Dayside-to-nightside dust coma brightness asymmetry and its implications for nightside activity at Comet 67P/Churyumov–Gerasimenko

Context. The dust-brightness phase curves that have been measured by the OSIRIS cameras on board the Rosetta spacecraft within the coma of comet 67P/Churyumov-Gerasimenko (67P) present a remarkable flattened u-shape. Aims. Our goal is to compare these phase curves with those of tentatively analog dust samples to assess the key dust properties that might induce this shape. Methods. Light-scattering measurements have been made with the PROGRA2 instrument in the laboratory and in microgravity conditions on samples of different physical properties and compositions that are likely to be representative of cometary dust particles. Results. We find that the brightness phase curves of a series of interplanetary dust analogs that have been recently developed (to fit the polarimetric properties of the inner zodiacal cloud and their changes with heliocentric distance) are quite comparable to those of 67P. Key dust properties seem to be related to the composition and the porosity. Conclusions. We conclude that the shape of the brightness phase curves of 67P has to be related to the presence of a significant amount of organic compounds (at least 50% in mass) and of fluffy aggregates (of a size range of 10–200 μm). We also confirm similarities between the dust particles of this Jupiter-family comet and the particles within the inner zodiacal cloud.

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MUSE observations of comet 67P/Churyumov-Gerasimenko

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039017 ◽

2020 ◽

Vol 644 ◽

pp. A143

Author(s):

C. Opitom ◽

A. Guilbert-Lepoutre ◽

S. Besse ◽

B. Yang ◽

C. Snodgrass

Keyword(s):

Spatial Information ◽

Rosetta Mission ◽

Simultaneous Study ◽

Novel Method ◽

Dust Coma ◽

Water Production Rate ◽

Field Unit ◽

Comet 67P ◽

High Quality Spectrum ◽

Integral Field

Aims. Observations of comet 67P/Churyumov-Gerasimenko were performed with MUSE at large heliocentric distances post-perihelion between 3 and 7 March 2016. These observations are part of a simultaneous ground-based campaign aimed at providing broad-scale information about comet 67P to complement the ESA/Rosetta mission. Methods. We obtained a total of 38 datacubes over five nights. We took advantage of the integral field unit nature of the instrument to carry out a simultaneous study of the spectrum of 67P’s dust and its spatial distribution in the coma. We also looked for evidence of gas emission in the coma. Results. We produced a high-quality spectrum of the dust coma over the optical range that could be used as a reference for future comet observations with this instrument. The slope of the dust reflectivity is of 10%∕100 nm over the 480–900 nm interval, with a shallower slope towards redder wavelengths. We used the Afρ to quantify the dust production and measure values of 65 ± 4 cm, 75 ± 4 cm, and 82 ± 4 cm in the V, R, and I bands, respectively. We detected several jets in the coma as well as the dust trail. Finally, using a novel method combining spectral and spatial information, we detected the forbidden oxygen emission line at 630 nm. Using this line, we derived a water production rate of 1.5 ± 0.6 × 1026 molec. s−1, assuming all oxygen atoms come from the photo-dissociation of water.

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Dust tail observation and modeling of the interstellar comet 2I/Borisov

10.5194/epsc2020-903 ◽

2020 ◽

Author(s):

Gabriele Cremonese ◽

Marco Fulle ◽

Pamela Cambianica ◽

Giovanni Munaretto ◽

Maria Teresa Capria ◽

...

Keyword(s):

Loss Rate ◽

Water Flux ◽

Activity Model ◽

Orbit Eccentricity ◽

Dust Tail ◽

Dust Coma ◽

Comet 67P

On 30 August 2019 the amateur Borisov discovered a new comet; after few days it was clear from the characteristics of its orbit (eccentricity > 3 and high hyperbolic excess velocity) that the second interstellar object had been detected and the object received the name of 2I/Borisov. It appears to be very different from 1I/&#8217;Oumuamua and can be considered as the first interstellar comet. According to the first observations the comet had a nucleus with a radius of few km and a dust coma and tail due to the activity started in June 2019 (Jewitt et al., 2019). At the beginning of October we submitted the Discretionary Director Time (DDT) proposal to the TNG in order to monitor the comet. Some images have been acquired, in November and December 2019, with the DOLORES instrument in the R filter. We have applied the dust model described in Fulle et al. (2010), that has been tested on the comet 67P/Churyumov-Gerasimenko and validated with the Rosetta measurements. According to the results of our dust model and the activity model (Fulle et al., 2020) we derived a water flux from the nucleus of 8x10-6 kg m-2 s-1 and a dust loss rate of 35 and 30 kg s-1 in November and December 2019 respectively (Cremonese et al., 2020). This slight decrease has been observed around the perihelion on 8 December, few months later the comet fragmented. In this work we will describe the dust tail observations and the dust model results, even comparing them with the Jupiter family comet 67P. References: G.Cremonese, et al., 2020, ApJL, 893, L12 M.Fulle et al., 2010, A&A, 522, A63. M.Fulle et al., 2020, MNRAS, 493, 4039. Jewitt et al., 2019, ApJ, 886, L29.

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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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834764 ◽

2019 ◽

Vol 630 ◽

pp. A22 ◽

Cited By ~ 7

Author(s):

D. Bockelée-Morvan ◽

C. Leyrat ◽

S. Erard ◽

F. Andrieu ◽

F. Capaccioni ◽

...

