\begin{table}%t3
\caption{\object{Saturn} and \object{Uranus} physical characteristics      \citep{1992AJ....103..967L,1987JGR....9215003C,2000Icar..144..124C,1997AetA...321L..13D,1995Icar..114..328B}.}\label{planets} 
%\centering
\small
    \begin{tabular}{c c c}
    \hline\hline	
                          & \object{Saturn}        & \object{Uranus}        \\
    \hline
    Rotation period       & 10.2 h         & 17.9 h        \\
    Equatorial radius     & 60~268 km     & 25~559 km     \\
    Polar radius          & 54~364 km     & 24~973 km     \\
    H$_2$ molar fraction  & 0.8606        & 0.8320        \\
    He molar fraction     & 0.135         & 0.152         \\
    CH$_4$ molar fraction & 4.4 $\times$ 10$^{-3}$ & 1.6 $\times$ 10$^{-4}$ \\
    \hline				     
    \end{tabular}
  \end{table}