雅思阅读 22: Ice Clouds on a Distant Jupiter（遥远木星上的冰云）

改编自 Max Planck Institute / EarthSky（2026年4月）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://earthsky.org/space/jupiter-like-exoplanet-water-ice-clouds-epsilon-indi-ab/

Reading Passage

A. When astronomers want to understand a Jupiter-like planet, they usually look at Jupiter itself. It is, after all, the giant in our own cosmic backyard — a world whose belts, zones and Great Red Spot have been studied for four centuries. But Jupiter has a limitation: it is a cold world, its atmosphere shaped by gravity, rotation and an internal heat source that no human experiment can fully reproduce. Finding another Jupiter — one that can be observed in detail with modern telescopes — offers a chance to test whether our understanding of the solar system's largest planet applies elsewhere. In April 2026, researchers at the Max Planck Institute for Astronomy announced that the James Webb Space Telescope (JWST) had done exactly that: it detected water-ice clouds on Epsilon Indi Ab, a cool Jupiter-like exoplanet orbiting a star about 12 light-years from Earth. At that distance the planet is close enough in galactic terms that its own faint glow, rather than mere reflected starlight, can be isolated from its host. Direct imaging of exoplanets remains rare precisely because it requires that rare combination of proximity, contrast and age.

B. Epsilon Indi Ab is an unusual target. Most exoplanets studied in detail are "hot Jupiters" — gas giants orbiting so close to their stars that their temperatures exceed a thousand degrees. Epsilon Indi Ab, by contrast, orbits far enough from its host star to be relatively cool, roughly 200 degrees Celsius, and it is massive enough — about twice Jupiter's mass — to retain a thick atmosphere. Its distance from its star means it is never lost in the stellar glare; astronomers can observe it directly, separating its light from the star's. That combination — cool, massive, directly observable — is rare among known exoplanets. It also means that its atmospheric chemistry should resemble Jupiter's more closely than any hot Jupiter's, because the temperatures at which water ice condense are found not in a searing hot-Jupiter atmosphere but in a cold, Jupiter-like one. Cold, directly imaged giants are rare because they are faint and easy to mistake for background stars. Most known examples are young and hot, glowing brightly from their formation; Epsilon Indi Ab is among the few that has cooled to temperatures where familiar condensates like water ice can persist.

C. The JWST observations were designed to look for specific chemical signatures. Water vapour, methane and ammonia all absorb light at characteristic infrared wavelengths, and JWST's spectrometers are sensitive enough to detect them in the faint light of a directly imaged exoplanet. What the team found, however, was not just the expected gases: the spectrum also showed a distinctive dip in brightness at wavelengths where water ice — not vapour — absorbs light. The dip was consistent with a layer of tiny ice crystals high in the atmosphere, floating above the deeper gaseous layers. The finding was not entirely unexpected — Jupiter itself has ammonia ice clouds, and water ice is a natural condensation product in cold hydrogen atmospheres — but it is the first time such clouds have been detected on a directly imaged exoplanet. The ice crystals themselves are expected to be microscopic, too small to see directly; their presence is betrayed only by the specific way they scatter and absorb infrared light. Reconstructing a cloud layer from such indirect evidence is a familiar exercise in planetary science — the same puzzle, scaled up from Jupiter's atmosphere to another system entirely.

D. The detection also corrects a prior uncertainty. Earlier observations of Epsilon Indi Ab, made with ground-based telescopes and the Hubble Space Telescope, had produced ambiguous spectra that could not clearly distinguish between water vapour and water ice. Some models suggested the planet was relatively cloud-free; others predicted thick cloud decks. JWST's higher sensitivity and broader wavelength range resolved the ambiguity: the clouds are present, and they are made of water ice. The team, led by MPIA scientist Mark Marley, cautioned that the exact altitude and thickness of the cloud layer remain uncertain, and that further observations are needed to determine whether the clouds are persistent or vary seasonally — though Epsilon Indi Ab's long year, which lasts more than 200 Earth years, means seasonal changes would be extremely slow to observe. The contrast with earlier efforts is useful here. Ground-based telescopes and Hubble had hinted at clouds but could not say what they were made of; JWST, with its sharper infrared vision, settled the question in a single observing programme. The remaining uncertainty — how thick the layer is, and how it varies — is the kind that accumulates slowly over years of follow-up rather than in one decisive observation.

E. Why does this matter? Epsilon Indi Ab is, in effect, a laboratory for comparing Jupiter to another gas giant under almost identical physical conditions. If both planets show water-ice clouds at similar altitudes, it suggests that the atmospheric physics governing cloud formation in hydrogen-rich atmospheres is universal — that the processes which produce Jupiter's belts and zones do not depend on the specific history of our solar system. If the two worlds differ, the differences reveal something about how giant planets evolve. The detection also demonstrates that JWST can study directly imaged exoplanets in sufficient detail to identify condensate clouds — a capability that will be applied to a growing list of gas giants as the telescope's observing programme expands. In a field once limited to point-source spectroscopy of hot, glaring worlds, a cool, cloudy Jupiter — seen in its own light, 12 light-years away — is the closest thing astronomy has to a second planet to compare against the first. Future instruments will extend the same comparison to more such worlds, testing whether cold giant atmospheres everywhere condense the same chemicals in the same order. For now, Epsilon Indi Ab stands as the first of a hoped-for class: a distant cousin close enough, cold enough and bright enough to be read as a weather report rather than merely as a point of light.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. What makes Epsilon Indi Ab a special target ii. The history of Jupiter observations iii. What JWST found — and what was unexpected iv. Resolving earlier ambiguity about the clouds v. Why the comparison with Jupiter is scientifically valuable vi. How water ice is formed in laboratories vii. The cost of the JWST mission

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. Why is Epsilon Indi Ab different from most studied exoplanets? A. It orbits extremely close to its star. B. It is a cool, massive gas giant observable directly. C. It has no atmosphere. D. It is smaller than Earth.

6. What did JWST detect that was notable? A. Liquid water oceans on the surface. B. A layer of water-ice crystals high in the atmosphere. C. Signs of biological activity. D. A ring system like Saturn's.

7. How did earlier observations compare? A. They had already clearly detected water-ice clouds. B. They were ambiguous between water vapour and water ice. C. They showed the planet was cloud-free. D. They found no atmosphere at all.

8. Why is the comparison with Jupiter scientifically important? A. It proves that all gas giants are identical. B. It tests whether atmospheric physics in hydrogen-rich atmospheres is universal. C. It shows that Jupiter is unique in the galaxy. D. It confirms that Epsilon Indi Ab is a copy of Jupiter.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Epsilon Indi Ab is about 12 light-years from Earth.
10. The planet is hotter than most hot Jupiters.
11. Epsilon Indi Ab's year lasts more than 200 Earth years.
12. The cloud layer's exact altitude has been precisely determined.
13. Astronomers have detected one or more moons orbiting Epsilon Indi Ab.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

JWST detected water- (14) __________ clouds high in Epsilon Indi Ab's atmosphere, the first such detection on a (15) __________ imaged exoplanet.

答案与解析

← 上一篇 | 返回雅思焦点 | 下一篇 →