67P/Churyumov-Gerasimenko activity evolution during its last perihelion before the Rosetta encounter

Abstract

Context. The comet 67P/Churyumov-Gerasimenko, target of the Rosetta Mission (ESA) was monitored from January to April 2009 during its last perihelion passage before the Rosetta spacecraft encounters the comet nucleus in May 2014. Photometric data were obtained only from January 25 to March 19, 2009 and they were used to monitor the comet gas and dust activity. Non-photometric data are considered for analysing the evolution of the dust coma morphology. Aims. The goal of the campaign was to characterize the comet activity evolution as it approaches the Sun. We aimed to assess gas and dust production rates shortly before perihelion and after perihelion, as well as to follow the evolution of the dust coma morphology during this passage. Methods. Long-slit spectra and optical broadband images were acquired with the instrument CAFOS mounted at the 2.2. m telescope at Calar Alto Observatory (CSIC-MPG), and with the camera at the 1-m telescope of the Lulin Optical Observatory in Taiwan. We investigated the evolution of the dust coma morphology from the R Johnson images with image enhancing techniques. When possible, we studied the dust and gas production rate, the radial profiles of the dust brightness azimuthally averaged and in the Sun-antisunward direction, and the Sun-antisunward profiles of the CN, C 2 , C 3 , and NH 2 column densities.Results. The morphological analysis of the dust coma reveals that structures indeed exist. Aside from the dust tail in the SW direction, four more small-scaled structures have been detected by using the adaptive Laplacian filtering, the radial renormalization and the Sekanina-Larson method. These structures are also confirmed by the distortion of the isophotes at the same position angles (PA). During January and February, a faint structure could be seen at PA 330• , whereas this feature seems to have disappeared after perihelion. Additionally, the broad structure at PA ∼ 45• seemed to split into two narrower ones on February 26, to become only a considerably fainter one at PA ∼ 75• during March. The Afρ values show considerable scatter in the few days we could measure them. There is a clear increase when the comet approaches the perihelion, however it is not possible to conclude where the peak dust activity is reached when the comet is at or beyond the closest distance to the Sun. The CN, C 2 , C 3 , and NH 2 production rates, Q, have been obtained at r h 1.25 AU. These Q's are very similar to the ones derived from previous passages around perihelion. The decrease in the perihelion distance in (1.24 AU in 2009 vs. 1.30 AU in 1982and 1995 has not induced a noticeable increase either in the gas production rates or in the dust production rates, as measured from the Afρ parameter. The azimuthally averaged surface brightness profiles of the continuum from the broad band images can be well fitted with −1.92 ≤ m ≤ −1.35 in log B − log ρ representation for ρ ≤ 100 000 km projected cometocentric distance from the R broadband images. On the other hand, when the fit is done in the sun-...

Beginning of activity in 67P/Churyumov-Gerasimenko and predictions for 2014–2015

“…There is a peak around perihelion requiring an increase of the active area to ∼ 4% of the surface. Lara et al (2011). The A f ρ value quoted here has been corrected to zero phase (Lara measurements were all taken at ∼ 36 • ).…”

“…Schulz et al (2004), Lamy et al (2006) and Lara et al (2005) obtained the first dedicated characterisation observations after it was selected, when the comet was on the outbound leg of its orbit, and still highly active, following its perihelion passage in 2002. As the comet passed through aphelion its inactive nucleus was studied by Tubiana et al (2008Tubiana et al ( , 2011 and Lowry et al (2012), before it was observed in an active state again as it returned to perihelion in 2008 (Tozzi et al 2011;Lara et al 2011). Further authors have studied the longer lived dust trail associated with the comet (Ishiguro 2008;Kelley et al 2008;Agarwal et al 2010), the dust's polarisation (Hadamcik et al 2010), the nucleus thermal properties (Kelley et al 2006;Lamy et al 2008;Kelley et al 2009), and the morphology (Vincent et al 2013) and composition (Schleicher 2006) of its coma over multiple apparitions.…”

Photometric observations of comet 81P/Wild 2 during the 2010 perihelion passage

“…2. An error around 10% on the measures can be estimated from the absolute flux calibration, as already assumed in previous analogous cometary photometric studies (e.g Schulz et al 2003;Tozzi et al 2007;Bertini et al 2009;Lara et al 2011). In our analysis of the Afρ profiles we considered the longest nucleocentric distances to be corresponding to ρ ∼ 50 000 km except in the last observations on September 9.…”

Spin and activity of comet 67P/Churyumov-Gerasimenko

“…We discuss below whether our estimation agrees well with that was presented by these authors, and how the dynamical simulations allow the proposed solution to be refined. Lara et al (2011) have shown that the coma of 67P exhibits several dust jets, which indicates that the activity is not isotropically distributed on the surface, but rather enhanced in specific regions of the nucleus. Because these dust jets can potentially be a serious hazard for the spacecraft, especially for the lower orbital phases of the mission, we need to constrain them better.…”