No. 63: May-Jun 1989
A few of the hundreds of meteorites picked up in the Antarctic wastes have chemical properties consistent with a Martian origin. Calculations, too, support the notion that a large meteoric impact could propel bits of the Martian surface into space where, statistically speaking, a tiny fraction would be captured by the earth's gravitational field. Some of these would fall to earth; others would remain in orbit.
Now, the reverse scenario has been investigated numerically. S.A. Phinney and colleagues at the University of Arizona have calculated what would happen to small chunks of the earth's crust if a large meteor impact excavated a 60milewide crater.
"Phinney's group used a computer to calculate where 1,000 particles would go if ejected from Earth in random directions, moving about 2.5 kilometers per second faster than the minimum speed necessary to escape. Of the 1,000 hypothetical particles, 291 hit Venus and 165 returned to Earth; 20 went to Mercury, 17 to Mars, 14 to Jupiter and 1 to Saturn. Another 492 left the solar system completely, primarily due to gravitational close encounters with either Jupiter or Mercury that 'slingshot' them on their way."
(Eberhart, Jonathan; "Have Earth Rocks Gone to Mars?" Science News, 135:191, 1989.)
Comment. One implication from the preceding analysis is that terrestrial bacteria and spores could well have infected every planet in the solar system and perhaps even planets in nearby star systems! Conceivably, if other star systems had histories like ours, biological traffic might be quite heavy in interstellar space. In fact, extraterrestrial life forms may be arriving here continually; and we may be such ourselves!