Jets of carbon dioxide gas erupting from the ice cap as it warms in the spring carry dark sand and dust high aloft. The dark material falls back to the surface, creating dark patches on the ice cap which have long puzzled scientists. Deducing the eruptions of carbon dioxide gas from under the warming ice cap solves the riddle of the spots. It also reveals that this part of Mars is much more dynamically active than had been expected for any part of the planet.
"If you were there, you'd be standing on a slab of carbon-dioxide ice," said Phil Christensen of Arizona State University, Tempe, principal investigator for Odyssey's camera. "All around you, roaring jets of carbon dioxide gas are throwing sand and dust a couple hundred feet into the air."
You'd also feel vibration through your spacesuit boots, he said. "The ice slab you're standing on is levitated above the ground by the pressure of gas at the base of the ice."
The team began its research in an attempt to explain mysterious dark spots, fan-like markings, and spider-shaped features seen in images that cameras on Odyssey and on NASA's Mars Global Surveyor have observed on the ice cap at the Martian south pole.
The dark spots, typically 15 to 46 meters (50 to 150 feet) wide and spaced several hundred feet apart, appear every southern spring as the sun rises over the ice cap. They last for several months and then vanish -- only to reappear the next year, after winter's cold has deposited a fresh layer of ice on the cap. Most spots even seem to recur at the same locations.
An earlier theory proposed that the spots were patches of warm, bare ground exposed as the ice disappeared. However, the camera on Odyssey, which sees in both infrared and visible-light wavelengths, discovered that the spots are nearly as cold as the carbon dioxide ice, suggesting they were just a thin layer of dark material lying on top of the ice and kept chilled by it. To understand how that layer is produced, Christensen's team used the camera -- the Thermal Emission Imaging System -- to collect more than 200 images of one area of the ice cap from the end of winter through midsummer.
Some places remained spot-free for more than 100 days, then developed many spots in a week. Fan-shaped dark markings didn't form until days or weeks after the spots appeared, yet some fans grew to half a mile in length. Even more puzzling was the origin of the "spiders," grooves eroded into the surface under the ice. The grooves converge at points directly beneath a spot.
"The key to figuring out the spiders and the spots was thinking through a physical model for what was happening," said Christensen. The process begins in the sunless polar winter when carbon dioxide from the atmosphere freezes into a layer about three feet thick on top of a permanent ice cap of water ice, with a thin layer of dark sand and dust in between. In spring, sunlight passing through the slab of carbon dioxide ice reaches the dark material and warms it enough that the ice touching the ground sublimates -- turns into gas.
Before long, the swelling reservoir of trapped gas lifts the slab and eventually breaks through at weak spots that become vents. High-pressure gas roars through at speeds of 161 kilometers per hour (100 miles per hour) or more. Under the slab, the gas erodes ground as it rushes toward the vents, snatching up loose particles of sand and carving the spidery network of grooves.
Christensen, Hugh Kieffer (U.S. Geological Survey, retired) and Timothy Titus (USGS) report the new interpretation in the Aug. 17, 2006, issue of the journal
Nature.
Source: NASA/JPL
Related stories:
Return to Europa: A closer look is possible
Jupiter’s moon Europa is just as far away as ever, but new research is bringing scientists closer to being able to explore its tantalizing ice-covered ocean and determine its potential for harboring life.
Decoding Mars's cryptic region
Mars Express's OMEGA instrument has given planetary scientists outstanding new clues to help solve the mystery of Mars's so-called 'cryptic region'.
Damage Detectives Inspect Shuttle on Orbit
When the shuttle Discovery streaked into the clear, blue sky this summer, millions of Americans sat on the edges of their seats, staring in awe at computer screens and television sets.
Global sea-rise levels by 2100 my be lower than some predict, says new study
(PhysOrg.com) -- Despite projections by some scientists of global seas rising by 20 feet or more by the end of this century as a result of warming, a new University of Colorado at Boulder study concludes that global sea rise of much more than 6 feet is a near physical impossibility.
Cassini Prepares to Swoop by Saturn's Geyser-Spewing Moon
(PhysOrg.com) -- Fractures, or "tiger stripes," where icy jets erupt on Saturn's moon Enceladus will be the target of a close flyby by the Cassini spacecraft on Monday, Aug. 11.
Professor talks about latest in Younger Dryas work in Science article
University of Cincinnati Professor of Geology Tom Lowell is featured in the July 18 issue of Science, discussing the latest research into the question of whether the significant climate change event about 12,900 years ago known as Younger Dryas impacted the climate all around the globe.
Ice cores map dynamics of sudden climate changes
New, extremely detailed data from investigations of ice cores from Greenland show that the climate shifted very suddenly and changed fundamentally during quite few years when the ice age ended. Researchers from the Niels Bohr Institute of University of Copenhagen have together with an international team analysed the ice cores from the NorthGRIP drilling through the Greenland ice cap, and the epoch-making new results have been published in the highly esteemed scientific journal Science and in Science Express.
New wireless sensor network keeps tabs on the environment
Have you ever wondered what happens in the rainforest when no one is looking? Research in the University of Alberta's Faculty of Science may soon be able to answer that question.
