We present intermediate-resolution ( R=1500 ) near-infrared spectroscopy from 1.17 \mu m to 1.37 \mu m of the spectral type T planetary candidate member in the \sigori cluster S Ori 70 reported by Zapatero Osorio et al .
( 2002 ) .
The new data have been obtained with NIRSPEC at the Keck II telescope .
The best fit of our mid-resolution spectrum of S Ori 70 with theoretical spectra gives log g=3.5 \pm 0.5 cm s ^ { -2 } and T _ { eff } =1,100 ^ { +200 } _ { -100 } K. The low gravity of this object derived from spectral synthesis supports its youth and membership to the young \sigori cluster .
Using evolutionary models for an age of 3 Myr , we obtain a mass of 3 M _ { Jup } and a radius of 0.16 R _ { \odot } , independent of the distance to the object .
Our analysis confirms that S Ori 70 is the lowest mass cluster planet so far identified in the galaxy .