  The SHINE program is a large high-contrast near-infrared survey of 600 young,
nearby stars. It is aimed at searching for and characterizing new planetary
systems using VLT/SPHERE's unprecedented high-contrast and high-angular
resolution imaging capabilities. It also intends at placing statistical
constraints on the occurrence and orbital properties of the giant planet
population at large orbits as a function of the stellar host mass and age to
test planet formation theories. We use the IRDIS dual-band imager and the IFS
integral field spectrograph of SPHERE to acquire high-constrast coronagraphic
differential near-infrared images and spectra of the young A2 star HIP65426. It
is a member of the ~17 Myr old Lower Centaurus-Crux association. At a
separation of 830 mas (92 au projected) from the star, we detect a faint red
companion. Multi-epoch observations confirm that it shares common proper motion
with HIP65426. Spectro-photometric measurements extracted with IFS and IRDIS
between 0.95 and 2.2um indicate a warm, dusty atmosphere characteristic of
young low surface-gravity L5-L7 dwarfs. Hot-start evolutionary models predict a
luminosity consistent with a 6-12 MJup, Teff=1300-1600 K and R=1.5 RJup giant
planet. Finally, the comparison with Exo-REM and PHOENIX BT-Settl synthetic
atmosphere models gives consistent effective temperatures but with slightly
higher surface gravity solutions of log(g)=4.0-5.0 with smaller radii (1.0-1.3
RJup). Given its physical and spectral properties, HIP65426b occupies a rather
unique placement in terms of age, mass and spectral-type among the currently
known imaged planets. It represents a particularly interesting case to study
the presence of clouds as a function of particle size, composition, and
location in the atmosphere, to search for signatures of non-equilibrium
chemistry, and finally to test the theory of planet formation and evolution.
