12

EARTH
AND BEYOND
A view of the moon and Earth’s
atmosphere as seen from the
International Space Station

WARM UP

Discuss these questions

with a partner.

1. What can we learn about

Earth from studying our
solar system?

2. Can you think of any

recent, interesting news
stories about space
exploration?

203

203-220_16296_REX_SB4_U12_ptg01.indd 203 8/26/19 4:44 PM

 12A
BEFORE YOU READ

DISCUSSION A. Read the caption below. Why might astronomers be interested

in finding exoplanets like CT Cha b? Discuss with a partner.

SKIMMING B. Look at the reading title and headings on the next three pages,
and quickly skim the passage and infographic. Check (✓) the
topics you think will be covered in the passage. Then check your
answers as you read.

a. how astronomers locate other Earth-like planets

b. the search for life on other Ear th-like planets
c. establishing human colonies on other Ear th-like planets

Jupiter and Saturn may be large relative to our home planet, but they’re
small compared to CT Cha b, one of the 3,900-plus exoplanets—planets
circling stars outside our own solar system—that astronomers have so
far discovered.

204 Unit 12A

203-220_16296_REX_SB4_U12_ptg01.indd 204 8/26/19 4:44 PM

 P LA N ET
HU N TERS
A It took humans thousands of years to explore our a firefly in a fireworks display. Yet by pushing
own planet, and centuries to comprehend our technology to the limits, astronomers are
neighboring planets. Nowadays, though, new rapidly approaching the day when they can
worlds are being discovered every week. find another Earth.
B To date, astronomers have identified more InS
ear chof O
er
th ar th s
E
1
than 3,900 “exoplanets”—worlds orbiting stars
D The most direct approach to finding a planet
other than the sun. There’s a “hot Saturn” 260
is to take a picture of it with a telescope.
light-years from Earth that orbits its parent star
Astronomers have detected more than half of
so rapidly that a year there lasts less than three
the confirmed exoplanets this way. All of them
days. Circling another star 150 light-years out
are big and bright and conveniently far away
is a “hot Jupiter,” whose upper atmosphere
from their stars.
is being blown away by the star’s solar winds.
Astronomers have also found five planets E A more effective way to detect an exoplanet,
orbiting a pulsar—the remains of a once though, is to use a method known as the
mighty star shrunk into an atomic city-size Doppler technique. This involves analyzing
nucleus2 that spins. Some worlds have fallen starlight for evidence that the star’s movement
into their suns. Others have been thrown out of is affected by the gravitational pull of a planet.
their systems to become “floaters” that wander In recent years, astronomers have refined the
in eternal darkness. technique. They can now tell when a planet is
pulling its star by only one meter a second—
C Among all these, astronomers are eager to find
about human walking speed. That’s enough to
a hint of the familiar: planets that resemble
detect a giant planet in a big orbit, or a small
Earth. That is, they are looking for planets that
planet if it’s close to its star.
orbit their stars at just the right distance—
neither too hot nor too cold—to support F Another approach is to watch a star for a slight
life. However, we have not yet found dip in its brightness. This occurs when an
planets that are quite like our orbiting planet passes in front of the star and
own. To see a planet as blocks part of its light. At most, a tenth of all
small and dim as ours planetary systems are oriented so that these
amid the glare of mini-eclipses3—called transits—are visible from
its star is like Earth. So, astronomers have to monitor a lot of
trying to see stars to capture just a few transits.

1 If a planet orbits a star, it circles or goes around it.

2 The nucleus is the central part of an atom or cell.
3 An eclipse occurs when the light from an object in the sky cannot be seen
because another object has come between it and the observer.

Unit 12A 205

203-220_16296_REX_SB4_U12_ptg01.indd 205 8/26/19 4:44 PM

 HUNTING FOR NEW WORLDS
Of the 3,900-plus exoplanets discovered so far, very
few are in a zone that supports life as we know it.
STAR
STAR
To find more planets within this zone, NASA
launched the Transiting Exoplanet Survey Satellite HOTHOT
ORBITAL
ORBITAL
ZONEZONE
in 2018. Its mission? To monitor 500,000 nearby stars WARM
WARM
ORBITAL
ORBITAL
ZONE
ZONE
for possible Earth-sized exoplanets. COLD
COLD
ORBITAL
ORBITAL
ZONE
ZONE

TOO HOT JUST RIGHT TOO COLD

Planets here orbit close to Water present on planets Here, planets orbit far from
their suns, so any surface in this zone could remain their suns, so any surface
water evaporates into space. in liquid form. water stays frozen.

MERCURY
MERCURY

0.1 0.1
LIFE IN A BOX
MARS
MARS Planets in the box have the right
atmospheric pressure and the right
VENUS
VENUSEARTH
EARTH
temperature to keep surface water
in a liquid state. In our solar system,
1 1
EARTH
EARTH Earth and Mars are in the box.
MASS
MASS

10 10

100 100

1,000
1,000

10,000
10,000
EARTH
EARTH MostMost
of the
of exoplanets
the exoplanets
MASSES
MASSES discovered
discovered
so far
soare
far are
muchmuch
larger
larger
and and
hotter
hotter
thanthan
Earth.
Earth.

