VIRTIS-H observations of the dust coma of comet 67P/Churyumov-Gerasimenko: spectral properties and color temperature variability with phase and elevation

Bockelée‐Morvan, Dominique; Leyrat, C.; Erard, S.; Andrieu, F.; Capaccioni, F.; Filacchione, G.; Hasselmann, P. H.; Crovisier, J.; Drossart, P.; Arnold, Gabriele; Ciarniello, M.; Kappel, David; Longobardo, A.; Capria, M. T.; Sanctis, M. C. De; Rinaldi, G.; Taylor, F. W.

doi:10.1051/0004-6361/201834764

Cited by 24 publications

(15 citation statements)

References 68 publications

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“…With the exclusion of the two peaks, a similar asymmetric, or cusp-like trend with a maximum occurring about one month after perihelion, has been measured by other Rosetta's instruments for the water production rate which is associated to the ejection of the dust [3]. Apart from the greater column density, we have clues that larger particle albedo could contribute to the increase of the integrated radiance: according to [4] the albedo of the dust particles increases up to 20% near perihelion for observations acquired at 90° solar phase angle. Similar albedo changes could be the result of a different composition of the dominant grain population in the coma along the orbit, as discussed in the main paper.…”

Section: Temporal Evolution Of the Coma Coloursupporting

confidence: 70%

“…The low thermal capacity of the dust (700 J/kg/K) and the high solar flux can raise rapidly the temperature of the grains causing the sublimation of the volatiles. A colour temperature as high as 630 K is measured on dust grains during outbursts [37] and in the 260-320 K range on quiescent coma [4]. Besides, the grains observed by Rosetta's dust instruments appear dehydrated [30,44].…”

Section: Temporal Evolution Of the Nucleus Colourmentioning

confidence: 87%

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An orbital water-ice cycle on comet 67P from colour changes

Filacchione

Capaccioni

Ciarniello

et al. 2020

Nature

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The solar heating reaching a cometary surface provides the energy input necessary to sustain gaseous activity through which dust is removed from the nucleus [1,2]. In this dynamical environment, both coma [3,4] and nucleus [5,6] evolve during the orbit, changing their physical and compositional properties. The environment encircling an active cometary nucleus is populated by dust grains with complex and variegated shapes [7] lifted and diffused by gases freed from the sublimation of surface ices [8,9]. Visible colour of dust particles is highly variable: carbonaceous-organic material-rich grains [10] appear red while Mg-silicate [11,12] or water ice [13,14] rich grains are blue with further dependence from grain size distribution, viewing geometry, activity level and comet family type. By integrating spacecraft with telescopic data from the Earth, we know that local colour changes are associated with grain size variations, like in the bluer jets made of submicron grains on comet Hale-Bopp [15] or in fragmented grains on C/1999 S4 (LINEAR) coma [16]. Apart from grain size, also composition influences coma's colour response because transparent volatiles can introduce a significant blueing in scattered light as observed in the dust particles ejected after Deep Impact event [17]. Here we report about the observation of two opposite seasonal colour cycles developing in the coma dust particles and on the surface of comet 67P/CG (Churyumov-Gerasimenko) as observed by Rosetta spacecraft during its perihelion passage in 2015 [18]. Spectral analysis indicates an enrichment of submicron grains made of organic material and amorphous carbon in the coma causing the escalating colour reddening observed during the perihelion passage. At the same time, the progressive removal of dust from the nucleus causes the exposure of more pristine and bluish icy layers on the surface. Far from the Sun, we find that the abundance of water ice on the nucleus is reduced due to redeposition of dust and/or dehydration of the surface layer while water ice contribute to less-red coma's colours. MAIN TEXT Understanding how comets work and evolve is one of the most compelling questions to which the Rosetta mission [18] has been trying to answer. Unlike past flyby missions to comets, Rosetta was designed to enter the same orbit and accompany 67P through its perihelion passage giving us the unique opportunity to follow the colour changes developing on a comet nucleus and coma in its active phase through the inner Solar System. So far, several studies have investigated how dust and gas (H 2 O, CO 2) production [3] are correlated among them during one cometary rotation showing that the water ice sublimation on 67P surface is the driving mechanism for dust ejection in the coma [2]. In fact, the dust emission flux appears lower above high-cohesion consolidated terrains while it is maximum when the subsolar direction is aligned above volatile-rich areas. Since the illumination conditions continuously change on 67P, rather than focusing on coma and nucleus ...

