Some astrophysicists have postulated that the rings of Saturn are a relatively young feature of the solar system, and data received from the Cassini spacecraft have corroborated this theory. Launched by the United States in 1997, Cassini provided 13 years of close observation of the planet and its rings. Cassini's data not only reinforced the recent-creation view but also engendered a new theory about how the rings came into being: a cataclysmic collision that created Saturn's rings as well as several of the planet's current inner moons. One of these moons, Enceladus, is widely considered the most promising site in the solar system for the search for extraterrestrial life, and Cassini discovered an ocean containing organic molecules and hydrothermal sites beneath the moon's icy crust. It is these components that scientists believe were responsible for the emergence of life on Earth. If Enceladus is determined to both be young and possess life, it would lend support to the argument that life on Earth also appeared quickly after the planet's formation.

Luminosity is one of the ways in which objects in the solar system can be dated. Because the solar system is full of the dark residual dust from comets, the longer objects have been in existence, the more dust they have absorbed, and the darker they appear. The effect is similar to the accumulation of soot on a statue in a city with polluted air; after a number of years, the pollution will settle on the statue and darken its surface. Younger objects, on the other hand, appear brighter. Jeff Cuzzi, a scientist working on the Cassini project, and his colleagues compared the density of comet dust on Saturn's rings with the density closer to Saturn's surface, and their preliminary analysis determined the age of Saturn's rings to be somewhere between 200 million and 70 million years. This would put the formation of the rings sometime when dinosaurs walked on Earth, a relatively recent period in Earth's 4-billionyear existence.

The other, and perhaps more remarkable, evidence of the recent creation of Saturn's rings comes from the work of Matija Ćuk and his team, who used the known rate at which the orbits of Saturn's moons are lengthening to extrapolate backward and project the orbits in the past. The results indicate that, about 100 million years ago, two of Saturn's moons would have interacted in such a way as to tilt their orbits, but their orbits are not tilted. Therefore, Ćuk believes this interaction could not have happened. To explain this phenomenon, Ćuk and his colleagues propose that Saturn originally had two moons and that evection, the effect of the sun's attraction on the orbit of the outer moon, destabilized that moon's orbit. The outer moon eventually crashed into the other moon, creating a huge debris field. Some of this debris clumped together due to gravity and formed the set of moons seen today. However, within the Roche limit, the orbital distance within which Saturn's gravity would pull a moon apart, the debris would have been pulled into a disk-the disk that formed Saturn's rings.

If the hypotheses of Cuzzi and Ćuk are confirmed, then further research on Enceladus may offer an intriguing glimpse into the start of life, a glimpse that may add to our knowledge of how life began on Earth.

The primary purpose of the passage is to

(A) compare two theories about how the rings of the planet Saturn were formed.
(B) discuss reasons Enceladus should be examined for evidence of extraterrestrial life.
(C) examine new evidence that may contribute to the discussion of how life began on Earth.
(D) question the proposition that Saturn was one of the older planets in the solar system.
(E) show how the data from Cassini have proven the recent-creation view of the rings of Saturn.



Select the sentence in the second or third paragraph that explains a process by which Enceladus may have been created relatively recently.





Consider each of the following choices separately and select all that apply.

It can be inferred from the passage that the dark residual dust from comets

A. is evenly distributed throughout the solar system
B. provides evidence supporting the recent creation of Saturn's rings
C. can change the appearance of celestial bodies