GIADA: shining a light on the monitoring of the comet dust production from the nucleus of 67P/Churyumov-Gerasimenko

Abstract

oro.open.ac.uk Aims. We aim to describe the dust spatial distribution in the coma of comet 67P by means of in situ measurements. We determine dynamical and physical properties of cometary dust particles to support the study of the production process and dust environment modification. Methods. We analyzed GIADA data with respect to the observation geometry and heliocentric distance to describe the coma dust spatial distribution of 67P, to monitor its activity, and to retrieve information on active areas present on its nucleus. We combined GIADA detection information with calibration activity to distinguish different types of particles that populate the coma of 67P: compact particles and fluffy porous aggregates. By means of particle dynamical parameters measured by GIADA, we studied the dust acceleration region.Results. GIADA was able to distinguish different types of particles populating the coma of 67P: compact particles and fluffy porous aggregates. Most of the compact particle detections occurred at latitudes and longitudes where the spacecraft was in view of the comet's neck region of the nucleus, the so-called Hapi region. This resulted in an oscillation of the compact particle abundance with respect to the spacecraft position and a global increase as the comet moved from 3.36 to 2.43 AU heliocentric distance. The speed of these particles, having masses from 10 −10 to 10 −7 kg, ranged from 0.3 to 12.2 m s −1 . The variation of particle mass and speed distribution with respect to the distance from the nucleus gave indications of the dust acceleration region. The influence of solar radiation pressure on micron and submicron particles was studied. The integrated dust mass flux collected from the Sun direction, that is, particles reflected by solar radiation pressure, was three times higher than the flux coming directly from the comet nucleus. The awakening 67P comet shows a strong dust flux anisotropy, confirming what was suggested by on-ground dust coma observations performed in 2008.

67P/C-G inner coma dust properties from 2.2 au inbound to 2.0 au outbound to the Sun

“…star tracker performance, the trajectories were mostly constrained to large nucleus distances (> 100 km) and high phase angles, (the angle Sun -67P -Rosetta), i.e. outside dust-rich areas as observed by Della Corte et al (2015). Despite these operational limitations, GIADA was able to monitor efficiently 67P's dust environment and its evolution, determining detection time, mass and speed for individual dust particles.…”

“…GIADA detections are classified according to which GIADA subsystem detects the individual particle entering the instrument. For easier comprehension, we present here a brief summary of the detection and particle types, described in detail by Della Corte et al (2015). GIADA detects individual dust particles in the following combinations: 1) only with the Grain Detection System (GDS), i.e.…”

“…IS-only and GDS+IS detections are of compact particles with density of (1.9 ± 1.1) x 10 3 kg m −3 (Rotundi et al 2015), the only difference being the particle cross-section (i.e. IS-only particles are too small to be detected by the GDS sub-system (Della Corte et al 2015). Although the number of fluffy fragments is larger than that of compact particles, the number of fluffy aggregates (parents) is negligible with respect to the compact particles throughout the Rosetta mission, but especially in the period under analysis January -2016.…”

“…GIADA could do better for a two reasons: 1) due to Rosetta's trajectory, essentially matched to that of the comet, long-term monitoring of the comet's activity was possible for the very first time; 2) for the first time a dust instrument measured mass, speed, crosssection and the exact detection time/position of individual dust particles simultaneously. GIADA was able to (1) characterize 67P's dust environment (Fulle et al 2015); (2) monitor the dust loss rate and the particle mass distribution at the surface of the sunlit nucleus; (3) monitor the dust mass distribution of 67P as it evolved with time (Rotundi et al 2015;Fulle et al 2016); and (4) in the case of dust detected along closely-bound orbits, provide a hint of the region of the nucleus from where the dust originated (Della Corte et al 2015). Even when 67P's coma dust structures are studied by in situ measurements combined with ground-based observations, understanding their formation mechanisms and connecting them to specific active areas on the nucleus is a very challenging process.…”

“…Crifo et al (2002) and Zakharov et al (2009) demonstrate, by means of ab-initio physical models, that coma dust structures can be induced by nucleus asphericity and focussed gas flows due to local topography. Topological diversity can create physical conditions, such as higher temperatures, which will affect the sublimation of different volatiles, explaining the spatial correlation between the high rate of dust ejection and of H 2 O sublimation (Della Corte et al 2015;Migliorini et al 2016). Thus, what could be interpreted as a chemical heterogeneity-driving factor for activity would actually be attributable to a topographic one.…”