Magnetic data is one of the most common geophysics datasets available on the surface of the Earth. At long wavelengths it pertains information on the depth at which rocks lose their magnetism. This is called the Curie depth - often interpreted as the 580C isotherm, which is the Curie point of magnetite. In this talk I will outline the methodologies to compute Curie depth and the resolution of thermal structures it can detect. The ongoing acquisition of the magnetic anomaly by Tellus presents a unique opportunity to glean precise estimates of the 580C isotherm, which can be assimilated into large scale thermo-chemical models of the lithosphere.