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The shape of (7) Iris as evidence of an ancient large impact?
- Source :
- Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, 2019, 624, pp.A121. ⟨10.1051/0004-6361/201834541⟩, Astronomy and Astrophysics-A&A, EDP Sciences, 2019, 624, pp.A121. ⟨10.1051/0004-6361/201834541⟩, Astronomy & Astrophysics
- Publication Year :
- 2019
- Publisher :
- HAL CCSD, 2019.
-
Abstract
- Asteroid (7) Iris is an ideal target for disk-resolved imaging owing to its brightness (V$\sim$7-8) and large angular size of 0.33 arcsec during its apparitions. Iris is believed to belong to the category of large unfragmented asteroids that avoided internal differentiation, implying that its current shape and topography may record the first few 100 Myr of the solar system's collisional evolution. We recovered information about the shape and surface topography of Iris from disk-resolved VLT/SPHERE/ZIMPOL images acquired in the frame of our ESO large program. We used the All-Data Asteroid Modeling (ADAM) shape reconstruction algorithm to model the 3D shape of Iris, using optical disk-integrated data and disk-resolved images from SPHERE as inputs. We analyzed the SPHERE images to infer the asteroid's global shape and the morphology of its main craters. We present the volume-equivalent diameter D$_{{\rm eq}}$=214$\pm$5 km, and bulk density $\rho$=2.7$\pm$0.3 g cm$^{-3}$ of Iris. Its shape appears to be consistent with that of an oblate spheroid with a large equatorial excavation. We identified eight putative surface features 20--40 km in diameter detected at several epochs, which we interpret as impact craters. Craters on Iris have depth-to-diameter ratios that are similar to those of analogous 10 km craters on Vesta. The bulk density of Iris is consistent with that of its meteoritic analog, namely LL ordinary chondrites. Considering the absence of a collisional family related to Iris and the number of large craters on its surface, we suggest that its equatorial depression may be the remnant of an ancient (at least 3 Gyr) impact. Iris's shape further opens the possibility that large planetesimals formed as almost perfect oblate spheroids. Finally, we attribute the difference in crater morphology between Iris and Vesta to their different surface gravities.<br />Comment: Accepted for publication in Astronomy and Astrophysics
- Subjects :
- Solar System
Planetesimal
010504 meteorology & atmospheric sciences
[SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP]
FOS: Physical sciences
Context (language use)
Astrophysics
01 natural sciences
methods: numerical
Impact crater
Angular diameter
0103 physical sciences
medicine
Iris (anatomy)
010303 astronomy & astrophysics
0105 earth and related environmental sciences
Physics
Earth and Planetary Astrophysics (astro-ph.EP)
[SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph]
Collisional family
Astronomy and Astrophysics
15. Life on land
medicine.anatomical_structure
13. Climate action
Space and Planetary Science
Asteroid
[SDU]Sciences of the Universe [physics]
minor planets
asteroids: individual: 7 Iris
methods: observational
Astrophysics - Earth and Planetary Astrophysics
Subjects
Details
- Language :
- English
- ISSN :
- 00046361
- Database :
- OpenAIRE
- Journal :
- Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, 2019, 624, pp.A121. ⟨10.1051/0004-6361/201834541⟩, Astronomy and Astrophysics-A&A, EDP Sciences, 2019, 624, pp.A121. ⟨10.1051/0004-6361/201834541⟩, Astronomy & Astrophysics
- Accession number :
- edsair.doi.dedup.....15cf194c598010a6370e769b4e20775a