WARMER
WARMER EXOPLANET
EXOPLANET
TEMPERATURE
TEMPERATURE COLDER
COLDER

206 Unit 12A

203-220_16296_REX_SB4_U12_ptg01.indd 206 8/26/19 4:44 PM

 G The dream of astronomers is to discover a rocky L The challenge facing scientists is not just having
planet roughly the size of Earth orbiting in a to perform a chemical analysis of planets they
habitable zone—that is, not so close to a star cannot see. They must also keep in mind that
that the planet’s water has boiled away, but life there may be very different from life here
not so far out that it has frozen into ice. If they at home. The lack of the red edge from an
succeed, they will have found what biologists exoplanet, for instance, does not exclude the
believe could be a promising abode4 for life. possibility of life. Life thrived on Earth for
billions of years before land plants appeared
H The best places to look may be dwarf stars,
and populated the continents.
which are smaller than the sun. Dwarf stars are
plentiful; seven of the ten stars nearest to Earth M The problem is that biological evolution is very
are dwarf stars. They also provide a steady unpredictable. It is possible that life originated
supply of sunlight to any life-bearing planets on an Earth-like planet at the same time it did
within their habitable zone. here. But life on that planet today would almost
certainly be very different. As the biologist
I Additionally, dwarf stars are dim, so the
Jacques Monod once commented, life evolves
habitable zone lies closer in. If the planet is
not only through necessity, but also through
closer to the star, it’s easier for astronomers to
chance—the unpredictable intervention of
detect a transit observation. A close-in planet
countless accidents.
also has a stronger pull on its star. That makes
it easier to detect with the Doppler method. N Chance has played a role many times in our own
Indeed, one of the most promising planets yet planet’s history. The most dramatic examples
found—the “super Earth” Gliese 581 d—orbits are the mass extinctions that wiped out millions
in the habitable zone of a red dwarf star only of species and created room for new life forms
one-third the mass of the sun. to evolve. Some of these accidents appear to
have been caused by asteroids6 or comets7
if e—
L B u
tN
otas eK
Wow
n I t? colliding with Earth. An impact 66 million years
J If an Earth-like planet is found within a star’s ago, for instance, helped kill off the dinosaurs
habitable zone, a space telescope could be used and opened up opportunities for the distant
to look for signs of life. Most likely, scientists ancestors of human beings. Hence, scientists
will examine the light coming from the planet look not just for exoplanets identical to modern
for possible indications of past or present life, Earth, but for planets resembling the Earth as it
such as atmospheric methane and oxygen. They used to be, or that it might have been.
might also look for the “red edge” produced
O It was not easy for earlier pioneers to undertake
when chlorophyll5-containing plants reflect
explorations of the ocean floors, map the far
red light.
side of the moon, or find evidence of oceans
K Directly detecting and analyzing the planet’s beneath the frozen surfaces of Jupiter’s moons.
own light will not be easy. Its light might be Neither will it be easy to find life on the
just one ten-billionth the light of the star’s. planets of other stars. But we now have reason
But when a planet transits, starlight shining to believe that billions of such planets exist.
through the atmosphere could reveal clues to They hold the promise of expanding not only
its composition that a space telescope might the scope of human knowledge, but also the
be able to detect. richness of the human imagination.

4 An abode is another word for home. 6 An asteroid is a large rock moving through outer space.
5 Chlorophyll is the green substance in plants that enables 7 A comet is a bright, icy object that travels around the sun and
them to convert sunlight into energy. has a long “tail” of gas.

Unit 12A 207

203-220_16296_REX_SB4_U12_ptg01.indd 207 8/26/19 4:44 PM

 READING COMPREHENSION

A. Choose the best answer for each question.

GIST 1. What could be another title for this reading?

a. How Ex oplanets Were First Discovered
b. Is There Intelligent Life on Other Planets?
c. The Sear ch for Ear th-like Planets Around Other St ars
d. The Story of “H ot Sat urn,” “Hot Jupiter,” and “
S u per Ear th”
DETAIL 2. When this article was written, how many exoplanets had been discovered?
a. 2
0
6 c. nearly 4, 0
b. about 390 d. billions
UNDERSTANDING 3. Look at the infographic on page 206. Which of these statements is true?
INFOGRAPHICS
a. Mercury orbits at a great distance from its sun.
b. Mercury is larger than Ear th.
c. Any water found on Venus would be frozen.
d. Venus and Earth are similar in size.
INFERENCE 4. The author indicates in paragraph K that observing and analyzing light from
an exoplanet .
a. will probably show signs of life
b. will be difficult but not impossible
c. has been accomplished several times
d. will require technology not presently available
INFERENCE 5. The author implies that on some exoplanets, .
a. life may have evolved without chlorophyll-bearing plants
b. chlorophyll-bearing plants would not produce a “red edge”
c. atmospheric methane and oxygen may produce a “red edge”
d. life will be similar to that on Ear th if it originated at the same•time

