We use data from five stellar occultations observed between 2013 and 2016 to constrain Chariklo ’ s size and shape , and the ring reflectivity .
We consider four possible models for Chariklo ( sphere , Maclaurin spheroid , tri-axial ellipsoid and Jacobi ellipsoid ) and we use a Bayesian approach to estimate the corresponding parameters .
The spherical model has a radius R = 129 \pm 3 km .
The Maclaurin model has equatorial and polar radii a = b = 143 ^ { +3 } _ { -6 } km and c = 96 ^ { +14 } _ { -4 } km , respectively , with density 970 ^ { +300 } _ { -180 } kg m ^ { -3 } .
The ellipsoidal model has semiaxes a = 148 ^ { +6 } _ { -4 } km , b = 132 ^ { +6 } _ { -5 } km and c = 102 ^ { +10 } _ { -8 } km .
Finally , the Jacobi model has semiaxes a =157 \pm 4 km , b =139 \pm 4 km and c =86 \pm 1 km , and density 796 ^ { +2 } _ { -4 } kg m ^ { -3 } .
Depending on the model , we obtain topographic features of 6-11 km , typical of Saturn icy satellites with similar size and density .
We constrain Chariklo ’ s geometric albedo between 3.1 % ( sphere ) and 4.9 % ( ellipsoid ) , while the ring I / F reflectivity is less constrained between 0.6 % ( Jacobi ) and 8.9 % ( sphere ) .
The ellipsoid model explains both the optical light curve and the long-term photometry variation of the system , giving a plausible value for the geometric albedo of the ring particles of 10 - 15 \% .
The derived Chariklo ’ s mass of 6-8 \times 10 ^ { 18 } kg places the rings close to the 3:1 resonance between the ring mean motion and Chariklo ’ s rotation period .