Orbital elements of material surrounding comet 67P/Churyumov–Gerasimenko

Context. The dust coma within the Hill sphere of comet 67P/Churyumov–Gerasimenko. Aims. To determine osculating orbital elements for individual distinguishable but unresolved slow–moving grains in the vicinity of the nucleus. To perform photometry and constrain grain sizes. Methods. Astrometry and photometry using images acquired by the OSIRIS Wide Angle Camera on the European Space Agency spacecraft Rosetta. Standard orbit determination and orbit improvement techniques were employed. Results. Orbital elements and effective diameters of four grains could be constrained but not uniquely determined. Two of the grains have lightcurves indicative of grain rotation. Conclusions. The four grains have diameters nominally in the range 0.14–0.50 meters. For three of the grains, elliptic orbits can be found, which is consistent with a cloud of bound particles around the nucleus. However, hyperbolic escape trajectories cannot be excluded for any of the grains, and for one grain this is the only known option. One grain may have originated from the surface shortly before observation. These results have possible implications for the understanding of dispersal of the cloud of bound debris around comet nuclei, as well as the ejection of large grains far from the sun