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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.07.047 Byline: BenoA[R]t Carry (a)(b), Pierre Vernazza (c), Christophe Dumas (b), Marcello Fulchignoni (a) Keywords: Asteroid vesta; Asteroids, Surfaces; Adaptive optics; Infrared observations Abstract: Vesta, the second largest Main-Belt Asteroid, will be the first to be explored in 2011 by NASA's Dawn mission. It is a dry, likely differentiated body with spectrum suggesting that is has been resurfaced by basaltic lava flows, not too different from the lunar maria. Here we present the first disk-resolved spectroscopic observations of an asteroid from the ground. We observed (4) Vesta with the ESO-VLT adaptive optics equipped integral-field near-infrared spectrograph SINFONI, as part of its science verification campaign. The highest spatial resolution of [approximately equal to]90km on Vesta's surface was obtained during excellent seeing conditions (0.5.sup.a[sup.3]) in October 2004. We observe spectral variations across Vesta' surface that can be interpreted as variations of either the pyroxene composition, or the effect of surface aging. We compare Vesta's 2[mu]m absorption band to that of howardite-eucrite-diogenite (HED) meteorites that are thought to originate from Vesta, and establish particular links between specific regions and HED subclasses. The overall composition is found to be mostly compatible with howardite meteorites, although a small area around 180[degrees]E longitude could be attributed to a diogenite-rich spot. We finally focus our spectral analysis on the characteristics of Vesta's bright and dark regions as seen from Hubble Space Telescope's visible and Keck-II's near-infrared images. Author Affiliation: (a) LESIA, Observatoire de Paris-Meudon, 5 Place Jules Janssen, 92195 Meudon Cedex, France (b) ESO, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile (c) Research and Scientific Support Department, European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands Article History: Received 24 July 2008; Revised 13 July 2009; Accepted 31 July 2009 Article Note: (footnote) [star] Based on observations collected at the European Southern Observatory, Paranal, Chile - 60.A-9041.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.04.014 Byline: Pierre Vernazza (a), Alessandro Rossi (b), Mirel Birlan (c), Marcello Fulchignoni (a), Alin Nedelcu (c)(d), Elisabetta Dotto (e) Keywords: Asteroids; rotation; Spectroscopy; Asteroids; surfaces; Regoliths Abstract: 832 Karin is the largest member of the young Karin cluster that formed 5.75[+ or -]0.05Myr 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 [mu]m) and near-infrared (0.7-2.5 [mu]m) 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. Author Affiliation: (a) LESIA, Observatoire de Paris, 5 Place Jules Janssen, 92195 Meudon Principal Cedex, France (b) Spaceflight Dynamics Section, ISTI-CNR, Via Moruzzi 1, 56124 Pisa, Italy (c) IMCCE, Observatoire de Paris, 77 Av. Denfert Rochereau, 75014 Paris Cedex, France (d) Astronomical Institute of the Romanian Academy, Cutitul de Argint-5, Bucharest, Romania (e) INAF, Osservatorio Astronomico di Roma, Via Frascatti 33, 00040 Monteporzio Catone, Italy Article History: Received 6 December 2006; Revised 11 April 2007

We define a new approach to model asteroidal space weathering. We started from recent results of ion irradiation experiments (60-400 keV) of meteorites and silicates to give an accurate description of space weathering, and we included its effects in the Shkuratov model. We found that the reddening and darkening process (in the range 0.3-2.5 [micro]m) does not significantly affect the position or relative intensities of the mafic silicate absorption features and it mainly affects the continuum of reflectance spectra. This continuum is parameterized by a [C.sub.S] coefficient, which is strongly related with the number of displacements per unit area (damage parameter); we consequently obtained an exposure time curve, and corresponding astrophysical timescales. We applied this new description of space weathering to model observed spectra of Asteroid 832 Karin, in the 0.4-2.4 [micro]m spectral region. The obtained exposure time is slightly lower than the age of the impact and collisional breakup which originated the Karin asteroidal family, i.e., about 5.75 x [10.sup.6] years. Keywords: Asteroid, surfaces; Spectroscopy; Experimental techniques; Meteorites

A study shows that the rotational lightcurve of Apollo asteroid 4179 Toutatis is not periodic and has a large amplitude of about 1.2 magnitudes. This could be due to complex and tumbling rotation of the asteroid, with a characteristic period of three to seven days. The study is done using data collected from asteroid observation in Dec 1992, when it passed within 0.0242 AU of Earth.

In this short note the differences induced in the taxonomy obtained with the G-mode analysis by the corrected values of the IRAS albedo are presented. The results reveal the consistence of the nine main taxonomic classes.

Barucci et al. (1987. Icarus 72, 304-324) developed their asteroid taxonomy based on the G-mode statistical method, applied to a sample of 438 asteroids, where each asteroid was described by eight variables (seven ECAS colors and the IRAS albedo). They found that the asteroid population separates into nine major taxonomic classes (C, S, M, D, B, G, E, A, V) and that three of these (S, D, B) can be further subdivided into subclasses. Birlan et al. (1996b. Icarus 124, 352-354) found that the values of the corrected IRAS albedos do not influence the bulk structure of this taxonomy. The aim of this paper is to define an algorithm that allows us to extend this classification system to any asteroid for which the ECAS reflectances and the albedos become available through new observations. The algorithm which allows us to extend the G-mode method is presented, along with a test of the procedure utilizing color and albedo measurements for 465 asteroids. Key Words: asteroids, compositional types; asteroid taxonomy.

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: Methane is key to sustaining Titan''s thick nitrogen atmosphere. However, methane is destroyed and converted to heavier hydrocarbons irreversibly on a relatively short timescale of approximately 10–100 million years. Without the warming provided by CH4-generated hydrocarbon hazes in the stratosphere and the pressure induced opacity in the infrared, particularly by CH4–N2 and H2–N2 collisions in the troposphere, the atmosphere could be gradually reduced to as low as tens of millibar pressure. An understanding of the source–sink cycle of methane is thus crucial to the evolutionary history of Titan and its atmosphere. In this paper we propose that a complex photochemical–meteorological–hydrogeochemical cycle of methane operates on Titan. We further suggest that although photochemistry leads to the loss of methane from the atmosphere, conversion to a global ocean of ethane is unlikely. The behavior of methane in the troposphere and the surface, as measured by the Cassini–Huygens gas chromatograph mass spectrometer, together with evidence of cryovolcanism reported by the Cassini visual and infrared mapping spectrometer, represents a “methalogical” cycle on Titan, somewhat akin to the hydrological cycle on Earth. In the absence of net loss to the interior, it would represent a closed cycle. However, a source is still needed to replenish the methane lost to photolysis. A hydrogeochemical source deep in the interior of Titan holds promise. It is well known that in serpentinization, hydration of ultramafic silicates in terrestrial oceans produces H2(aq), whose reaction with carbon grains or carbon dioxide in the crustal pores produces methane gas. Appropriate geological, thermal, and pressure conditions could have existed in and below Titan''s purported water-ammonia ocean for “low-temperature” serpentinization to occur in Titan''s accretionary heating phase. On the other hand, impacts could trigger the process at high temperatures. In either instance, storage of methane as a stable clathrate–hydrate in Titan''s interior for later release to the atmosphere is quite plausible. There is also some likelihood that the production of methane on Titan by serpentinization is a gradual and continuous on-going process. [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]