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BEST IELTS General Reading Test 199
IELTS GENERAL READING TEST 199 – PASSAGE – 3
IELTS GENERAL READING TEST
READING PASSAGE – 3
Shoemaker-Levy 9 Collision with Jupiter
A. The last half of July 1994 witnessed much interest among the astronomical community and the wider public in the collision of comet Shoemaker-Levy 9 with Jupiter. The comet was discovered on 25 March 1993 by Eugene and Carolyn Shoemaker and David Levy, using a 450 mm Schmidt camera at the Mount Palomar Observatory.
The discovery was based on a photographic plate exposed two days earlier. The Shoemakers are particularly experienced comet hunters with 61 discoveries to their credit. Their technique relied on the proper motion of a comet to identify the object as a non-stellar body. They photograph large areas of the sky, typically with an eight minute exposure, and repeat the photograph 45 minutes later. Comparison of the two photographs with a stereo-microscope reveals any bodies which have moved against the background of fixed stars.
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B. As so often in science, serendipity played a large part in the discovery of the Shoemaker-Levy 9. The weather in the night of 23 March was so poor that the observers would not normally have bothered putting film into their camera. However, they had a box of old film to hand which had been partially exposed by accident some days previously, so decided to insert it into the camera rather than waste good film. Fortunately, two of the film plates, despite being fogged round the edges captured the first image of a very strange, bar-shaped object. This object, which Carolyn Shoemaker first described as a squashed comet, later became known as comet Shoemaker-Levy 9.
C. Other, more powerful, telescopes revealed that the comet was in fact composed of 21 cemetery fragments, strung out in a line, which accounted for the unusual shape. The term string of pearls was soon coined. Some graphic proofs obtained by the Hubble Space Telescope shows the main fragments which at that time spanned a linear distance of approximately 600,000 km. Initially the fragments were surrounded by extensive dust clouds in the line of the nuclei but these later disappeared. Some of the nuclei also faded out, while others split into multiple fragments.
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D. The size of the original comet and each of the fragments was, and still is, something of a mystery. The first analysis of the orbital dynamics of the fragments suggested that the comet was originally some 2.5 km in diameter with an average fragment diameter of 0.75 km. Later work gave corresponding diameters of approximately 10 km and 2 km and these values are now considered more likely. There was considerable variation in the diameters of different fragments.
E. Further calculations revealed that the cemetery fragments were on course to collide with Jupiter during July 1994, and that each fragment could deliver an energy equivalent to approximately 500,000 million tons of TNT. The prospect of celestial fireworks on such a grand scale immediately captured the attention of astronomers worldwide!
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F. Each fragment was assigned an identity letter A-W and a coordinated program of observations was put in place worldwide to track their progress towards impact with Jupiter. As the cemetery fragments reached the cloud tops of Jupiter, they were travelling at approximately 30,000,000 km. The impacts occurred during 16-22 July. All took place at a latitude of approximately 48 degrees south which nominally placed them in the SSS Temperate Region, however visually they appeared close to the Jovian polar region.
The impacts all occurred some 10-15 degrees round the limb in the far side of the planet as seen from Earth. However the rapid rotation of the planet soon carried the impact sites into the view of Earth-based telescopes. The collisions lived up to all but the wildest expectations and provided a truly impressive spectacle.
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G. Jupiter is composed of a relatively small core of iron and silicates surrounded by hydrogen. In the depths of the planet the hydrogen is so compressed that it is metallic in form; further from the center, the pressure is lower and the hydrogen is in its normal molecular form. The Jovian cloud tops visible from Earth consist primarily of methane and ammonia. There are other elements and compounds lurking in the cloud tops and below which are thought to be responsible for the colors seen in the atmosphere.
H. The smaller cemetery fragments plunged into Jupiter, rapidly disintegrated and left little trace; three of the smallest fragments, namely T, U and V left no discernible traces whatsoever. However, many of the cemetery fragments were sufficiently large to produce a spectacular display. Each large fragment punched through the cloud tops, heated the surrounding gases to some 20,000 K on the way, and caused a massive plume or fireball up to 2,000 km in diameter to rise above the cloud tops.
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Before encountering thicker layers of the atmosphere and disintegrating in a mammoth shock wave, the large fragments raised dark dust particles and ultra violet absorbing gases high into the Jovian cloud tops. The dark particles and ultra violet absorbing gases manifested themselves as a dark scar surrounding the impact site in visible light.
I. Somedays after collision the impact sites began to evolve and fade as they became subject to the dynamics of Jupiter’s atmosphere. No one knows how long they will remain visible from Earth, but it is thought that the larger scars may persist for a year or more. The interest of professional astronomers in Jupiter is now waning and valuable work can therefore be performed by amateurs in tracking the evolution of the collision scars. The scars are easily visible in a modest telescope, and a large reflector will show them in some detail. There is scope for valuable observing work from now until Jupiter reaches conjunction with the Sun in November 2004.
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J. Astronomers and archivists are now searching old records for possible previously unrecognized impacts on Jupiter. Several spots were reported from 1690 to 1872 by observers including William Herschel and Giovanni Cassini. The records of the BAA in 1927 and 1948 contain drawings of Jupiter with black dots or spots visible. It may be possible that comet impacts have been observed before, without their identity being realized, but no one can be sure.
Questions 27-31
Choose the most suitable headings for paragraphs B-F from the list of headings below
Write appropriate numbers (i-x) in boxes 27-31 on your answer sheet.
NB There are more headings than paragraphs, so you will not use them all.
List of Headings
i. Camera settings for observation
ii. Collisions on stage
iii. Size of comet
iv. String of pearls
v. Scientific explanations
vi. Hubble Space Telescope
vii. First discovery of the squashed comet
viii. Power generated from the collisions
ix. Calculations, expectations and predictions
x. Change of the fragment’s shape
27. Paragraph B
28. Paragraph C
29. Paragraph D
30. Paragraph E
31. Paragraph F
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Questions 32 -35
Reading Passage 3 contains 10 paragraphs A-J.
Which paragraphs state the following information?
Write the appropriate letters A-J in boxes 32-35 on your answer sheet.
32. Shoemaker-Levy 9 comets had been accidentally detected.
33. The collision caused a spectacular vision on Jupiter.
34. Every single element of Shoemaker-Levy 9 was labeled.
35. Visual evidence explains the structure of Shoemaker-Levy 9.
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Questions 36 -40
Choose NO MORE THAN THREE WORDS from the passage for each answer.
The core of Jupiter, which is enclosed by hydrogen, consists of (36)……… and (37)……… . Hydrogen is in metallic form as it is squeezed by pressure generated from the depths of the planet. The pressure is gradually reduced from the center to the outside layers, where hydrogen is in normal form of (38)……… . Far from the ground, methane and ammonia structures the (39)………. , which can be observed from earth. Colors seen in the atmosphere is largely due to other particles (40)……… in the cloud.
ANSWERS ARE BELOW
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ANSWERS
27. vii
28. iv
29. iii
30. viii
31. ii
32. B
33. H
34. F
35. C
36. IRON
37. SILICATES
38. MOLECULE
39. JOVIAN CLOUD TOPS
40. LURKING
IELTS General Reading Test