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Comets have been studied from a long time and are believed to preserve pristine materials, so they are fundamental to understand the origin of the solar system and life. Starting in the early 1990s, ESA decided to have a more risky and fantastic mission to a comet. As Planetary Cornerstone mission of the ESA Horizon 2000 program, the Rosetta mission was selected with the aim of realizing two asteroid fly-bys, a rendezvous with a comet to deliver a surface science package and to hover around the comet from 4 AU inbound up to perihelion and outbound back to 3.7 AU. The mission was successfully launched on March 2, 2004 with Ariane V that started its 10-year journey toward comet 67P/Churyumov-Gerasimenko. After several planetary gravity assists, Rosetta flew by two asteroids-on September 5, 2008 (Steins) and on July 10, 2010 (Lutetia), respectively, and performed the comet orbit insertion maneuver on August 6, 2014. The onboard instruments characterized the nucleus orbiting the comet at altitudes down to few kilometers. On November 12, 2014, the lander Philae was delivered realizing the first landing ever on a comet surface. Although the exploration of the comet was planned up to the end of 2015, the mission duration was extended for nine more months than the nominal one, to follow the comet on its outbound orbit. To terminate the mission, following a series of very low orbits, a controlled impact of Rosetta spacecraft with the comet was realized on September 30, 2016. The scientific objectives of the mission have been largely achieved. The challenging mission provided the science community with an enormous quantity of data of extraordinary scientific value. In this paper, a detailed description of the mission and the highlights of the obtained scientific results on the exploration of an extraordinary world are presented. The paper also includes lessons learned and directions for the future. [ABSTRACT FROM AUTHOR]

With the European Space Agency's Rosetta space mission to comet 67P/Churyumov-Gerasimenko, a gas chromatograph, part of the COmetary Sampling And Composition (COSAC) experiment, travelled for about 10 years in the interplanetary medium before operating at the surface of the cometary nucleus in November 2014. During its journey in space, the instrument was exposed to the constraining conditions of the interplanetary medium, including reduced environmental pressures. In order to estimate the potential influence of this severe condition on the chromatographic capillary columns, their stationary phase and the subsequent separation capability, a set of flight spare columns were kept under reduced environmental pressure in the laboratory for the same duration as the probe sent to the comet. The columns’ analytical performances were evaluated recently and compared to the original ones obtained just before the launch of the Rosetta probe. The results presented here show that the chromatographic performances of the spare chromatographic columns were not altered in time. From this result, it can be expected that the flight instrument will perform nominally for the analysis of the first cometary nucleus sample to be collected ever, and that the preparation of the interpretation of the data to be taken at the cometary surface nucleus can be done through calibration of these spare columns, and other spare components of the instrument. [ABSTRACT FROM AUTHOR]

We report here the observations of the hydrogen cloud in Lyman alpha emission of Comet 67P/Churyumov–Gerasimenko at the last three passages through its perihelion, in 1996, 2002 and 2009. This comet became the target of ESA space mission Rosetta in 2003, and is therefore of particular interest. The data were collected with the SWAN instrument on board SOHO, the main mission of which is to record all-sky images of interplanetary neutral hydrogen, in order to monitor the solar wind latitude distribution. For the 2009 perihelion, a dedicated campaign was implemented and allowed to collect 26 smaller and more refined images around the position of the comet, from which a unique series of H2O production rates could be derived by comparison with a model, for the period from 2 to 50 days after perihelion. To our knowledge, these are the only determination of H2O production rate for 2009. In addition, we could retrieve the H emission at the two previous perihelia in 1996 and 2002, thanks to serendipitous observations of comets as part of the all-sky monitoring program: 4 and 10 respectively for 1996 and 2002. While the perihelion distance to sun decreased continuously (1.300, 1.292, 1.246AU respectively for 1996, 2002, 2009), the average production Q(H2O) just after perihelion did not increase accordingly: 1.30×1028, 1.70×1028, and 5.65×1027 mols−1. Comparison with 1982 IUE measurement of 6×1027 mols−1 suggests no rapid aging of the comet, and we may expect a similar level of activity at the next perihelion in August 2015. The production rate in 2009 showed a peak around 16.4 days post-perihelion, with a suggestion of a second peak at ~40 days, and a somewhat reduced rate in between (though SWAN measurements are incomplete). These measurements may help in planning of Rosetta activities around the next perihelion. [ABSTRACT FROM AUTHOR]

