Question

The closest distance from which an asteroid has been photographed using ground-based radar is 2.2 million miles, the distance from which the asteroid Toutatis was recently photographed. The closest photograph of an asteroid is of Gaspra, which was photographed from a distance of only 10,000 miles.
Which of the following can be properly concluded from the statements above?

• A. Toutatis is more likely to collide with the Earth than Gaspra is.
• B. Toutatis, unlike Gaspra, has only recently been discovered.
• C. Asteroids can be photographed only by using ground-based radar.
• D. Ground-based radar photography cannot take photographs of objects much beyond 2.2 million miles from Earth.
• E. The photograph of Gaspra was not taken using ground-based radar.

Hint:

In inference questions, pay close attention to modifying phrases and superlatives like "closest," "only," or "best." The logic often turns on comparing two statements that use these specific qualifiers. Here, the comparison is between "closest by this method" and "closest overall."

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
This is an inference question. We are given two facts and must determine what can be logically concluded by combining them.
Step 2: Detailed Explanation:
Let's break down the given facts:

Fact 1: The closest photograph taken using ground-based radar was of Toutatis, at a distance of 2.2 million miles.
Fact 2: The closest photograph taken of any asteroid (by any method) was of Gaspra, at a distance of 10,000 miles.
The key is to compare these two records. The record for "closest photo by ground-based radar" is 2.2 million miles. The record for "closest photo overall" is 10,000 miles (for Gaspra). Since 10,000 miles is much closer than 2.2 million miles, the method used to photograph Gaspra could not have been ground-based radar, because if it had been, it would have broken the record mentioned in Fact 1. Let's evaluate the options based on this deduction:

(A) The distance at which a photograph was taken does not provide enough information to conclude anything about collision probability.
(B) The passage mentions a recent photograph of Toutatis, but gives no information about when either asteroid was discovered.
(C) The passage implies the opposite. Since the Gaspra photo was taken from much closer than the ground-based radar record, it must have been taken by another method (e.g., a space probe).
(D) The passage states that 2.2 million miles is the "closest" distance achieved by this method, not the "farthest" it can reach. It gives a record, not a limit.
(E) This is the correct conclusion. The Gaspra photograph was taken from 10,000 miles. The closest a ground-based radar has ever photographed an asteroid is 2.2 million miles. Since \(10,000<2,200,000\), the method used for Gaspra cannot have been ground-based radar.
Step 3: Final Answer:
By comparing the two records given, it is logical to conclude that the method used to take the much closer photograph of Gaspra was not ground-based radar.