  Combining the resolving power of long-baseline interferometry with the
high-dynamic range capability of nulling still remains the only technique that
can directly sense the presence of structures in the innermost regions of
extrasolar planetary systems. Ultimately, the performance of any nuller
architecture is constrained by the partial resolution of the on-axis star whose
light it attempts to cancel out. However from the ground, the effective
performance of nulling is dominated by residual time-varying instrumental phase
and background errors that keep the instrument off the null. Our work
investigates robustness against instrumental phase. We introduce a modified
nuller architecture that enables the extraction of information that is robust
against piston excursions. Our method generalizes the concept of kernel, now
applied to the outputs of the modified nuller so as to make them robust to
second order pupil phase error. We present the general method to determine
these kernel-outputs and highlight the benefits of this novel approach. We
present the properties of VIKiNG: the VLTI Infrared Kernel NullinG, an
instrument concept within the Hi-5 framework for the 4-UT VLTI infrastructure
that takes advantage of the proposed architecture, to produce three
self-calibrating nulled outputs. Stabilized by a fringe-tracker that would
bring piston-excursions down to 50 nm, this instrument would be able to
directly detect more than a dozen extrasolar planets so-far detected by radial
velocity only, as well as many hot transiting planets and a significant number
of very young exoplanets.
