GRE Reading Comprehension
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Source: XDF
According to astronomer S.A. Phinney, kicking a rock hard enough to free it from Earth's gravity would require a meteorite capable of making a crater more than 60 miles across. Moreover, even if Earth rocks were freed by meteorite impact, Mars's orbit is much larger than Earth's, so Phinney estimates that the probability of these rocks hitting Mars is about one-tenth as great as that of Mars's rocks hitting Earth. To demonstrate this estimate, Phinney used a computer to calculate where 1,000 hypothetical particles would go if ejected from Earth in random directions. He found that 17 of the 1,000 particles would hit Mars.
Question List: 1
Which of the following, if true, would cast most doubt on Phinney's estimate of the probability of Earth rocks hitting Mars?
- A Rather than going in random directions, about 25 percent of all particles ejected from Earth go in the same direction into space.
- B Approximately 100 meteorites large enough to make a noticeable crater hit the Earth each year.
- C No rocks of Earth origin have been detected on Mars.
- D The velocity of rocks escaping from Earth's gravity is lower than the velocity of meteorites hitting the Earth.
- E No craters more than 60 miles across have been found on Mars.