Radio-interferometric imaging of the subsurface emissions from the planet Mercury

Abstract

Mercury is the least studied of the terrestrial planets. Its interior and subsurface properties are still largely unknown. The subsurface can be probed at microwave frequencies where the electrical skin depth is ∼70 cm at 5 GHz¹. Previous ground-based observations^2,3 were unable to resolve details of Mercury's disk, and Mariner 10 did not carry a microwave radiometer. The Very Large Array (VLA) was used to make the first centimetre-wavelength interferometric observations that resolve the disk. We have mapped the distribution of total and polarized intensities from the planet's subsurface layers. We report the first detection of a hot pole along the hermean equator, which we model as black-body reradiation from preferential diurnal heating. These observations appear to rule out any internal sources of heat within Mercury. We also find polarized emission from the limb of the planet, which is understood in terms of the dielectric properties of the hermean surface.