Keyword(s):

Phase Angle ◽

Thermal Inertia ◽

Color Temperature ◽

Dust Particles ◽

Infrared Thermal Imaging ◽

Imaging Spectrometer ◽

Fixed Phase ◽

Dust Coma ◽

Solar Phase ◽

Comet 67P

We analyze 2–5 μm spectroscopic observations of the dust coma of comet 67P/Churyumov-Gerasimenko obtained with the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H) instrument on board Rosetta from 3 June to 29 October 2015 at heliocentric distances rh = 1.24–1.55 AU. The 2–2.5 μm color, bolometric albedo, and color temperature were measured using spectral fitting. Data obtained at α = 90° solar phase angle show an increase in bolometric albedo (0.05–0.14) with increasing altitude (0.5–8 km), accompanied by a possible marginal decrease in color and color temperature. Possible explanations include dark particles on ballistic trajectories in the inner coma and radial changes in particle composition. In the phase angle range 50°–120°, phase reddening is significant (0.031%/100 nm deg−1) for a mean color of 2%/100 nm at α = 90°, which might be related to the roughness of the dust particles. Moreover, a decrease in color temperature with decreasing phase angle is also observed at a rate of ~0.3 K deg−1, consistent with the presence of large porous particles, with low thermal inertia, and showing a significant day-to-night temperature contrast. Comparing data acquired at fixed phase angle (α = 90°), a 20% increase in bolometric albedo is observed near perihelion. Heliocentric variations in dust color are not significant in the time period we analyzed. The measured color temperatures vary from 260 to 320 K, and follow a rh−0.6 variation in the rh = 1.24–1.5 AU range, which is close to the expected rh−0.5 value.

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Blocks Size Frequency Distribution in the Enceladus Tiger Stripes Area: Implications on Their Formative Processes

Universe ◽

10.3390/universe7040082 ◽

2021 ◽

Vol 7 (4) ◽

pp. 82

Author(s):

Maurizio Pajola ◽

Alice Lucchetti ◽

Lara Senter ◽

Gabriele Cremonese

Keyword(s):

Frequency Distribution ◽

Power Law ◽

Size Frequency Distribution ◽

Surface Stresses ◽

Size Frequency ◽

The One ◽

Power Law Index ◽

Comet 67P ◽

South Polar ◽

Degree Of Fragmentation

We study the size frequency distribution of the blocks located in the deeply fractured, geologically active Enceladus South Polar Terrain with the aim to suggest their formative mechanisms. Through the Cassini ISS images, we identify ~17,000 blocks with sizes ranging from ~25 m to 366 m, and located at different distances from the Damascus, Baghdad and Cairo Sulci. On all counts and for both Damascus and Baghdad cases, the power-law fitting curve has an index that is similar to the one obtained on the deeply fractured, actively sublimating Hathor cliff on comet 67P/Churyumov-Gerasimenko, where several non-dislodged blocks are observed. This suggests that as for 67P, sublimation and surface stresses favor similar fractures development in the Enceladus icy matrix, hence resulting in comparable block disaggregation. A steeper power-law index for Cairo counts may suggest a higher degree of fragmentation, which could be the result of localized, stronger tectonic disruption of lithospheric ice. Eventually, we show that the smallest blocks identified are located from tens of m to 20–25 km from the Sulci fissures, while the largest blocks are found closer to the tiger stripes. This result supports the ejection hypothesis mechanism as the possible source of blocks.

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Author Correction: Far-ultraviolet aurora identified at comet 67P/Churyumov-Gerasimenko

Nature Astronomy ◽

10.1038/s41550-021-01373-5 ◽

2021 ◽

Author(s):

M. Galand ◽

P. D. Feldman ◽

D. Bockelée-Morvan ◽

N. Biver ◽

Y.-C. Cheng ◽

...

Keyword(s):

Far Ultraviolet ◽

Comet 67P

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Ultraviolet Albedo of Comet West (1976 VI)

Symposium - International Astronomical Union ◽

10.1017/s007418090006681x ◽

1980 ◽

Vol 90 ◽

pp. 263-266

Author(s):

P. D. Feldman

Keyword(s):

Solar Radiation ◽

Solar Spectrum ◽

Ultraviolet Spectrum ◽

The Moon ◽

Lunar Dust ◽

Cometary Dust ◽

A Value ◽

Dust Coma ◽

Spectrometer Slit ◽

The Continuum

The ultraviolet spectrum of Comet West (1976 VI) in the range 1200-3200 Å was recorded by rocket-borne instruments on March 5.5, 1976. At the time of launch, r = 0.385, Δ = 0.84 and the phase angle was 78°. Longward of 2100 Å the continuum of solar radiation scattered by cometary dust is detected and is found to closely follow the solar spectrum. Since the dust coma is completely included in the spectrometer slit, the ultraviolet albedo can be determined relative to the visible and this ratio is found to be ≈0.3 at 2700 Å. There is evidence for a further decrease in albedo near 2200 Å. Using a visible albedo of 0.2 gives a value of 0.06 for the cometary albedo at 2700 Å, a value similar to that found for the moon and lunar dust in this spectral region.

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