Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk

Aims: We aim to characterize the orbital and atmospheric properties of PDS 70 b, which was first identified on May 2015 in the course of the SHINE survey with SPHERE, the extreme adaptive-optics instrument at the VLT. Methods: We obtained new deep SPHERE/IRDIS imaging and SPHERE/IFS spectroscopic observations of PDS 70 b. The astrometric baseline now covers 6 years which allows us to perform an orbital analysis. For the first time, we present spectrophotometry of the young planet which covers almost the entire near-infrared range (0.96 to 3.8 micrometer). We use different atmospheric models covering a large parameter space in temperature, log(g), chemical composition, and cloud properties to characterize the properties of the atmosphere of PDS 70 b. Results: PDS 70 b is most likely orbiting the star on a circular and disk coplanar orbit at ~22 au inside the gap of the disk. We find a range of models that can describe the spectrophotometric data reasonably well in the temperature range between 1000-1600 K and log(g) no larger than 3.5 dex. The planet radius covers a relatively large range between 1.4 and 3.7 R_jupiter with the larger radii being higher than expected from planet evolution models for the age of the planet of 5.4 Myr. Conclusions: This study provides a comprehensive dataset on the orbital motion of PDS 70 b, indicating a circular orbit and a motion coplanar with the disk. The first detailed spectral energy distribution of PDS 70 b indicates a temperature typical for young giant planets. The detailed atmospheric analysis indicates that a circumplanetary disk may contribute to the total planet flux.