In 2006, the International Astronomical Union changed the definition of planet. Controversially, the new definition disqualifies Pluto as a planet....
GMAT Reading Comprehension : (RC) Questions
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In 2006, the International Astronomical Union changed the definition of planet. Controversially, the new definition disqualifies Pluto as a planet. Such a change is not unprecedented. The first asteroids discovered were initially classified as planets. But astronomers soon realized that asteroids are much smaller than the other objects captured by their definition and so numerous that it is impractical to consider them all planets. So planets were redefined to be bodies larger than asteroids. Similarly, astronomers now know that Pluto belongs to a vast population of bodies—several much larger than the largest asteroid—called Kuiper belt objects (KBOs). Eris, a KBO discovered in 2005, is larger than Pluto. If Pluto were a planet, then Eris would also be one, along with many other large KBOs. The number of official planets again threatened to become unwieldy. So, as before, the term planet needed redefinition.
The new definition of planet effectively requires a planet to have more mass than all other bodies in its orbital zone combined (roughly speaking, two bodies share an orbital zone if their orbits cross). Pluto, Eris, and the asteroids do not. But each planet in our solar system has at least 5,000 times the combined mass of the other bodies in its orbital zone. Thus, the definition both restricts the number of planets and captures an important natural division between planets and all other bodies in our solar system.
Ques. 1/3
According to the passage, Eris
Solution
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| In 2006, the International Astronomical Union changed the definition of planet. Controversially, the new definition disqualifies Pluto as a planet. | What it says: Scientists changed how they define what counts as a planet, and now Pluto doesn't qualify anymore. People disagreed with this decision. What it does: Sets up the main issue/controversy the passage will address Source/Type: Factual statement about a scientific decision Connection to Previous Sentences: This is the opening - establishes the central topic Visualization: Before 2006: 9 planets (including Pluto) → After 2006: 8 planets (Pluto removed) What We Know So Far: Pluto lost planet status in 2006 What We Don't Know Yet: Why this happened, what the new definition is, whether it makes sense Reading Strategy Insight: The word "controversially" signals the author will likely defend this decision |
| Such a change is not unprecedented. | What it says: This kind of reclassification has happened before in astronomy What it does: Provides reassurance that changing definitions is normal in science Source/Type: Author's contextual statement Connection to Previous Sentences: This builds on the controversy mentioned in sentence 1 by suggesting the change wasn't unusual or wrong Visualization: Pattern: Scientific definitions get updated as knowledge improves Reading Strategy Insight: Feel relieved here - the author is setting up to defend the decision by showing it's part of normal scientific progress |
| The first asteroids discovered were initially classified as planets. But astronomers soon realized that asteroids are much smaller than the other objects captured by their definition and so numerous that it is impractical to consider them all planets. So planets were redefined to be bodies larger than asteroids. | What it says: Long ago, scientists first called asteroids "planets" but then realized asteroids were too small and too numerous, so they changed the definition to exclude them What it does: Provides the historical precedent promised in the previous sentence Source/Type: Historical facts about astronomical classification Connection to Previous Sentences: This is the specific example of "not unprecedented" from sentence 2 - shows exactly how planet definitions have changed before Visualization: Early 1800s: Asteroids = planets (hundreds of "planets") → Later 1800s: Only large bodies = planets (back to manageable number) What We Know So Far: Planet definitions change when old definitions become impractical; asteroids were reclassified before What We Don't Know Yet: How this connects to Pluto specifically Reading Strategy Insight: This historical parallel is setting up the same logic for Pluto's case |
| Similarly, astronomers now know that Pluto belongs to a vast population of bodies—several much larger than the largest asteroid—called Kuiper belt objects (KBOs). | What it says: Just like with asteroids, Pluto is part of a large group of similar objects called KBOs What it does: Creates the parallel between the asteroid situation and Pluto's situation Source/Type: Current scientific knowledge Connection to Previous Sentences: The word "Similarly" explicitly connects this to the asteroid example - we're seeing the same pattern repeat with Pluto and KBOs Visualization: Asteroids: Small, numerous objects that were reclassified KBOs: Pluto + many other similar-sized objects Reading Strategy Insight: This is NOT new complexity - it's the same pattern! The author is showing us Pluto's situation mirrors the asteroid situation |
| Eris, a KBO discovered in 2005, is larger than Pluto. | What it says: There's a specific KBO called Eris that's actually bigger than Pluto What it does: Provides concrete evidence that Pluto isn't unique or special among KBOs Source/Type: Factual observation Connection to Previous Sentences: This builds on "several much larger than the largest asteroid" by giving us a specific example of a KBO larger than Pluto Visualization: Size comparison: Eris > Pluto, and Eris is just one of many KBOs Reading Strategy Insight: This concrete example makes the abstract concept of "vast population" feel real and immediate |
