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2d€ Test n°1

In his famous popular science book “A Short History of Nearly Everything”, Bill Bryson

wrote in 2003:

1 “Statistically the probability that there are other thinking beings out there is good.

2 Nobody knows how many stars there are in the Milky Way- estimates range from a

3 hundred billion or so perhaps four hundred billion- and the Milky Way is just one of a

4 hundred and forty billion or so other galaxies.

5 Unfortunately, space being spacious, the average distance between any two of these

6 civilisations is reckoned to be at least two hundred light years.

7 It means that even if these beings know we are here and are somehow able to see us in

8 their telescope, they’re not seeing at you and me. There are watching the French

9 Revolution and Thomas Jefferson.

10 Two hundred light years is a distance so far beyond us as to be, well, just beyond us. So

11 even if we were not really alone, in all practical terms we are.”

12 “In December 2011 the Kepler Space Telescope spotted a staggeringly exciting object.

13 Kepler is a planet hunter and, since its launch in March 2009, it has been staring intently

14 along the spiral arm of our Milky Way galaxy, looking for telltale winks* of starlight. Each

15 wink is potentially the result of a planetary companion of a distant sun passing between its

16 parent star and Kepler’s sensitive light-gathering instruments. So far, Kepler has detected

17 more than 2300 planetary candidates using this “transit” method; many of these are large

18 worlds on close, hot orbits around their star. But on 5 December last year the Kepler

19 science team announced the discovery of a very special kind of world: a roughly Earth- 20 sized planet orbiting within the so-called habitable zone of its Sun-like star. This planet,

21 Kepler-22b, is just over twice the radius of our home world, making it a smallish “super- 22 Earth” in planetary terms. Its presence in the habitable zone means it could contain liquid

23 water on its surface: warm seas and oceans, the perfect cradle** for life. The discovery of

24 Kepler-22b stands out as a high point in the short history of astrobiology, the field of

25 science concerned with the possibility of life beyond our Earth. This young discipline is

26 blossoming*** thanks not just to Kepler, but also to the extensive evidence for a watery era

27 on ancient Mars and Earthbound discoveries of “extremophile” life in incredibly hostile

28 niches. With the Kepler data suggesting that there are more planets than stars in our

29 galaxy, and that around 2% of Sun-like stars are expected to host Earth-like planets in their

30 habitable zones, it seems likely that other life-bearing worlds exist. On some of these, it is

31 possible that evolution has progressed beyond primitive micro-organisms to yield

32 multicellular lifeforms: analogues of terrestrial animals and plants.”

Physics World Magazine

*A wink: the action of quickly closing and opening one eye as a sign to someone

Telltale signs of something are obvious signs that it exists or it has happened

**A cradle: a small bed for a baby that you can move gently from side to side

***To blossom: to develop and become more successful

1. How does Bryson argue for the existence of other forms of life somewhere in the Universe?

2. What is, expressed in scientific notation, the rough number of stars in the Universe

according to Bryson’s estimate?

3. The speed of light is c=3,00×108 m.s-1. Define and figure out the order of magnitude of the

unit of distance that astronomers call a light-year.

4. Explain lines 7 to 10.

5. What are today’s advances in the search for life in the Universe?

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Correction test n°1

1. Knowing that the number of stars in the Universe is huge, it is statistically possible

that there is another form of life somewhere on an Earth-like planet orbiting

another Sun-like star.

2. According to Bryson’s estimate, there are four hundred billion=400×109 stars in

our galaxy and he counts forty billion=40×109 other galaxies similar to the Milky

Way; this makes the number of stars roughly equal to 1.6×1022 stars.

3. By definition a light-year is the distance travelled by light in a vacuum during one

year. It is a unit of distance used by astronomers to chart the universe.

One year is 365×24×3600 s. Light is not instantaneous but travels at the highest

speed which is c=3,00×108 m.s-1.

Therefore one light-year is obtained by multiplying the speed of light in m/s by the

number of seconds in one year: 3,00×108×365×24×3600=9.4×1015m.

The corresponding order of magnitude is 1016 m.

4. If other beings situated 200 light years away from us were staring at us, they would

receive the light emitted by the Earth 200 years ago and they would see the Earth

like it was 200 years ago; in this way they could go back in our past.

Peering through a telescope is, to some extent, like travelling in a time machine.

5. Today more and more Exoplanets, such as Kepler-22b, are discovered, these objects

are planets orbiting Sun-like stars. They could be the cradles for life, as we know on

Earth. Thanks to sophisticated probes equipped with sensors of greater and

greater sensitivity, astronomers have been capable to see objects in other ranges of

the electromagnetic spectrum (like I.R), objects that old optical telescopes such as

the Hubble telescope couldn’t see. In this way scientists and researchers in many

connected fields have achieved a seminal progress in the endeavour to find life

elsewhere in the Universe.