Surface Albedo and Spectral Variability of Ceres

Abstract

Previous observations suggested that Ceres has active, but possibly sporadic, water outgassing as well as possibly varying spectral characteristics over a timescale of months. We used all available data of Ceres collected in the past three decades from the ground and the Hubble Space Telescope, as well as the newly acquired images by the Dawn Framing Camera, to search for spectral and albedo variability on Ceres, on both a global scale and in local regions, particularly the bright spots inside the Occator crater, over timescales of a few months to decades. Our analysis has placed an upper limit on the possible temporal albedo variation on Ceres. Sporadic water vapor venting, or any possibly ongoing activity on Ceres, is not significant enough to change the albedo or the area of the bright features in the Occator crater by >15%, or the global albedo by >3% over the various timescales that we searched. Recently reported spectral slope variations can be explained by changing Sun-Ceres-Earth geometry. The active area on Ceres is less than 1 km 2 , too small to cause global albedo and spectral variations detectable in our data. Impact ejecta due to impacting projectiles of tens of meters in size like those known to cause observable changes to the surface albedo on Asteroid Scheila cannot cause detectable albedo change on Ceres due to its relatively large size and strong gravity. The water vapor activity on Ceres is independent of Ceres' heliocentric distance, ruling out the possibility of the comet-like sublimation process as a possible mechanism driving the activity.

Cryovolcanism on Ceres

“…The Framing Camera is equipped with filters covering the range 0.4 mm to 1.0 mm (12) for multi-spectral analyses. We used the global average photometric models of Ceres derived from 400 m/pixel data (46) to correct the local scattering geometry to incidence angle 30°, emission angle 0°, and phase angle 30°and remove the effect of local topography in~135 m/pixel images (Fig. 4A).…”

Thermal Evolution of the Impact‐Induced Cryomagma Chamber Beneath Occator Crater on Ceres

“…Here we are interested in the origin of the bright salt-rich surface deposits called faculae, which are observed widely on Ceres' surface (De Sanctis et al, 2016;Li et al, 2016;Longobardo et al, 2018;Stein et al, 2017). The faculae associated with large impact craters have been preferentially related to the brine reservoir located at the base of the crust (Buczkowski et al, 2018;Nathues et al, 2018;Quick et al, 2018).…”

The Formation and Evolution of Bright Spots on Ceres

“…The average geometric albedo measured by Dawn's Visible and Infrared spectrometer (VIR) at 0.55 μm is 0.094 ± 0.008, and the average bond albedo measured with the Framing Camera (FC) clear filter is 0.034 ± 0.001 Ammannito et al, 2016;Li et al, 2016 ). Ceres' dark surface materials, whose reflectance ranges between located in the central pit and floor of Occator crater and were visible upon Dawn's approach to Ceres ( Nathues et al, 2015( Nathues et al, , 2017a.…”