This image taken by the Mars Reconnaissance Orbiter shows the rock debris pattern that scientists believe was left by a glacier that rose at least one kilometer from the surrounding plain and flowed into the canyon.
A vanished glacier with a mysterious calling card suggests Mars went through many ice ages in its very recent past.
A fresh look at images from the Mars Reconnaissance Orbiter indicates thick glaciers may have existed in the past 100 million years in the planet's equatorial region, but vanished after planetary wobbles changed the climate in certain areas.
"We've gone from seeing Mars as a dead planet for three-plus billion years to one that has been alive in recent times," said Jay Dickson, a geologist at Brown University and lead author of the study. "[The finding] has changed our perspective from a planet that has been dry and dead to one that is icy and active."
Dickson and other researchers looked at a dead-ended box canyon that slopes down into a larger valley, and discovered glacial deposits of rocks marking a glacier's advance heading upslope into the canyon ? something which seems physically impossible.
Here's how it happened, according to the team's calculations: An ice pack at least .62 miles (1 kilometer) thick filled the larger valley to a height exceeding that of the box canyon walls. Glacial ice flowed in the larger valley upstream of the box canyon. So when the glacier reached the box canyon, the ice actually pushed uphill into it.
When the glacier ice retreated, it left behind the mystery of the box canyon and a freshly-paved surface that suggests a recent event.
"We don't see many craters on the glacial deposits," Dickson told SPACE.com. "That's a yardstick we can use for measuring geological age."
Craters on Mars, caused by meteor impacts, remain for hundreds of millions of years, and their prevalence in an area can, like a wrinkled face, indicate an old surface. Newer surfaces lack the multitudes of scars.
The finding further suggests that Mars has endured repeated periods of glacial activity instead of just one single event, Dickson said, whose new work on this topic is detailed in the May issue of the journal Geology.
The past presence of glaciers could also spark further debate about whether water flowed recently on Mars, given that pressure from the weight of glaciers can melt ice. However, no direct evidence of recent flowing water has been found.
"We don't yet see evidence for melt water at this location, but the fact that there was so much ice here expands our understanding of how active Mars climate has been," said Dickson.
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