Surface Albedo and Spectral Variability of Ceres

Kavli Affiliate: Maria T. Zuber

| First 5 Authors: Jian-Yang Li, Vishnu Reddy, Andreas Nathues, Lucille Le Corre, Matthew R. M. Izawa

| Summary:

Previous observations suggested that Ceres has active but possibly sporadic
water outgassing, and possibly varying spectral characteristics in a time scale
of months. We used all available data of Ceres collected in the past three
decades from the ground and the Hubble Space Telescope, and the newly acquired
images by Dawn Framing Camera to search for spectral and albedo variability on
Ceres, in both a global scale and local regions, particularly the bright spots
inside Occator crater, over time scales 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 Occator crater by >15%, or the global albedo by >3% over various
time scales 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, rulling out the
possibility of comet-like sublimation process as a possible mechanism driving
the activity.

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