ACT Reading OG Test 1 - Passage IV

Questions 31-40 are based on the following passage.


NATURAL SCIENCE: This passage is adapted from the article “Worlds Apart Seeking New Earths" by Timothy Ferris (©2009 by National Geographic Society).



It took humans thousands of years to explore our

own planet and centuries to comprehend our neighbor­

ing planets, but nowadays new worlds are being discov­

ered every week. To date,astronomets have identified
5 more than 370 “exoplanets,” worlds orbiting stars other

than the sun. Many are strange. There's an Icarus - like

"hot Saturn" 260 light-years from Earth, whirling

around its parent star so rapidly that a year there lasts

less than three days. Circling another star 150 light-
10 years out is a scorched “hot Jupiter,” whose upper

atmosphere is being blasted off to form a gigantic

comet- like tail. Three benighted planets have been

found orbiting a pulsar-the remains of a once mighty

star snrunk into a spinning atomic nucleus the size of a
15 city - while untold numbers of worlds have evidently

fallen into their suns or been flung out of their systems

to become ‘floaters” that wander in eternal darkness.

Amid such exotica, scientists are eager for a hint

of the famibar: planets, resembling Earth, orbiting their
20 stars at just the right distance - neither too hot nor too

cold-to support life as we know it. No planets quit

like our own have yet been found, presumably beause

they’re inconspicuou. To see a planet as small and dim

as ours amid the glare of its star is like trying to see a
25 firely in a fireworks display; to detect its gravitational

influence on the star is like listening for a cricket in a

tornado. Yet by pushing technology to the limits,

astronomers are rapidly approaching the day when they

can find another Earth and interrogate it for signs of
30 life.

Only 11 exoplanets, all of them big and bright and

conveniently far away from their stars, have as yet had

their pictures taken. Most of the others have been

detected by using the specttoscopic Doppler techniqu,
35 in which starlight is analyzed for evidence that the star

is being tugged ever so slightly back and forth by the

gravitational pull of its planets. In recent years

astronomers have refined the Doppler technique so

exquisitely that they can now tell when a star is pulled
40 from its appointed rounds by only one meter a

second - about human walking speed. That s sufficient

to detect a giant planet in a big orbit, or a small one if

it’s very close to its star, but not an Earth at anything

like our Earth's 93-million-mile distance from its star.
45 The Earth tugs the sun around at only one-tenth walk­

ing speed, or about the rate that an infant can crawl;

astronomers cannot yet prize out so tiny a signal from

the light of a distant star.

Another approach is to watch a star for the slight
50 periodic dip in its brightness that will occur should an

orbiting planet circle in front of it and block a fraction

of its light. At most a tenth of all planetary systems are

likely to be oriented so that these mini-eclipses, called

transits, are visible from Earth, which means that
55 astronomers may have to monitor many stars patiently

to capture just a few transits. The French COROT satel­

lite, now in the third and final year of its prime mission,

has discovered seven transiting explanets, one of

which is only 70 percent larger than Earth.

60 The United States’ Kepler satellite is COROT’S

more ambitious successor. Launched from Cape

Canaveral in March 2008, Kepler is essentially just a

big digital camera with a 95 meter aperture and a

95 - megapixel detector. It makes wide-field pictures
65 every 30 minutes, capturing the light of more than

100,000 stars in a single patch of sky between the

bright stars Deneb and Vega. Computers on Earth moni-

tor the brightness of all those stars over time, alerting

humans when they detect the slight dimming that could
70 signal the transit of a planet.

Because that dimming can be mimicked by other

phenoillena, such as the pulsations of a variable star or

a large sunspot moving across a star's surface, the

Kepler scientists won’ t announce the presence of a
75 planet until they have seen it transit at least three

times - a wait that may be only a few days or weeks for

a planet rapidly circling close to its star but years for a

terrestrial twin. By combining Kepler results with .

Doppler observations, astronomers expect to determine
80 the diameters and masses of transiting planets. If they

manage to discover a rocky planet roughly the size of

Earth orbiting in the habitable zone - not so close to the

star that the planet's water has been baked away, nor so

far out that it has frozen into ice-they will have found
85 what biologists believe could be a promising aboae for

life.