Having delivered its first stellar catalogue on September 14th 2016, Gaia has continued its mission to map a billion celestial objects, to which has now been added a new function - an asteroid alerter.
Although alerts involving transitory phenomena of fixed celestial objects have been taking place for several months (photometric flashes, novae and supernovae, gravitational lenses,…), nothing has as yet been done for solar system objects. However, since October 2016, this type of alert, validated by the astronomers from the Paris Observatory, is now a daily operation using the data base Gaia-FUN-SSO accessible to astronomers.
The alert system
The Paris Observatory astronomers and engineers at the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE), and those from the Observatoire de la Côte d’Azur (OCA), together with scientists from Besançon, Brussels, Helsinki, Torino and Florence within the Gaia data analysis consortium, have made a special effort to create this system. The data processing system for data acquired by Gaia reacts to motion with respect to the fixed stars. A comparison with the ephemeris (apparent positions of solar system objects) furnished by the Paris Obserrvatory’s IMCCE enables one to know whether this is a known body or not.
If the body is unknown, a subprocess calculates various orbital possibilities which correspond to Gaia’s observations.
These solutions then enable one to predict and see the region in the sky where a terrestrial observateur could find the object. The alert is then included in the data base Gaia-FUN-SSO.
A participative scientific project
Interested observers can [sign up on the web site>https://gaiafunsso.imcce.fr] so as to be identified on the Gaia-FUN-SSO network, and thus work on the ground based rediscovery of these bodies.
The validation procedure
Before officially making the site available to the public for asteroïd hunting, it is vital to validate the information. That is why two observing missions were carried out in October 2016 using the 1.2 m telescope at the Observatoire de Haute-Provence (OHP). They enabled, in particular, the ground based confirmation on October 26th 2016 of an asteroïd discovered a few days earlierr by Gaia and provisionally named GAIA-606.
This hitherto unknown object was followed during three nights. Its successive positions were sent to and registered by the Minor Planet Center, at the Smithsonian Astrophysical Observatory, USA, which is responsible, under the aegis of the International Astronomical Union, for the world-wide collection of this information.
The discovery could have been atributed to Gaia if there had not been any ealier observations. However, this was not the case, since there had been a few, which nevertheless had not been put together. The observations made at the OHP have enabled the computation of an orbit linking all these observations, and this body is now designated as 2016 UV56.
This was due to OHP’s observational alert, but of prime importance is that the observations have validated the alert procedure and the alert warning system Gaia-FUN-SSO for solar system objects.