Space: Mariner’s Progress

Last week the Mariner II spacecraft was 7,651,352 miles away from the earth and 28.9 million miles this side of Venus, its destination. As Mariner barreled away from the earth at 7,724 miles an hour toward a scheduled approach to Venus on Dec. 14, Pasadena’s Jet Propulsion Laboratory announced that it will pass somewhat farther away from Venus than predicted —20,900 miles instead of 9,000 miles. The small rocket that adjusted its course on Sept. 4 seems to have pushed it slightly too hard, increasing its speed by 47 m.p.h. instead of 45.

But Mariner II will pass plenty close enough to Venus to get a good look. Even at 40,000 miles, its radar and other scientific instruments will be effective if they work properly. Meanwhile, its en route instruments are measuring the solar wind, the great blast of electrically charged particles that the sun shoots out in all directions. At present the wind is rather gentle, but it can rise to hurricane force when a brilliant flare erupts on the sun’s surface.

Another instrument carried by Mariner II counts micrometeorites. According to its latest reports, these tiny particles of cosmic dust are surprisingly scarce in interplanetary space, about one-thousandth as numerous as near the earth. Apparently the earth somehow concentrates them; they may be falling toward it or revolving around it like microscopic satellites.