  Solar neutrinos upscattering inside the Earth can source unstable particles
that can decay inside terrestrial detectors. Contrary to naive expectations we
show that when the decay length is much shorter than the radius of the
\emph{Earth} (rather than the detector), the event rate is independent of the
decay length. In this paper we study a transition dipole operator (neutrino
dipole portal) and show that Borexino's existing data probes previously
untouched parameter space in the 0.5--20 MeV regime, complementing recent
cosmological and supernova bounds. We briefly comment on similarities and
differences with luminous dark matter and comment on future prospects for
analogous signals stemming from atmospheric neutrinos.
