Ixlr8 sends in a BBC story suggesting that
up to half of Mars may have ice at varying depths below the surface. Quoting:
"Up until now, scientists had been able to search for water deposits using a spectrometer fixed to the orbiting Mars Odyssey spacecraft. However, only readings that are accurate to within several hundred kilometers can be obtained. By comparing seasonal changes in thermal infrared patterns, detected by the same Odyssey spacecraft, [scientists] can make readings accurate to within just hundreds of meters."