SPECIAL REPORT: Kohoutek: Comet of the Century

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Scorched Planet. Kohoutek's arrival comes at a remarkable stage in man's exploration of the solar system. Scientists are still sifting through the mass of lunar measurements, pictures and rocks brought back to earth by the Apollo astronauts. From the data gathered by Russia's Venera 7 and 8 landers, America's Mariner 2 and 5 flybys, and radar observations by the Mojave telescope, astronomers can now describe in some detail the hellish surface temperature (900°F.), cratered topography and atmospheric conditions of cloud-shrouded Venus. Using the startlingly good pictures transmitted by Mariner 9, scientists at the Jet Propulsion Laboratory in Pasadena have just completed a huge model of Mars that shows craters, plains and valleys more clearly than lunar features can be seen through earth-bound telescopes.

Last week four unmanned Soviet spacecraft were about halfway along on a journey to Mars. When they arrive in February and March, two of the ships are expected to make soft landings while the other two remain in orbit around the Red Planet. Meanwhile, the U.S.'s Mariner 10 spacecraft was well on its way to Venus on the initial lap of the first two-planet, photo-reconnaissance flight. After Mariner has swept by Venus in February, using the braking force of that planet's gravity to change course, it will pass next March within 621 miles of Mercury, the tiny, scorched planet closest to the sun.

Still another solar-system explorer, Pioneer 10, last week briefly eclipsed even the growing excitement over Comet Kohoutek. Completing a 21-month voyage across the bleak, cold reaches of more than half a billion miles of space, the 570-lb. robot gave man his first close-up look at the giant planet Jupiter. After penetrating intense radiation belts that pack radiation dosages at least 1,000 times the level regarded as lethal for humans, Pioneer passed just 81,000 miles above the multicolored Jovian cloud tops, took color pictures, gathered oth er data and then was hurled by the enormous gravitational pull of the sun's larg est planet onto a course that will eventually carry it out of the solar sys tem, toward the stars — the first object from earth ever to embark on such a cosmic odyssey.

Hula-Hoop. "An engineer's dream come true," exulted NASA Boss James Fletcher. He had every reason to be proud. Pioneer had not only survived its encounter with electron intensities 1,000,000 times greater than those in the earth's own radiation belts but continued to radio back data after the historic encounter. Indeed, if Pioneer's tiny nu clear power packs and instruments keep functioning, the spacecraft's signals may well be received on earth until it reaches the orbit of the planet Uranus about 14 years from now. What is more, Pioneer's success clears the way for a twin, Pioneer 11, already en route to Jupiter and then possibly to Saturn.