Spacecraft Finds a Magnetic Patchwork on Mars
Future Boy Scouts on Mars won’t be able to use compasses to get around, because the magnetic field of Earth’s sister planet swings wildly from one spot to the next as if the Red Planet were littered with small but extremely powerful magnets.
The finding, announced Thursday at the Jet Propulsion Laboratory in Pasadena, comes from the Mars Global Surveyor six months ahead of schedule, as the spacecraft coasts far out from the planet, slowly skidding into orbit on its solar-panel wings.
Strong magnetic fields, which shield planets from intense space radiation, are essential to the evolution of life, according to some scientists. And because the concentrated magnetic splotches on Mars are 40 times stronger than similar areas on Earth, it is likely that Mars once had a substantial magnetic core.
“They’re surprisingly strong,” said Jack Connerney, a magnetometer scientist with the NASA Goddard Space Center in Maryland.
Planetary scientists had expected to find a magnetic field around Mars that was relatively uniform, similar to those encircling all the other planets except Venus, and weak. Mars is the only planet in the solar system with such a peculiar magnetic patchwork, Connerney said.
Down on the Martian surface, meanwhile, Pathfinder and its little rover, Sojourner, stand mute, apparently because the spacecraft’s batteries have finally died, mission manager Brian Muirhead said Thursday. Without batteries, the craft hasn’t had enough power to “wake up” at the right time, “so the clocks are all screwed up,” he said
Still, “reports of the death of Pathfinder have been greatly exaggerated,” Muirhead said, paraphrasing Mark Twain. “There’s a lot of life left.”
While the probable battery failure doesn’t mean the end of the probe’s mission, he said, it does limit explorations to two to four daytime hours, when the craft can use the sun’s energy for power. Reconfiguring communications now that the spacecraft can operate only on solar power may put the mission on hold for a couple of weeks, he said.
Almost 70 miles above the martian surface, Global Surveyor continues its long spiral toward the planet--and its eventual parking orbit--slowing down each time it dips into the atmosphere. Although the craft wasn’t due to begin sending back scientific data until next year, it has already returned some “remarkable, interesting results,” said project scientist Arden Albee, “just a foretaste of things to come.”
Foremost among these findings is the unusual magnetic character of the Red Planet. As Global Surveyor plowed through the layer of electrically charged particles surrounding Mars, electronic compasses on board recorded a sudden and surprising drop in magnetic field strength. “Mars no longer has a global magnetic field,” Connerney concluded.
While the magnetic fields surrounding other planets are generated by swirling electric currents deep within their cores, the pockets of magnetism on Mars appear to be entirely on the crust. Whatever planetwide field once encircled Mars “is gone but not forgotten,” Connerney said. The patches are thought to be remnants of that ancient field, frozen into the rock as the planet cooled after a hotter, more turbulent past.
“They are thumbprints of a now dead event,” said JPL magnetometer scientist Daniel Winterhalt. “It’s the first time we can say for sure that Mars once had a magnetic field. Now what’s left are bar magnets scattered all over the surface.”
In some places, the field points straight up out of the planet; in other patches, straight down; in others, flat across the surface.
As a result, a compass carried about on Mars would not point consistently in one direction, but swing completely around as one traveled across a patch, Connerney said.
If geologists can piece together this patchwork, they should be able to reconstruct the geological history of Mars back to a time when the parched, airless planet was a lot more like Earth. And while the existence of a strong magnetic field on ancient Mars doesn’t in itself mean life once existed there, the finding does make those speculations more plausible.
The camera on Global Surveyor has sent back images of steep cliffs, rolling sand dunes, sharp ridges and what appear to be ancient, striated riverbeds.
First tests of the laser altimeter--which measures ups and downs on the surface of the planet--revealed surprisingly flat plains, dropping off into canyons much smoother and at least three times steeper than the Grand Canyon. But even that is a small scale feature for Mars, which because of its weaker gravity has both higher mountains and deeper valleys than Earth.
The large flat plains, however, were a surprise, said altimeter scientist David Smith of the Goddard Space Center. “We asked ourselves, ‘Where on Earth do you find this flatness?’ ”
The answer is either in a desert, like the Sahara, or on the ocean floor. Whether or not the flat surfaces on Mars were the bottoms of ancient seas will not be known for sure, however, until scientists piece together all the data gathered by Surveyor’s six instruments over the next 2 1/2 years of its mission, Albee said.
Infrared measurements have indicated that the planet’s atmospheric temperatures can be extremely cold--about 150 degrees below zero Fahrenheit--and that the weather is clear, with no major dust storms on the horizon. That’s good news for the spacecraft’s flight directors: Dust warms the atmosphere, and a warm atmosphere rises like a cake, bringing denser air higher, where it can increase drag on the craft to dangerous levels.
With its solar panels outspread like wings, Global Surveyor glides through the atmosphere, buffeted about like a light plane. The temperature measurements allow engineers to adjust the orbits so the craft brakes just enough to enter orbit in the right place at the right time.
The purpose of the $250-million mission is to map the entire surface of the planet, pinpointing the distribution of minerals, ice and rocks, and analyzing the atmosphere and gravity field. Such a thorough assessment will help scout promising landing sites for future Mars missions.
Surveyor carries many spare parts that had been built for its ill-fated predecessor, the nearly $1-billion Mars Observer, which was lost in space in 1993 as it prepared to enter Martian orbit.
The only glitch thus far in the Surveyor mission is a solar panel’s failure to completely unfold. The descent into the atmosphere over the last few weeks, however, has moved the panel into an almost flat position, Albee said.
