HESTROFFER , Daniel

The Gaia ESA space mission has started to provide its harvest with the first Gaia data release DR1, published in September 2016. Gaia DR1 provides positions for about 1 billion stars and proper motion for the Tycho-Gaia TGAS of 2 million stars with unprecedented accuracy. The second data release DR2 will be the major step in the Gaia mission,...

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Since the beginning of its scientific programme, in mid-2014, the ESA space mission Gaia has regularly scanned the whole scan, providing astrometry, spectrometry, and spectro-photometry, of about a billion of stars and also Solar System Objects (SSOs). Although it is not specifically designed for observation of moving objects, the Gaia...

The ESA astrometric mission Gaia, due for launch in late 2011, will observe a very large number of

The ESA astrometric mission Gaia, due for launch in late 2011, will observe a very large number of asteroids (~ 350,000 down to the magnitude 20), most from the main belt, with an unprecedented positional precision (at the sub-milliarcsecond level). Such high-precision astrometry will enable to considerably improve the orbits of a large number...

Gaia will collect asteroid observations over 5 years, with a limiting magnitude V~20 (>300,000 objects). Observations will include very precise astrometry and photometry, and low resolution spectra. Over the last few years, the Coordination Unit 4 of Gaia's Data Processing and Analysis Consortium has built the data reduction pipeline that will...

Gaia will collect asteroid observations over 5 years, with a limiting magnitude V~20 (>300,000 objects). Observations will include very precise astrometry and photometry, and low resolution spectra. Over the last few years, the Coordination Unit 4 of Gaia's Data Processing and Analysis Consortium has built the data reduction pipeline that will...

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The simple evidence that asteroid are composed by solid rocks suggests that their shape can be rather far from the theoretical equilibrium for rotating fluid bodies. The possible fragmented ("rubble-pile") nature of most of them has suggested interpretations based on elasto-plastic models (such as the Mohr-Coulomb theory) that take into account...

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...

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...

After the catastrophic disruption of a parent body, new objects are formed by the re-accumulation of the resulting fragments. A new dynamical family is thus formed. This phase is dominated by gravity, and the resulting bodies are cohesionless gravitational aggregates, also known as "rubble piles". Several lines of evidence suggest that a large...

Apart from producing a huge improvement in the determination of asteroid orbits, Gaia is also expected to trigger a revolution in the field of the determination of asteroid physical properties. This includes the determination of accurate values of the mass and bulk density for about 100 of the largest objects in the main belt; the determination...

The first data release of star astrometry by Gaia (Sept. 2016) has given an anticipation of the mission capabilities. By providing positions with uncertainties at the level of few milli-arcsec (mas) a new frame to calibrate ground-based observations has immediately become available, thus disclosing a new possibility of exploitation for archive...

Several lines of evidences suggest that, after the breakup following a catastrophic disruption, the fragments can form asteroids that are kept together only by gravity. The details of the gravitational reaccumulation process are however poorly known. In particular, the angular momentum transported by the fragments could directly influence the...

We present the results of the observations of five Main Belt asteroids and one Trojan obtained using the Fine Guidance Sensors (FGS) of the Hubble Space Telescope. For each object, estimates of the spin axis orientation, angular size and overall shape, as well as possible indications of a binary structure, are derived. This enables the...

The Gaia mission will observe between 2.5 and 3x105 Solar System objects. Most of them will be asteroids. As described elsewhere (Cellino et al. 2007, Tanga et al. 2007, Mignard et al. 2008) Gaia will provide a complete dynamical and physical characterisation of these bodies, that has no comparisons with the datasets ever obtained by a single...

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Numerical N-body models adopting self-gravitating spherical particles have proven to have interesting properties and are very useful for describing some aspects of the expected behaviour of rubble-piles. In fact, particle interlocking can simulate a certain degree of shear strength (corresponding to a non-zero critical slope in the Mohr-Coulomb...

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Since their formation, asteroids since their formation have experienced little physical, geological or thermal evolution. Like comets they are thought to be among the most pristine remnants of the early solar system. One physical process, however, has played a major role since the ancient times: collisions. Dynamical families were produced by...

Asteroids, since the formation of the solar system, are known to have experienced catastrophic collisions, which---depending on the impact energy---can produce a major disruption of the parent body and possibly give birth to asteroid families or binaries [1]. We present a general study of the final shape and dynamical state of asteroids...

Non-gravitational effects may change the angular momentum of asteroids up to a few tens of km in size to the point that rotational stability is lost at high spin rates. Once instability is initiated, mass loss may happen and potentially create satellites or dynamically detached components (pairs). We have studied this problem by means of...

We review recent results of a project for building a large number of comprehensive physical asteroid models from combined photo- and interferometric observations, occultation timings, and other complementary data. Photometric data form the robust and stable basis for modelling, while particularly HST/FGS-interferometry and CW radar data can add...

Non-gravitational effects (such as the "YORP" acceleration by thermal emission) may change their angular momentum of asteroids up to a few tens of km to the point to prevent any kind of rotational stability. Once instability is enforced mass loss may happen in more or less abrupt ways and potentially create satellites. We are studying this...

We report on the status of a project to measure eclipse-induced changes in surface temperature on the major Uranian satellites. Such measurements enable a uniquely direct determination of the thermal inertia, a measure of the resistance to changes in surface temperature. Thermal inertia is a very sensitive indicator for the presence or absence...