In some places, the water-ice content is more than 90 percent by volume, reports Odyssey's Igor Mitrofanov of the Russian Space Research Institute, Moscow, in the June 27 issue of the journal Science. He and his co-researchers assessed MGS laser altimeter data taken more than two years ago to explore the implications of the seasonal changes.

Another report, to be published in the Journal of Geophysical Research-Planets, combines measurements from the two Mars orbiting probes to provide indications of how densely the winter layer of carbon-dioxide frost or snow is packed at northern latitudes greater than 85 degrees. William Feldman of Los Alamos National Laboratory in New Mexico led that study.

Feldman and his associates also found that, once the dry ice disappears, the remaining surface near the pole is composed almost entirely of water ice.

Meanwhile Mars researchers James Head of Brown University and David Marchant of Boston University report that cold-based mountain glaciers exist on the red planet.

In the July issue of the Geological Society of Americas magazine, Geology, they provide evidence that large cold-based mountain glaciers existed on the flanks of the large Tharsis Montes equatorial volcanoes in the recent geological past.

Using newly acquired MGS data, backed by a trek to Antarctica, the investigators point to Arsia Mons, Tharsis Rise as the site of mountain glacier formation. Moreover, deposits there may still contain glacial ice below the surface and thus hold the record of ancient climatic conditions on Mars. Such deposits may provide water resources for future human explorers, the Mars experts suggest.