Mars, now dry and extremely cold planet, may have had ancient lakes or seas of water, according to new evidence and interpretations presented by scientists at the Jet Propulsion Laboratory.
Studying photos of Martian terrain taken by NASA's Viking Orbiter spacecraft from 1976 to 1981, researchers have identified features that resemble islands, sandbars and shorelines on Earth. The lakes or seas were formed in Mars' northern lowlands as result of massive floods which created the large Martian channels some 2 billion to 3 billion years ago.
Most of the photos, however, lack sufficient resolution to allow detailed study of what may have been ancient Martian beaches and shorelines. For that reason -- and because wide disagreement remains in the scientific community over Mars' geological past -- the researchers are careful to label their concept as hypothesis that may not be settled until future missions produce new images or data.
The hypothesis is described in paper by JPL research geologists Timothy Parker, Dale Schneeberger, David Pieri and Stephen Saunders, presented recently at Washington, D.C., conference on Mars's climatic evolution.
While some scientists have suggested that the large channels on Mars could have been formed by volcanic lava, ice or wind, most agree that they were probably created by groundwater released when the overlying rock suddenly collapsed. Most of the channels empty into large, seemingly featureless plains.
As Parker and his colleagues studied images of the regions at channel mouths, the question remained of what happened to the water as it reached the ends of the channels. If the floodwaters, carrying along large quantities of sediment, soaked into the ground, they should have left behind deposits similar to enormous alluvial fans. No channeling common on alluvial fans on Earth, however, can be seen in the Viking images.
If the water had collected in the Martian lowlands to form sea, on the other hand, it should have left delta- like deposits at the channel mouths. Such deposits should be relatively thin and widespread, because of both the nature of the flooding and Mars' lower gravity. (The gravity on Mars is about one-third Earth's.)
That prompted Parker and his colleagues to study landforms at the edges of the plains to determine if any resembled features typically found along the shores of lakes and oceans on Earth. They eventually came up with several sites that seem to support their hypothesis.
One site is in Cydonia Mensae, region in Mars' northern hemisphere, marked by clusters of eroded mountains and mesas connected by curved ridges. Parker says they are "strikingly similar" to groups of islands on Earth linked by coastal barriers and sandbars.
Another example is an eroded crater in Acidalia Planitia, region west of the first site. The crater's rim has been eroded into loose, broken chain of mountain-like knobs. The shape of the knobs -- unique to the Martian lowland plains -- could possibly have been produced by wave action, the researchers believe.
A third region the geologists cited is what could be evidence of an actual shoreline in Deuteronilus Mensae, another area of eroded mesas along the lowland margin in Mars' northern hemisphere.
Photographs from Mars Observer, NASA mission scheduled for launch in August 1990, may provide additional detail to study the features more closely.
The paper was presented at symposium on Martian climate and atmosphere co-sponsored by the Lunar and Planetary Institute and the National Air and Space Museum.
The JPL research is sponsored by NASA's Office of Space Science and Applications.