The Mutual Orbit, Mass, and Density of the Large Transneptunian Binary System Varda and Ilmar\"e

TL;DR

This study determines the mutual orbit, mass, and density of the transneptunian binary system Varda and Ilmarë using multiple telescopes, revealing insights into its physical properties and composition.

Contribution

First precise measurement of the mutual orbit, mass, and density of the Varda-Ilmarë system from high-resolution telescope observations.

Findings

Mutual orbit period of 5.75 days with a semimajor axis of 4810 km.

System mass estimated at approximately 2.664 x 10^20 kg.

Bulk density of the system determined to be about 1.24 g/cm^3.

Abstract

From observations by the Hubble Space Telescope, Keck II Telescope, and Gemini North Telescope, we have determined the mutual orbit of the large transneptunian object (174567) Varda and its satellite Ilmar\"e. These two objects orbit one another in a highly inclined, circular or near-circular orbit with a period of 5.75 days and a semimajor axis of 4810 km. This orbit reveals the system mass to be (2.664 +/- 0.064) x 10^20 kg, slightly greater than the mass of the second most massive main-belt asteroid (4) Vesta. The dynamical mass can in turn be combined with estimates of the surface area of the system from Herschel Space Telescope thermal observations to estimate a bulk density of 1.24 +0.50 -0.35 g cm^-3. Varda and Ilmar\"e both have colors similar to the combined colors of the system, B-V = 0.886 +/- 0.025 and V-I = 1.156 +/- 0.029.