FACT OR B. Are the statements below (1–6) presented as fact or speculation in the reading
SPECULATION passage? Write F (fact) or S (speculation) next to each statement. Then circle the
Review this words in the passage that indicate the speculations.
reading skill
in Unit 5B 1. A year on “
hot Sat urn” lasts less than three days. (paragraph B
)
2. Some planets have fallen into their suns. (paragraph B
)
3. Astronomers have used telescopes to detect more than half of the confirmed
exoplanets. (paragraph D)
4. The best place to look for Earth-like planets is around dwarf stars. (paragraph H)
5. Life thrived on Ear th for billions of years before land plants appeared.
(paragraph L)
6. Any form of life on an Ear th-like planet will be very different from that on Ear th.
(paragraph M)

208 Unit 12A

203-220_16296_REX_SB4_U12_ptg01.indd 208 8/26/19 4:44 PM

 READING SKILL

Recognizing Cause and Effect Relationships (3)

As you learned in Units 3A and 10 A , signal words such as because (of), due to, and thus indicate
cause and effect relationships. Often, though, the author may not state these relationships
directly—
y ou have to infer them from the context. Take a look at the cause (underlined) and the
effect•(circled ) in this example from the reading passage:

There’s a “hot Saturn” 260 light-years from Earth that orbits its parent star so rapidly that
a year there lasts less than three days.

In this example, the effect of the “

hot Sat urn” exoplanet traveling so quickly around its star is that
a•year there is very short.

CAUSE AND A. Match these effects (1–6) with their causes (a–g) according to information from
EFFECT Reading A. One cause is extra.
1. To observe transits, astronomers will have to observe many stars.
2. Sc ientists have been able to detect these exoplanets using a telescope.
3. When searching for signs of life on an exoplanet, scientists look for a “red edge.”
4. These exoplanets become “floaters” that wander in eternal darkness.
5. The upper atmosphere of this exoplanet is being blasted off by the star’s
solar•winds.
6. Mass extinctions of plants and animals took place.

a. Only about 10 percent of transits, or “

m ini-eclipses,” can be seen from
our planet.
b. Some exoplanets are thrown out of their original orbits.
c. Chlorophyll-bearing plants reflect a red light.
d. In the distant past, the Ear th was struck by asteroids and comets.
e. The “
hot Jupiter” exoplanet orbits relatively close to its parent star.
f. Life existed on Ear th for a very long time before land plants appeared.
g. More than half of the known exoplanets are big, bright, and far away from
their•stars.

CRITICAL THINKING Jus tifying an Opinion Space exploration requires a great deal of money,
time, and effort. Which of the following statements do you agree with the most? Why?
Check (✓) the option that best reflects your opinion. Then discuss your reasons with a partner.
I think space exploration is very important and is worth all the resources we invest in it.
I think space exploration is a waste of resources that could be better used on Ear th.
I think space exploration is important, but we should limit it to just within our own solar system.

Unit 12A 209

203-220_16296_REX_SB4_U12_ptg01.indd 209 8/26/19 4:44 PM

 VOCABULARY PRACTICE

COMPLETION A. Circle the correct words to complete the

information below.

1
Hence / To date, scientists hoping to make
contact with aliens have focused on sending radio
waves through our 2atmosphere / exclusion
and out into space. B
ut a new study suggests
sending physical material—
a sort of message in a
bottle—
may be preferable. A physical message can
hold more information and journey farther than
radio waves.

The problem, though, is that this method is slow.

As astronomer Seth Sh ostak says, “It’s like the NASA’s Kepler Space Telescope
difference between sea post and airmail.” So me discovered over 2,600 exoplanets
astronomers feel we should forget about trying to during its lifetime.

communicate within the 3exclusion / scope of our own lifetimes. It would

take thousands of years for a physical message to reach and return from an
exoplanet. A two-way conversation is 4spun / hence out of the question.

WORDS IN B. Complete the sentences. Circle the correct words.

CONTEXT
1. Atomic energy is another term for solar / nuclear / electrical energy.
2. If something spins, it goes in and out / up and down / around and around quickly.
3. If you resemble someone, you are similar to / different from / identical to them.
4. If you thrive in a new job, you are really / moderately / not very good at it.
5. If you exclude someone from a group, they are part / occasionally part / not part
of•it.
6. The composition of an object refers to its total cost / the parts it is made of /
its various colors.

WORD PARTS C. The prefix com- in composition means “together” or “with.” Complete the
sentences using the words in the box. One word is extra.

combine compared compile composed

1. Mars’s atmosphere is mostly of carbon dioxide, argon, and nitrogen.

2. Hydrogen and oxygen atoms to make water molecules.
3. The exoplanet Kepler-4
52b’ s star is apparently older than the Ear th’s sun—
6 billion
years, to 4. 5 billion years.

210 Unit 12A

203-220_16296_REX_SB4_U12_ptg01.indd 210 8/26/19 4:44 PM