Winds of change strike Mars, too

February 3, 2011
Mars. Image: NASA

Mysterious dark sand dunes around Mars' northern polar cap are shifting with the seasons, as carbon dioxide gas changes form and sparks landscape-altering avalanches, said a study published Thursday.

Sand dunes in a vast area of northern long thought to be frozen in time are changing with both sudden and gradual motions, as revealed by images from a high-resolution camera aboard NASA's , or MRO.

These dune fields cover an area the size of Texas in a band around the planet at the edge of Mars' north polar cap. Although the new findings suggest they are among the most active landscapes on Mars, few changes in these dark-toned dunes had been detected before a campaign of repeated imaging by the (HiRISE) camera on NASA's Mars Reconnaissance Orbiter, which reached Mars five years ago next month. The HiRISE camera is operated by the University of Arizona's Lunar and Planetary Laboratory.

Scientists had considered the dunes to be fairly static, shaped long ago when winds on the planet's surface were much stronger than seen today, said HiRISE Deputy Principal Investigator Candice Hansen of the Planetary Science Institute, Tucson, Ariz. Several sets of before-and-after images from HiRISE over a period covering two Martian years -- four Earth years -- tell a different story.

"The numbers and magnitude of the changes have been really surprising," said Hansen.

A report by Hansen and co-authors in this week's edition of the journal Science identifies the seasonal coming and going of ice as one agent of change, and stronger-than-expected gusts of wind as another.

Three images of the same location taken at different times show seasonal activity causing sand avalanches and ripple changes on a Martian dune. Every year, dune fields at high latitudes are covered by a seasonal polar cap of condensed carbon dioxide (dry ice). Sand sliding down the dune carves out new alcoves at the top and adds to the debris apron on the bottom. The top image was taken in the Martian summer when the dunes were free of seasonal dry ice. Spring found the region covered by a layer of seasonal ice (middle). Evaporation of this seasonal ice layer shows up as dark streaks of fine particles carried to the top of the ice layer by escaping gas. As the ice changes from solid to gas, gas flowing underneath destabilizes the sand and causes it to avalanche down the dune. The bottom image shows the resulting changes, revealed during the following summer after the ice was gone. New wind ripples can be seen on the debris apron. The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter took these images, each showing an area of 285 x 140 meters, centered at 84 degrees North latitude and 233.2 degrees East longitude. Credit: NASA/JPL/The University of Arizona

A seasonal layer of frozen carbon dioxide, or dry ice, blankets the region in winter and changes directly back to gaseous form in the spring.

"This gas flow destabilizes the on Mars' sand dunes, causing sand avalanches and creating new alcoves, gullies and sand aprons on Martian dunes," she said. "The level of erosion in just one Mars year was really astonishing. In some places hundreds of cubic yards of sand have avalanched down the face of the dunes."

Wind drives other changes. Especially surprising was the discovery that scars of past sand avalanches could be partially erased in just one Mars year. Models of Mars' atmosphere do not predict wind speeds adequate to lift sand grains, and data from Mars landers such as Phoenix show high winds are a rare occurrence.

"Perhaps polar weather is more conducive to high wind speeds," Hansen said.

In all, modifications were seen in about 40 percent of these far-northern monitoring locations over the two-Mars-year period of the study.

Related research with HiRISE previously identified gully-cutting activity in smaller fields of sand dunes covered by seasonal carbon-dioxide ice in Mars' southern hemisphere. A report four months ago showed that those changes coincided with the time of year when ice builds up.

"The role of the carbon-dioxide ice is getting clearer," said Serina Diniega of NASA's Jet Propulsion Laboratory, Pasadena, Calif., lead author of the earlier report and a co-author of the new report. "In the south, we saw before-and-after changes and connected the timing with the carbon-dioxide ice. In the north, we're seeing more of the process of the seasonal changes and adding more evidence linking gully activity with the carbon dioxide."

An image recieved from NASA in 2009 shows Mars' seasonal cap of carbon dioxide ice as it sublimates (goes directly from ice to vapor) in the Martian spring. Mysterious dark sand dunes around Mars' northern polar cap are shifting with the seasons, as carbon dioxide gas changes form and sparks landscape-altering avalanches, said a study published Thursday.

Researchers are using HiRISE to repeatedly photograph at all latitudes, in an effort to understand winds in the current climate on Mars," Hansen said. "It's becoming clear that there are very active processes on Mars associated with the seasonal polar caps."

The new findings help scientists to better understand what features and landscapes on Mars can be explained by current processes and which require environmental conditions no longer present on the planet.

"Understanding how Mars is changing today is a key first step to understanding basic planetary processes and how Mars changes over time," said HiRISE Principal Investigator Alfred McEwen, a professor in the UA's department of planetary sciences and a co-author of both reports. "There's lots of current activity in areas covered by seasonal carbon-dioxide frost, a process we don't see on Earth. It's important to understand the current effects of this unfamiliar process so we don't falsely associate them with different conditions in the past."

Explore further: Recurring martian streaks: flowing sand, not water?

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1.4 / 5 (11) Feb 03, 2011
Yes, climates change continuously for the planets that orbit a variable star.

That was well known before the Climategate scandal.

Continuous climate change is in the geologic record. It will remain as a concern for mankind. Hopefully it will not be used again for political purposes.
5 / 5 (8) Feb 03, 2011
Omatumr, this article is about Mars, please keep your comments on topic. I don't want to see another thread derailed by childish namecalling.
1 / 5 (1) Feb 04, 2011
Oh, let him play! We could all do with the light relief his comedy workshop provides!
5 / 5 (2) Feb 04, 2011
I guess it's shocking that we are shocked by this, or that only now are we seeing how dynamic a place Mars is. So now we know that there are "real-time" geologic, climatologic, and meteorologic processes, we've seen avalanches, dust-devils, and possible water melt/sediment, when can we go and actually SEE these? I hope that some of the private spaceflight companies put landing people on Mars as a coup-de-gras goal...
1 / 5 (1) Feb 04, 2011
Oh, let him play! We could all do with the light relief his comedy workshop provides!

At least this time he's half right with his crackpot theories. The sun is resposible for Mars climate change. The sun, and the newly exposed darker sections of the planet. Land use change doesn't necessarily need a human vector to occur.
not rated yet Feb 05, 2011
Mars is fascinating, and it is so close, I hope, that I will visit it, maybe as a tourist, between 2040-2050 :]
not rated yet Feb 06, 2011
Who knows. The old period of Martian 'good climate' is billions of years old. But enough time elapsed in that period to develope life. And spread it. Suppose in some dusty cave is a hidden stainless nickel steel door at the back, impossibly old on monstrous rusty hinges that on earth would have been gone yet here it survives. Some scientist opens it to find air at the consistancy of primordial Mars. A museum...a storehouse of seeds, pine, deciduous trees, books, a special book on a stand. Translated with the aid of local references placed with it: ...and the Hand of God moved across the face of the deep, for In the Beginning God created Heaven and Mars....all seemingly written in a language similar to Vedic and to early Babylonian, precursors to Aramaic. Happens sometimes when one says......'If'.

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