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Section: Temporal Evolution Of the Coma Coloursupporting

confidence: 70%

Section: Temporal Evolution Of the Nucleus Colourmentioning

confidence: 87%

An orbital water-ice cycle on comet 67P from colour changes

Filacchione

Capaccioni

Ciarniello

et al. 2020

Nature

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“…When dust scattering is accounted for, it is modeled either by an isotropic phase function or by an anisotropic phase function that only includes forward scattering. Neither phase function is actually consistent with that of the dust coma of comet 67P/C-G, which features both moderate backward and forward scattering at optical and near-infrared wavelengths (Bertini et al 2017;Bockelée-Morvan et al 2019). Adopting this observed phase function to the MWC 758 disk model of Baruteau et al (2019) leads to a lower level of flux and an enhancement of the disk emission between the two asymmetric bright rings (Fig.…”

Section: Figurementioning

confidence: 78%

Linking studies of tiny meteoroids, zodiacal dust, cometary dust and circumstellar disks

Levasseur-Regourd

Lasue

Milli

et al. 2020

Planetary and Space Science

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Tiny meteoroids entering the Earth's atmosphere and inducing meteor showers have long been thought to originate partly from cometary dust. Together with other dust particles, they form a huge cloud around the Sun, the zodiacal cloud. From our previous studies of the zodiacal light, as well as other independent methods (dynamical studies, infrared observations, data related to Earth's environment), it is now established that a significant fraction of dust particles entering the Earth's atmosphere comes from Jupiterfamily comets (JFCs).This paper relies on our understanding of key properties of the zodiacal cloud and of comet 67P/Churyumov-Gerasimenko, extensively studied by the Rosetta mission to a JFC. The interpretation, through numerical and experimental simulations of zodiacal light local polarimetric phase curves, has recently allowed us to establish that interplanetary dust is rich in absorbing organics and consists of fluffy particles. The ground-truth provided by Rosetta presently establishes that the cometary dust particles are rich in organic compounds and consist of quite fluffy and irregular aggregates. Our aims are as follows: (1) to make links, back in time, between peculiar micrometeorites, tiny meteoroids, interplanetary dust particles, cometary dust particles, and the early evolution of the Solar System, and (2) to show how detailed studies of such meteoroids and of cometary dust particles can improve the interpretation of observations of dust in protoplanetary and debris disks. Future modeling of dust in such disks should favor irregular porous particles instead of more conventional compact spherical particles.

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“…Finally, no correlation between the coma color and phase angle (Sun-Target-Observer angle, STO in Table 1) over the range between 20 • and 50 • is observed (Figure 8, panel D). An increase of reddening with phase angle for cometary dust has been reported for the first time by Bockelée-Morvan et al (2019) for comet 67P. Specifically, Bockelée-Morvan et al ( 2019) reported a phase reddening in the near-IR of the dust coma in the near-nucleus of 67P of 0.031%/100 nm deg −1 in the phase angle range 50 • -120 • .…”

Section: Coma Reddeningmentioning

confidence: 84%

Non-detection of water-ice grains in the coma of comet 46P/Wirtanen and implications for hyperactivity

Protopapa¹,

Kelley²,

Woodward³

et al. 2021

Preprint

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Hyperactive comets have high water production rates, with inferred sublimation areas of order the surface area of the nucleus. Comets 46P/Wirtanen and 103P/Hartley 2 are two examples of this cometary class. Based on observations of comet Hartley 2 by the Deep Impact spacecraft, hyperactivity appears to be caused by the ejection of water-ice grains and/or water-ice rich chunks of nucleus into the coma. These materials increase the sublimating surface area, and yield high water production rates. The historic close approach of comet Wirtanen to Earth in 2018 afforded an opportunity to test Hartley 2 style hyperactivity in a second Jupiter-family comet. We present high spatial resolution, near-infrared spectroscopy of the inner coma of Wirtanen. No evidence for the 1.5-or 2.0-µm water-ice absorption bands is found in six 0.8-2.5 µm spectra taken around perihelion and closest approach to Earth. In addition, the strong 3.0-µm water-ice absorption band is absent in a 2.0-5.3 µm spectrum taken near perihelion. Using spectroscopic and sublimation lifetime models we set constraints on the physical properties of the ice grains in the coma, assuming they are responsible for the comet's hyperactivity. We rule out pure water-ice grains of any size, given their long lifetime. Instead, the hyperactivity of the nucleus and lack of water-ice absorption features in our spectra can be explained either by icy grains on the order of 1 µm in size with a small amount of low albedo dust (greater than 0.5% by volume), or large chunks containing significant amounts of water ice.

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VIRTIS-H observations of the dust coma of comet 67P/Churyumov-Gerasimenko: spectral properties and color temperature variability with phase and elevation

Cited by 24 publications

References 68 publications

An orbital water-ice cycle on comet 67P from colour changes

An orbital water-ice cycle on comet 67P from colour changes

Linking studies of tiny meteoroids, zodiacal dust, cometary dust and circumstellar disks

Non-detection of water-ice grains in the coma of comet 46P/Wirtanen and implications for hyperactivity

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