J/A+A/638/L15 (16) Psyche. VLT/SPHERE images and shape models (Ferrais+, 2020)
Asteriod (16) Psyche's primordial shape: A possible Jacobi ellipsoid.
Ferrais M., Vernazza P., Jorda L., Rambaux N., Hanu J., Carry B.,
Marchis F., Marsset M., Viikinkoski M., Broz M., Fetick R., Drouard A.,
Fusco T., Birlan M., Podlewska-Gaca E., Jehin E., Bartczak P., Berthier J.,
Castillo-Rogez J., Cipriani F., Colas F., Dudzinski G., Dumas C., Durech J.,
Kaasalainen M., Kryszczynska A., Lamy P., Le Coroller H., Marciniak A.,
Michalowski T., Michel P., Santana-Ros T., Tanga P., Vachier F., Vigan A.,
Witasse O., Yang B.
<Astron. Astrophys. 638, L15 (2020)>
=2020A&A...638L..15F 2020A&A...638L..15F (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Minor planets ; Morphology
Keywords: minor planets, asteroids: general -
minor planets, asteroids: individual: (16) Psyche -
methods: observational - techniques: high angular resolution
Abstract:
Asteroid (16) Psyche is the largest M-type asteroid in the main belt
and the target of the NASA Psyche mission. It is also the only
asteroid of this size (D>200km) known to be metal rich. Although
various hypotheses have been proposed to explain the rather unique
physical properties of this asteroid, a perfect understanding of its
formation and bulk composition is still missing.
We aim to refine the shape and bulk density of (16) Psyche and to
perform a thorough analysis of its shape to better constrain possible
formation scenarios and the structure of its interior.
We obtained disk-resolved VLT/SPHERE/ZIMPOL images acquired within our
ESO large program (ID 199.C-0074), which complement similar data
obtained in 2018. Both data sets offer a complete coverage of Psyche's
surface. These images were used to reconstruct the three-dimensional
(3D) shape of Psyche with two independent shape modeling algorithms
(MPCD and ADAM). A shape analysis was subsequently performed,
including a comparison with equilibrium figures and the identification
of mass deficit regions.
Our 3D shape along with existing mass estimates imply a density of
4.20±0.60g/cm^3, which is so far the highest for a solar system
object following the four telluric planets. Furthermore, the shape of
Psyche presents small deviations from an ellipsoid, that is,
prominently three large depressions along its equator. The flatness
and density of Psyche are compatible with a formation at hydrostatic
equilibrium as a Jacobi ellipsoid with a shorter rotation period of
∼3h. Later impacts may have slowed down Psyche's rotation, which is
currently ∼4.2h, while also creating the imaged depressions.
Our results open the possibility that Psyche acquired its primordial
shape either after a giant impact while its interior was already
frozen or while its interior was still molten owing to the decay of
the short-lived radionuclide 26Al.
Description:
We obtained 35 images of Psyche at 7 epochs in July and August 2019
using VLT/SPHERE/ZIMPOL. This data set complements the first 25 images
taken within our ESO large program that was already presented in
Viikinkoski et al. (2018A&A...619L...3V 2018A&A...619L...3V), for a total of 60 images
taken at 12 epochs. All images were reduced following the procedure
described in Vernazza et al. (2018A&A...618A.154V 2018A&A...618A.154V).
object:
-------------------------------------------------------------------
Planet Name H Diam i e a
mag km deg AU
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16 Psyche 5.90 222.0 3.096560 0.13353119 2.92277557
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
spinadam.dat 42 1 Spin parameter of the ADAM shape model
spinmpcd.dat 42 1 Spin parameter of the MPCD shape model
psyche_adam.obj 32 2354 ADAM shape model in OBJ format
psyche_adam.ver 48 3923 ADAM shape model in lightcurve-inversion format
psyche_mpcd.obj 49 9698 MPCD shape model in OBJ format
psyche_mpcd.ver 48 16163 MPCD shape model in lightcurve-inversion format
list.dat 128 70 List of fits images
fits/* . 70 Individual fits images
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See also:
J/A+A/662/L15 : (22) Kalliope SPHERE images and shape models (Ferrais+, 2022)
http://astro.troja.mff.cuni.cz/projects/asteroids3D/web.php : DAMIT Home Page
Description of files: psyche_mpcd.obj and psyche_adam.obj
First column:
Flag for vertices "v" or facets "f" line
Columns 2 to 4:
For vertices lines: Cartesian coordinates (x,y,z) of the vertex
For facet lines: Index of the three vertices in the triangular facet
Description of files: psyche_mpcd.ver and psyche_adam.ver
First line: Number of vertices (#v) and number of facets (#f)
Then, for #v lines: Cartesian coordinates (x,y,z) of the vertex
Then, for #f lines: Index of the three vertices in the triangular facet
Byte-by-byte Description of file: spinadam.dat spinmpcd.dat
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Bytes Format Units Label Explanations
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1- 7 F7.4 deg LongP Ecliptic longitude of the pole (J2000)
9- 16 F8.4 deg LatP Ecliptic latitude of the pole (J2000)
18- 27 F10.8 h Period Sidereal rotation period
29- 40 F12.4 d t0 Reference epoch (Julian date, JD)
42 I1 deg phi0 Initial rotation angle for t0
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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- 26 F7.5 arcsec/pix scale Scale of the image
28- 31 I4 --- Nx Number of pixels along X-axis
33- 36 I4 --- Ny Number of pixels along Y-axis
38- 60 A23 "datime" Obs.date Observation date
62- 65 I4 Kibyte size Size of FITS file
67-128 A62 --- FileName Name of FITS file, in subdirectory fits
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Acknowledgements:
Marin Ferrais, marin.ferrais(at)lam.fr
(End) Patricia Vannier [CDS] 15-Jun-2020