An observation of a mutual event between two satellites of Uranus

TL;DR

This paper reports the first observed mutual event between Uranus satellites, providing precise measurements that improve understanding of their orbits and physical characteristics.

Contribution

It presents the first observation of a mutual event between Uranus satellites and offers more precise measurements of their orbital parameters.

Findings

Mid-event time measured with 4 seconds precision

Impact parameter estimated at 500 +/- 80 km

Measurements surpass current ephemerides accuracy

Abstract

We present observations of the occultation of Umbriel by Oberon on 4 May, 2007. We believe this is the first observed mutual event between satellites of Uranus. Fitting a simple geometric model to the lightcurve, we measure the mid-event time with a precision of 4 seconds. We assume previously measured values for the albedos of the two satellites (Karkoschka 2001), and measure the impact parameter to be 500 +/- 80 km. These measurements are more precise than estimates based on current ephemerides for these satellites. Therefore observations of additional mutual events during the 2007-2008 Uranian equinox will provide improved estimates of their orbital and physical parameters.