Science from NEOs - Limitations and Perspectives

6 p.International audienceThe Gaia mission, in addition of doing astrometry of stars and a 3D census of our Milky Way, has specific objectives for solar system objects (Tanga, 2011). In that respect it follows the Hipparcos/Tycho mission that already observed a few solar system objects. The astrometric accuracy involved with Gaia is however 1 to 2 orders of magnitude higher, and the total number of targets observed is incomparably larger. Here we describe several scientific outcomes from the astrometry of asteroids and comets with particular emphasis on the Near Earth Objects (NEOs), their specificities and limitations

Statistical and Numerical Study of Asteroid Orbital Uncertainty

The knowledge of the orbit or the ephemeris uncertainty of asteroid presents a particular interest for various purposes. These quantities are for instance useful for recovering asteroids, for identifying lost asteroids or for planning stellar occultation campaigns. They are also needed to estimate the close approach of Near-Earth asteroids, and subsequent risk of collision. Ephemeris accuracy can also be used for instrument calibration purposes or for scientific applications. Asteroid databases provide information about the uncertainty of the orbits allowing the measure of the quality of an orbit. The aims of this paper is to analyse these different uncertainty parameters and to estimate the impact of the different measurements on the uncertainty of orbits. We particularly deal with two main databases ASTORB and MPCORB providing uncertainty parameters for asteroid orbits. Statistical methods are used in order to estimate orbital uncertainty and compare with parameters from databases. Simulations are also generated to deal with specific measurements such as future Gaia or present radar measurements. Relations between the uncertainty parameter and the characteristics of the asteroid (orbital arc, absolute magnitude, ...) are highlighted. Moreover, a review of the different measuments are compiled and the impact of these measures on the accuracy of the orbit is also estimated.Comment: 11 pages, 10 figures, accepted by A&

Imaging sub-milliarcsecond stellar features with intensity interferometry using air Cherenkov telescope arrays

Recent proposals have been advanced to apply imaging air Cherenkov telescope arrays to stellar intensity interferometry (SII). Of particular interest is the possibility of model-independent image recovery afforded by the good (u, v)-plane coverage of these arrays, as well as recent developments in phase retrieval techniques. The capabilities of these instruments used as SII receivers have already been explored for simple stellar objects, and here the focus is on reconstructing stellar images with non-uniform radiance distributions. We find that hot stars (T > 6000 K) containing hot and/or cool localized regions (T \sim 500 K) as small as \sim 0.1 mas can be imaged at short wavelengths ({\lambda} = 400 nm).Comment: Accepted for publication in MNRAS. 6 pages, 10 figure

Global Dynamics and Ephemerides

International audienceWhen speaking of Gaia it is instructive to remember the first ESA mission dedicated to high precision astronometry HIPARRCOS launched in August 1989. HIPPARCOS can be considered as Gaia's precursor, indeed the observing strategy aspects are similar and both missions were designed specifically for high precision astronmetry. After three and a half years of observations HIPPARCOS produced three catalogues. In 1997 the HIPARCOS catalogue of ∼120000 stars and the first Tycho catalogue containing about one million stars. In 2000 the consolidated catalogue Tycho-2 was released. It contains 99% of all stars down to magnitude 11, approximately ∼ 2.5 million objects

Numerical integration of dynamical systems with Lie series

The original publication is available at www.springerlink.comInternational audienceThe integration of the equations of motion in gravitational dynamical systems--either in our Solar System or for extra-solar planetary systems--being non integrable in the global case, is usually performed by means of numerical integration. Among the different numerical techniques available for solving ordinary differential equations, the numerical integration using Lie series has shown some advantages. In its original form (Hanslmeier and Dvorak, Astron Astrophys 132, 203 1984), it was limited to the N-body problem where only gravitational interactions are taken into account. We present in this paper a generalisation of the method by deriving an expression of the Lie terms when other major forces are considered. As a matter of fact, previous studies have been done but only for objects moving under gravitational attraction. If other perturbations are added, the Lie integrator has to be re-built. In the present work we consider two cases involving position and position-velocity dependent perturbations: relativistic acceleration in the framework of General Relativity and a simplified force for the Yarkovsky effect. A general iteration procedure is applied to derive the Lie series to any order and precision. We then give an application to the integration of the equation of motions for typical Near-Earth objects and planet Mercury

Near-Earth Asteroids Orbit Propagation with Gaia Observations

International audienceGaia is an astrometric mission that will be launched in 2013 and set on L2 point of Lagrange. It will observe a large number of Solar System Objects (SSO) down to magnitude 20. The Solar System Science goal is to map thousands of Main Belt Asteroids (MBAs), Near Earth Objects (NEOs) (including comets) and also planetary satellites with the principal purpose of orbital determination (better than 5 mas astrometric precision), determination of asteroid mass, spin properties and taxonomy. Besides, Gaia will be able to discover a few objects, in particular NEOs in the region down to the solar elongation 45° which are harder to detect with current ground-based surveys. But Gaia is not a follow-up mission and newly discovered objects can be lost if no ground-based recovery is processed. The purpose of this study is to quantify the impact of Gaia data for the known NEAs population and to show how to handle the problem of these discoveries when faint number of observations and thus very short arc is provided

Near-Earth Asteroids Astrometry with Gaia and Beyond

4 p.International audienceGaia is an astrometric mission that will be launched in 2012 and will observe a large number of Solar System Objects down to magnitude 20. The Solar System Science goal is to map thousand of Main Belt Asteroids (MBAs), Near Earth Objects (NEOs) (including comets) and also planetary satellites with the principal purpose of orbital determination (better than 5 mas astrometric precision), determination of asteroid mass, spin properties and taxonomy. Besides, Gaia will be able to discover a few objects, in particular NEOs in the region down the solar elongation (45°) which are harder to detect with current ground-based surveys

Orbit of potentially hazardous asteroids using Gaia and ground-based observations

International audiencePotentially Hazardous Asteroids (PHAs) are Near Earth Asteroids characterized by a Minimum Orbital Intersection Distance (MOID) with Earth less to 0,05 A.U and an absolute magnitude H<22. Those objects have sometimes a so significant close approach with Earth that they can be put on a chaotic orbit. This kind of orbit is very sensitive for exemple to the initial conditions, to the planetary theory used (for instance JPL's model versus IMCCE's model) or even to the numerical integrator used (Lie Series, Bulirsch-Stoer or Radau). New observations (optical, radar, flyby or satellite mission) can improve those orbits and reduce the uncertainties on the Keplerian elements