  High resolution images of Mercury's surface, from the MESSENGER spacecraft,
reveal many bright deposits associated with irregular, shallow, rimless
depressions whose origins were attributed to volatile-related activity, but
absent information on the nature and origin of that volatile matter. Here I
describe planetary formation, unlike the cited models, and show that primordial
condensation from an atmosphere of solar composition at pressures of one
atmosphere or above will lead to iron condensing as a liquid and dissolving
copious amounts of hydrogen, which is subsequently released as Mercury's core
solidifies and escapes from the surface, yielding the observed pit-like
features with associated highly-reflecting matter. The exiting hydrogen
chemically reduces some iron compound, probably iron sulfide, to the metal,
which accounts for the bright deposits.
