Strange Martian Spirals Explained

Jun 16, 2010 by Dauna Coulter
A 1972-era TV image of Mars' north polar cap.

Almost 40 years ago, NASA's Mariner 9 spacecraft relayed to Earth the first video images of Mars' northern polar ice cap, revealing a strange pattern of spiral swirls that has puzzled scientists ever since. Using new data from the Mars Reconnaissance Orbiter (MRO), researchers have finally uncovered the secrets of the troughs that snake through the ice cap like a spiraled maze.

Jack Holt of the University of Texas and his graduate student Isaac Smith used radar data from MRO's Shallow Subsurface Radar to crack the case. Examining the details of this new data set has laid open the cap's internal structure, revealing clues to the massive ice troughs' formation.

Apparently, the wind did it.

"Radar cross sections reveal layers of ice deposited throughout the ice cap's history," says Holt. "The size and shape of those layers indicate that wind has played a key role in creating and shaping the spiral troughs."

Not only does wind shape the spirals, but also it causes them to move. They rotate around the north pole, turning like a excruciatingly slow pinwheel, curiously enough, against the wind.

Alan Howard of the University of Virginia first suggested the ice trough migration model based on Viking spacecraft data back in 1982. His theory, that wind erosion and sunlight shape and move the troughs, was never widely accepted, but the new data supports it.

Smith explains the process: "Cold air from the top of the sweeps down the slope, gaining speed and picking up and ice particles along the way. As this wind blows across the trough and starts up the other slope (the cooler side, facing away from the sun), it slows and precipitates the ice it holds. All of this ice is deposited on this cool slope, building it up, so the trough actually grows and migrates, over time, against the wind."

The Coriolis force generated by Mars' rotation twists the winds sweeping down from the ice cap.

"That explains the troughs' spiral design," says Smith.

Similar formations can be found in Antarctic regions of Earth, but without the spiral shape.

"You don't see spirals in Earth's because local topography there prevents the winds from being steered by the Coriolis force."

The radar data have solved another icy mystery, too--the origin of Chasma Boreale.

Icy megadunes in Antarctica do not spiral like the ice troughs of Mars.

Chasma Boreale is a Grand Canyon-sized chasm that slashes through the midst of the spiraled troughs. Theories to date suggested that either wind erosion or a single melt event excavated Chasma Boreale within the past 5 to 10 million years.

"Not so," says Holt. "The MRO data clearly show the chasm formed [long before the spirals did] in a much older ice sheet dating back billions of years. Due to the shape of that ancient sheet, the chasm grew deeper as newer ice deposits built up around it. Winds sweeping across the ice cap likely prevented new ice from building up inside the chasm [so it never filled up]."

The radar data also revealed a second chasm matching Boreale in size.

"This chasm's never been seen before -- unlike Boreale, it did fill up with ice, probably because it's in a different location. Boreale is closer to the highest points of the ancient ice cap, where the winds are stronger and more consistent."

By discovering that both Chasma Boreale and the ice troughs were shaped by similar processes over different timescales, Holt and Smith answer some questions about Martian climate history. But they're also sparking new ones.

"For a long stretch of Martian history the ice layers were regular and uniform, then there was a distinct period when the spiral ice troughs got started," says Smith. "Something changed. There must have been a very fast (relatively speaking) and powerful change in climate. We still don't know what that change was."

"To figure that out, we need to look at the rest of Mars for evidence of other changes at that same time," says Holt. "This is just the tip of the ice berg."

Explore further: NASA image: Sunrise from the International Space Station

Related Stories

New structure found deep within West Antarctic Ice Sheet

Sep 23, 2004

Ice sheet more susceptible to change than previously thought Scientists have found a remarkable new structure deep within the West Antarctic Ice Sheet which suggests that the whole ice sheet is more susceptible to future ch ...

Scientists observe drumlin beneath ice sheet

Jan 23, 2007

Scientists have discovered a warehouse-sized drumlin – a mound of sediment and rock – actively forming and growing under the ice sheet in Antarctica. Its discovery, and the rate at which it was formed, sheds new light ...

Recommended for you

Cassini sees sunny seas on Titan

16 hours ago

(Phys.org) —As it soared past Saturn's large moon Titan recently, NASA's Cassini spacecraft caught a glimpse of bright sunlight reflecting off hydrocarbon seas.

Is space tourism safe or do civilians risk health effects?

19 hours ago

Several companies are developing spacecraft designed to take ordinary citizens, not astronauts, on short trips into space. "Space tourism" and short periods of weightlessness appear to be safe for most individuals ...

An unmanned rocket exploded. So what?

22 hours ago

Sputnik was launched more than 50 years ago. Since then we have seen missions launched to Mercury, Mars and to all the planets within the solar system. We have sent a dozen men to the moon and many more to ...

NASA image: Sunrise from the International Space Station

23 hours ago

NASA astronaut Reid Wiseman posted this image of a sunrise, captured from the International Space Station, to social media on Oct. 29, 2014. Wiseman wrote, "Not every day is easy. Yesterday was a tough one. ...

Copernicus operations secured until 2021

Oct 30, 2014

In a landmark agreement for Europe's Copernicus programme, the European Commission and ESA have signed an Agreement of over €3 billion to manage and implement the Copernicus 'space component' between 2014 ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

ChiRaven
2 / 5 (4) Jun 16, 2010
Undoubtedly global climate change. The Martians were putting too much CO2 into their atmosphere, and ... BOOM ... global catastrophe.
HealingMindN
3 / 5 (2) Jun 16, 2010
Undoubtedly global climate change. The Martians were putting too much CO2 into their atmosphere, and ... BOOM ... global catastrophe.


You mean they drilled too the same as BP? Boom, Pow!? Crap.
kevinrtrs
1 / 5 (4) Jun 17, 2010
Ahhh... the billions of years does the trick again on earth [ gives an explanation that cannot be verified in any way ].

But on Mars,
"Something changed. There must have been a very fast (relatively speaking) and powerful change in climate. We still don't know what that change was."

So now we're either waiting for the predictable asteroid strike or some Mars shattering quake [ can't be an EARTHquake since it's on Mars?] to provide the way out.

OK, I'm just being cynical here. It's good that they have put forward some theory to explain what formed those patterns - I just hope they stay honest.
mysticshakra
1 / 5 (3) Jun 17, 2010
In order to STAY honest, wouldn't they have to start out honest?
Royale
5 / 5 (1) Jun 17, 2010
It's not rocket science guys. We're not going to see another quake. Period. The planet's core is just an unmoving lump. No plates, no quakes.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.