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Read the passage and choose the one best answer to each question.


Saturn’s largest moon, Titan, has recently become a source of interest to atmospheric scientists. Atmospheric scientists focus on the way moisture and weather patterns within an atmosphere interact. Eager to find new environments to observe, scientists have begun looking at Titan. It is the only one of Saturn's moons large enough to support an atmosphere. Given its distance from the sun, Titan is significantly colder than Earth. However, its atmospheric conditions are nearly identical to Earth's in many regards. On Earth, liquid water evaporates and rises into the atmosphere, where various forces move the air. These atmospheric air currents dictate the formation of clouds, wind direction, and the places where precipitation occurs. Scientists observing Titan have found that its atmospheric currents are similar to those on Earth and are responsible for similar events.

Unlike Earth, however, the vapor in Titan’s atmosphere is not evaporated water. As Titan is much colder than Earth, water can only exist as a solid. Methane on Titan, on the other hand, behaves in a manner similar to water on Earth. We are accustomed to seeing methane as a gas, as that is how it commonly occurs on Earth. Titan's lower temperatures, however, allow methane to coalesce into a liquid and become a vapor. Given Titan's atmosphere, the evaporated and liquefied vapor acts in a manner similar to the way water behaves on Earth. It puddles on Titan’s surface, evaporates, and forms into clouds. As a result, the atmospheric conditions on Titan mimic those observed on Earth.

By observing the atmospheric events on Earth and comparing them to those on Titan, scientists can improve their understanding of atmospheric behavior. On Earth, for instance, the atmospheric forces result in a large concentration of clouds and precipitation along the equator. This area of concentration, known as the inter-tropical convergence zone (ITCZ), can also be observed on Titan. However, the ITCZ on Titan is not limited to its equatorial region. Instead, liquid methane actually evaporates into vapor along the middle section of the planet. It then moves toward the poles, where it is deposited as precipitation. This unusual behavior can most, likely be attributed to the fact that Titan lacks an ocean, which plays a key role in evaporation on Earth.

The outcomes of the atmospheric activity on Titan and Earth are quite different. Yet, this difference can be very helpful in honing our understanding of the way moisture in the atmosphere interacts and produces different atmospheric events. Since atmospheric science studies complex systems with a number of factors, these environments are nearly impossible to accurately reproduce in a lab. As such, it is difficult to test theories that scientists may have on atmospheric behavior. The fact that we are now able to study another atmosphere and compare and contrast it with that of Earth is valuable in improving our understanding of atmospheric sciences.

1. According to paragraph 1, what do scientists hope to do by studying Titan′s atmosphere?
A. Gain more understanding of how methane behaves at lower temperatures
B. Improve their knowledge of atmospheric events and their causes
C. Begin finding atmospheres other than Earth that are friendly to life
D. Prove that any element can play a part in generating atmospheric events

2. According to paragraph 3, an inter-tropical convergence zone is:
A. An area of concentrated moisture within an atmosphere
B. An atmospheric event occurring in equatorial regions
C. An area that only occurs along the middle section of Titan
D. An event observed exclusively in Earth's atmosphere

3. According to paragraph 4, why is it helpful to have another atmosphere to compare with Earth′s?
A. Reproducing atmospheric variables in a lab is nearly impossible.
B. Most planetary bodies simply lack atmospheres that we can observe.
C. We are not familiar with the way methane behaves at lower temperatures.
D. Most theories concerning atmospheric behavior are only relevant to Earth.
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