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&

10 years of the IAU Efforts for Capitalizing the Ground-Based Astrometry

4 p.International audienceIn 2000 a new IAU working group was founded (IAU GA, Manchester): Future Development of Ground-Based Astrometry (FDGBA). It was revised in 2003 during the IAU GA in Sydney. A new one replaced it in 2006 (IAU GA, Prague): Astrometry by Small Ground-Based Telescopes (ASGBT). It was renewed for other three years during the IAU GA in Rio de Janeiro. The main aim of the working groups followed the Newsletter No. 1 of the IAU Commission 8, which says: The post-Hipparcos era has brought an element of uncertainty as to the goals and future programs for all of ground-based astrometry The purpose of the WGs was "to update and maintain information on astrometric programmes and activities carried out by small telescopes, to diffuse news through these pages and e-mails, to facilitate the collaborations and to help for the coordination of the activities, when possible, in astrometry from ground-based telescopes"

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

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

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

Dynamics of asteroids and near-Earth objects from Gaia astrometry

The original publication is available at www.sciencedirect.com/science/journal/00320633International audienceGaia is an astrometric mission that will be launched in spring 2013. There are many scientific outcomes from this mission and as far as our Solar System is concerned, the satellite will be able to map thousands of main belt asteroids (MBAs) and near-Earth objects (NEOs) down to magnitude ≤20. The high precision astrometry (0.3-5 mas of accuracy) will allow orbital improvement, mass determination, and a better accuracy in the prediction and ephemerides of potentially hazardous asteroids (PHAs).We give in this paper some simulation tests to analyse the impact of Gaia data on known asteroids's orbit, and their value for the analysis of NEOs through the example of asteroid (99942) Apophis. We then present the need for a follow-up network for newly discovered asteroids by Gaia, insisting on the synergy of ground and space data for the orbital improvement

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

Statistical analysis on the uncertainty of asteroid ephemerides

International audienceThe large number of asteroids allows a statistical analysis especially for their orbital uncertainty. It presents a particular interest for Near-Earth asteroids in order to estimate their close approach from Earth and eventually their risk of collision. Using ASTORB and MPCORB databases, we analyse the different uncertainty parameters (CEU, U) and highlight relations between the uncertainty parameter and the characteristics of the asteroid (orbital arc, absolute magnitude, ...)