WASHINGTON -- NASA scientists have discovered strong evidence that ancient Mars had a magnetic field and a churning molten interior, features that on Earth might have been critical to the development of life.
The findings, made using the Mars Global Surveyor spacecraft, are consistent with an emerging view of the early Mars as Earthlike, with oceans and rivers, volcanoes spewing gas and lava, and perhaps a significant atmosphere.
Those dynamic geologic forces must have shut down on the 4.5 billion-year-old planet, leaving the surface frigid, arid and barren, with an atmosphere far thinner than on Earth's highest peaks. Some scientists think that when the Earth's molten interior cools and hardens in a few billion years, the planet will come to resemble Mars.
The discovery's implications for Mars intrigue scientists. "There could well have been a period of time when life formed on Mars," said Mario Acuna of the National Aeronautics and Space Administration's Goddard Space Flight Center in Greenbelt, the lead scientist on the study, which was published in this week's editions of the journal Science.
Acuna and a Goddard team used the spacecraft to study the magnetism of Mars' surface and were surprised to discover long stripes of strongly magnetized rock in one of Mars' oldest regions, fossil evidence of a magnetic field.
The stripes resemble similar features on Earth, formed near magma-spewing cracks in the crust called the mid-ocean ridges. As the molten rock cools, it freezes in place a record of the strength and polarity -- or direction of flow -- of the Earth's magnetic field.
The Earth's field is generated by the swirl of molten iron and other materials around its core. The field wobbles like a top, occasionally reversing polarity.
Acuna and his team found evidence of a similarly wobbly magnetic field in the ancient Mars rocks.
"Mars is far more geologically active and interesting and complex than we had reason to believe," said Jack Connerney, a member of the Goddard team. A geologically active planet will create many environments, which give life more chances to gain a foothold, he said.
Besides mapping magnetic fields, Mars Global Surveyor is measuring altitudes with a laser beam and taking high-resolution photographs, some of which have depicted ancient lava flows and deep canyons carved by floods.
No one is sure where the water went, but some geologists suspect that it is trapped and frozen beneath the planet's rocky surface.