NASA - National Aeronautics and Space Administration

In 2000, the Mars science community received its first images from the Mars Orbiter Camera, as part of the Mars Global Surveyor mission. These scientists were impressed by the deep V-shaped gullies on Mars' surface, and soon started imagining how they could have formed.

Presently, the most popular scientific theory is that underground water surfaced and spilled onto the slopes to carve out the gullies. Because liquid water is a key prerequisite for life, scientists soon began to speculate on the existence of life on Mars. However, before scientists can hypothesize about life on Mars, they must first explain how liquid water can exist in such a cold, dry place.

Left: Researcher Darlene Lim sampling water from a lake on Devon Island, Nunavut. Photo credit: Marc Webb.

To search for clues, researchers traveled to the most Mars-like conditions on Earth. "We went to Earth's polar regions because they provide the best analogs for possible martian hydrology. By studying the springs, rivers and streams, we were able to develop models that show how liquid water could have persisted on Mars in freezing conditions," said Chris McKay, lead research scientist at NASA's Ames Research Center, Moffett Field, Calif.

Scientists believe that Mars during its earliest phase was quite cold, even when it was wet. To help understand how liquid water persisted in freezing conditions, scientists decided to study water cycles of the polar regions and to compare physical and geological findings to possible martian counterparts. Areas included the Axel Heiberg Island in the Canadian High Arctic and the McMurdo Dry Valleys of Antarctica. Both sites have temperatures that range from -15 to -30 degrees Celsius and very little rainfall that creates desert-like conditions.

Most of the year, the Axel Heiberg Island is only 5 degrees Fahrenheit (-15 degrees C.), causing the soil temperature to drop to or below the freezing point of water, and is referred to as a continuous permafrost. The area is so cold that the permafrost measures nearly one half mile (600 m.) thick.

Right: Researchers retrieving sediment cores from an unexplored lake on Banks Island, N.W.T. Sediment is collected from lakes and ponds to track environmental change in the Arctic. Photo credit: Darlene Lim.

Two springs on the island have salinity values five times that of seawater. Analysis of the spring water indicated that the source of water is equal parts glacial melt and lake water. Scientists explain this phenomenon by tracking the spring water as it flowed through a permeable subsurface of concentrated salt beds that lay beneath the lakes, glaciers and ice-caps.

At this depth, the groundwater temperature was freezing, but it continued to flow below the surface to a depth of nearly one-half mile, warmed by the internal heat of the Earth of up to 40 degrees Fahrenheit (6 degrees Celsius). The water traveled fast enough to the surface that the temperature did not change significantly. Surprisingly, scientists report that the Arctic springs on the Axel Heiberg Island flow all year with little temperature variation.

The McMurdo Dry Valleys of Antarctica are the largest ice-free region on the continent. The valleys have large, perennial ice-covered lakes that are fed by glacial meltwater in the summertime. Temperatures range from -15 to -30 degrees Celsius and are only a few degrees above freezing in the summer. Annually, water precipitation measures less than an inch (1-2 cm) and is mostly snow. "This is the most Mars-like climate on Earth," said McKay.

Scientists report that despite these conditions, these valleys actively cycle water into a large ice-covered lake that has rich microbial communities on the lake bottom, in the liquid water, and within the ice cover. According to McKay, enough light penetrates the ice cover to allow photosynthesis.

Research suggests that the dry valley water cycle begins with snow at high altitudes that accumulates as glaciers and melts in the summer. When temperatures rise above freezing the meltwater flows into the lowest point in the valleys and forms lakes. Although the lakes are perennially ice-covered, they are not frozen solid.

Above: The myriad of lakes and ponds in the Canadian High Arctic are important to understanding past, present and future environmental conditions. These aquatic systems are under-going ecological change in response to recent global warming. Photo credit: Darlene Lim; captured on Banks Island, NWT.

"Liquid water is maintained beneath ice-covered lakes by the energy generated from actively flowing meltwater. Additional energy is released when the water freezes at the bottom of the ice cover," McKay explained. "The ice is maintained at a steady thickness because the water freezes at the same rate as the ice surface evaporates and erodes. The key to the existence of such ice-covered lakes is summer temperatures rising above freezing and the constant supply of water from glacier snowmelts."

To predict the existence of permanently ice-covered lakes on early Mars, scientists have applied Earth's polar water-habitats models to such Mars features as the Gusev Crater, which may have been an ice-covered lake at one time. Modeling results suggest that ice-covered lakes on Mars could have occurred. "Even if average temperatures on Mars were never above freezing and there was never any rain on Mars, the large ice-covered lakes could have existed due to water levels being restored by snow," said McKay.

Scientists developed and applied a dry-valley model to the Chryse region of Mars as well. In this model, moisture from evaporated ice accumulates to form glaciers, which provides a source of meltwater that flows into valley lakes. Mars studies suggest that evidence for life would be in sediments from such lake deposits. McKay adds that it is important to note that such lakes on Mars today could never exist, due to the low pressure which causes ice to evaporate, rather than melt.

Right: Captured on Banks Island, Nunavut. Photo credit: Darlene Lim.

Scientists believe that liquid water produced by summer melts could have persisted on Mars, even when temperatures were freezing, floating ice would have insulated the liquid water. According to scientists, life flourishes in these liquid habitats on Earth, and similarly life may have been present in ice-covered lakes and permafrost springs on Mars.

"Evidence for past life on Mars may therefore be preserved in the sediments and mineral precipitates related with these features," said McKay.

These and related studies appeared in the Advances in Astrobiology and Biogeophysics, 2005.

For further information, please visit:

http://www.marsonearth.org/

http://www.nasa.gov/home

Ruth Marlaire
NASA Ames Research Center