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17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Martian Rivers and Volcanoes Go With the Flow
17 February 1999 7:00 pm
New pictures of Mars suggest that water gushed from within the red planet billions of years ago and lingered on the surface for some time. The images also indicate that volcanoes belched far more lava onto Mars than suspected, and hot spots of molten rock may still lie beneath the surface, according to reports in tomorrow's Nature.
Mars is cold, dry, and dusty today. But researchers believe the planet's early atmosphere may have been thick enough to sustain a warm and wet climate, creating a hospitable cradle for life (Science, 29 January, p. 648). Volcanoes might have contributed to that climate by spewing greenhouse gases into the martian air. Indeed, robotic surveyors have seen signs of watery flows and major eruptions in the planet's youth, before 3.5 billion years ago. But it wasn't clear whether this water rained upon the surface or burbled up from within, nor did researchers agree about the extent and duration of volcanic activity.
Sharp images from Mars Global Surveyor address both issues. The images, taken about a year ago, resolve features just 4 to 8 meters across. Networks of valleys arise suddenly and disappear in spots, like the sinkholes in limestone country--clear evidence that underground water carved many martian channels, says planetary geologist Michael Carr of the U.S. Geological Survey in Menlo Park, California. And sinuous channels scoured into the bases of canyons indicate that water probably lingered on the surface in some places, Carr notes. Rainfall, on the other hand, would have created far more small tributaries than Surveyor has seen, he says.
Other images of rocky layers in the Valles Marineris canyon point to extensive volcanism during the first billion years on Mars, says planetary geologist Alfred McEwen of the University of Arizona in Tucson. Martian volcanoes may have unleashed enough lava to cover the United States to a depth of more than 6 kilometers, McEwen says--about 10 times more than previously believed. Moreover, few impact craters exist in some regions, suggesting that fresh lava may have erupted onto the surface as recently as 40 to 100 million years ago. "It's likely that there is still magma under the surface of Mars, and it's conceivable that subsurface ice could melt in isolated warm areas," McEwen says.
The evidence for groundwater on early Mars is inarguable, says planetary scientist Maria Zuber of the Massachusetts Institute of Technology in Cambridge. "It will be difficult to argue for precipitation after this," she says. However, Zuber isn't yet convinced that the layers in Valles Marineris are volcanic, because sediments deposited by flowing water could leave similar patterns. Dust also might obscure many impact craters, she notes, making the surface appear younger than it really is.