Download Part 1 ( pp. 2-5) In considerable detail To display a diversity

Part 1 ( pp. 2-5)
1. In considerable detail
2. To display a diversity
3. Composition
4. Presumably
5. The wealth of data
6. Propagation
7. To be poorly understood
8. All encompassing theory
9. State of affairs
10. To reveal
11. To make up
12. The planetary system
13. The solar system
14. To constrain a theory
15. To emerge
16. Chemical composition
17. The solar nebula
18. To strengthen an idea
19. Stellar evolution
20. A relative newcomer
21. Internal/external
22. To dazzle
23. To be destined
24. To occur
25. Constellation
26. To absorb
27. To spawn
28. Sensitive telescope
29. Unaltered material
30. Universality of processes
31. Stellar component
32. Rate of rotation
33. To heat up/to cool down
34. Conversion
35. To result from
36. Angular momentum
37. Nuclear fusion
38. Assemblage of matter
39. Ejection
40. To achieve certainty
41. To convert smth into smth
42. To rotate on the axis
43. To revolve around
44. As early as the Xth century
45. To challenge a theory
46. Large-scale
47. It’s enlightening
48. To invoke
49. To encounter resistance
50. To postulate
51. An accurate estimate
52. To account for
53. Phenomenon – phenomena
54. Satellites
55. Asteroids
56. Comets
57. To condense
58. To survey
59. A perspective on smth
60. Array of species
Part 1
1. Context of the Planetary System
In this book we have discussed more than fifty worlds; some in considerable detail. These planets, satellites,
asteroids and comets display an incredible diversity of composition and history. Yet they were all
presumably formed at about the same time, condensing from the primordial solar nebular that also gave birth
to the Sun. In spite of their individual diversity, these bodies carry many clues concerning their origins.
Lurking in the background is the question of the likelihood that there are other, perhaps similar, planetary
systems around other stars. If we can understand the processes that formed the planets we know, we can then
try to predict how probable it is that these same processes produced other planets, including some like ours.
Similarly, if we could find planets orbiting other stars, their existence might help us to understand the origins
and evolution of our own system.
Having stated what we would like to do, we must admit right away that it is not yet possible to do it. We are
unable to work backward from the wealth of data on the present state of the solar system to derive a unique,
detailed picture of how the system began. Neither can we work forward from a theory of star formation to
the production of a solar system with all the properties we find today. Even the first and most important step,
the formation of the Sun itself, is only poorly understood. Instead of a unique and all encompassing theory,
we must work with a collection of reasonable explanations for those properties of the solar system that seem
especially basic.
This somewhat unsatisfactory state of affairs may change dramatically within the next decade or two. Spacebased telescopes launched before the end of this century should have the capability to survey hundreds of
nearby stars for planets substantially smaller than Jupiter. At the same time, infrared and radio astronomy are
constantly revealing more about the formation and early evolution of stars. The direct detection of other
planetary systems, together with a deeper understanding of the star-formation process, may provide a much
sharper perspective on these problems than is possible with our present limited information.
2. The ages of the Sun and Stars
At the beginning of the 20th century, many astronomers thought that the planets were formed as the result of
a remarkable accident, such as the near-collision of the Sun with another star. Since then, we have come to
realize that stars naturally form in a cloud of dust and gas, what we have called the solar nebula in the case
of our own system. Further, a variety of kinds of matter have been located orbiting nearby stars, and while
none of these has yet turned out to be another planetary system like our own, their existence strengthens the
idea that stars do not form alone. Finally, we now know that the ages of the Sun and of the planetary system
are approximately the same. As we have seen, the Moon, the meteorites, and the Earth all formed 4.5 billion
years ago. Astrophysicists who study stellar evolution give this same value for the age of the Sun. From all
of these arguments, we conclude that the Sun and the planets probably formed together from a common
source of material.
Of course, not all stars have the same age. The galaxy is at least 12 billion years old, and many of the stars
have been present since its formation. Stars that formed early in the life of the galaxy contain much smaller
quantities of the heavier elements, and for this reason they may be less likely to have formed planets. The
very existence of the building blocks of our planetary system depends on the presence of heavy elements
formed in previous generations of star and ejected back into interstellar space before our own system
formed.
On a galactic time scale, the Sun is a relative newcomer. We are not among the latest arrivals, however.
Stars that are more massive than the Sun have much shorter lifetimes. Their internal temperatures are hotter
and their nuclear fires burn with greater intensity. The bright blue-white stars that dazzle us at night are all
younger than the Sun. some of them have ages of only a few millions of years instead of billions. The most
brilliant and massive of these stars are destined to explode as supernovas, generating a very special group of
elements that can only be created in the unique conditions that briefly occur during these cosmic cataclysms.
3. Stellar Nurseries
Even younger stars exist, since they are being formed today. Star formation takes place in clouds of
interstellar gas and dust such as those in the constellation of Orion. A typical interstellar cloud in which star
formation is occurring has a mass hundreds of times greater than that of the Sun. It is composed primarily of
hydrogen and helium, the predominant elements in the stars that it will spawn. The other elements that can
be studied appear to be present in roughly the same proportions as they are found in the Sun and other young
stars.
