior face, which has not had time to become space-weathered. This result is at odds with recent results including seismic and geomorphic modeling, modeling of the Karin cluster formation and measurements of the space weathering rate. Consequently, we aimed to confirm/infirm this surprising result by sampling Karin''s spectrum well throughout its rotation. Here, we present new visible (0.45–0.95 μm) and near-infrared (0.7–2.5 μm) spectroscopic observations of 832 Karin obtained in January and April 2006, covering most of Karin''s longitudes. In the visible range, we find that Karin shows no rotational spectral variations. Similarly, we find that Karin exhibits very little (to none) spectral variations with rotation in the near-IR range. Our results imply that 832 Karin has a homogeneous surface, in terms of composition and surface age. Our results also imply that the impact that generated the family refreshed entirely Karin''s surface, and probably the surfaces of all members. [Copyright &y& Elsevier]

In the frame of the international campaign to observe potential target asteroids for the Rosetta mission, remote observations have been carried out between Observatoire de Paris, in Meudon-France and the NASA Infrared Telescope Facility on Mauna Kea. The SpeX instrument was used in the 0.8–2.5 μm spectral region, for two observing runs in March and June 2003.This paper presents near-IR spectra of the asteroids 21 Lutetia, 89 Julia, 140 Siwa, 2181 Fogelin and 5480 (1989YK8).Near-IR spectra of the asteroids 21 Lutetia and 140 Siwa are flat and featureless. The spectrum of 89 Julia reveals absorption bands around 1 and 2 μm, which may indicate the presence of olivine and olivine-pyroxene mixtures and confirm the S-type designation.The small main-belt asteroids 2181 Fogelin and 5480 (1989YK8) are investigated spectroscopically for the first time. Near-IR spectra of these asteroids also show an absorption feature around 1 μm, which could be and indicator of igneous/metamorphic surface of the objects; new observations in visible as well as thermal albedo data are necessary to draw a reliable conclusion on the surface mineralogy of both asteroids. [Copyright &y& Elsevier]

With the surface properties and shapes of solar system small bodies (comets and asteroids) now being routinely revealed by spacecraft and Earth-based radar, understanding their interior structure represents the next frontier in our exploration of these worlds. Principal unknowns include the complex interactions between material strength and gravity in environments that are dominated by collisions and thermal processes. Our purpose for this review is to use our current knowledge of small body interiors as a foundation to define the science questions which motivate their continued study: In which bodies do “planetary” processes occur? Which bodies are “accretion survivors”, i.e., bodies whose current form and internal structure are not substantially altered from the time of formation? At what characteristic sizes are we most likely to find “rubble-piles”, i.e., substantially fractured (but not reorganized) interiors, and intact monolith-like bodies? From afar, precise determinations of newly discovered satellite orbits provide the best prospect for yielding masses from which densities may be inferred for a diverse range of near-Earth, main-belt, Trojan, and Kuiper belt objects. Through digital modeling of collision outcomes, bodies that are the most thoroughly fractured (and weak in the sense of having almost zero tensile strength) may be the strongest in the sense of being able to survive against disruptive collisions. Thoroughly fractured bodies may be found at almost any size, and because of their apparent resistance to disruptive collisions, may be the most commonly found interior state for small bodies in the solar system today. Advances in the precise tracking of spacecraft are giving promise to high-order measurements of the gravity fields determined by rendezvous missions. Solving these gravity fields for uniquely revealing internal structure requires active experiments, a major new direction for technological advancement in the coming decade. We note the motivation for understanding the interior properties of small bodies is both scientific and pragmatic, as such knowledge is also essential for considering impact mitigation. [Copyright &y& Elsevier]