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Monday, January 3, 2005; Page A05

Mars Rovers Are Still Going

One Mars rover has a touch of arthritis in one wheel, and the other spent six months in a crater and almost got stuck, but NASA's historic exploration mission completed a year of discovery today with both Spirit and Opportunity in excellent health.

One year after it bounced to a halt on Mars's Gusev Crater, the rover Spirit is perched in the "Columbia Hills" more than 400 feet above its landing site examining a rock dubbed "Wishstone."

A rover is shown before deploying onto Mars. Built to explore for 90 days, the two rovers have lasted much longer, and they continue sending data to Earth. (Cornell University / Maas Digital Llc Via AP)

Half a planet away, Opportunity is motoring along the Meridiani Planum, having escaped Endurance Crater after six months of explorations. It is embarked on a 220-yard journey to visit the heat shield that protected it when it landed Jan. 23.

The two rovers were designed to explore for 90 days. They have survived a Martian winter, lasted four times as long as expected and show no signs of slowing down.

After only six weeks on the job, Opportunity found compelling evidence that liquid water once soaked at least part of Mars.

Spirit's closest brush with catastrophe came when software problems caused the rover's computers to cramp up for the first three weeks of the mission. Today Spirit's chief difficulty is a right front wheel that draws too much electricity, a problem that can be eased by traveling backward.

Opportunity was deliberately driven into Endurance Crater in the belief that the science benefits far outweighed the risk of getting stuck in the sand. But after the rover finished its work, its handlers found a way out.

-- Guy Gugliotta

New Theory of Antarctic Ice Cap

A sharp drop in the atmospheric concentration of carbon dioxide 34 million years ago helped form the mile-thick ice sheet now covering Antarctica, according to Purdue University scientists.

The new findings, which were published online in the journal Paleoceanography, are significant because researchers had previously thought a shift from warm to cold ocean currents prompted the ice sheet to form. Matthew Huber, the paper's lead author and an assistant professor in Purdue College of Science's earth and atmospheric sciences department, attributes the ice formation to the fact that carbon dioxide levels dropped by about 80 percent during the Eocene period between 55 million and 35 million years ago.

Huber said the discovery -- based on sediment samples containing fossils of plankton that thrived in cold water for millions of years -- was "very disturbing," because it meant the ice sheet could disappear, since carbon dioxide levels are expected to rise rapidly over the next 200 years.

"You just play the movie in reverse. You in due time would end up melting back the Antarctic ice sheet," Huber said. "It should give us pause that today humans are effecting changes in the amount of carbon dioxide in the atmosphere."

Huber and colleagues based their conclusions on core samples taken on both sides of Tasmania, an island that 35 million years ago was positioned like a stepping stone between Australia and Antarctica before the two continents drifted apart. If the warm-water theory about Antarctica were correct, Huber said, there would be evidence of warmth-loving microorganisms on both sides of the island. Researchers found such fossils only on Tasmania's west side.

-- Juliet Eilperin

Heartbeat, 'Body Clock' Linked

Scientists have long known that more heart attacks occur at midmorning than any other time of day, and while they are not sure why this happens, new research shows that the human "body clock" influences heartbeat patterns, which become more erratic between 9 a.m. and 11 a.m.

Reporting in last week's Proceedings of the National Academy of Sciences, researchers from Boston University, Harvard Medical School and Boston's Brigham and Women's Hospital found that "interbeat intervals" -- the length of time between successive heartbeats -- in five healthy individuals most closely resembled the variability of heart disease patients during the forenoon hours.

Physiologist Steven Shea, of Harvard Medical School and Brigham and Women's Hospital, said the team isolated its five subjects in a dimly lighted, windowless environment for 10 days, varying sleeping patterns and other behaviors so that they could not "signal" the body's internal circadian clock.

Left to fend for itself, each individual's body clock operated on a 24.2-hour cycle, marked by regular changes in body temperature -- lowest around 5 a.m. Beginning around 9 a.m., the team noticed significant fluctuations in the heartbeat pattern.

"We're not quite sure why this happens, but it seems to be a transition period during the day," Shea said in a telephone interview. "We know behaviors have a significant effect on the heart, but we've been able to isolate another factor that may play a role, and that's the internal body clock."

-- Guy Gugliotta

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