WASHINGTON - Imagine waking up in the Ares Valley of Mars on a late summer day, just before dawn. Wispy, white stratus clouds drift overhead against a salmon-pink sky. As the small white disk of the sun rises in the reddening sky, the ice clouds evaporate. By midday, you can stand with your bare toes sifting idly through the rusty, sun-warmed dust, but your head is freezing.
Looking around, you see what seem to be salt deposits left by old puddles, undulating dunes and ridges, strewn with boulders all leaning the same way as if swept along in a mighty current and, in the distance, lines of mud from receding waters. If you dig deep enough into the fine red soil, you hit a layer of white, cement-like stuff that could have been compacted by water. By now, the sun is setting beyond the Twin Peaks, the northerly wind is shifting and will soon be blowing through the valley from the south. The temperature is plummeting toward minus 109 degrees Fahrenheit.
After a month on Mars, NASA's Pathfinder robots have assembled a rich, detailed portrait of what it might be like to land with human senses on the Red Planet. In a continuing torrent of data and images - all flowing almost immediately onto the Internet - the first Mars lander in more than two decades has sent to Earth a virtual breath of Mars - its winds and weather, the alien shape of its sunsets, the crunch of its dust and rocks.
In the mission's most recent major discovery, Pathfinder bowled over scientists last week with unprecedented temperature measurements of the low-level Martian atmosphere, taken every four seconds for a whole day. The lander's weather station recorded unexpected, huge swings of as much as 40 degrees Fahrenheit within seconds or minutes - a sign of extreme turbulence, scientists said.
At midday, the sensors recorded temperatures of about 70 balmy degrees Fahrenheit at ground level but a chilly 10 to 15 degrees just five feet above the same spot. In other words, "it's warm enough to go barefoot, if you were brave enough," said Mars "weatherman" Robert Haberle of NASA's Ames Research Center. But on your upper extremities, you would want to bundle up in a warm hat and gloves (actually, of course, a human would have to wear a spacesuit to breathe and function in the thin, oxygen-free atmosphere).
Though Martian temperatures are known to change dramatically on large scales between night and day, such detailed small-scale measurements had never been taken of the Martian atmosphere until now, and no one had expected such extreme and rapid fluctuations. "This is kind of a big discovery," chief Pathfinder scientist Matthew Golombek, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in an interview. "It implies there are eddies of warm air bubbling off the surface ... All our jaws dropped when we saw that data."
In the weeks since its July 4 arrival on Mars, the Pathfinder lander and its roving sidekick Sojourner have achieved all of their mission goals, including a demonstration that the technology itself works. Formally, the lander's prime mission was to last only a month, while the rover had contracted to operate for only a week. But Golombek said Friday, "It looks like we don't have an end in sight."
Ground controllers apparently have cleared up pesky communications glitches that had slowed the scientific work from time to time, Golombek said. Having worked virtually non-stop since the July 4 landing, both the robots and their handlers are taking a couple of days off Sunday and Monday to recharge the mothership's batteries. The robots can run indefinitely on solar power during daylight. The most likely cause of their demise, scientists say, is stress on the hardware caused by the constant, wild Martian temperature swings.
Along with the latest discovery of the extreme temperature fluctuations, Golombek said the mission's other two top discoveries to date are:
Some insights seem as much poetry as science. Like any good tourists, the robots have sent back scenic postcards - but theirs are sensational. Most recently, they transmitted images of roiling, rose-colored stratus clouds, composed of ice and dust, drifting over the landing site in the glow that preceded the Martian sunrise. The clouds of ice and dust were at altitudes of about 10 miles, traveling about 15 mph out of the northeast.
These images represented the first ever taken from the Martian surface of an overcast sky. The imaging team had hoped to show Earth twinkling like a blue star overhead, they said, but instead just put an "X" on the cloudy image, with the words, "You are here."
Another series of images shows the sun setting in a darkening magenta sky, behind the hills known as the Twin Peaks, and trailing a pink glow in a distinct fan shape that scientists said they cannot yet explain.
For anyone who had assumed the Martian skies were boring, said Pathfinder scientist Mark Lemmon, of the University of Arizona, "I'm here to tell you you're wrong."
The spectacular sunrises and sunsets generally are enhanced by the ubiquitous Martian dust that apparently is mixed throughout the atmosphere, giving the sky as well as the surface their red hue. In these "twilight studies," the team has found that the sky stays bright for up to two hours after sunset, indicating that the dust extends to high altitudes.