Abstract
Comet 67P/Churyumov-Gerasimenko (67P hereinafter) is characterized by a dust transfer from the southern hemi-nucleus to the night-side northern dust deposits, which constrains the ...dust-to-ices mass ratio inside the nucleus to values a factor of 2 larger than that provided by the lost mass of gas and non-volatiles. This applies to all comets because the gas density in all night comae cannot prevent the dust fallback. Taking into account Grain Impact Analyser and Dust Accumulator (GIADA) data collected during the entire Rosetta mission, we update the average dust bulk density to $\rho {}{}_{\rm D} = 785_{-115}^{+520}$ kg m−3 that, coupled to the 67P nucleus bulk density, confirms an average dust-to-ices mass ratio δ = 7.5 inside 67P. The improved dust densities are consistent with a mixture of (20 ± 8) per cent of ices, (4 ± 1) per cent of Fe sulphides, (22 ± 2) per cent of silicates and (54 ± 5) per cent of hydrocarbons, on average volume abundances. These values correspond to solar chemical abundances, as suggested by the elemental C/Fe ratio observed in 67P. The ice content in 67P matches that inferred in Kuiper belt objects, (20 ± 12) per cent on average volume abundance and suggests a water content in all trans-Neptunian objects lower than in CI chondrites. The 67P icy pebbles and the dust collected by GIADA have a microporosity of (49 ± 5) and (59 ± 8) per cent, respectively.
Context. During the period between 15 September 2014 and 4 February 2015, the Rosetta spacecraft accomplished the circular orbit phase around the nucleus of comet 67P/Churyumov-Gerasimenko (67P). The ...Grain Impact Analyzer and Dust Accumulator (GIADA) onboard Rosetta monitored the 67P coma dust environment for the entire period. 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.
ABSTRACT The COmetary Secondary Ion Mass Analyser instrument on board ESA's Rosetta mission has collected dust particles in the coma of comet 67P/Churyumov-Gerasimenko. During the early-orbit phase ...of the Rosetta mission, particles and particle agglomerates have been imaged and analyzed in the inner coma at distances between 100 km and 10 km off the cometary nucleus and at more than 3 AU from the Sun. We identified 585 particles of more than 14 m in size. The particles are collected at low impact speeds and constitute a sample of the dust particles in the inner coma impacting and fragmenting on the targets. The sizes of the particles range from 14 m up to sub-millimeter sizes and the differential dust flux size distribution is fitted with a power law exponent of −3.1. After impact, the larger particles tend to stick together, spread out or consist of single or a group of clumps, and the flocculent morphology of the fragmented particles is revealed. The elemental composition of the dust particles is heterogeneous and the particles could contain typical silicates like olivine and pyroxenes, as well as iron sulfides. The sodium to iron elemental ratio is enriched with regard to abundances in CI carbonaceous chondrites by a factor from ∼1.5 to ∼15. No clear evidence for organic matter has been identified. The composition and morphology of the collected dust particles appear to be similar to that of interplanetary dust particles.
Context. The ESA Rosetta spacecraft will reach the short-period comet 67P/Churyumov-Gerasimenko in 2014. Orbiting strategy, orbiter safety conditions, landing scenarios and expected results from dust ...collectors depend on models of the 67P dust environment. Many papers already tackled this matter, analysing a limited set of observations, and therefore often reaching conflicting conclusions. Aims. We consider a set of observations representative of all ground-based and IR (thermal infrared) Spitzer data collected over the last three perihelion passages, to determine the 67P dust environment after the end of the gas drag on dust (at about 20 nucleus radii) consistent with available 67P gas and dust coma photometry, images of the dust coma, tail and trail, at optical and IR wavelengths. Methods. In order to obtain the best fit to 67P data, we consider three independent tail and trail simulation codes (developed by three independent groups), which parametrise cometary dust by the quantity β, the ratio between solar radiation pressure and gravity forces. GIADA, the dust monitor instrument of the Rosetta orbiter, will provide an experimental determination of the β-dust mass relation. Results. A 67P environment model based on a perihelion-symmetric dust velocity and on a perihelion-asymmetric dust size distribution, is consistent with all available data. During most Rosetta operations, the dust cross-section is dominated by mm to cm-sized grains, while the ejected dust mass is dominated by grains larger than a few mm, with a dust-to-gas ratio of 3 around perihelion. Conclusions. 67P onsets its activity at Sun-distances rh ≥ 3.4 AU; the dust geometric albedo is 0.04 ± 0.02; at 3.0 AU, 10 g grains escape the nucleus gravity field (10 kg grains at perihelion) with a dust mass-loss rate of 10−40 kg s-1 (500 kg s-1 at perihelion); 67P’s activity depends on seasons, with the northern heminucleus (rich in large grains and CN depleted) active before perihelion.
