Since 2014, stationed at the L2 Lagrange point 1.5 million km away, the Gaia satellite scans the sky while rotating : the objective is to do a 3D map of over a billion objects in the Galaxy of the sky before the end of 2020. It thus measures all luminous sources brighter than magnitude 20,7.
During this systematic scan, Gaia detects bodies which are moving with respect to fixed sources : these are essentially asteroids.
An extremely efficient alert system
Just recently, Gaia has led to the discovery of three new asteroids : 2018 YK4, 2018 YL4, 2018 YM4.
Gaia’s detection of heretofore unknown and not catalogued asteroids involves an extremely sophisticated alert system, whose implementation since 2016 is ensured by a consortium with considerable contributions from astronomers and engineers from the Paris Observatory, from the Institute for Celestial Mechanics and ephemeris computation (IMCCE), and from the Côte d’Azur Observatory.
The comparison with the ephemeris (apparent positions of bodies in the solar system) furnished by the IMCCE of the Paris Observatory enables one to know whether the body is known or not.
If the body is unknown, a procedure is launched for the computation of the various possible orbits corresponding to the observations made by Gaia, which, while very accurate, involve short orbital arcs and cannot lead to a unique orbit.
This calculation enables one to predict and visualize the region in the sky in which ground based observations could find the body. An alert is hence injected into the data base Gaia-FUN-SSO.
The IMCCE astronomers were thus able to observe and follow with the 1,20 m telescope of the Observatoire de Haute-Provence the three new bodies and thereby validate their detection.
The positions of the three new objects measured from space by Gaia, which discovered them, and subsequently from the ground, were sent to the USA, to the Minor Planet Center, at the Smithonian Astrophysical Observatory.
Under the aegis of the IAU (International Astronomical Union), this latter organization centralizes all the observations made world-wide and attributes to each body found an official label : 2018 YK4, 2018 YL4, 2018 YM4.
Over 120 asteroids already validated
Published in April 2018, the DR2 catalogue (second Data Release) of the Gaia satellite furnished the measurements of over 14 000 known asteroids observed from 2014 to 2016.
The next catalogue, whose publications is programmed for 2020 will complete this sample and include many measurements of other known asteroids.
And since the end of 2016, the Gaia data for newly discovered asteroids are made available continuously, and are available to all.
Thus, over 120 new asteroids have been detected by Gaia, and subsequently validated by ground based observations.
These bodies are essentially within the main belt lying between Mars and Jupiter.
Contributions
The alert and validation system for newly detected bodies is the fruit of an international effort involving the CU4-SSO group of the Gaia DPAC consortium, the engineers of the DPCC-CNES in charge of the Gaia data analysis, the astronomers from the observatories, and in particular those of the : Observatoire de Haute-Provence, Kyiv Comet station, Odessa-Mayaki, Terskol, C2PU-Calern-Observatoire at the Côte d’Azur, LCOGT-Las Cumbres Observatory Global Telescope Network.
The Paris Observatory contributes to this work via the Observatoire de la Côte d’Azur alert transmission system (P. David, J. Berthier et S. Vaillant IMCCE), via the coordination of the Gaia-FUN-SSO network, as well as via the observations themselves (K. Baillié, D. Hestroffer, V. Robert, W. Thuillot).
A dedicated observational program at the OHP has in particular been led by the IMCCE since 2014 for the validation of astrometric alerts for solar system objects and for photometric and other scientific alerts (in collaboration with S. Bouquillon, D. Souami et F. Taris, SYRTE ; B. Carry, M. Delbo, F. Spoto, P. Tanga OCA ; M. Dennefeld, IAP). This program at the OHP is financed by the Service National d’Observation Gaia (National Office for Gaia Observations). Another program has been launched at the LCOGT as part of an international collaboration for the detection of new bodies in the framework of Gaia-FUN-SSO and Ground Based Optical Tracking GBOT (R. A. Mendez Santiago Univ., S. Bouquillon and D. Souami, SYRTE, F. Spoto, OCA, W. Thuillot, IMCCE).
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