| If Pluto were a planet, then Eris would also be one, along with many other large KBOs. The number of official planets again threatened to become unwieldy. | What it says: Keeping Pluto as a planet would mean Eris and many other KBOs would also have to be planets, making the list too long to manage What it does: Completes the parallel with the asteroid situation - shows the same "too numerous" problem Source/Type: Logical reasoning based on fair classification Connection to Previous Sentences: This restates the exact same logic used for asteroids: "so numerous that it is impractical" = "threatened to become unwieldy" Visualization: Asteroid era: Hundreds of "planets" became unmanageable Modern era: Dozens of KBO "planets" would be unmanageable What We Know So Far: Same problem (too many similar objects) requires same solution (redefine planet) What We Don't Know Yet: What the new definition actually is Reading Strategy Insight: The author has now fully justified the need for redefinition using historical precedent |
| So, as before, the term planet needed redefinition. | What it says: Just like with asteroids, scientists needed to redefine "planet" again What it does: Explicitly restates the main argument in simple terms Source/Type: Author's logical conclusion Connection to Previous Sentences: This is pure restatement - "as before" directly references the asteroid redefinition, showing the pattern is complete Reading Strategy Insight: Feel confident here! This is simplification, not new information. The author is helping by clearly stating the conclusion of their argument |
| The new definition of planet effectively requires a planet to have more mass than all other bodies in its orbital zone combined (roughly speaking, two bodies share an orbital zone if their orbits cross). | What it says: The new rule says planets must be the dominant object in their orbital area - much more massive than everything else in that zone What it does: Finally provides the specific technical definition Source/Type: Official scientific definition (with author's clarifying explanation in parentheses) Connection to Previous Sentences: This gives us the concrete details of the "redefinition" mentioned in the previous sentence Visualization: True planet: Massive object >> all other objects in its orbital zone combined Reading Strategy Insight: The parenthetical explanation shows the author helping us understand technical language |
| Pluto, Eris, and the asteroids do not. | What it says: Pluto, Eris, and asteroids fail this test - they don't dominate their orbital zones What it does: Shows what fails the new definition Source/Type: Factual application of the definition Connection to Previous Sentences: This directly applies the new definition from the previous sentence to the objects we've been discussing Visualization: Pluto + Eris + asteroids = NOT dominant in their orbital zones Reading Strategy Insight: Simple, clear elimination of the problematic cases |
| But each planet in our solar system has at least 5,000 times the combined mass of the other bodies in its orbital zone. | What it says: Real planets are absolutely massive compared to other objects in their areas - at least 5,000 times heavier than everything else combined What it does: Shows what passes the new definition with concrete numbers Source/Type: Factual measurements Connection to Previous Sentences: This contrasts with the previous sentence - while Pluto/Eris/asteroids fail, real planets dramatically exceed the requirement Visualization: Real planets: 5,000+ times more massive than orbital zone competitors Pluto/Eris/asteroids: Less massive than their orbital zone competitors Reading Strategy Insight: The huge number (5,000x) shows there's a clear, dramatic difference between real planets and the excluded objects |
| Thus, the definition both restricts the number of planets and captures an important natural division between planets and all other bodies in our solar system. | What it says: The new definition accomplishes two goals: keeps the planet list manageable AND reflects a real scientific distinction What it does: Provides the final summary of why the new definition is good Source/Type: Author's concluding evaluation Connection to Previous Sentences: This restates the entire argument's conclusion - "restricts the number" refers back to the "unwieldy" problem, and "natural division" refers to the mass dominance criterion What We Now Know: The Pluto redefinition was justified, followed historical precedent, solved a practical problem, and reflects real scientific differences Reading Strategy Insight: Complete confidence boost! The author has systematically defended the controversial decision and shown it makes perfect sense. This conclusion ties together all the threads of the argument. |
2. Passage Summary:
Author's Purpose:
To defend the controversial 2006 decision to reclassify Pluto as a non-planet by showing that this change follows normal scientific practice and makes logical sense.
Summary of Passage Structure:
The author builds their defense of the Pluto decision by drawing a clear parallel with historical precedent:
- First, the author introduces the controversial topic - Pluto losing its planet status in 2006 - and immediately reassures readers that such changes are normal in science.