Abstract: The ESA ROSETTA mission will perform a rendezvous with comet 67P/Churyumov-Gerasimenko and will follow and study it from about 3.25AU to perihelion at 1.34AU and, during the foreseen extended mission, up to 2AU post-perihelion, in order to observe for the first time the onset of activity of a comet and to follow its evolution. The GIADA (Grain Impact Analyser and Dust Accumulator) instrument, on board the ROSETTA orbiter, is aimed to analyse physical and dynamical properties of individual particles ejected by the nucleus and to monitor the dust flux and spatial distribution as a function of time. To achieve these scientific goals, GIADA is composed of different modules: an optical detection system, to monitor the light scattered by single particles entering the instrument, an impact sensor, to detect the momentum carried by the particles, and five micro-balances, to measure the dust flux from different directions. In this work we will describe the technical characteristics and the scientific performances of the flight model of the instrument. The preliminary results of GIADA calibration demonstrate that the instrument is perfectly compatible with design specifications and is suitable to achieve unprecedented scientific results about cometary dust physics. [Copyright &y& Elsevier]

In 2003, comet 67P/Churyumov–Gerasimenko was selected as the new target of the Rosetta mission as the most suitable alternative to the original target, comet 46P/Wirtanen, on the basis of orbital considerations even though very little was known about the physical properties of its nucleus. In a matter of a few years and based on highly focused observational campaigns as well as thorough theoretical investigations, a detailed portrait of this nucleus has been established that will serve as a baseline for planning the Rosetta operations and observations. In this review article, we present a novel method to determine the size and shape of a cometary nucleus: several visible light curves were inverted to produce a size–scale free three–dimensional shape, the size scaling being imposed by a thermal light curve. The procedure converges to two solutions which are only marginally different. The nucleus of comet 67P/Churyumov–Gerasimenko emerges as an irregular body with an effective radius (that of the sphere having the same volume) = 1.72 km and moderate axial ratios a/b = 1.26 and a/c = 1.5 to 1.6. The overall dimensions measured along the principal axis for the two solutions are 4.49–4.75 km, 3.54–3.77 km and 2.94–2.92 km. The nucleus is found to be in principal axis rotation with a period = 12.4–12.7 h. Merging all observational constraints allow us to specify two regions for the direction of the rotational axis of the nucleus: RA = 220°+50° −30° and Dec = −70° ± 10° (retrograde rotation) or RA = 40°+50° -30° and Dec = +70°± 10° (prograde), the better convergence of the various determinations presently favoring the first solution. The phase function, although constrained by only two data points, exhibits a strong opposition effect rather similar to that of comet 9P/Tempel 1. The definition of the disk–integrated albedo of an irregular body having a strong opposition effect raises problems, and the various alternatives led to a R-band geometric albedo in the range 0.045–0.060, consistent with our present knowledge of cometary nuclei. The active fraction is low, not exceeding ~ 7% at perihelion, and is probably limited to one or two active regions subjected to a strong seasonal effect, a picture coherent with the asymmetric behaviour of the coma. Our slightly downward revision of the size of the nucleus of comet 67P/Churyumov-Gerasimenko resulting from the present analysis (with the correlative increase of the albedo compared to the originally assumed value of 0.04), and our best estimate of the bulk density of 370 kg m−3, lead to a mass of ~ 8 × 1012 kg which should ease the landing of Philae and insure the overall success of the Rosetta mission. [ABSTRACT FROM AUTHOR]