TOEFL Experts Reading Practice 32
Prior to 2006, the International Astronomical Union (IAU) had no formal definition of a planet, and it was generally assumed that the Solar System contained nine planets. Before the astronomical discoveries of the early twenty-first century, the definition of a planet seemed self-evident: a large body orbiting the Sun, readily distinguishable from moons, which orbit planets. In the early 1800s, smaller orbiting bodies were discovered; these were eventually classified as asteroids. Around the same time, astronomers also used increasingly powerful telescopes to identify additional planets beyond Saturn that were not readily visible to the naked eye. The first planet discovered was Uranus, sighted in 1781 by astronomer William Herschel. The charting of Uranus’s unusual orbit then led scientists to predict the presence of another planet, whose gravitational pull would account for the irregularities in Uranus’s movement around the sun. The resulting calculations of the new planet’s position were so accurate that, in 1846, astronomer Johann Galle finally observed Neptune within a degree of its predicted location. Subsequently, additional observations of Uranus led astronomers to conclude that there was yet another planet in the outer reaches of the Solar System.
One of the early proponents of the existence of a new planet was Percival Lowell, a wealthy Bostonian who founded the Lowell Observatory in Arizona in 1894. He spearheaded extensive research into the existence of a ninth planet, known as “Planet X.” This research was unsuccessful during Lowell’s lifetime. After Lowell’s death, the search stalled for over a decade, resuming only in 1929, when the young astronomer Clyde Tombaugh was tasked with finding the planet. Tombaugh systematically took pairs of photographs of the night sky to look for a moving object, spending nearly a year on this painstaking task. His efforts were rewarded in January 1930, when he finally obtained evidence of Planet X’s existence.
This planet was named Pluto and remained the ninth planet until the early twenty-first century, when new discoveries called its status as a planet into question. These discoveries included the sightings, starting in the early 1990s, of a number of other large objects near Pluto, which are now known as Kuiper Belt objects. Discovered in 2005, Eris is the largest of these. Eris is significantly more massive than Pluto and was briefly called the tenth planet by some. The lack of consensus on Eris’s planetary status led the IAU to convene a meeting on the definition of a planet in 2006.
So is Pluto a planet? According to the definition produced by the IAU in 2006, it is not. A planet must meet three criteria: it orbits around the Sun; it is large enough to form itself into a sphere; and it is also large enough to clear other objects of significant size from its orbit. If one sticks rigorously to this definition, Pluto is not a planet; it meets only the first two criteria, as there are a number of other objects, like Eris, in its vicinity. However, not all astronomers agree with this definition; some believe that the presence of asteroids in the orbit of planets like Earth, Mars, and Jupiter would similarly disqualify them as planets.
Scientists continue to disagree about Pluto’s status. Another debate on the subject was held in 2008, but the attendees did not reach agreement on the subject. Additionally, there was a wide public outcry, based largely on sentimental attachment, when Pluto’s new classification as a “dwarf planet” was announced. Given the existence of a number of other large objects near Pluto, continuing to define Pluto as a planet could lead to the classification of many other entities as planets. Demoting Pluto seems like a simpler solution.
This is not to say that claims supporting Pluto’s status as a planet don’t have merit. Pluto does, in many respects, resemble other planets in the Solar System in its orbit and shape. Unlike these planets, though, Pluto is relatively small and has an unusual relationship with its large moon, Charon. Furthermore, the presence of many similar large bodies in Pluto’s vicinity suggests that, without a clear standard definition such as the one decided upon by the IAU, we could find ourselves one day including dozens of planets in our Solar System, making for some extremely complicated school science projects.
Prior to 2006, the International Astronomical Union (IAU) had no formal definition of a planet, and it was generally assumed that the Solar System contained nine planets. Before the astronomical discoveries of the early twenty-first century, the definition of a planet seemed self-evident: a large body orbiting the Sun, readily distinguishable from moons, which orbit planets. In the early 1800s, smaller orbiting bodies were discovered; these were eventually classified as asteroids. Around the same time, astronomers also used increasingly powerful telescopes to identify additional planets beyond Saturn that were not readily visible to the naked eye. The first planet discovered was Uranus, sighted in 1781 by astronomer William Herschel. The charting of Uranus’s unusual orbit then led scientists to predict the presence of another planet, whose gravitational pull would account for the irregularities in Uranus’s movement around the sun. The resulting calculations of the new planet’s position were so accurate that, in 1846, astronomer Johann Galle finally observed Neptune within a degree of its predicted location. Subsequently, additional observations of Uranus led astronomers to conclude that there was yet another planet in the outer reaches of the Solar System.
One of the early proponents of the existence of a new planet was Percival Lowell, a wealthy Bostonian who founded the Lowell Observatory in Arizona in 1894. He spearheaded extensive research into the existence of a ninth planet, known as “Planet X.” This research was unsuccessful during Lowell’s lifetime. After Lowell’s death, the search stalled for over a decade, resuming only in 1929, when the young astronomer Clyde Tombaugh was tasked with finding the planet. Tombaugh systematically took pairs of photographs of the night sky to look for a moving object, spending nearly a year on this painstaking task. His efforts were rewarded in January 1930, when he finally obtained evidence of Planet X’s existence.
This planet was named Pluto and remained the ninth planet until the early twenty-first century, when new discoveries called its status as a planet into question. These discoveries included the sightings, starting in the early 1990s, of a number of other large objects near Pluto, which are now known as Kuiper Belt objects. Discovered in 2005, Eris is the largest of these. Eris is significantly more massive than Pluto and was briefly called the tenth planet by some. The lack of consensus on Eris’s planetary status led the IAU to convene a meeting on the definition of a planet in 2006.
So is Pluto a planet? According to the definition produced by the IAU in 2006, it is not. A planet must meet three criteria: it orbits around the Sun; it is large enough to form itself into a sphere; and it is also large enough to clear other objects of significant size from its orbit. If one sticks rigorously to this definition, Pluto is not a planet; it meets only the first two criteria, as there are a number of other objects, like Eris, in its vicinity. However, not all astronomers agree with this definition; some believe that the presence of asteroids in the orbit of planets like Earth, Mars, and Jupiter would similarly disqualify them as planets.
Scientists continue to disagree about Pluto’s status. Another debate on the subject was held in 2008, but the attendees did not reach agreement on the subject. Additionally, there was a wide public outcry, based largely on sentimental attachment, when Pluto’s new classification as a “dwarf planet” was announced. Given the existence of a number of other large objects near Pluto, continuing to define Pluto as a planet could lead to the classification of many other entities as planets. Demoting Pluto seems like a simpler solution.
This is not to say that claims supporting Pluto’s status as a planet don’t have merit. Pluto does, in many respects, resemble other planets in the Solar System in its orbit and shape. Unlike these planets, though, Pluto is relatively small and has an unusual relationship with its large moon, Charon. Furthermore, the presence of many similar large bodies in Pluto’s vicinity suggests that, without a clear standard definition such as the one decided upon by the IAU, we could find ourselves one day including dozens of planets in our Solar System, making for some extremely complicated school science projects.
- Until the twenty-first century, astronomers did not have a standard definition of a planet.