First disk-resolved spectroscopy of (4) Vesta

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 ~90 km on Vesta's surface was obtained during excellent seeing conditions (0.5") in October 2004. We observe spectral variations across Vesta's surface that can be interpreted as variations of either the pyroxene composition, or the effect of surface aging. We compare Vesta's 2 micron 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 overallcomposition is found to be mostly compatible with howardite meteorites, although a small area around 180 deg. East 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.Comment: 13 pages, 11 figures, 3 table

Deficit of primitive compositions in binary asteroids and pairs

Context. Small binary asteroid systems and pairs are thought to form through fission induced by spin up via the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. This process is expected to depend on their structural strength, hence composition. Aims. We aim to determine how taxonomic classes, used as a proxy for composition, distribute amongst binary asteroids and asteroid pairs compared to the general population. Methods. We compare the distribution of taxonomic classes of binary systems and pairs with that of a reference sample of asteroids. We build this sample by selecting asteroids to reproduce the orbital and size distribution of the binaries and pairs to minimize potential biases between samples. Results. A strong deficit of primitive compositions (C, B, P, D types) among binary asteroids and asteroid pairs is identified, as well as a strong excess of asteroids with mafic-silicate rich surface compositions (S, Q, V, A types). Conclusions. Amongst low mass, rapidly rotating asteroids, those with mafic-silicate rich compositions are more likely to form multiple asteroid systems than their primitive counterparts.Comment: 12 pages, 7 figures, last 5 pages are table

Asteroid Systems: Binaries, Triples, and Pairs

In the past decade, the number of known binary near-Earth asteroids has more than quadrupled and the number of known large main belt asteroids with satellites has doubled. Half a dozen triple asteroids have been discovered, and the previously unrecognized populations of asteroid pairs and small main belt binaries have been identified. The current observational evidence confirms that small (<20 km) binaries form by rotational fission and establishes that the YORP effect powers the spin-up process. A unifying paradigm based on rotational fission and post-fission dynamics can explain the formation of small binaries, triples, and pairs. Large (>20 km) binaries with small satellites are most likely created during large collisions.Comment: 31 pages, 12 figures. Chapter in the book ASTEROIDS IV (in press

Gaia-FUN-SSO: a network for Solar System transient Objects

International audienceDuring the Gaia mission, Solar System Object alerts will be triggered toward the ground. We have set up the Gaia-FUN-SSO network in order to coordinate fast reaction for the observation of these targets. In this article, we describe this network at the present stage, its recent activity for training campaigns of observation, and its next activity. We discuss also some points related to this organization and the strategy of observation

Current status and development of the SSO FUN alerts

International audienceThe astrometry mission Gaia of the European Space Agency (ESA) will scan the entire sky several times over 5 years, down to a visual apparent magnitude of 20. Apart for its primary targets, the stars, that will be mapped during the course of the mission, Gaia is expected to observe more than 300,000 asteroids (Mignard et al., 2007). Although our census of asteroids is about complete at a such magnitude limit, the location of Gaia at L2 may allow the detection of yet-unknown near-Earth asteroids (NEAs). The predefined and smooth scanning law of Gaia, however, is not meant for pointed or follow-up observations. A ground-based network of observers has therefore been set up, the Follow-Up Network for the Solar System Objects (FUN SSO), centered around a central node (the DU459 of the Gaia Data Processing and Analysis Consortium, the DPAC). The aim of this network is to quickly observe from the ground the NEAs newly discovered by Gaia to secure an accurate orbit

Searching the pole solution of NEA 162173 (1999 JU3)

Conference at the Korean Space Science Society, April 24-26 2013, Jeju island, KoreaNear-Earth asteroid (NEA) 162173 (1999 JU3) (hereafter 1999 JU3) is the primary target of JAXA's Hayabusa 2 mission and also a backup target of NASA's OSIRIS-REx mission, not only because of its accessibility but also because it would be the first C-type asteroid for exploration missions. Knowing the information about spin status, such as rotational period, the ecliptic longitude and latitude of the pole is essential for the design of mission sequence such as the remote sensing observation. In order to get the physical properties of 1999 JU3, a total of 75 days ground-based observations at various geometries were carried out during 2007 - 2012 apparitions. Observations in the thermal infrared were also conducted with the Subaru, Akari, and Spitzer telescopes. We have analyzed the optical lightcurve of 1999 JU3, and derived a sidereal rotational period of 7.631 ± 0.001 hour. Using the lightcurve inversion method in conjunction with the thermal physical modeling, we determined a nearly spherical shape with a diameter of 823 ± 38 m, a geometric albedo of 0.058 ± 0.003, and a thermal inertia of 231 ± 76 J m-2 s-0.5 K-1. Although the pole orientation of 1999 JU3 is not strongly constrained, the best solution we derived is within 30 degree of (103,-20) in the ecliptic reference frame

