Extensive simulations of planetary transits in the epoch photometry of the future space astrometry mission has been performed. Thousands to tens of thousands of transiting planets should be detected with GAIA.

A detailed knowledge about the galactic extinction is mandatory to obtain the astrophysical/kinematical parameters time variation outside the solar neighbourhood. One may hope that the GAIA photometry itself will contribute to colour excess determinations for most of the sample otherwise the extinction must be deduced from external sources. 3D galactic models where the dust distribution is an integral part seems a viable solution.

The GAIA mission will produce an extraordinary database from which we should be able to deduce not only the Galaxy's current structure, but also much of its history, and thus cast a powerful light on the way in which galaxies in general are made up of components, and of how these formed. The database can be fully exploited only by fitting to it a sophisticated model of the entire Galaxy. Steady-state models are of fundamental importance even though the Galaxy cannot be in a steady state. A very elaborate model of the Galaxy will be required to reproduce the great wealth of detail that GAIA will reveal. A systematic approach to model-building will be required if such a model is to be successfully constructed, however. The natural strategy is to proceed through a series of models of ever increasing elaborateness, and to be guided in the specification of the next model by mismatches between the data and the current model. An approach to the dynamics of systems with steady gravitational potentials that we call the "torus programme" promises to provide an appropriate framework within which to carry out the proposed modelling programme. The basic principles of this approach have been worked out in some detail and are summarized here. Some extensions will be required before the GAIA database can be successfully confronted. Other modelling techniques that might be employed are briefly examined.

The capabilities of the GAIA satellite for the detection of microlensing events are analyzed. The all-sky averaged photometric optical depth is ~7×10-8 and there are ~4000 photometric microlensing events during the five year mission lifetime. The all-sky averaged astrometric microlensing optical depth is ~5×10-5 and ~50 000 sources will have a significant variation of the centroid shift, together with a closest approach, during the mission lifetime. We show that GAIA is the first instrument with the capability to measure the mass locally in very faint objects like black holes and very cool white and brown dwarfs.

GAIA will be of paramount importance to understand the Galactic structure. Here we focus on the determination of the star formation history (SFH) of the Galactic disk and bulge. We discuss whether GAIA will be able to isolate a sample of stars with the same characteristics of Hipparcos data (completeness over a certain critical magnitude and high precision in the distance) which will cast light on the SFH of the whole disk. We analyze the expected results in two directions, namely the BW and the Galactic pole. Finally we discuss the contribution of GAIA to the study of the SFH of the bulge.

Presently data from several ongoing surveys, and in particular from the Spaghetti Project Survey have allowed us to map substructure in the halo associated to multiple passages of the Sagittarius dwarf. Future astrometric missions such as GAIA will be able to recover truly ancient accretion, thus providing us with the formation history of the Milky Way.

The exquisite astrometric data to be delivered by GAIA can only be successfully exploited if complemented by accurate astrophysical information on all observed objects. In this contribution I will discuss the preparations that are necessary for obtaining this information. The emphasis will be on the task of optimising the GAIA photometric system and the development of photometric data analysis algorithms.

GAIA will measure with precision, position, velocity, and colours of tens of thousands of stars in the Magellanic Clouds and thus, will provide an important contribution to our knowledge of these two close dwarf irregular galaxies. We will consider here the impact of GAIA on the determination of the distance modulus of the LMC and the SMC, on our understanding of the global dynamics of the Magellanic system and of its star formation history. The existence of a stellar pressure-supported halo around the Magellanic Clouds can be also tested from the velocities measurements of the old stars. Moreover we show that the first generation of stars in the Magellanic Clouds could be detected from the GAIA spectra, if it could be possible to obtain spectra of stars as faint as, at least, V=17.5. A resolution of R=5000 would be sufficient for this detection.

The large galaxies in the Local Group, as all disk galaxies, have diverse stellar populations. A better understanding of these differences, and a physical understanding of the causes, requires more detailed study of the older populations. This presents a significant challenge to GAIA but the scientific returns are also significant.

The GAIA satellite will bring about a revolution in the understanding of the dynamics of the Local Group. Here I discuss some salient problems that may be solved with the expected GAIA dataset.

