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(10) Hygiea is the fourth largest main belt asteroid and the only known asteroid whose surface composition appears similar to that of the dwarf planet (1) Ceres 1 , 2 , suggesting a similar origin for these two objects. Hygiea suffered a giant impact more than 2 Gyr ago 3 that is at the origin of one of the largest asteroid families. However, Hygeia has never been observed with sufficiently high resolution to resolve the details of its surface or to constrain its size and shape. Here, we report high-angular-resolution imaging observations of Hygiea with the VLT/SPHERE instrument (~20 mas at 600 nm) that reveal a basin-free nearly spherical shape with a volume-equivalent radius of 217 ± 7 km, implying a density of 1,944 ± 250 kg m − 3 to 1 σ . In addition, we have determined a new rotation period for Hygiea of ~13.8 h, which is half the currently accepted value. Numerical simulations of the family-forming event show that Hygiea’s spherical shape and family can be explained by a collision with a large projectile (diameter ~75–150 km). By comparing Hygiea’s sphericity with that of other Solar System objects, it appears that Hygiea is nearly as spherical as Ceres, opening up the possibility for this object to be reclassified as a dwarf planet. SPHERE at the VLT observed Hygiea, the fourth largest body in the main belt and the parent body of a big asteroid family, at unprecedented spatial resolution. Its unexpected spherical shape without any impact crater is explained by numerical simulations with a big impact that fluidized the body, reassembling it in a rotational equilibrium regime.

Numerical simulations of the collisional disruption of large asteroids show that although the parent body is totally shattered, subsequent gravitational reaccumulation leads to the formation of an entire family of large and small objects with dynamical properties similar to those of the parent body. Simulations were performed in two different collisional regimes representative of asteroid families such as Eunomia and Koronis. Our results indicate that all large family members must be made of gravitationally reaccumulated fragments; that the post-collision member size distribution and the orbital dispersion are steeper and smaller, respectively, than for the evolved families observed today; and that satellites form frequently around family members.

According to current plans of the European space agency, Gaia will be launched in 2011. By performing a systematic survey of the whole sky down to magnitude V = 20, this mission will provide a fundamental contribution in practically all branches of modern Astrophysics. Gaia will be able to survey with repeated observations spanning over 5 years several 100,000 s asteroids. It will directly measure sizes of about 1,000 objects, obtain the masses of about 100 of them, derive spin properties and overall shapes of more than 10,000 objects, yield much improved orbits and taxonomic classification for most of the observed sources. The final harvest will very likely include new discoveries of objects orbiting at heliocentric distances less than 1 AU. At the end of the mission, we will know average densities of about 100 objects belonging to all the major taxonomic classes, have a much more precise knowledge of the inventory and size and spin distributions of the population, of the distribution of taxonomic classes as a function of heliocentric distance, and of the dynamical and physical properties of dynamical families.

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU₆₉). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.

In this work, the general framework in which fits our investigation is that of modeling the dynamics of dust grains therein dusty plasma (complex plasma) in the presence of electromagnetic fields. The generalized discrete complex Ginzburg-Landau equation (DCGLE) is thus obtained to model discrete dynamical structure in dusty plasma with Epstein friction. In the collisionless limit, the equation reduces to the modified discrete nonlinear Schrödinger equation (MDNLSE). The modulational instability phenomenon is studied and we present the criterion of instability in both cases and it is shown that high values of damping extend the instability region. Equations thus obtained highlight the presence of soliton-like excitation in dusty plasma. We studied the generation of soliton in a dusty plasma taking in account the effects of interaction between dust grains and theirs neighbours. Numerical simulations are carried out to show the validity of analytical approach.

We present in the following some capabilities of the Gaia mission for performing local test of General Relativity (GR) based on the astrometry of asteroids. This ESA cornerstone mission, to be launched in Spring 2012, will observe—in addition to the stars and QSOs—a large number of small solar system bodies with unprecedented photometric and, mostly, astrometric precisions. Indeed, it is expected that about 250,000 asteroids will be observed with a nominal precision ranging from a few milli-arcsecond (mas), to sub-mas precision, depending on the target's brightness. While the majority of this sample is constituted of known main-belt asteroids orbiting between Mars and Jupiter, a substantial fraction will be made of near-Earth objects, and possibly some newly discovered inner-Earth or co-orbital objects. Here we show the results obtained from a simulation of Gaia observations for local tests of GR in the gravitational field of the Sun. The simulation takes into account the time sequences and geometry of the observations that are particular to Gaia observations of solar system objects, as well as the instrument sensitivity and photon noise. We show the results from a variance analysis for the nominal precision of the joint determination of the solar quadrupole J2 and the PPN parameter β. Additionally we include the link of the dynamical reference frame to the conventional kinematically non-rotating reference frame (as obtained in the visible wavelength by Gaia observations of QSOs). The study is completed by the determination of a possible variation of the gravitational constant /G, and deviation from Newtonian 1/r2 gravitational law. Comparisons to the results obtained from other techniques are also given.

