Welcome to TOEFL Reading Practice Passage 2. Read the academic text below and use your elimination strategies on the single-column formatted questions below it. Aim to finish this mock terminal within 18 minutes.
The Jovian Moons and Tidal Heating
[Paragraph 1] Prior to the Voyager expeditions in the late twentieth century, planetary scientists assumed that small planetary bodies distant from the Sun would be geologically inert. It was hypothesized that standard radioactive decay within their cores would be insufficient to maintain internal heat over billions of years, leaving these worlds frozen and structurally static. However, explorations of the Jovian system revealed surprising geological activity on Jupiter’s innermost Galilean moons, particularly Io and Europa. This unexpected dynamism is driven not by solar radiation or radioactive decay, but by a process known as tidal heating, generated by gravitational interactions.
[Paragraph 2] Io, the closest large moon to Jupiter, exhibits extreme volcanic activity, continuously reshaping its surface with sulfurous lava plains. This phenomenon is a direct consequence of its orbital configuration. Io is locked in an orbital resonance with its neighboring moons, Europa and Ganymede. For every single orbit completed by Ganymede, Europa completes exactly two orbits, and Io completes exactly four, causing the moons to pass each other at regular, predictable intervals. This precise gravitational alignment continuously perturbs Io's trajectory, warping its orbit from a perfect circle into an eccentric, elongated ellipse.
[Paragraph 3] ⬛ [A] As Io travels along this elliptical path, the gravitational pull exerted by Jupiter varies dramatically based on distance. ⬛ [B] When Io reaches its closest point to the massive planet, the intense gravitational field pulls stretching forces across its dynamic mass. ⬛ [C] Conversely, as Io moves further away, the gravitational strain decreases, allowing the moon to snap back into a more spherical shape. ⬛ [D] This continuous physical flexing creates vast internal friction within Io's mantle. This friction converts mechanical orbital energy into immense thermal energy, melting its interior structure and fueling widespread surface volcanism.
Practice Questions
1. According to paragraph 1, what did planetary scientists believe about distant, small planetary bodies before the Voyager missions?
A. They would exhibit high levels of volcanic activity due to intense solar radiation.
B. Their geological activity would be sustained exclusively by rapid orbital resonance.
C. They would be geologically inactive because radioactive decay would fail to maintain internal heat.
D. Their internal temperatures would gradually rise over billions of years.
2. The word "perturbs" in paragraph 2 is closest in meaning to:
A. Disturbs
B. Stabilizes
C. Accelerates
D. Illuminates
3. Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 2?
A. Ganymede and Europa move much faster than Io, which alters how frequently the moons cross paths.
B. The mathematical ratio of the moons' orbits creates regular encounters that alter their gravitational stability.
C. Io requires four times as much energy to complete its orbit compared to the outer moon Ganymede.
D. Regular alignments occur because Io completes its orbit at the exact same moment as Ganymede and Europa.
4. Look at the four squares [⬛] in paragraph 3 that indicate where the following sentence could be added to the passage:
"This constant tidal distortion acts like a repeated physical squeezing, generating heat much like bending a metal paperclip back and forth."
Where would the sentence best fit?
A. Square [A]
B. Square [B]
C. Square [C]
D. Square [D]
Answer Key & Analysis
Question 1: C — Paragraph 1 directly notes that scientists hypothesized "standard radioactive decay within their cores would be insufficient to maintain internal heat... leaving these worlds frozen and structurally static."
Question 2: A — In this astronomical context, to "perturb" an orbit means to disrupt or alter its normal circular path due to gravitational pull. "Disturbs" is the closest matching option.
Question 3: B — This option captures the essential meaning of the orbital resonance description (the 4:2:1 mathematical relationship) and explains that this patterns brings them together at regular intervals.
Question 4: D — The sentence describes the overall consequence of the structural contraction and elongation mentioned in the preceding lines. Placing it at Square [D] perfectly connects the physical description of stretching and snapping back to the subsequent mention of internal friction.
