Potential asteroid discoveries by the ESA Gaia mission

Results from follow-up observations

¹ Institut de Mécanique Céleste et de Calcul des Éphémérides IMCCE, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Lille, 77 av. Denfert Rochereau, 75014 Paris, France
² Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Boulevard de l’Observatoire, CS34229, 06304, Nice Cedex 4, France
e-mail: benoit.carry@oca.eu
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS 15, Cambridge, MA 02138, USA
⁴ SYRTE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC Univ. Paris 06, LNE, 61 avenue de l’Observatoire, 75014 Paris, France
⁵ Departamento de Astronomía, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Casilla 36-D, Santiago, Chile
⁶ Aix Marseille University, CNRS, Institut Pytheas-Observatoire Haute Provence, 04870 St-Michel-l’Observatoire, France
⁷ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁸ Department of Physics, Gustaf Hällströmin katu 2, University of Helsinki, PO Box 64, 00014, Finland
⁹ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
¹⁰ CNES Centre Spatial de Toulouse, 18 avenue Edouard Belin, 31401 Toulouse Cedex 9, France
¹¹ Asteroid Engineering Lab, Onboard Space Systems, Luleå University of Technology, Box 848, 981 28 Kiruna, Sweden
¹² Finnish Geospatial Research Institute, Geodeetinrinne 2, 02340, Masala, Finland
¹³ Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Bruxelles, Belgique
¹⁴ Observatoire de Besançon, UMR CNRS 6213, 41 bis avenue de l’Observatoire, 25000, Besançon, France
¹⁵ Kharadze Abastumani Astrophysical Observatory, Ilya State University, K. Cholokashvili Avenue 3/5, Tbilisi 0162, Georgia
¹⁶ Samtskhe-Javakheti State University, Rustaveli Street 113, Akhaltsikhe 0080, Georgia
¹⁷ Astronomical Observatory, Taras ShevChenko National University of Kyiv, 3 Observatorna str., Kyiv, 04053, Ukraine
¹⁸ Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095, 98 bis bd Arago, 75014, Paris, France
¹⁹ Institut Polytechnique des Sciences Avancées IPSA, 63 bis Boulevard de Brandebourg, 94200 Ivry-sur-Seine, France
²⁰ Vera C. Rubin Observatory/DIRAC Institute, Department of Astronomy, University of Washington, 15th Ave. NE, Seattle, WA 98195, USA
²¹ ICAMER Observatory of NASU, 27 Acad. Zabolotnogo str., Kyiv, 03143, Ukraine
²² Astronomical Observatory of Odessa I.I. Mechnikov National University, 1v Marazlievska str., Odessa, 65014, Ukraine
²³ Institute of Astronomy, V.N. Karazin Kharkiv National University, Sumska Str. 35, Kharkiv, 61022, Ukraine
²⁴ Keldysh Institute of Applied Mathematics, RAS, Miusskaya sq. 4, Moscow, 125047, Russia
²⁵ Astronomy and Space Physics Department, Taras Shevchenko National University of Kyiv, 60 Volodymyrska str., Kyiv, 01601, Ukraine
²⁶ National Center “Junior Academy of Sciences of Ukraine”, 38-44, Degtyarivska St., Kyiv, 04119, Ukraine
²⁷ Terskol Branch of INASAN RAN, 48 Pyatnitskaya str., Moscow, 119017, Russia
²⁸ LESIA, Observatoire de Paris, Sorbonne Université, Université PSL, CNRS, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
²⁹ naXys, University of Namur, Rempart de la Vierge, Namur 5000, Belgium
³⁰ Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland

Received: 2 October 2020
Accepted: 18 February 2021

Abstract

Context. Since July 2014, the Gaia mission of the European Space Agency has been surveying the entire sky down to magnitude 20.7 in the visible. In addition to the millions of daily observations of stars, thousands of Solar System objects (SSOs) are observed. By comparing their positions, as measured by Gaia, to those of known objects, a daily processing pipeline filters known objects from potential discoveries. However, owing to Gaia’s specific observing mode, which follows a predetermined scanning law designed for stars as “fixed” objects on the celestial sphere, potential newly discovered moving objects are characterized by very few observations, which are acquired over a limited time. Furthermore, these objects cannot be specifically targeted by Gaia itself after their first detection. This aspect was recognized early on in the design of the Gaia data processing.

Aims. A daily processing pipeline dedicated to these candidate discoveries was set up to release calls for observations to a network of ground-based telescopes. Their aim is to acquire follow-up astrometry and to characterize these objects.

Methods. From the astrometry measured by Gaia, preliminary orbital solutions are determined, allowing us to predict the position of these potentially newly discovered objects in the sky while accounting for the large parallax between Gaia and the Earth (separated by 0.01 au). A specific task within the Gaia Data Processing and Analysis Consortium has been responsible for the distribution of requests for follow-up observations of potential Gaia SSO discoveries. Since late 2016, these calls for observations (nicknamed “alerts”) have been published via a Web interface with a quasi-daily frequency, together with observing guides, which is freely available to anyone worldwide.

Results. Between November 2016 and the end of the first year of the extended mission (July 2020), over 1700 alerts were published, leading to the successful recovery of more than 200 objects. Among them, six have a provisional designation assigned with the Gaia observations; the others were previously known objects with poorly characterized orbits, precluding identification at the time of Gaia observations. There is a clear trend for objects with a high inclination to be unidentified, revealing a clear bias in the current census of SSOs against high-inclination populations.