What may seem surprising, however, is the richness of the molecular chemistry that takes place in these
clouds. Instead of just simple compounds like methane and ammonia, a large array of molecular species is
being formed. A list of those known at the time of this writing would include more than sixty entries. Among
the more interesting compounds, we call attention to ethyl alcohol, formaldehyde, used for preserving
corpses, and hydrogen cyanide, a deadly poison. New molecules are constantly being discovered as
astronomers use more sensitive radio telescopes and study new segments of the radio spectrum.
It is interesting to compare a list of interstellar molecules with the molecules found in comets. Some
scientists think that the icy nuclei of comets contain unaltered interstellar material, trapped during the
earliest stages of the formation of the solar system. Alternatively, it may be that the similarities simply
reflect the universality of the processes that produce these compounds, whether they take place in the solar
nebula or in the interstellar clouds.
4. A star is born
One of the first things to notice about stars is that most of them are members of multiple systems. Doubles
and triples are more common than singles, but it seems unlikely on dynamical grounds that such multiple
star systems will have many planets. Depending on the masses and distances of the stars, however, there
may be regions around one or more of the stellar components where planetary orbits could be stable. Since
we have neither the observations nor a theory for such systems, we will concentrate our attention on the
much simpler case of single stars, like the Sun.
We start with a slowly rotating cloud of interstellar gas and dust that may itself be part of a much larger
complex such as one of the giant clouds in Orion. At some point the cloud begins to collapse. Perhaps some
gravitational instability has been created in its interior, by a random coming together of some of the material,
or a nearby star has exploded as a supernova, perhaps seeding the cloud with short-lived radioactive
elements and sending out shock waves that begin to compress the cloud. The collapse is possible as long as
the energy of motion of the gas in the cloud is less than the gravitational energy represented by the mass of
the cloud and the distance through which it collapses.
As the cloud becomes smaller, three things happen: 1) its rate of rotation increases, 2) it flattens into a disk,
3) it heats up. The heating is simply the conversion of gravitational energy to thermal energy. The increase
in rotation rate results from conservation of angular momentum: as the mass of the cloud comes closer to the
center, the angular velocity must increase to keep the momentum constant. The more rapid spin in turn
causes the material to flatten into a disk.
In the disk, the gas and dust can radiate energy to space much more easily than in the center, where a
spherical condensation develops. Here the temperature continues to rise until it finally reaches the point
where nuclear fusion of hydrogen to helium can occur. At this stage, the Sun turns on and this spherical
assemblage of matter begins its life as a star.
5. The mass and Dimensions of the Disk
There is still a great deal of dispute about the mass and the dimensions of the original solar nebula and of the
disk itself. The central condensation must have had a mass nearly equal to that of the present Sun, but about
the disk.
We can gain an idea of the minimum amount of mass that must have been present if we simply ask how
much material of cosmic composition would be required to make all the present planets. The idea behind this
calculation is that the solar nebula started with cosmic composition and then the individual planets formed
from it with compositions reflecting the local temperature. If it had been cooler close to the Sun, massive
planets like Jupiter and Saturn might have formed there.
To discover what these hypothetical planets would have been like, we can perform the thought experiment of
adding hydrogen and helium to the existing planets until the ratio of these light elements to a key heavy
element like silicon or iron is the same as it is in the Sun. The masses of the resulting planets are indeed
similar to those of Jupiter and Saturn. Thus we might conclude that the initial disk must have had a mass
roughly equal to at least ten times the present mass of Jupiter.
More likely, planet formation will not be efficient, and there was probably much more material available that
has since been lost by the blowing away of the nebula or by gravitational ejection of larger bodies after the
planets formed. Hence these days scientists generally adopt a value for the entire nebula of about 1.1 to 1.2
times the mass of the Sun. Recent observations of similar disks of matter around young stellar objects
indicate masses of this magnitude. However, some theories hold out for much higher masses, on the order of
twice the solar mass, which simply demonstrates how much more work to be done in this field to achieve
some real certainty.
6. Dynamics of the Disk
We now have a newly born star at the center of a disk of gas and dust. This configuration can still be thought
of as the primordial solar nebula, despite the fact that deep in the interior of the central condensation, nuclear
reactions, are beginning to convert hydrogen to helium.
The disk is revolving around this central condensation in the same sense that the condensation itself is
rotating on its axis. Immanuel Kant and Pierre Simon Laplace proposed nebular theories for the origin of the
solar system as early as the 18th century. The main reason these theories were challenged was the attention
given to the fact how the Sun could slow down by transferring angular momentum to the disk and hence the
planets.
It’s enlightening to put this problem in context. It turns out that all stars with masses 15% or more greater
than that of the Sun rotate much more rapidly than our star. If one calculates the rotation rate the Sun should
have, given conservation of angular momentum as the original cloud collapsed, this rate turns out to be
similar to that of the more massive stars. It is also the rate that would result if the present angular momentum
of the planets were put back into the Sun.
