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1 There's a dimmer switch inside the sun that causes its brightness to rise
and fall on timescales of around 100,000 years - exactly the same period as
between ice ages on Earth. So says a physicist who has created a computer model
of our star's core.
2 Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled
the effect of temperature fluctuations in the sun's interior. According to the
standard view, the temperature of the sun's core is held constant by the
opposing pressures of gravity and nuclear fusion. However, Ehrlich believed that
slight variations should be possible.
3 He took as his starting point the work of Attila Grandpierre of the Konkoly
Observatory of the Hungarian Academy of Sciences. In 2005, Grandpierre and a
collaborator, Gábor ágoston, calculated that magnetic fields in the sun's core
could produce small instabilities in the solar plasma. These instabilities would
induce localised oscillations in temperature.
4 Ehrlich's model shows that whilst most of these oscillations cancel each
other out, some reinforce one another and become long-lived temperature
variations. The favoured frequencies allow the sun's core temperature to
oscillate around its average temperature of 13.6 million kelvin in cycles
lasting either 100,000 or 41,000 years. Ehrlich says that random interactions
within the sun's magnetic field could flip the fluctuations from one cycle
length to the other.
5 These two timescales are instantly recognisable to anyone familiar with
Earth's ice ages: for the past million years, ice ages have occurred roughly
every 100,000 years. Before that, they occurred roughly every 41,000 years.
6 Most scientists believe that the ice ages are the result of subtle changes
in Earth's orbit, known as the Milankovitch cycles. One such cycle describes the
way Earth's orbit gradually changes shape from a circle to a slight ellipse and
back again roughly every 100,000 years. The theory says this alters the amount
of solar radiation that Earth receives, triggering the ice ages. However, a
persistent problem with this theory has been its inability to explain why the
ice ages changed frequency a million years ago.
7 "In Milankovitch, there is certainly no good idea why the frequency should
change from one to another," says Neil Edwards, a climatologist at the Open
University in Milton Keynes, UK. Nor is the transition problem the only one the
Milankovitch theory faces. Ehrlich and other critics claim that the temperature
variations caused by Milankovitch cycles are simply not big enough to drive ice
ages.
8 However, Edwards believes the small changes in solar heating produced by
Milankovitch cycles are then amplified by feedback mechanisms on Earth. For
example, if sea ice begins to form because of a slight cooling, carbon dioxide
that would otherwise have found its way into the atmosphere as part of the
carbon cycle is locked into the ice. That weakens the greenhouse effect and
Earth grows even colder.
9 According to Edwards, there is no lack of such mechanisms. "If you add
their effects together, there is more than enough feedback to make Milankovitch
work," he says. "The problem now is identifying which mechanisms are at work."
This is why scientists like Edwards are not yet ready to give up on the current
theory. "Milankovitch cycles give us ice ages roughly when we observe them to
happen. We can calculate where we are in the cycle and compare it with
observation," he says. "I can't see any way of testing [Ehrlich's] idea to see
where we are in the temperature oscillation."
10 Ehrlich concedes this. "If there is a way to test this theory on the sun,
I can't think of one that is practical," he says. That's because variation over
41,000 to 100,000 years is too gradual to be observed. However, there may be a
way to test it in other stars: red dwarfs. Their cores are much smaller than
that of the sun, and so Ehrlich believes that the oscillation periods could be
short enough to be observed. He has yet to calculate the precise period or the
extent of variation in brightness to be expected.
11 Nigel Weiss, a solar physicist at the University of Cambridge, is far from
convinced. He describes Ehrlich's claims as "utterly implausible". Ehrlich
counters that Weiss's opinion is based on the standard solar model, which fails
to take into account the magnetic instabilities that cause the temperature
fluctuations.
Questions 1-4
Complete each of the following statements with One or Two names of the
scientists from the box below.
Write the appropriate letters A-E in boxes 1-4 on your answer sheet.
A. Attila Grandpierre
B. Gábor ágoston
C. Neil Edwards
D. Nigel Weiss
E. Robert Ehrlich
1. ...claims there a dimmer switch inside the sun that causes its brightness
to rise and fall in periods as long as those between ice ages on Earth.
2. ...calculated that the internal solar magnetic fields could produce
instabilities in the solar plasma.
3. ...holds that Milankovitch cycles can induce changes in solar heating on
Earth and the changes are amplified on Earth.
4. ...doesn't believe in Ehrlich's viewpoints at all.
Questions 5-9
Do the following statements agree with the information given in the reading
passage?
In boxes 5-9 on your answer sheet write
TRUE if the statement is true according to the passage
FALSE if the statement is false according to the passage
NOT GIVEN if the information is not given in the passage
5. The ice ages changed frequency from 100,000 to 41,000 years a million
years ago.
6. The sole problem that the Milankovitch theory can not solve is to explain
why the ice age frequency should shift from one to another.
7. Carbon dioxide can be locked artificially into sea ice to eliminate the
greenhouse effect.
8. Some scientists are not ready to give up the Milankovitch theory though
they haven't figured out which mechanisms amplify the changes in solar
heating.
9. Both Edwards and Ehrlich believe that there is no practical way to test
when the solar temperature oscillation begins and when ends.
Questions 10-14
Complete the notes below.
Choose one suitable word from the Reading Passage above for each answer.
