ner_tags: O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O B-Instrument O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O B-CelestialObject I-CelestialObject O B-CelestialObject I-CelestialObject O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-CelestialObject O O O B-Citation I-Citation I-Citation I-Citation O B-Citation I-Citation I-Citation I-Citation O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B-Citation I-Citation I-Citation I-Citation O O O O O O O O O O O B-Dataset I-Dataset O B-Citation I-Citation O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O
tokens: come back to this problem in Sect. 4.4 and discuss how our findings can describe the smallest diameter of a jet. 2.2. Geometric inversion of local sources As seen in our observations, jet-like features are detected in most images and rotate with the nucleus. Similar studies of other comets have shown that jets can often be associated with specific locations on the surface, presenting a different composition and/or morphology than other areas. For instance, some areas of comet 9P/Tempel 1 would remain active and produce jets even when far into the night, hinting at sublimation of material that is much more volatile than water ice ( Feaga et al. 2007 ; Vincent et al. 2010 ). The high resolution provided by OSIRIS allows an accurate determination of active sources in principle, although the process is not straightforward. Indeed, single images provide only two-dimensional information, and one needs to combine several observations to reconstruct the true three-dimensional structures we want to investigate. To achieve this we developed two independent techniques: blind and direct inversion, as explained in the following sections. These methods are very similar to those used by Sekanina et al. (2004) and Farnham et al. (2013) in their respective studies of the jets of comets 81P/Wild 2 and 9P/Tempel 1. Another aspect of jet studies is the detailed investigation of the physics taking place in the jet itself, as cometary material arises from the surface and possibly fragments or sublimates. We focus here on the use of our inversions to understand the sources themselves better and describe their morphology, evolution, and the associated surface physical processes. Readers interested in photometric properties of dust jets from 67P are referred to Lara et al. (2015) and Lin et al. (2015) or to Vincent et al. (2013) for a numerical modeling of these features on a larger scale. 2.2.1. Blind inversion This first algorithm considers each feature in the images as an isolated jet. Although it seems obvious that a jet can be tracked from one image to another, appearance can be deceiving, and we do not impose this condition for the inversion. For each collimated structure, it is safe to assume that the dust is emitted in a plane defined by the observer (Rosetta) and the central line of the jet. A single image does not allow us to determine whether the jet is inclined toward or away from the observer. In a second step, we calculate the intersection between the jet plane and a shape model of the nucleus, oriented beforehand to match the geometric conditions of our observations. We used a shape model reconstructed by photogrammetry ( Preusker et al. 2015 ). Spacecraft and comet attitudes and trajectories were retrieved with the SPICE library ( Acton 1996 ). Each jet-plane/comet intersection defines a line of possible sources on the surface of the nucleus. For the same jet observed at different times, this technique provides different sets of source lines, but