TY  - JOUR
T1  - The shape of (7) Iris as evidence of an ancient large impact?
A1  - Hanuš, J.
A1  - Marsset, M.
A1  - Vernazza, P.
A1  - Viikinkoski, M.
A1  - Drouard, A.
A1  - Brož, M.
A1  - Carry, B.
A1  - Fetick, R.
A1  - Marchis, F.
A1  - Jorda, L.
A1  - Fusco, T.
A1  - Birlan, M.
A1  - Santana-Ros, T.
A1  - Podlewska-Gaca, E.
A1  - Jehin, E.
A1  - Ferrais, M.
A1  - Grice, J.
A1  - Bartczak, P.
A1  - Berthier, J.
A1  - Castillo-Rogez, J.
A1  - Cipriani, F.
A1  - Colas, F.
A1  - Dudziński, G.
A1  - Dumas, C.
A1  - Ďurech, J.
A1  - Kaasalainen, M.
A1  - Kryszczynska, A.
A1  - Lamy, P.
A1  - Le Coroller, H.
A1  - Marciniak, A.
A1  - Michalowski, T.
A1  - Michel, P.
A1  - Pajuelo, M.
A1  - Tanga, P.
A1  - Vachier, F.
A1  - Vigan, A.
A1  - Witasse, O.
A1  - Yang, B.
JA  - Astronomy and Astrophysics
Y1  - 2019
VL  - 624
SP  - A121
SN  - 0004-6361
UR  - https://ui.adsabs.harvard.edu/abs/2019A&A...624A.121H
KW  - asteroids: individual: 7 Iris
KW  - Astrophysics - Earth and Planetary Astrophysics
KW  - methods: numerical
KW  - methods: observational
KW  - minor planets
N2  - Context. Asteroid (7) Iris is an ideal target for disk-resolved imaging
M1  - ={owing to its brightness (V 7-8) and large angular size of 0.33'' during
M1  -  its apparitions. Iris is believed to belong to the category of large
M1  -  unfragmented asteroids that avoided internal differentiation
M1  -  implying
M1  -  that its current shape and topography may record the first few 100 Myr
M1  -  of the solar system's collisional evolution. <BR /> Aims: We recovered
M1  -  information about the shape and surface topography of Iris from disk-
M1  -  resolved VLT/SPHERE/ZIMPOL images acquired in the frame of our ESO large
M1  -  program. <BR /> Methods: We used the All-Data Asteroid Modeling (ADAM)
M1  -  shape reconstruction algorithm to model the 3D shape of Iris
M1  -  using
M1  -  optical disk-integrated data and disk-resolved images from SPHERE and
M1  -  earlier AO systems as inputs. We analyzed the SPHERE images and our
M1  -  model to infer the asteroid's global shape and the morphology of its
M1  -  main craters. <BR /> Results: We present the 3D shape
M1  -  volume-equivalent
M1  -  diameter D<SUB>eq</SUB> = 214 ± 5 km
M1  -  and bulk density ρ = 2.7 ± 0.3 g
M1  -  cm<SUP>-3</SUP> of Iris. Its shape appears to be consistent with that of
M1  -  an oblate spheroid with a large equatorial excavation. We identified
M1  -  eight putative surface features 20-40 km in diameter detected at several
M1  -  epochs
M1  -  which we interpret as impact craters
M1  -  and several additional
M1  -  crater candidates. Craters on Iris have depth-to-diameter ratios that
M1  -  are similar to those of analogous 10 km craters on Vesta. <BR />
M1  -  Conclusions: The bulk density of Iris is consistent with that of its
M1  -  meteoritic analog based on spectroscopic observations
M1  -  namely LL
M1  -  ordinary chondrites. Considering the absence of a collisional family
M1  -  related to Iris and the number of large craters on its surface
M1  -  we
M1  -  suggest that its equatorial depression may be the remnant of an ancient
M1  -  (at least 3 Gyr) impact. Iris's shape further opens the possibility that
M1  -  large planetesimals formed as almost perfect oblate spheroids. Finally
M1  -  we attribute the difference in crater morphology between Iris and Vesta
M1  -  to their different surface gravities
M1  -  and the absence of a substantial
M1  -  impact-induced regolith on Iris. <P />The reduced images are only
M1  -  available at the CDS via anonymous ftp to <A
M1  -  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
M1  -  (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-
M1  -  bin/qcat?J/A+A/624/A121">http://cdsarc.u-strasbg.fr/viz-
M1  -  bin/qcat?J/A+A/624/A121</A>Based on observations made with ESO
M1  -  Telescopes at the Paranal Observatory under programme ID 199.C-0074 (PI:
M1  -  P. Vernazza) and 086.C-0785 (PI: B. Carry).
M1  -  10.1051/0004-6361/201834541
M1  -  eprint: arXiv:1902.09242}
ER  -