Write your answers in boxes 10-14 on your answer sheet.
The standard view assumes that the opposing pressures of gravity and nuclear
fusions hold the temperature ...10...in the sun's interior, but the slight
changes in the earth's ...11... alter the temperature on the earth and cause ice
ages every 100,000 years. A British scientist, however, challenges this view by
claiming that the internal solar magnetic ...12... can induce the temperature
oscillations in the sun's interior. The sun's core temperature oscillates around
its average temperature in ...13... lasting either 100,000 or 41,000 years. And
the ...14... interactions within the sun's magnetic field could flip the
fluctuations from one cycle length to the other, which explains why the ice ages
changed frequency a million years ago.
1. A European spacecraft took off today to spearhead the search for another
"Earth" among the stars.
2. The Corot space telescope blasted off aboard a Russian Soyuz rocket from
the Baikonur cosmodrome in Kazakhstan shortly after 2.20pm.
3. Corot, short for convection rotation and planetary transits, is the first
instrument capable of finding small rocky planets beyond the solar system. Any
such planet situated in the right orbit stands a good chance of having liquid
water on its surface, and quite possibly life, although a leading scientist
involved in the project said it was unlikely to find "any little green men".
4. Developed by the French space agency, CNES, and partnered by the European
Space Agency (ESA), Austria, Belgium, Germany, Brazil and Spain, Corot will
monitor around 120,000 stars with its 27cm telescope from a polar orbit 514
miles above the Earth. Over two and a half years, it will focus on five to six
different areas of the sky, measuring the brightness of about 10,000 stars every
512 seconds.
5. "At the present moment we are hoping to find out more about the nature of
planets around stars which are potential habitats. We are looking at habitable
planets, not inhabited planets. We are not going to find any little green men,"
Professor Ian Roxburgh, an ESA scientist who has been involved with Corot since
its inception, told the BBC Radio 4 Today programme.
6. Prof Roxburgh said it was hoped Corot would find "rocky planets that could
develop an atmosphere and, if they are the right distance from their parent
star, they could have water".
7. To search for planets, the telescope will look for the dimming of
starlight caused when an object passes in front of a star, known as a "transit".
Although it will take more sophisticated space telescopes planned in the next 10
years to confirm the presence of an Earth-like planet with oxygen and liquid
water, Corot will let scientists know where to point their lenses.
8. Measurements of minute changes in brightness will enable scientists to
detect giant Jupiter-like gas planets as well as small rocky ones. It is the
rocky planets - that could be no bigger than about twice the size of the Earth -
which will cause the most excitement. Scientists expect to find between 10 and
40 of these smaller planets.
9. Corot will also probe into stellar interiors by studying the acoustic
waves that ripple across the surface of stars, a technique called
"asteroseismology".
10. The nature of the ripples allows astronomers to calculate a star’s
precise mass, age and chemical composition.
11. "A planet passing in front of a star can be detected by the fall in light
from that star. Small oscillations of the star also produce changes in the light
emitted, which reveal what the star is made of and how they are structured
internally. This data will provide a major boost to our understanding of how
stars form and evolve," Prof Roxburgh said.
12. Since the discovery in 1995 of the first "exoplanet" - a planet orbiting
a star other than the Sun - more than 200 others have been found by ground-based
observatories.
13. Until now the usual method of finding exoplanets has been to detect the
"wobble" their gravity imparts on parent stars. But only giant gaseous planets
bigger than Jupiter can be found this way, and they are unlikely to harbour
life.
14. In the 2010s, ESA plans to launch Darwin, a fleet of four or five
interlinked space telescopes that will not only spot small rocky planets, but
analyse their atmospheres for signs of biological activity.
15. At around the same time, the US space agency, Nasa, will launch
Terrestrial Planet Finder, another space telescope designed to locate Earth-like
planets.
Choose the appropriate letter from A-D for question 1.
1. Corot is an instrument which
(A) can help to search for certain planets
(B) is used to find planets in the orbit
(C) can locate planets with human beings
(D) can spot any planets with water.
Do the following statements agree with the information given in the reading
passage? For questions 2-5 write
TRUE if the statement agrees with the information
FALSE if the statement contraicts the information
NOT GIVEN if there is no information on this in the passage
2. Scientists are trying to find out about the planets that can be
inhabited.
3. BBC Radio 4 recently focuses on the broadcasting of Corot.
4. Passing objects might cause a fall in light.
5. Corot can tell whether there is another Earth-like planet.
Based on your reading of the passage, complete the sentences below with words
taken from the passage. Use NO MORE THAN THREE WORDS for each answer.
With measurements, scientists will be able to search for some gaseous and
rocky planets. They will be extremely excited if they can discover some small 6.
__________, the expected number of which could be up to 7. __________ .
Corot will enable scientists to study the 8. __________ of stars. In this
way, a star’s mass, age and chemical composition can be calculated.
According to Prof Roxburgh, changes in light can be caused by passing planets
or star 9. __________. The related statistics can gain us a better 10.
__________ of the star formation and evolvement.
Observatories have found many exoplanets, which are 11. __________ other
stars than the Sun. The common way used in finding exoplanets can only detect
huge gas planets, which do not 12. ___________ .
With the launching of Darwin, astronomers will be able to analyse whether
those rocky planets have 13. __________ for life.
