David Perlman, Chronicle Science Editor
Friday,April 30, 1999
1999 San Francisco Chronicle
Surprising evidence from a spacecraft flying in orbit around Mars suggests that the planet was once much like Earth is today -- with a hot dynamo at its core, intense magnetism in its crust and massive continental plates adrift on its surface.
There's even a possibility that deep rifts cleaving the beds of early Martian oceans between the continents harbored primitive life, said some of the astonished scientists as they speculated about the implications of their findings.
The new evidence reported yesterday comes from the discovery of a series of broad magnetic stripes frozen in the rocky Martian surface and stretching halfway across the planet. The stripes were detected and measured by the Mars Global Surveyor spacecraft now orbiting from pole to pole to create the first high-resolution map of the entire planet.
``It's a pretty incredible observation, and we're all blown away,'' said planetary astronomer David Mitchell at the University of California's Space Sciences Laboratory in Berkeley, a member of the spacecraft's magnetometer team.
The report on ancient Martian magnetism is being published today in the journal Science, and it indicates that Mars was much different when it first formed from the dust and gas surrounding the early sun about 4 billion years ago.
Early Mars must have had a molten, iron- rich core that acted as a dynamo to create a major planetary magnetic field, like the Earth has now, according to Mario Acuna of NASA's Goddard Space Flight Center -- the principal investigator of the magnetometer project aboard the spacecraft.
The planet's north and south magnetic poles must have reversed themselves every few thousand years as the hot internal dynamo rotated, he and his colleagues believe. The dynamo cooled down and died after no more than a few hundred million years, the researchers have inferred from the remaining surface evidence, leaving remnants of the magnetism frozen in the rocks.
The discovery of a series of broad bands of magnetism -- each about 20 miles wide and more than 1,600 miles long -- was a total surprise because it means that Mars in its earliest times was much more like Earth is today than previously suspected.
On Earth, the discovery about 40 years ago of similar bands of magnetism at ``spreading centers'' between the vast continental plates of crust on the ocean beds was the epochal confirmation of the long-held but then still-controversial theory that Earth's continents have been ponderously moving and reforming during eons of geologic time.
That tectonic motion is responsible for some of the Earth's most furious activity -- its catastrophic earthquakes and its furious volcanic eruptions.
Now, it seems, the earliest days of Mars may also have been marked by a hot rotating dynamo in its interior and by epochs of continental drift and intense magnetism -- although it most likely ended when the dynamo cooled and died some time before 3.9 million years ago, according to the scientists monitoring the spacecraft.
Looking at Mars today, Mitchell noted, the planet reveals striking differences between its northern and southern hemispheres. The northern half, with its vast smooth plains, lies well below the average height of the planet's entire surface, and appears much younger than the highlands of the southern hemisphere, which are heavily scarred with impact craters and wide channels.
But across the southern hemisphere, the Global Surveyor spacecraft found the broad bands of magnetism akin to Earth's, which
appear somewhat like the bar codes on grocery packages.
The particles of magnetism, generated by the interior dynamo billions of years ago, were frozen into the rocks as they cooled from a molten state, and in each band discovered by the spacecraft, the magnetism points alternately north and south -- evidence that polar reversal occurred on the planet just as it has for millions of years on Earth.
There is no evidence left on Mars of the kind of sea-floor spreading that still occurs on Earth, because the Red Planet's surface was so furiously churned up by impacts from huge meteorites and asteroids during its early days. And Mitchell said yesterday he does not think it's likely that ``hydrothermal vents'' beneath the oceans ever existed on Mars to harbor living organisms as they do on Earth.
But to Norman F. Ness of the University of Delaware's Bartol Research Institute, the idea is not at all impossible. ``It seems an inevitable conclusion that sea- floor spreading could have occurred during the earliest history of Mars,'' Ness said, ``and if so, it could have produced deep-sea vents that were able to harbor life.''
©1999 San Francisco Chronicle