单选题
In the 1970s, Charles Kowal at mount Palomar
Observatory discovered Chiron, an asteroid whose orbit was in the vicinity of
Saturn and Uranus, far from other known asteroids. In the
1990s, robotic telescopes began to comb the Kuiper Belt, the region of the solar
system beyond the obit of Neptune. More than 400 objects were discovered there,
with the biggest object about half the size of Pluto. Last
year, the farthest asteroid to date was found: Sedna, named after an Inuit
goddess who dwells in a cave at the bottom of the Arctic Ocean. Sedna has a very
eccentric orbit that takes it nearly 1,000 times farther from the Sun than Pluto
and outside the Kuiper Belt. In early January 2005, the same
team that discovered Sedna found a larger body. From its light and absence of
infrared radiation, the team of Brown, Trujillo, and Rabinovitz are certain that
the object's size is between that of Pluto (1,485 miles across) and our moon
(2,160 miles across). Its temporary name is 2003 UB313.
Presently, the object is 9 billion miles from the sun, about three times as far
as Pluto. At this distance from the Sun, 2003 UB313 has a surface temperature of
415~ below zero. This Kuiper Belt object takes 560 Earth years
to orbit the Sun. 2003 UB313's orbit has a tilt of 44 degrees to the plane of
the solar system, more than twice the tilt of Pluto (the previous planet record
holder). Its minimum solar distance is 3.3 billion years, close to the edge of
Neptune's orbit. 2003 UB313's orbit is well-known due to its
being captured on wide angle photographs taken in 2003 by the 4-foot-wide
Schmidt telescope on Mount Palomar. Will UB313 be called the
tenth planet? The decision is up to the International Astronomical
Union. Asteroids are mini-planets, most of which are located in
the asteroid belt, between the orbits of Mars and Jupiter. The largest of the
belt asteroids is Ceres, about 700 miles across (i. e. roughly the size of
Texas). Most asteroids are much smaller, typically less than a mile
across. While most asteroids keep their distance from Earth,
there are probably 1,000 asteroids that are located in the inner solar system
and may cross Earth's orbit. Last summer, a robotic telescope
discovered a 1,000-foot-wide asteroid that crosses Earth's orbit. The object is
99942 Apophis. Once Apophis' orbit was determined, its future positions decades
ahead were generated by computer. There was a shock when an
early study showed Apophis to be on a collision course with Earth in 2029. More
early observations were utilized to refine Apophis' orbit; new calculations
showed that on April 13,2029, Apophis would instead pass 22,000 miles from
Earth, which is a little less than three Earth diameters. Apophis will then be
visible to the naked eye from Europe and western Africa.
单选题
The author provides information that would answer which of the
following questions?