The recently separated Galileo satellites 15–18 seen in space as four closely clustered dots above their Ariane 5 EPS upper stage, which is venting propellant (the brilliant cloud from both sides of the EPS) as part of its passivation process.
The two brighter spots/areas at each side is due to the passivation process itself, in which − after the opening of the valves − the pressure falls quite quickly and therefore a higher concentration of discarded propellant is found further from the EPS.
This image was acquired by the CNES/CNRS-operated TAROT telescope on Réunion Island at 17:23 GMT (18:23 CET) on 17 November 2016, approximately 21 minutes after the second separation of paired Galileo satellites. The agile TAROT telescopes are used to hunt out optical evidence of Gamma-ray burst events as well as observe and catalogue space objects in high orbit.
TAROT refers to 'Télescope à Action Rapide pour les Objets Transitoires – Rapid Action Telescope for Transient Objects' and comprises a network of telescopes, which is jointly operated by the French space agency (CNES) and France's CNRS - Centre national de la recherche scientifique (Artemis and IRAP Laboratories).
TAROT consists of two 25-cm aperture instruments located at the Calern Observatory (part of the Observatoire de la Côte d'Azur, France), the La Silla Observatory (European Southern Observatory, Chile), and an 18-cm telescope at Les Makes Observatory (Reunion, France). Since 1999, TAROT has conducted observations of Resident Space Objects (RSO) − mostly debris − on geostationary orbit, and of passing objects in eccentric (such as Geostationary transfer orbit or Medium Earth Orbit). Such observations are used to feed an automatic cataloguing system of RSOs.