J/A+A/650/A129 SPHERE (87) Sylvia images (Carry+, 2021)
Evidence for differentiation of the most primitive small bodies.
Carry B., Vernazza P., Vachier F., Neveu M., Berthier J., Hanus J.,
Ferrais M., Jorda L., Marsset M., Viikinkoski M., Bartczak P.,
Behrend R., Benkhaldoun Z., Birlan M., Castillo-Rogez J., Cipriani F.,
Colas F., Drouard A., Dudzinski G. P., Desmars J., Dumas C. Durech J.,
Fetick R., Fusco T., Grice J., Jehin E., Kaasalainen M., Kryszczynska A.,
Lamy P., Marchis F., Marciniak A., Michalowski T., Michel P., Pajuelo M.,
Podlewska-Gaca E., Rambaux N., Santana-Ros T., Storrs A., Tanga P.,
Vigan A., Warner B., Wieczorek M., Witasse O., Yang B.
<Astron. Astrophys. 650, A129 (2021)>
=2021A&A...650A.129C 2021A&A...650A.129C (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Minor planets
Keywords: minor planets, asteroids: general - Kuiper belt: general -
minor planets, asteroids: individual: Sylvia
Abstract:
Dynamical models of Solar System evolution have suggested that the
so-called P- and D-type volatile-rich asteroids formed in the outer
Solar System beyond Neptune's orbit and may be genetically related
to the Jupiter Trojans, comets, and small Kuiper belt objects (KBOs).
Indeed, the spectral properties of P- and D-type asteroids resemble
that of anhydrous cometary dust.
We aim to gain insights into the above classes of bodies by
characterizing the internal structure of a large P- and D-type
asteroid.
We report high-angular-resolution imaging observations of the P-type
asteroid (87) Sylvia with the the Very Large Telescope (VLT)
Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE)
instrument. These images were used to reconstruct the 3D shape of
Sylvia. Our images together with those obtained in the past with large
ground-based telescopes were used to study the dynamics of its two
satellites. We also modeled Sylvia's thermal evolution.
The shape of Sylvia appears flattened and elongated (a/b∼1.45;
a/c∼1.84). We derive a volume-equivalent diameter of 271±5km and
a low density of 1378±45kg/m3. The two satellites orbit Sylvia on
circular, equatorial orbits. The oblateness of Sylvia should imply a
detectable nodal precession which contrasts with the fully-Keplerian
dynamics of its two satellites. This reveals an inhomogeneous internal
structure, suggesting that Sylvia is differentiated.
Sylvia's low density and differentiated interior can be explained by
partial melting and mass redistribution through water percolation. The
outer shell should be composed of material similar to interplanetary
dust particles (IDPs) and the core should be similar to aqueously
altered IDPs or carbonaceous chondrite meteorites such as the Tagish
Lake meteorite. Numerical simulations of the thermal evolution of
Sylvia show that for a body of such a size, partial melting was
unavoidable due to the decay of long-lived radionuclides. In addition,
we show that bodies as small as 130-150km in diameter should have
followed a similar thermal evolution, while smaller objects, such as
comets and the KBO Arrokoth, must have remained pristine, which is in
agreement with in situ observations of these bodies. NASA Lucy mission
target (617) Patroclus (diameter ∼140km) may, however, be
differentiated.
Description:
Sylvia was observed with the SPHERE instrument (ESO/VLT) around its
opposition at eleven different epochs. We used IRDIS in broad band
(Y filter; filter central wavelength 1041.4nm, width = 135.2nm) and
ZIMPOL in narrowband imaging mode (N_R filter; filter central
wavelength = 645.9nm, width = 56.7nm).
Each observational sequence consisted of a series of images, where
each image corresponded to a series of detector integration times
(DITs) of 10s, during which Sylvia was used as a natural guide star
for adaptive optics (AO) corrections. Observations were performed
under good seeing conditions (≤0.8") with an airmass usually below
1.6. Standard calibrations, which include detector flat-fields and
darks, were acquired in the morning as part of the instrument
calibration plan.
objects:
-------------------------------------------------------------------
Planet Name H Diam i e a
mag km deg AU
-------------------------------------------------------------------
87 Sylvia 6.86 261.0 10.87567 0.09351718 3.48178042
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 97 121 Table A1 (lightcurves)
tableb1.dat 70 100 List of observers of the five stellar occultations
tablec1.dat 80 130 Table C1 (astrometry Romulus)
tablec2.dat 80 67 Table C2 (astrometry Remus)
list.dat 127 104 List of fits images
fits/* . 104 Individual fits images
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Id Lightcurve identifier
6- 15 A10 "YYYY-MM-DD" Obs.date Date of observation
17- 19 F3.1 s Dur Length of the lightcurve
21- 23 I3 --- Npoints Number of measurements in the lightcurve
25- 28 F4.1 deg Phase Phase angle at the time of observations
30- 34 A5 --- Filter Filter used
36- 40 F5.3 --- rms Root mean square residuals
42- 44 A3 --- IAUCode IAU Observatory Code
46- 97 A52 --- Observer Bibcode or observer name
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "YYYY-MM-DD" Obs.date Occultation date
12- 70 A59 --- Observer Observer name
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Byte-by-byte Description of file: tablec1.dat tablec2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "YYYY-MM-DD" Obs.date Date of observation
12- 22 A11 "h:m:s" Obs.time Time UTC of observation
24- 29 A6 --- Tel Telescope used
31- 36 A6 --- Camera Camera used
38- 39 A2 --- Filter Filter used
41- 46 F6.1 mas Xo Satellite position along RA
48- 53 F6.1 mas Yo Satellite position along Dec
55- 59 F5.1 mas Xomc Satellite residuals along RA
61- 65 F5.1 mas Yomc Satellite residuals along Dec
67- 70 F4.1 mas sigma Uncertainty
72- 75 F4.1 mag deltamag ?=0 Satellite differential magnitude
77- 80 F4.2 mag e_deltamag ?=0 Uncertainty on the differential
magnitude
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 51 A22 "datime" Obs.date Observation date
53- 56 I4 Kibyte size Size of FITS file
58-127 A70 --- FileName Name of FITS file, in subdirectory fits
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Acknowledgements:
Benoit Carry, benoit.carry(at)oca.eu
(End) Patricia Vannier [CDS] 26-Mar-2021