The performance expected from a galaxy survey to be carried out with GAIA, the GAIA Galaxy Survey, is outlined. From a statistical model of galaxy number density, size and surface brightness distribution, and from detailed numerical simulations based on real images, it is conservatively estimated that GAIA would be able to detect and observe about 3 million galaxies brighter than V ≅ 17 and to provide multi-colour and multi-epoch broad-band photometry of these with an end-of-mission angular resolution of ≅0.35 arcsec and a photometric accuracy of ≅0.2 mag/arsec2 at μV=20 mag/arsec2. The substantial scientific case for performing such a survey and the additional efforts required in terms of mission preparation, operations and telemetry are also discussed.

The report discusses the possible multi-colour photometry of the diffuse sky surface with the Astro and Spectro telescopes of GAIA. The ordinary photometry of faint stars will give good results of the background for at least 500 million spots on the sky. Measurement from about 100 of these spots in a small area could be averaged to obtain a precision of about 0.5 S10 of GAIA medium-band photometry in each of the 5 million areas. It is concluded that GAIA medium-band photometry is suited to tackle a whole range of astrophysically interesting diffuse sky components. After modelling and subtracting the time-variable Zodiacal Light, GAIA could provide multi-wavelength all sky maps of the low galactic latitude Diffuse Galactic Light and the high latitude Galactic Cirrus Clouds. Possibly also the Extragalactic Background Light could be detected.

The astrometric mission GAIA will provide a flux limited census of quasi stellar objects to V=20 mag. This paper addresses the main physical and observational properties of the quasars, the existing surveys and the relevant statistical distributions of the compilation catalogue of Véron-Cetty & Véron. Then I consider the detection and recognition with GAIA which should be based on the multicolour photometry complemented by hints on the parallaxes and proper motions. In the last section I discuss the possibility to materialize directly in the optical the quasi-inertial frame to the sub-μas accuracy. It is shown that that with a clean sample of less than 10 000 quasars the residual spin of the GAIA reference frame can be determined to 0.5 μas yr-1.

GAIA will likely be a real milestone for asteroid science. Its unprecedented astrometric accuracy can be exploited to compute orbits better than those obtained by using the whole set of available astrometric observations carried out from ground during the last 100 years. GAIA will make it possible to measure asteroid masses through the measurement of the tiny displacements caused by asteroid mutual encounters. This will be a major breakthrough for physical studies of minor planets. Moreover, sizes will be also directly measured for a big sample of more than 1000 objects. From masses and sizes, estimates of the average densities will be also obtained. The spectrophotometric capability of GAIA will be used for purposes of taxonomic classification, with important implications for surface mineralogical characterization. Finally, GAIA will be an ideal platform to detect near-Earth asteroids having orbits interior to that of the Earth.

Trojans, Centaurs and Trans-Neptunian objects are small dark objects orbiting in the outer Solar System. These objects, still very poorly known, can be considered as fossils of our Solar System, and, as such, they can still contain information about some primordial processes which governed the evolution of the early Solar System. In the next decade, GAIA with its large sky surveys, can allow the discovery of many new objects belonging to these outer solar system populations. In addition, it will provide very precise orbits and visible broad-band colours for many of them.

The GAIA satellite will observe a large number of solar system objects, mainly asteroids, and although most of them shall be already known in the next decade, it will possibly discover new ones. The major scientific outcomes of this mission for the science of the Solar System is the survey of the inner-Earth orbits region, the determination of asteroids' physical parameters (masses, sizes, taxonomy...) for a large number of objects, detection of binary asteroids, accurate orbits determination, and tests of general relativity. Here we discuss the preparative work that should be done before launch regarding the scientific case, the software or instruments requirements, the catalogues output, and complementary ground-based observations.

A method for inverting the equation of stellar statistic including proper motions is tested. The supplementary constraint required by dynamical consistency is used in order to break the degeneracy. The inversion gives access to both the kinematics and the luminosity function of each population. Its application to data such as the Tycho catalog (and in the near future GAIA) will lead - provided the vertical potential, and/or the asymmetric drift or ω⊙ are known - to a non-parametric determination of the local neighbourhood luminosity function without any reference to stellar evolution tracks. It should also yield the proportion of stars for each kinematic component and a kinematic diagnostic to split the thin disk from the thick disk or the halo.