(1) Quick—how many planets are there in the solar system? It's a simple question, but there's no easy answer. You might have learned there are nine: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. But now that view of the solar system is out of date. Depending on who you talk to today, the answer could be eight, 12, or even 208 and counting.
(2) How is that possible? Over the past 15 years, larger and stronger telescopes have given astronomers a better look at the far reaches of the solar system. Over that time, they have discovered an entire new class of objects orbiting the Sun well beyond the orbit of Neptune. Some of these objects are just as big—or bigger—than Pluto. These discoveries have forced scientists to think deeply about what it means to be a planet.
(3) In 2006, the International Astronomical Union (IAU) defined "planet" in a way that kicked Pluto out of the planet tribe. But many astronomers disagreed with the definition. This summer, they and their colleagues met in Maryland for "The Great Planet Debate." There scientists on both sides discussed how to define the new objects being discovered far out in the solar system every year. Some hope the IAU will re-visit the definition of a planet when the organization meets again next year.
(4) The questions they're wrestling with are hardly new. Scientists have been naming, re-naming and categorizing the various parts of the solar system ever since people began looking at and documenting the objects in the night sky thousands of years ago. Over time, new observations and improvements in technology led to a better understanding of the nature of the universe. As a result, scientists have sometimes been forced to re-name objects they thought were planets. Or they have had to define new categories of objects entirely. That's just what's happening with Pluto today. And it has been happening for as long as people have been looking toward the night sky.
From Seven to Sixteen
(5) It was the ancient Greeks who first coined the name "planet." The word means "wandering star," explains David Weintraub. He's an astronomer at Vanderbilt University in Nashville, Tenn. Aristotle, the Greek natural philosopher who lived more than 2,000 years ago, identified seven "planets" in the sky. They're the objects that today we call the sun, moon, Mercury, Venus, Mars, Jupiter and Saturn. It was a view of planets that held for 1,500 years, Weintraub notes.
(6) "The seven planets according to the Greeks were the seven planets at the time of Copernicus, and those seven included the sun and the moon," he says.
(7) Nicolaus Copernicus was the Polish astronomer who suggested that the sun, and not the Earth, was at the center of what we today call the solar system. This was in the early 1500s. He removed the sun from the planet tally. Then, in 1610, Galileo Galilei pointed a telescope to the sky. This Italian mathematician saw, for the first time, the objects we know today at the four moons of Jupiter.
(8) Later that century, the astronomers Christiaan Huygens and Jean-Dominique Cassini spotted five additional objects orbiting Saturn. At the end of the 1600s, astronomers agreed that the objects orbiting Jupiter and Saturn, along with those two planets, Mercury, Venus, Earth, Earth's moon and Mars should all be called planets. This brought to 16 the number of objects called planets.
(9) Between that time and the early 1900s, the number of objects astronomers called planets fluctuated. It went from a high of 16, back to six when the objects circling planets were reclassified as moons. Then it went up to seven when Uranus was discovered, and up still more, to 13. This was after the initial discovery of several objects lying between Mars and Jupiter—objects we know today as asteroids.
The Trouble With Pluto
(10) In 1992, University of Hawaii astronomers David Jewitt and Jane Luu (who is now at the Massachusetts Institute of Technology) discovered a new object in Pluto's neighborhood which is beyond the orbit of Neptune. Within one year alone, scientists identified five more objects in the region of the solar system called the Kuiper belt, named for the astronomer who predicted its existence about 60 years ago.
(11) And all these new objects are what got Pluto into trouble, says Guy Consolmagno. He's an astronomer at the Vatican Observatory and past president of the IAU commission on planets and moons.
(12) "When we first discovered Pluto, it was the only thing out there," he says.
(13) And so in 2006, the International Astronomical Union passed a rule that changed Pluto from "planet" to a new classification: "dwarf planet." And just this year, they changed its designation yet again. This time it became part of a new class called "plutoid."
(14) The new classification considers an object a planet based largely on how it interacts with other objects in the solar system, Consolmagno explains. "The eight major planets are so big they control everything around them," he says. The larger a space object is, the more powerful is its gravity, the invisible pull that keeps moons circling planets and the planets circling the sun. The gravitational control a planet exerts influences the overall structure of the solar system, Consolmagno says.
(15) "But Pluto is not so big that it defines the gravitational structure of its neighbors," he says. For that reason, he says, it shouldn't be considered in the same category as the rest of the planets.
(16) Not all astronomers agree these are the most important traits to consider in planet hood. Many others say planets should be classified based on physical characteristics, such as shape, size and geology.
This question has two parts. First. answer Part A. Then, answer Part B.
Part A
Which statement describes a central idea of the passage?
A. Planets have a large gravitational pull that brings other objects into their orbit.
B. There is widespread disagreement among modern scientists about the definition of a planet.
C. New technologies have allowed astronomers to learn more about the planets in our universe.
D. The number of planets we have identified has increased greatly since the early days of astronomy.
Part B
Which quotation from the passage best supports the answer to Part A?
A. "Depending on who you talk to today, the answer could be eight, 12, or even 208 and counting." (paragraph 1)
B. "Over time, new observations and improvements in technology led to a better understanding of the nature of the universe." (paragraph 4)
C. "At the end of the 1600s, astronomers agreed that the objects orbiting Jupiter and Saturn, along with those two planets, Mercury, Venus, Earth, Earth's moon and Mars, should all be called planets." (paragraph 8)
D. "The larger a space object is, the more powerful is its gravity, the invisible pull that keeps moons circling planets and the planets circling the sun." (paragraph 14)
For part A I think the answer is C because there's not a lot of debate and argument about the number of planets, but the passage is written in chronological order which shows the advances thought time, for part B the answer is B because it shows the thesis statement. Btw keep in mind I skimmed over the passage and am just trying to be useful, thanks :)
Please someone help me. :)
I'm the one who posted the question
Yeah right. I'm the one who posted it, I'm the one who needs help with it. I'm not great at reading.
Only if people weren't plain out stupid.
*Dummy
Part A
The central idea of the passage is: B. There is widespread disagreement among modern scientists about the definition of a planet.
Part B
The quotation from the passage that best supports the answer to Part A is: A. "Depending on who you talk to today, the answer could be eight, 12, or even 208 and counting." (paragraph 1)