Daily variability of Ceres' Albedo detected by means of radial velocities changes of the reflected sunlight

TL;DR

This study detects short-term and diurnal albedo variability on Ceres by analyzing radial velocity changes in reflected sunlight, revealing complex brightness dynamics linked to surface features and solar exposure.

Contribution

It demonstrates the use of high-precision radial velocity measurements to monitor and analyze Ceres' surface albedo variability over hours to months.

Findings

Radial velocity modulation of about +/- 6 m/s linked to Ceres' rotation.

Detection of unexpected diurnal effects indicating surface brightness changes.

Confirmation that radial velocity observations can track short-term albedo variability.

Abstract

Bright features have been recently discovered by Dawn on Ceres, which extend previous photometric and Space Telescope observations. These features should produce distortions of the line profiles of the reflected solar spectrum and therefore an apparent radial velocity variation modulated by the rotation of the dwarf planet. Here we report on two sequences of observations of Ceres performed in the nights of 31 July, 26-27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m La Silla ESO telescope. The observations revealed a quite complex behaviour which likely combines a radial velocity modulation due to the rotation with an amplitude of approx +/- 6 m/s and an unexpected diurnal effect. The latter changes imply changes in the albedo of Occator's bright features due to the blaze produced by the exposure to solar radiation. The short-term variability of Ceres' albedo is on timescales ranging from hours to months and can both be confirmed and followed by means of dedicated radial velocity observations.