Apr. 30, 1999 The cold, barren crust of Mars conceals ancient remnants of its fiery youth 4 billion years ago, when an "active dynamo" in the red planet's interior hummed with magnetism, much like Earth, researchers report in the April 30 issue of Science.
Like faded tattoos on an aging space sailor, magnetic stripes now adorn the Martian crust, running east-and-west, perhaps where segments of sea floors spread apart, says Norman F. Ness, president of the Bartol Research Institute at the University of Delaware, coauthor of two Science articles based on the latest Mars Global Surveyor (MGS) findings.
"In the early Naochian epoch, Mars was magnetic, and this new data suggests that it was far more similar to Earth's global magnetic field than we had previously assumed," says Ness, a coinvestigator on the MGS project, who has served as a principal investigator on 18 prior space missions.
Magnetic remnants further support the notion of a once-lush Martian paradise, where volcanoes belched hot gas and meandering rivers carved valleys into the planet's russet plains, Ness says.
With scientists from the National Aeronautics and Space Administration's Goddard Space Flight Center, lead authors on the Science papers, Ness and other collaborators analyzed data from an instrument on the MGS spacecraft. The craft completed 916 orbits, capturing key data from just 62 to 124 miles above the planet.
Magnetized crustal regions were found mainly within the heavily pitted terrain formed by impact cratering after the early Naochian epoch, suggesting that the Martian dynamo--"the generator that converts motion into electrical currents with magnetic fields"--had fallen silent by then, Ness says.
Within the planet's southern hemisphere, two regions, known as Terra Sirenum and Terra Cimmeria, reveal banded stripes of intensely magnetized crust. At their longest, the stripes extend as far as 1,240 miles along the planet's surface.
The magnetic stripes on Mars are reminiscent of regions on Earth where thin, plate-like pieces of crust beneath the sea are straining apart. Molten material such as magma spurts from the planet's hot interior through gaps between these plates, Ness explains. When the hot material cools, a process known as thermoremanent magnetization (TRM) then "freezes a memory of the magnetic field," he says.
So far, the strongest hot spot found within the Martian crust demonstrates only 1/20th the power of the Earth's magnetic field at the equator, Ness reports. Though theoretical extrapolations to the surface have not yet been completed, Ness suspects that those levels "may be as large as 20 to 50 percent of the Earth's magnetic field, within very small geographic regions, approximately 20 by 20 miles," he says.
Crustal magnetism on Mars was detected using data captured by a magnetic field experiment/electron reflectometer (MAG/ER), one of 6 MGS instruments to return new data, including highly detailed photographs. Launched by NASA in November 1996, the MGS spacecraft reached Mars in September 1997.
The 2,300-pound craft, now in its final mapping phase, will chronicle a 687-day Martian year, snapping photographs 20 times sharper than the Viking images of the 1970s, making it possible to see objects the size of a small car. Such clear images have revealed, for instance, that the "face" on Mars was merely an illusion, resulting from the poor resolution of the Viking data and specific lighting angles.
Images from the MGS camera also exposed highly layered deposits along the walls of the Valles Marineris canyon, suggesting that volcanic activity once played a key role in shaping the planet's surface. Other photographs provided clues to ancient lava flows and canyons carved by massive water flows, prompting some to wonder whether moisture or lava may still be trapped deep beneath the Martian surface.
Though magnetic measurements don't speak directly to these questions, Ness says, "This magnetic data and its interpretation will contribute to our understanding of the planet's formation, its evolution and the possibility of contemporary lava locations."
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