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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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17 September 1997 8:00 pm
NASA's Global Surveyor has detected a magnetic field around Mars. While it's unlikely that the geologically inactive planet is generating a field the way Earth does, the discovery may lend support to the contention that Mars once had a field nearly as strong as Earth's that has since faded. If so, that early, strong field might have fended off cosmic rays deleterious to life.
The discovery came Monday when the recently arrived Mars Global Surveyor made its first observations during a pass 250 kilometers above the planet. "It looks like strong evidence for a planetary magnetic field," says space physicist Mario Acuña of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who is the principal investigator for Surveyor's magnetometer. Magnetometers sent to Mars on previous missions did not pick up the field because they were not sensitive enough or, like the 1989 Russian Phobos spacecraft, did not pass close enough to the planet, he says.
"It's a somewhat surprising result," says planetary physicist David Stevenson of the California Institute of Technology, "because it's not that easy to get as large a field as the spacecraft has found." Theoreticians assume that Mars could not have long retained the internal heat that in Earth churns the molten-iron core to produce electrical currents and thus the magnetic field. If Mars ever had an Earth-like geodynamo, it's likely it has turned off, says Stevenson.
The field could be a remnant, imprinted on crustal rock before the geodynamo wound down, he adds. Such remnant magnetism has been reported in meteorites from Mars, including ALH84001 with its putative evidence of ancient life. Although twice as large as expected, the field is about 1/800 that of Earth.