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

Publication date: 
Main author: 
Hanuš, J.
IAA authors: 
Duffard, R.
Hanuš, J.;Vernazza, P.;Viikinkoski, M.;Ferrais, M.;Rambaux, N.;Podlewska-Gaca, E.;Drouard, A.;Jorda, L.;Jehin, E.;Carry, B.;Marsset, M.;Marchis, F.;Warner, B.;Behrend, R.;Asenjo, V.;Berger, N.;Bronikowska, M.;Brothers, T.;Charbonnel, S.;Colazo, C.;Coliac, J. -F.;Duffard, R.;Jones, A.;Leroy, A.;Marciniak, A.;Melia, R.;Molina, D.;Nadolny, J.;Person, M.;Pejcha, O.;Riemis, H.;Shappee, B.;Sobkowiak, K.;Soldán, F.;Suys, D.;Szakats, R.;Vantomme, J.;Birlan, M.;Berthier, J.;Bartczak, P.;Dumas, C.;Dudziński, G.;Ďurech, J.;Castillo-Rogez, J.;Cipriani, F.;Fetick, R.;Fusco, T.;Grice, J.;Kaasalainen, M.;Kryszczynska, A.;Lamy, P.;Michalowski, T.;Michel, P.;Santana-Ros, T.;Tanga, P.;Vachier, F.;Vigan, A.;Witasse, O.;Yang, B.
Astronomy and Astrophysics
Publication type: 
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 &gt; 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. <BR /> 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. <BR /> 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. <BR /> Results: Interamnia's volume-equivalent diameter of 332 ± 6 km implies a bulk density of ρ = 1.98 ± 0.68 g cm<SUP>-3</SUP>, 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. <BR /> 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 × 10<SUP>19</SUP> kg) bodies. <P />The reduced images are only available at the CDS via anonymous ftp to <A href='http://cdsarc.u-strasbg.fr'>http://cdsarc.u-strasbg.fr</A> ( or via <A href='http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/633/A65'>http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/633/A65</A> <P />Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program 199.C-0074 (PI: Vernazza).
ADS Bibcode: 
minor planets;asteroids: individual: (704) Interamnia;methods: observational;techniques: high angular resolution;techniques: photometric