- Next, the author provides a historical example where asteroids were originally called planets but then reclassified when scientists realized they were too small and too numerous to manage practically.
- Then, the author shows how Pluto's situation mirrors the asteroid case - Pluto belongs to a large group of similar objects called Kuiper Belt Objects, and keeping Pluto as a planet would force scientists to accept many other objects as planets too, making the list unmanageable again.
- Finally, the author explains the new planet definition and demonstrates how it both solves the practical problem of too many planets and reflects a real scientific distinction based on mass dominance in orbital zones.
Main Point:
The decision to reclassify Pluto was the right choice because it followed the same logical pattern used successfully in the past with asteroids, solved a practical problem, and created a definition that reflects genuine scientific differences between true planets and other space objects.
3. Question Analysis:
This is a detail question asking what the passage tells us about Eris specifically. We need to identify factual statements about Eris that are directly stated or logically implied in the passage.
Connecting to Our Passage Analysis:
From our passage analysis, we know several key facts about Eris:
- Eris is a Kuiper Belt Object (KBO) discovered in 2005
- Eris is larger than Pluto
- The passage states that "Pluto, Eris, and the asteroids do not" satisfy the new planet definition
- The new definition requires a planet to "have more mass than all other bodies in its orbital zone combined"
- Since Eris fails this test, it does not dominate its orbital zone
Prethinking:
Looking at what we know about Eris, the most definitive statement we can make is that Eris fails the new planet definition. The passage explicitly groups Eris with Pluto and asteroids as objects that "do not" meet the mass dominance requirement. This means Eris has no more mass than the combined mass of other bodies in its orbital zone - if it had more mass, it would qualify as a planet under the new definition.
Answer Choices Explained
A
satisfies the International Astronomical Union's "new definition of a planet"
Why It's Wrong:
- The passage explicitly states "Pluto, Eris, and the asteroids do not" satisfy the new planet definition
- If Eris satisfied the definition, it would be classified as a planet, but the passage indicates it is not
- This directly contradicts the passage's clear statement about Eris failing the mass dominance test
Common Student Mistakes:
- Did you think that because Eris is larger than Pluto, it must qualify as a planet?
→ Remember that the new definition is based on mass dominance in orbital zones, not absolute size - Did you miss the direct statement about what fails the definition?
→ Look for explicit groupings in the passage - Eris is clearly grouped with non-planets
B
is an asteroid larger than Pluto
Why It's Wrong:
- Eris is described as a "KBO" (Kuiper Belt Object), not an asteroid
- The passage treats asteroids and KBOs as two different categories of objects
- While Eris is larger than Pluto, it's not classified as an asteroid
Common Student Mistakes:
- Did you confuse KBOs with asteroids because both are non-planet objects?
→ Pay attention to the distinct categories the passage establishes - Did you focus only on the size comparison and miss the classification?
→ Note that objects can be large but still belong to specific categories
C
was classified as a planet when it was first discovered
Why It's Wrong:
- The passage states Eris was "discovered in 2005" but doesn't mention its initial classification
- The 2006 definition change occurred after Eris's discovery, so timing makes this unlikely
- No evidence in the passage supports this claim about Eris's original classification
Common Student Mistakes:
- Did you assume Eris followed the same pattern as asteroids historically?
→ Stick to what the passage actually states about Eris specifically - Did you confuse the timeline of discovery versus classification?
→ Note that Eris was discovered in 2005, and the definition changed in 2006
D
is the largest Kuiper belt object, but smaller than any planet
Why It's Wrong:
- While Eris is described as "larger than Pluto," the passage doesn't claim it's the largest KBO
- The passage mentions "several much larger than the largest asteroid" but doesn't rank KBOs by size
- No comparison is made between Eris and current planets in terms of size
Common Student Mistakes:
- Did you assume that because Eris is mentioned first, it must be the largest KBO?
→ The passage uses Eris as an example, not as a superlative case - Did you infer size rankings that aren't stated?
→ Be careful not to add information the passage doesn't provide
E
has no more mass than the combined mass of the other bodies in its orbital zone
Why It's Right:
- The passage explicitly states that "Pluto, Eris, and the asteroids do not" meet the new planet definition
- The new definition requires having "more mass than all other bodies in its orbital zone combined"
- Since Eris fails this test, it logically has no more mass than (meaning less than or equal to) the combined mass of other bodies in its orbital zone
Key Evidence: "The new definition of planet effectively requires a planet to have more mass than all other bodies in its orbital zone combined... Pluto, Eris, and the asteroids do not."
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