(704) Interamnia: a transitional object between a dwarf planet and a typical irregular-shaped minor body

Hanuš, J. and Vernazza, P. and Viikinkoski, M. and Ferrais, M. and Rambaux, N. and Szakáts, Róbert (2020) (704) Interamnia: a transitional object between a dwarf planet and a typical irregular-shaped minor body. ASTRONOMY & ASTROPHYSICS, 633. ISSN 0004-6361

Preview

Text 1911.13049.pdf Download (7MB) | Preview

Abstract

Context. With an estimated diameter in the 320-350 km range, (704) Interamnia is the fifth largest main belt asteroid and one of the few bodies that fills the gap in size between the four largest bodies with D > 400 km (Ceres, Vesta, Pallas and Hygiea) and the numerous smaller bodies with diameter ≤200 km. However, despite its large size, little is known about the shape and spin state of Interamnia and, therefore, about its bulk composition and past collisional evolution. Aims: We aimed to test at what size and mass the shape of a small body departs from a nearly ellipsoidal equilibrium shape (as observed in the case of the four largest asteroids) to an irregular shape as routinely observed in the case of smaller (D ≤ 200 km) bodies. Methods: We observed Interamnia as part of our ESO VLT/SPHERE large program (ID: 199.C-0074) at thirteen different epochs. In addition, several new optical lightcurves were recorded. These data, along with stellar occultation data from the literature, were fed to the All-Data Asteroid Modeling algorithm to reconstruct the 3D-shape model of Interamnia and to determine its spin state. Results: Interamnia's volume-equivalent diameter of 332 ± 6 km implies a bulk density of ρ = 1.98 ± 0.68 g cm-3, which suggests that Interamnia - like Ceres and Hygiea - contains a high fraction of water ice, consistent with the paucity of apparent craters. Our observations reveal a shape that can be well approximated by an ellipsoid, and that is compatible with a fluid hydrostatic equilibrium at the 2σ level. Conclusions: The rather regular shape of Interamnia implies that the size and mass limit, under which the shapes of minor bodies with a high amount of water ice in the subsurface become irregular, has to be searched among smaller (D ≤ 300 km) less massive (m ≤ 3 × 1019 kg) bodies. The reduced images are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr bin/cat/J/A+A/633/A65 Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program 199.C-0074 (PI: Vernazza).

Actions (login required)

Edit Item