The Gaia satellite, an ESA cornerstone mission to be launched at the end of the year 2011, will observe a large number of celestial bodies including also small bodies of the solar system. Albeit spread from the inner to the outer regions of the solar system, these are mainly near-Earth objects and main-belt asteroids. All objects brighter than magnitude V ≤ 20 that cross the field of view (i.e. with solar elongation 45° ≤ L ≤ 135°) of the survey-mode scanning telescope will be observed. The mission will provide, over its 5 years duration, high precision photometry and astrometry with an unprecedented accuracy ranging roughly from 0.3 to 3 milli-arcsecond on the CCD level, and depending on the target's magnitude. In addition, several hundreds of QSOs directly observed by Gaia will provide the kinematically non-rotating reference frame in the visible light, resulting in the construction of a ‘Gaia-ICRF’. The positions of the asteroids hence enable to relate the dynamical reference frame—as defined by the equations of motion—to the kinematic one, and to further check the non-rotating consistency between both frames' definition. Here we show the results of a variance analysis obtained from a realistic simulation of observations for such a link. The simulation takes into account the time sequences and geometry of the observations that are particular to Gaia observations of solar system objects, as well as the instrument sensitivity and photon noise. Additionally, we show the achievable precision for the determination of a possible time variation of the gravitational constant Ġ/G. Taking into account the non-completeness of the actually known population of NEOs, we also give updated values for the nominal precision of the joint determination of the solar quadrupole J2 and PPN parameter β.

Integrating HIV and AIDS into the academic curriculum is not engaged with vigorously enough in South African higher education institutions, for several reasons, ranging from lack of interest to complaints of belabouring the issue of HIV and AIDS, especially from the biomedical perspective. Through such integration the academic curriculum could be a key space and engine for persuading change and abating the effects of HIV and AIDS in higher education as well as in the communities served by the universities. We reflect on our three-year research project engagement and explore how collaboration facilitated integration of HIV and AIDS issues in our academic curriculum. Working from a critical paradigm and using a collaborative self-study approach, we utilised drawings and responses from questions which we compiled for ourselves. Textual and visual data generated were thematically analysed. The findings revealed that collaboration counteracts isolation; enables capacity development in integration for the collaborating researchers; and permits engaging with participatory visual methodologies to encourage integration. We conclude that collaboration is key in facilitating integration of HIV and AIDS in the higher education curriculum, and that collaboration using participatory visual methodologies enhances entry-points in engaging with HIV and AIDS in South Africa and beyond. This work has implications for integrating HIV and AIDS issues into the higher education curriculum.

Context. We report the exploitation of a sample of epoch astrometry for 157 000 asteroids, the same object in the Gaia Data Release 3, extended over the time coverage planned for the Gaia DR4, which is not expected before the end of 2025. This data set covers more than one full orbital period for the vast majority of these asteroids. The orbital solutions are derived from the Gaia data alone over a relatively short arc compared to the observation history of many of these asteroids. Aims. The work aims to produce orbital elements for a large set of asteroids based on 66 months of accurate astrometry provided by Gaia and to assess the accuracy of these orbital solutions with a comparison to the best available orbits derived from independent observations. A second validation is performed with accurate occultation timings. Methods. We processed the raw astrometric measurements of Gaia to obtain astrometric positions of moving objects with 1D sub-mas accuracy at the bright end. For each asteroid that we matched to the data, an orbit fitting was attempted in the form of the best fit of the initial conditions at the median epoch. Results. Orbits are provided in the form of state vectors in the International Celestial Reference Frame for 156 764 asteroids, including near-Earth objects, main-belt asteroids, and Trojans. For the asteroids with the best observations, the (formal) relative uncertainty is better than 1E10. Results are compared to orbits available from the Jet Propulsion Laboratory and MPC. Their orbits are based on much longer data arcs, but from positions of lower quality. The relative differences in semi-major axes have a mean of 5E10 and a scatter of 5E9.