Washington, March 20 : A new study has suggested that melting snow may have formed a large number of Martian gullies sometime in the past few million years.
According to a report in National Geographic News, gullies were first discovered on Mars eight years ago, and experts have been debating since then about what created them.
Despite initial theories that they might be proof of liquid water on modern Mars, the most recently formed gullies appear to have been made by dry landslides.
But experts agree that older gullies on the red planet were most likely carved by a fluid.
According to planetary scientist Jay Dickson of Brown University, recent evidence supports this theory-originally suggested several years ago-that these gullies were created by melting snow.
Dickson and colleague James Head III, also at Brown University, combined existing data with the latest high-resolution images to catalog the types of terrain on which the gullies formed.
They observed that the gullies tend to appear on slopes facing toward the equator in one range of latitudes and toward the pole at another range.
"The gullies also occurred only at elevations that would be conducive to ice and snow accumulating on the ground and then melting," said Dickson.
That means the climate of Mars has been much more variable in the past few hundred million years than was once believed.
"We see evidence for this in other areas," Dickson said, such as signs of now-vanished glaciers.
In fact, recent findings suggest that orbital variations cause Mars to change its tilt periodically, creating a cycle of ice ages like the one on Earth.
Currently, the red planet rotates on its axis at a 23-degree angle toward the sun. But in the past, it sometimes hit an angle of 45 degrees or more.
Each time the angle changed, climate would have altered across Mars.
Polar summers would have gotten warmer, melting ice at the poles and creating precipitation in the form of snow that fell at locations where the gullies are now seen.
"That's what the physics says, and we're seeing that in the glaciers and gullies we feel have been formed by melting snow," said Dickson.