The cometary activity of Centaur P/2004 A1 (LONEOS) Epifani, E. Mazzotta; Dall'Ora, M.; Perna, D. ...
Monthly Notices of the Royal Astronomical Society,
August 2011, Letnik:
415, Številka:
4
Journal Article
Recenzirano
Odprti dostop
P/2004 A1 (LONEOS) is one of the few active objects in the dynamical class of Centaurs. It has been recently injected into an inner orbit with a perihelion distance q = 5.5 au. The aim of this paper ...is to characterize the dust coma of this peculiar object, 2.5 yr after its first 'new' perihelion passage inside the Solar system. Broad-band visible images taken at the TNG telescope in 2007 February were analysed in order to characterize the dust coma of the Centaur: it was still quite active at r
h = 6.5 au post-perihelion, with a coma and a well-developed wide tail-like structure, with a measured R-Afρ= 162 ± 10 cm in an aperture radius ρ= 104 km. The (V − R) colour and the reddening values depict a scenario of a slightly red dust coma. A dust mass-loss rate of
= 133 kg s−1 is derived from a photometric model, consistent with a scenario of a quite constant emission rate along the Centaur orbit. An upper limit for the Centaur radius of 3.5 km is derived by some realistic hypotheses on CO molecular production rate and on the mean grain scatterer size in the coma. Dynamical lifetime estimates compared to modelled loss rate result in a radius lower limit of 0.5 km, indicating therefore that the Centaur size is likely of the same order of magnitude of the short-period comets.
The first results on the optical constants of three different amorphous carbon samples, possible analogues of interstellar and circumstellar dust grains, are presented. They have been deduced from ...recent laboratory data, making use of the Kramers-Kronig approach. It is shown that the physically correct simulation of clustering by the traditional ‘CDE’ model is not applicable here. A modified CDE (MCDE) model is proposed and used in the present calculations. The MCDE model allows one to take into account the effect of percolation of the analysed amorphous carbon clusters through the parameter go, interpreted as a percolation strength. The intervals of the probable MCDE models (go) have been chosen on the basis of the relevant estimates of Stognienko, Henning & Ossenkopf for the cluster—cluster aggregation (CCA) and particle—cluster aggregation (PCA) models. The ‘optimal’ percolation strengths and optical constants have been derived by using a least-squares procedure.
Despite a long tradition of dust instruments flown on-board space mission, the largest number of these can be considered unique as they used different detection techniques. GIADA (Grain Impact ...Analyzer and Dust Accumulator), is one of the dust instruments on-board the Rosetta spacecraft and is devoted to measure the dust dynamical parameters in the coma of comet 67P/Churyumov–Gerasimenko. It couples two different techniques to measure the mass and speed of individual dust particles. We report here the results of an extended calibration activity carried-out, during the hibernation phase of the Rosetta mission, on the GIADA Proto Flight Model (PFM) operative in a clean room in our laboratory. The main aims of an additional calibration campaign are:•to verify the algorithms and procedures for data calibration developed before Rosetta launch;•to improve the comprehension of GIADA response after the increased knowledge on cometary dust, e.g. the composition of dust particles after Stardust mission.These calibration improvements implied a final step, which consisted in defining transfer functions to correlate the new calibration curves obtained for the GIADA PFM to those to be used for GIADA onboard the Rosetta spacecraft. The extended calibration activity allowed us to analyze GIADA data acquired in the 67P/C–G coma permitting to infer additional information on cometary dust particles, e.g. density and tensile strength.