7. Magnetic Braking
One solution to this problem invokes magnetic braking. The material of the disk is following orbits defined
by Kepler’s laws. Thus it is orbiting the Sun more slowly than the Sun is rotating. The situation is analogous
to the interaction of the material in the Io plasma torus with the rapidly spinning magnetic field of Jupiter.
The material in the inner part of the disk is ionized. The Sun’s magnetic field encounters resistance from this
plasma as the Sun rotates, slowing down the spin.
This idea has several problems. It doesn’t explain why only stars with low masses exhibit slow rotation,
since it is well known that some stars with large masses have strong magnetic fields. A solution to this
dilemma would be to postulate that only low-mass stars form with disks, but we now know that disks are not
uncommon about young stars with masses greater than the Sun’s. Finally, magnetic braking would transfer
angular momentum to the disk and hence to the planets. Yet as we have seen, the problem is not that the
planets have too much momentum, but only that the Sun has too little.
8. The Solar Wind: Blowing the Problem Away
A second solution involves the solar wind. Recall that the gases in the outer fringes of the solar atmosphere
have enough energy to escape into space, flowing steadily outward through the solar system at speeds of
about 400 km/s. The amount of matter lost in this way is a tiny fraction of the Sun’s total mass.
Observations of very young stars with small masses like the Sun’s indicate that they generate intense stellar
winds shortly after they form. While it is difficult to make an accurate estimate of this effect, it appears
sufficient to account for the present slow rotation of the Sun.
An especially appealing aspect of this theory of solar wind braking is its natural explanation of the massdependence of stellar rotation. It turns out that only stars with masses comparable to or less than that of the
Sun have the proper atmospheric structures to produce steady stellar winds. Hence the same strong wind that
ultimately clears residual gas and dust from the disk can slow down the rapidly rotating star that generates it.
More massive stars will not produce such winds, so they will continue to exhibit rapid rotation.
Tasks
Task 1 Fill in the gaps in the sentences with the appropriate word from the list.
chemical composition, to dazzle, constellation, to postulate, to occur, to reveal, external, conversion(2), to
invoke, internal, ejection, to spawn
1. By means of a study of the typography and the ________ of the paper, they ascertained it to be a
fraud.
2. The tests detect genetic markers that _________ whether people share a common ancestor or relative.
3. It proved an ____________ combustion engine could power a vehicle and a human being could
control it.
4. Mudpuppies are easily distinguishable by their bushy, red _________ gills, which they grow as larva
and never lose.
5. Once again, that marvelous package of scientific instrumentation is free _________ our senses and
boggle our minds.
6. Some beta-blockers, however, are also useful in reducing the frequency of migraine attacks and their
severity when they _________.
7. He built the only truly global _________ of news, sports, and entertainment properties.
8. The number of indigenous fish was falling, since the floods that induce them __________ were
becoming rarer.
9. It is useful to examine the impacts of a monolithic energy ________ strategy using various energy
__________ technologies.
10. The term jet propulsion refers to the action produced by a reactor to the ________of matter.
11. One way out of that dilemma is __________ a phenomenon known to biologists as group selection.
12. Used and accurately applied their mental model of the world ___________ a physical explanation for
findings.
Task 2 Match the definitions with the terms.
The planetary system, The solar system, Chemical composition, Angular momentum, Solar nebula, Nuclear
fusion
1. The identities, and relative numbers, of the elements that make up any particular compound.
2. consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which
formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago.
3. the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier
nucleus.
4. The rotating flattened cloud of gas and dust from which the sun and the rest of the bodies in the solar
system formed, about 4.56 × 109 years ago.
5. a vector quantity that can be used to describe the overall state of a physical system. The angular
momentum L of a particle with respect to some point of origin.
6. a set of gravitationally bound non-stellar objects in orbit around a star or star system.
Task 3
Translate the sentences that are underlined in the text into Russian.
Task 4
Give full names to the following elements.
1. CH2OH2 –
2.
3.
4.
5.
6.
CH2O –
HCN –
CO2 –
OH –
H2O –
Task 5
Translate the sentences into English, using the active vocabulary above.
1. Результаты исследования, опубликованные в этом журнале, обнаружили недостатки метода,
применяемого ранее.
2. Его возражения только усилили убеждение оппонентов.
3. Внутренние механизмы организма способны как уберечь его от распространения раковых
клеток, так и ускорить его.
4. Необходимо избавиться от всего, что способствует размножению плесени, поскольку она
негативно повлияет на ход эксперимента.
5. Даже развитые страны еще не готовы к переходу от крупномасштабного использования
полезных ископаемых к использованию водорода как основного источника энергии.
6. В неизмененном состоянии эта вакцина не содержит загрязняющих кровь веществ.
7. Культурное и этническое разнообразие ценится выше в демократических странах.
8. Применяя новые материалы при конструировании солнечных батарей, можно утверждать, что
они поглощают теперь больше солнечного света и преобразуют его в энергию эффективнее.
9. При современном изобилии информации, ученые сочли возможным сослаться на ранее не
изученное явление “групповой селекции”.
10. Последнее время многие ученые придерживаются противоположных взглядов на данную
проблему, постоянно подвергая сомнению ее правильность.