  Geo-neutrino detection will determine the amount of long lived radioactive
elements within our planet and fix the debated radiogenic contribution to the
terrestrial heat. In addition, it will provide a direct test of the Bulk
Silicate Earth model, a fundamental cosmochemical paradigm about the origin of
the Earth. Unorthodox models of Earth's core (including the presence of
potassium or the possibility of a giant reactor) can also be checked. This
short review presents status and prospects of the field.