A spectral comparison of (379) Huenna and its satellite

We present near-infrared spectral measurements of Themis family asteroid (379) Huenna (D~98 km) and its 6 km satellite using SpeX on the NASA IRTF. The companion was farther than 1.5" from the primary at the time of observations and was approximately 5 magnitudes dimmer. We describe a method for separating and extracting the signal of a companion asteroid when the signal is not entirely resolved from the primary. The spectrum of (379) Huenna has a broad, shallow feature near 1 {\mu}m and a low slope, characteristic of C-type asteroids. The secondary's spectrum is consistent with the taxonomic classification of C-complex or X-complex. The quality of the data was not sufficient to identify any subtle feature in the secondary's spectrum.Comment: 6 pages, 4 figures, 2 tables - Accepted for publication in Icaru

Physical Properties of (2) Pallas

We acquired and analyzed adaptive-optics imaging observations of asteroid (2) Pallas from Keck II and the Very Large Telescope taken during four Pallas oppositions between 2003 and 2007, with spatial resolution spanning 32-88 km (image scales 13-20 km/pix). 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 occultation data. The shape model of Pallas derived here reproduces well both the projected shape of Pallas on the sky and light-curve behavior at all the epochs considered. We resolved the pole ambiguity and found the spin-vector coordinates to be within 5 deg. of [long, lat] = [30 deg., -16 deg.] in the ECJ2000.0 reference frame, indicating a high obliquity of ~84 deg., leading to high seasonal contrast. The best triaxial-ellipsoid fit returns radii of a=275 km, b= 258 km, and c= 238 km. From the mass of Pallas determined by gravitational perturbation on other minor bodies [(1.2 +/- 0.3) x 10-10 Solar Masses], we derive a density of 3.4 +/- 0.9 g.cm-3 significantly different from the density of C-type (1) Ceres of 2.2 +/- 0.1 g.cm-3. 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 70-180 km range and an albedo contrast of about 6% wrt the mean surface albedo.Comment: 16 pages, 8 figures, 6 table

The remarkable surface homogeneity of the Dawn mission target (1) Ceres

Dwarf-planet (1) Ceres is one of the two targets, along with (4) Vesta, that will be studied by the NASA Dawn spacecraft via imaging, visible and near-infrared spectroscopy, and gamma-ray and neutron spectroscopy. While Ceres' visible and near-infrared disk-integrated spectra have been well characterized, little has been done about quantifying spectral variations over the surface. Any spectral variation would give us insights on the geographical variation of the composition and/or the surface age. The only work so far was that of Rivkin & Volquardsen (2010, Icarus 206, 327) who reported rotationally-resolved spectroscopic (disk-integrated) observations in the 2.2-4.0 {\mu}m range; their observations showed evidence for a relatively uniform surface. Here, we report disk-resolved observations of Ceres with SINFONI (ESO VLT) in the 1.17-1.32 {\mu}m and 1.45-2.35 {\mu}m wavelength ranges. The observations were made under excellent seeing conditions (0.6"), allowing us to reach a spatial resolution of ~75 km on Ceres' surface. We do not find any spectral variation above a 3% level, suggesting a homogeneous surface at our spatial resolution. Slight variations (about 2%) of the spectral slope are detected, geographically correlated with the albedo markings reported from the analysis of the HST and Keck disk-resolved images of Ceres (Li et al., 2006, Icarus 182, 143; Carry et al., 2008, A&A 478, 235). Given the lack of constraints on the surface composition of Ceres, however, we cannot assert the causes of these variations.Comment: 8 pages, 5 figures, 2 tables, accepted for publication in Icaru

ASIME 2018 White Paper. In-Space Utilisation of Asteroids: Asteroid Composition -- Answers to Questions from the Asteroid Miners

In keeping with the Luxembourg government's initiative to support the future use of space resources, ASIME 2018 was held in Belval, Luxembourg on April 16-17, 2018. The goal of ASIME 2018: Asteroid Intersections with Mine Engineering, was to focus on asteroid composition for advancing the asteroid in-space resource utilisation domain. What do we know about asteroid composition from remote-sensing observations? What are the potential caveats in the interpretation of Earth-based spectral observations? What are the next steps to improve our knowledge on asteroid composition by means of ground-based and space-based observations and asteroid rendez-vous and sample return missions? How can asteroid mining companies use this knowledge? ASIME 2018 was a two-day workshop of almost 70 scientists and engineers in the context of the engineering needs of space missions with in-space asteroid utilisation. The 21 Questions from the asteroid mining companies were sorted into the four asteroid science themes: 1) Potential Targets, 2) Asteroid-Meteorite Links, 3) In-Situ Measurements and 4) Laboratory Measurements. The Answers to those Questions were provided by the scientists with their conference presentations and collected by A. Graps or edited directly into an open-access collaborative Google document or inserted by A. Graps using additional reference materials. During the ASIME 2018, first day and second day Wrap-Ups, the answers to the questions were discussed further. New readers to the asteroid mining topic may find the Conversation boxes and the Mission Design discussions especially interesting.Comment: Outcome from the ASIME 2018: Asteroid Intersections with Mine Engineering, Luxembourg. April 16-17, 2018. 65 Pages. arXiv admin note: substantial text overlap with arXiv:1612.0070