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From this experiment they soon learned that the air enveloping Mars is extraordinarily thin, about the density of Earth's atmosphere at altitudes of 93,000 ft. to 102,000 ft. Air pressure on the surface of Mars, estimates JPL Physicist Dr. A. J. Kliore, is between 10 and 20 millibars compared with Earth's average of 1,000. The Martian atmosphere is now believed to have only 1% to 2% the density of Earth's, and may also be far more turbulent. Being so thin, the Martian air would have to blow with tremendous velocity to kick up the dust storms thought to be characteristic of the red planet.
From the millions of measurements Mariner had already sent back, other scientists also began to draw their part of the portrait of the planet. Some preliminary conclusions:
> The magnetic field of Mars is almost nonexistent, about 1/1,000 to 1/10,000 that of Earth's.
> Mars does not appear to have any radiation belts similar to Earth's Van Allen belts.
> Heavy solar radiation slips through the planet's thin atmosphere to bombard its surface, but the level is not likely to be so high as to make all life impossible.
Garbage Collection. From these findings, scientists on the Mariner project could only draw a bleak, forbidding picture of Mars. They were surprised not to find signs of a magnetic field, but their instruments simply did not show any change in measurements during the encounter. Since most scientists believe that the Earth's magnetic field results from the motion of a hot liquid metal core, they now assume that Mars and Earth have basically different internal structures. Mars, in fact, may be more like the moon, which also lacks a magnetic field. "If there are any Martian men, they do not use a compass with any effectiveness," cracked Dr. James Van Allen of the State University of Iowa, who heads one of the Mariner scientific teams.
Discoverer of the Earth's radiation belt that is named after him, Dr. Van Allen (TIME cover, May 4, 1959) was particularly interested in the possibility of trapped radiation in the vicinity of Mars. But Mariner's instruments could not find any. Thus, man should be able to orbit Mars for long periods of time without heavy shields against radiation. And despite the high level of radiation on the surface of the planet, scientists say that it does not appear to be enough to discourage exploration. Man could probably visit Mars without wearing special radiation protection.
Before approaching Mars, scientists report, Mariner recorded ten solar flares (eruptions on the sun that spew out streams of particles), two of which were not noted on Earth. The cosmic dust team, nicknamed "the garbage collectors" because the dust is essentially waste material, also made an interesting discovery. They had expected the rate of dust to increase as the spacecraft traveled farther from Earth. It did—for a while. Then it abruptly diminished. "We are theorizing," says W. M. Alexander of the Goddard Space Flight Center, "that Earth and Mars act as sweepers of these dust particles, attracting them to the planets and cleaning out large paths along their orbits." No one knows how they do it.