Researchers creating scenarios for the ancient climate on Mars suggest that a cold, icy and frozen environment, rather than warm, Earth-like oceans, can best account for the surface features seen on the Red Planet today.
Features suggesting erosion and water drainage existing today have led many to suggest that the Mars of 3 billion to 4 billion years in the past was wet and warm, with liquid oceans, conditions that may have made the development of life possible.
However, some scientists have argued that Mars has for the most part possessed an icy, frigid character that kept most of whatever water the planet had locked in frozen masses in which life would have difficulty in evolving.
In an effort to determine which scenario may have been more likely, researchers at Harvard University created a 3D model of atmospheric circulation that could compare different scenarios of an ancient water cycle on the Red Planet.
Given what is understood of the history of our sun and of the tilt of the axis of Mars all those billions of years ago, the frozen scenario appears more likely than a warm, liquid one, the researchers report in the Journal of Geophysical Research -- Planets.
Mars only receives 43 percent of the amount of solar energy the Earth gets, and the sun in the skies of early Mars is thought to have been some 25 percent dimmer than it is today, they point out.
A frigid frozen past also better explains water erosion features seen today on Mars, they add, because the extreme tilting of the axis of Mars axis would have aimed the planet's poles at the sun and thus pushed polar ice toward the equator -- exactly where erosion and water drainage features are observed today.
Although the cold/icy climate scenario leaves a lot of questions unanswered, it's a better match with the results seen on Mars today, says Robin Wordsworth of Harvard's Paulson School of Engineering and Applied Sciences.
"I'm still trying to keep an open mind about this," he says. "But our results show that the cold/icy scenario matches the surface distribution of erosion features more closely.
Much more study remains to be done, he acknowledges.
Other experts agree, including planetary scientist Bethany Ehlmann at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who was not involved in the study.
There remains a "big question" of whether a cold and frozen climate in the early life of the Red Planet led to the features seen there today, she says.
The accumulation of snow in the frigid and icy scenario does correspond roughly to erosion-caused valley networks seen today, she notes, but that doesn't completely rule out the possibility of liquid water having a role.
"We know from rover- and orbiter-based data that there were lakes on ancient Mars," she says. "Key questions are: how long did they persist? Were they episodic or persistent? And does the feeder valley network demand rain or is snow and ice melt sufficient?"
Those kinds of questions likely will keep scientists mulling the possible climates of ancient Mars for some time to come.
