J/A+A/672/A136 67P/Churyumov-Gerasimenko volatile exposures (Fornasier+, 2023)
Volatile exposures on the 67P/Churyumov-Gerasimenko nucleus.
Fornasier S., Hoang H.V., Fulle M., Quirico E., Ciarniello M.
<Astron. Astrophys. 672, A136 (2023)>
=2023A&A...672A.136F 2023A&A...672A.136F (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Comets ; Photometry ; Optical
Keywords: comets: individual: 67P/Churyumov-Gerasimenko -
methods: data analysis - methods: observational -
techniques: photometric
Abstract:
We present the most extensive catalog of exposures of volatiles on the
67P/Churyumov-Gerasimenko nucleus generated from observations acquired
with the Optical, Spectroscopic, and Infrared Remote Imaging System
(OSIRIS) on board the Rosetta mission. We investigate the volatile
exposure distribution across the nucleus, their size distribution, and
their spectral slope evolution.
We analyzed medium- and high-resolution images acquired with the
Narrow Angle Camera (NAC) of OSIRIS at several wavelengths in the
250-1000nm range, investigating images from 109 different color
sequences taken between August 2014 and September 2016, and covering
spatial resolution from a few m/px to 0.1m/px. To identify the icy
bright spots, we adopted the following criteria: i) they should be at
least 50% brighter than the comet dark terrain; ii) they should have
neutral to moderate spectral slope values in the visible range
(535-882nm); iii) they should be larger than 3 pixels.
We identified more than 600 volatile exposures on the comet, and we
analyzed them in a homogeneous way. Bright spots are found isolated on
the nucleus or grouped in clusters, usually at the bottom of cliffs, and
most of them are small, typically a few square meters or smaller. The
isolated ones are observed in different types of morphological
terrains, including smooth surfaces, on top of boulders, or close to
irregular structures. Several of them are clearly correlated with the
cometary activity, being the sources of jets or appearing after an
activity event. We note a number of peculiar exposures of volatiles
with negative spectral slope values in the high-resolution
post-perihelion images, which we interpret as the presence of large
ice grains (>1000m) or local frosts condensation. We observe a clear
difference both in the spectral slope and in the area distributions of
the bright spots pre- and postperihelion, with these last having lower
average spectral slope values and a smaller size, with a median
surface of 0.7m2, even if the size difference is mainly due to the
higher resolution achieved post-perihelion. The minimum duration of
the bright spots shows three clusters: an area-independent cluster
dominated by short-lifetime frosts; an area-independent cluster with
lifetime of 0.5-2 days, probably associated with the seasonal fallout
of dehydrated chunks; and an area-dependent cluster with lifetime
longer than 2 days consistent with water-driven erosion of the
nucleus.
Even if numerous bright spots are detected, the total surface of
exposed water ice is less than 50000m2, which is 0.1% of the total
67P nucleus surface. This confirms that the surface of comet 67P is
dominated by refractory dark terrains, while exposed ice occupies only
a tiny fraction. High spatial resolution is mandatory to identify ice
on cometary nuclei surfaces. Moreover, the abundance of volatile
exposures is six times less in the small lobe than in the big lobe,
adding additional evidence to the hypothesis that comet 67P is
composed of two distinct bodies. The fact that the majority of the
bright spots identified have a surface lower than 1m2 supports a
model in which water ice enriched blocks (WEBs) of 0.5-1m size should
be homogeneously distributed in the cometary nucleus embedded in a
refractory matrix.
Description:
List of the volatile exposure positions, types, and characteristics
(slope, surface, duration) identified in this paper and in the
literature.
Orbital Elements:
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Code Name Elem q e i H1
d AU deg mag
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67P P/Churyumov-Gerasimenko 2457247.5 1.2432597 0.6408752 7.040364 11.48
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 116 603 List of the volatile exposure positions, types,
and characteristics (slope, surface, duration)
identified in this paper and in the literature
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See also:
J/A+A/520/A92 : Comet 67P global plasma parameter simulation (Gortsas+ 2010)
J/A+A/527/A113 : Comet 67P R-band light curve (Tubiana+, 2011)
J/A+A/548/A12 : 67P/Churyumov-Gerasimenko R-band light curve (Lowry+, 2012)
J/MNRAS/462/S138 : Robotic view of 67P perihelion (Snodgrass+, 2016)
J/A+A/603/A87 : Local production rates of 67P/CG from MIRO (Marshall+, 2017)
J/A+A/647/A119 : Comet 67P FUV aurora (Stephenson+, 2021)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- BS Bright spot number assigned here
5- 20 A16 "date" Start Start date is the first time a bright spot was
identified in the OSIRIS color sequences;
22- 23 I2 --- Type Feature type according to the Deshapriya et
al. (2018A&A...613A..36D 2018A&A...613A..36D) classification
scheme
25- 40 A16 "date" SelSate Date relative to the analysis of a given
bright spot to determine its surface and
spectral slope
42- 48 F7.2 deg LON Longitude where a bright spot is found
50- 55 F6.2 deg LAT Latitude where a bright spot is found
57- 64 A8 --- Region 67P comet region name where a bright spot
is found
66- 69 F4.2 m/pix Res Resolution of the images acquired in the
selected date
71- 77 F7.2 m+2 Area BS surface in the 535-882nm range
(evaluated in the selected date)
80- 84 F5.2 --- Slope ?=- BS spectral slope in the 535-882nm range
(evaluated in the selected date)
86- 96 A11 --- Dur Lifetime of bright spots when it was possible
to estimate it
98-116 A19 --- Ref Reference (1)
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Note (1): The majority of the BS were analyzed in the paper, but some were
already presented in the literature and are referenced as follows:
P2015 = Pommerol et al. (2015A&A...583A..25P 2015A&A...583A..25P)
O2017 = Oklay et al. (2017MNRAS.469S.582O 2017MNRAS.469S.582O)
D2018 = Deshapriya et al. (2018A&A...613A..36D 2018A&A...613A..36D)
Fi2016 = Filacchionet al. (2016Natur.529..368F 2016Natur.529..368F)
B2016 = Barucci et al. (2016A&A...595A.102B 2016A&A...595A.102B)
H2019 = Hasselmann et al. (2019A&A...630A...8H 2019A&A...630A...8H)
P2017 = Pajola et al. ( 2017NatAs...1...92P 2017NatAs...1...92P)
D2016 = Deshapriya et al. (2016MNRAS.462S.274D 2016MNRAS.462S.274D)
H2020 = Hoang et al. (2020MNRAS.498.1221V 2020MNRAS.498.1221V)
F2021 = Fornasier et al. (2021A&A...653A.132F 2021A&A...653A.132F)
F2016 = Fornasier et al. (2016Sci...354.1566F 2016Sci...354.1566F)
F2017 = Fornasier et al. (2017MNRAS.469A..93F 2017MNRAS.469A..93F)
F2019 = Fornasier et al. (2019A&A...630A..13F 2019A&A...630A..13F)
O2020 = O'Rourke et al. (2020Nat...586..698O 2020Nat...586..698O)
A2017 = Agarwal et al. (2017MNRAS.469S.606A 2017MNRAS.469S.606A)
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Acknowledgements:
Sonia Fornasier, Sonia.Fornasier(at)obspm.fr
(End) Patricia Vannier [CDS] 24-Feb-2023