•GIADA in situ dust instrument on board the Rosetta spacecraft.•Extended calibration activity on the GIADA Proto Flight Model (PFM).•Improve the comprehension of GIADA responses vs. knowledge on cometary dust.•Definition of instrument transfer functions to obtain the physical measurements.•Calibrations allowed us to infer cometary dust particles additional properties.
The limited knowledge about the majority of the Mercury surface leaves many open questions regarding its geological evolution, the anomalously high metal/silicate ratio, the magnetic field generation ...and exosphere evolution. An integrated suite of instruments, Spectrometer and Imagers for MPO BepiColombo-Integrated Observatory SYStem (SIMBIO-SYS), which includes a stereo imaging system (STC), a high-resolution imager (HRIC) and a visible–near-infrared imaging spectrometer (VIHI), has been selected for the ESA BepiColombo mission to Mercury. SIMBIO-SYS will scan the hermean surface with the three channels and map the physical, morphological, tectonic and compositional properties of the entire planet. The availability of high-resolution images will unveil details of specific target at an unprecedented resolution. The main scientific objectives and performances along with technical characteristics of SIMBIO-SYS are described in this paper.
The VIRTIS (Visual IR Thermal Imaging Spectrometer) experiment has been one of the most successful experiments built in Europe for Planetary Exploration. VIRTIS, developed in cooperation among Italy, ...France and Germany, has been already selected as a key experiment for 3 planetary missions: the ESA-Rosetta and Venus Express and NASA-Dawn. VIRTIS on board Rosetta and Venus Express are already producing high quality data: as far as Rosetta is concerned, the Earth-Moon system has been successfully observed during the Earth Swing-By manouver (March 2005) and furthermore, VIRTIS will collect data when Rosetta flies by Mars in February 2007 at a distance of about 200 kilometres from the planet. Data from the Rosetta mission will result in a comparison – using the same combination of sophisticated experiments – of targets that are poorly differentiated and are representative of the composition of different environment of the primordial solar system. Comets and asteroids, in fact, are in close relationship with the planetesimals, which formed from the solar nebula 4.6 billion years ago. The Rosetta mission payload is designed to obtain this information combining in situ analysis of comet material, obtained by the small lander Philae, and by a long lasting and detailed remote sensing of the comet, obtained by instrument on board the orbiting Spacecraft. The combination of remote sensing and in situ measurements will increase the scientific return of the mission. In fact, the “in situ” measurements will provide “ground-truth” for the remote sensing information, and, in turn, the locally collected data will be interpreted in the appropriate context provided by the remote sensing investigation. VIRTIS is part of the scientific payload of the Rosetta Orbiter and will detect and characterise the evolution of specific signatures – such as the typical spectral bands of minerals and molecules – arising from surface components and from materials dispersed in the coma. The identification of spectral features is a primary goal of the Rosetta mission as it will allow identification of the nature of the main constituent of the comets. Moreover, the surface thermal evolution during comet approach to sun will be also studied.
We present experimental results on the crystal–amorphous transition of forsterite (Mg2SiO4) silicate under ion irradiation. The aim of this work is to study the structural evolution of one of the ...most abundant crystalline silicates observed in space driven by ion irradiation. To this aim, forsterite films have been synthesised in the laboratory and irradiated with low energy (30–60 keV) ion beams. Structural changes during irradiation with H+, He+, C+, and Ar++ have been observed and monitored by infrared spectroscopy. The fraction of crystalline forsterite converted into the amorphous form is a function of the energy deposited by nuclear collision by ions in the target. Laboratory results indicate that ion irradiation is a mechanism potentially active in space for the amorphisation of silicates. Physical properties obtained in this work can be used to model the evolution of silicate grains during their life cycle from evolved stars, through different interstellar environments and up to being incorporated in Solar System objects.
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