holt

The concealed glaciers extend for tens of miles from edges of mountains or cliffs and are up to one-half mile thick. A layer of rocky debris covering the ice may have preserved the glaciers as remnants from an ice sheet covering middle latitudes during a past ice age. “Altogether, these glaciers almost certainly represent the largest reservoir of water ice on Mars that’s not in the polar caps. Just one of the features we examined is three times larger than

by Thomas Minor

Jack Holt, research scientist at the Institute for Geophysics (UTIG), is currently researching Amazonian ice deposits on Mars, both at the polar caps and at the middle latitudes. Holt offered an update on his research in the Nov. 22, 2011 UTIG weekly seminar, “A New View of Ice on Mars: Viscous Fluid, Sedimentary Rock, and Paleoclimate Record.”

Holt and colleagues are using images captured by the Shallow Surface Radar (SHARAD), a piece of equipment provided by the Italian Space Agency for the Mars Reconnaissance Orbiter, to create a series of three-dimensional models of Martian ice deposits. These models have led to new insights about the composition of polar and mid- latitudinal ice deposits and they provide clues about past Martian climate.

Holt’s research on mid-latitudinal ice deposits focuses on Lobate Debris Aprons (LDAs) which are located between 30° and 60° latitude on Mars.  SHARAD images have shown that LDAs are topped with a thick layer of water ice and that there is no layering of materials within the LDAs. This suggests a homogenous composition, analogous to a glacier rather than an ice-lubricated debris flow. Other images captured by the Mars Reconnaissance Orbiter have shown markings on the surface of LDAs that suggest past surface flow.

Regarding Mars’ polar ice, Dr. Holt and his team have focused on the Planum Boreum region of the northern polar cap. SHARAD images show there are two distinct layers of the Planum Boreum, a sand-rich basal layer and an overlying 2km-thick layer of water ice known as a North Polar Layered Deposit (NPLD).  Modeling from SHARAD data, from a basal sliding model, and from a balanced flow model with ablation zone led to the conclusion that the internal stratigraphy of the Planum Boreum does not support the presence of past flow.

The evidence of flow on LDAs and lack of evidence of flow at the poles led Dr. Holt and his team to hypothesize that polar ice is younger than mid-latitude ice and has not experienced the same temperature history.