Mars at tail-end of ice age that would
have seen red planet covered in ice
Close-up images of the north pole were combined with radar data to develop picture of Mars' ice age.
Mars is at the tail-end of an ice age that would have seen large swathes of the dusty red planet covered with ice.
Radar data from an instrument on board the Mars Reconnaissance Orbiter has given scientists an unprecedented glimpse into Mars' recent climatic history, etched into the layers of its northern polar ice cap.
The study of those ice layers, published today in Science, suggests the last ice age on Mars began retreating about 370,000 years ago.
Ice ages have long been predicted for Mars, based on a combination of the planet's changing tilt and its variable distance from the Sun — similar to the cycles that impact the Earth's climate over tens of thousands to hundreds of thousands of years.
But lead author and planetary scientist Dr Isaac Smith said this is the first time scientists have been able to see the evidence of these cycles in the northern polar ice cap.
"To think that this beautiful ice cap records the layers and the history of Mars is really cool," Dr Smith said.
Understanding how ice accumulated on the planet in relation to its tilt and orbit around the Sun can provide insights into how the Martian climate changed over time.
Anatomy of a Martian ice age
Ice ages on Mars happen quite differently to those on Earth, said Dr Smith, with factors such as the planet's tilt, which changes by as much as 60 degrees, the absence of atmosphere, oceans, and biology all playing a part.
"On Earth, when we have an ice age, it's because the poles get very cold and and when you build up a lot of ice at the north pole, it will start to flow outward towards Canada, US or if you're in the southern hemisphere it will flow northward through Africa and Australia," said Dr Smith, from the Southwest Research Institute in Boulder, Colorado.
"But on Mars it's the opposite; when it's really cold at the north pole, of course it accumulates, but it kind of sticks to the north pole and doesn't spread out."
Then when the north pole of Mars warms, that ice has to go somewhere but because it doesn't have oceans to melt into like on Earth, the ice instead spreads out across the surface of Mars, Dr Smith said.
"What that means is the ice covers more of the planet when the pole is warm."
Patterns in the lower layers of ice show where those layers have become exposed and have retreated in between Martian surface features.
These eroded layers of ice are then re-covered by continuous layers as the north pole cools and ice begins to build up again.
The radar carried aboard the Orbiter, 300 kilometres above the planet's surface, is able to penetrate to the very bottom of the ice cap, allowing scientists to build up a clear picture of features such as the spiral troughs and undulations in the layers of ice.
Dr Smith said the radar detects subtle changes in the composition of the different layers of ice, mainly due to changes in the amount of dust accumulating on the ice over different periods.
The red planet will turn white
While Mars' current ice age is in retreat, revealing the planet in its full crimson glory, Dr Smith said the next ice age will likely peak in around half a million years, covering the planet in ice once more.
"It will be whiter — it will be even brighter than it is now and it's really bright right now," he said.
The team are now hoping to look even deeper into the ice deposits at the northern pole for evidence of previous ice age cycles.
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