Probing the Earth with weakly interacting massive particles

Weakly interacting massive particles (WIMP's) with masses approx. >1 GeV are candidates for the dark matter in galactic halos. We discuss the distribution and detectability of coherently interacting particles (such as massive Dirac or scalar neutrinos, solar cosmions, and some Majorana fermions) that have been captured into orbits within the Earth. Coherent WIMP's in the mass range from 8 to 21 GeV in Earth orbits would give rise to count rates approx.(1--1000/kg eV day) in proposed cryogenic detectors operating at thresholds approx.1 eV. Over this mass and energy range, these rates are several orders of magnitude larger than those for direct detection of the corresponding particles coming from the halo. Since they orbit through the Earth's core, these Earth-bound WIMP's can be used to probe the temperature structure of the Earth's interior. The temperature of the Earth's inner core can be determined to within 300 K, compared with the present 1000--2000 K uncertainty.