A sizable portion of the general public knows that there has been some

A sizable portion of the general public knows that there has been some controversy regarding Pluto's classification, though officially it has remained a planet since its discovery. Less well known is the existence of at least 70,000 other small bodies orbiting the sun beyond Neptune. These objects, most likely formed during the accretional phases of the solar system, are primarily found within a ring known as the Kuiper Belt.

Classical Kuiper Belt Objects (KBOs) orbit far from Neptune, allowing them to survive for the age of the solar system. They also have relatively small eccentricities in their orbits, though some Classical KBOs have orbital inclinations high enough to imply that they had been excited, possibly by planetesimals, possibly by a passing star, or possibly by some as yet unknown means. The passing star hypothesis requires a star to pass about 100 Astronomical Units from our sun, a rare event, though certainly possible if our sun formed with others in a cluster. (One Astronomical Unit or AU is the average distance from the Earth to the Sun.)

Scattered KBOs have large, eccentric orbits. The scattering effect of their occasional proximity to Neptune can send them out of the solar system entirely, where they may end up orbiting in the Oort Cloud. The influence of Neptune can also send the objects into planet-crossing orbits, where these objects are then classified as short-period comets. KBOs in a third category orbit the sun twice during the time it takes Neptune to orbit three times. As the same can be said of Pluto, these objects are known as Plutinos. (This has led to a semantic conundrum, since Pluto fits the definition of a Plutino, which, however, means "little Pluto.")

The Kuiper Belt is actually much smaller than it once was. The development of Neptune caused collisions that turned many KBOs into dust that blown into interstellar space by the Solar wind. However, some objects, larger even than Pluto, may yet be found beyond 70 AUs.

1. According to the passage, which of the following can be inferred about Kuiper Belt Objects?

A.They orbit between Neptune and Pluto.
B.They are all affected by the presence of Neptune.
C.At least 70,000 of them are known to exist.
D.The number of them is decreasing.
E.Some of them travel beyond the solar system.


2. It can be inferred from the passage that Scattered KBOs

A.have orbits that are more eccentric than those of Plutinos
B.have smaller inclinations than Classical KBOs
C.end up as comets or as objects that orbit outside the solar system
D.are at times far enough from Neptune to escape its scattering effect
E.have been effected by planetesimals


3. According to the passage, which of the following can be inferred about Pluto?

A.It travels around the sun twice in the time it takes Neptune to orbit three times.
B.There is no consensus in the scientific community about Pluto's' official classification
C.It is the largest object in the Kuiper Belt.
D.It is located more than 70 AUs from the sun.
E.Its orbit is characterized by relatively small eccentricities.