Deck 20: Astrobiology

Question 1

There are now over 3700 known extrasolar planets. When astronomers consider them as possible homes for life, it is important to remember that MOST of them are

A) Earthlike planets with water on their surfaces.
B) hydrogen-rich planets like Jupiter.
C) in extremely elliptical orbits, like comets.
D) still in the process of forming and thus not old enough to have evolved life.

Answer 1

hydrogen-rich planets like Jupiter.

Question 2

Why is liquid water believed to be essential to the development of life on a planet or other body?

A) Liquid water provides an electricity-conducting medium in which lightning currents can create complex organic molecules.
B) Liquid water allows many other chemical elements to interact and form complex molecules.
C) Without water, there would be no shoreline onto which primitive fish could crawl to begin life on land.
D) Liquid water combines chemically with other compounds to form the building blocks of life.

Answer 2

Liquid water allows many other chemical elements to interact and form complex molecules.

Question 3

Which of these characteristics is NOT usually taken to be sufficient to rule out the existence of life on an extrasolar planet?

A) planet is too close to the star
B) star is 20 times more massive than the Sun
C) a planet in synchronous rotation around its star
D) star is older than the Sun

Answer 3

star is older than the Sun

Question 4

Which type of meteorite was found to contain large organic molecules that make up the building blocks of life and provide strong evidence for their extraterrestrial production?

A) iron meteorites
B) stony iron meteorites
C) carbonaceous chondrites
D) stony meteorites

Question 5

In which type of meteorite has evidence been found for organic molecules, some of which are in contrast to MOST life molecules on Earth?

A) iron meteorite
B) stony iron meteorite
C) stony meteorite
D) carbonaceous chondrite

Question 6

Is a planet with a large, nearby moon more likely to evolve life than a planet without a moon?

A) No. There is no reason to believe the existence of a moon has any effect on the evolution of life.
B) Yes. A planet almost certainly must have liquid water to evolve life. A moon will raise tides, which can help to wash minerals into the water where it can provide a rich mixture conducive to the evolution of life.
C) Yes. A moon can help shield a planet from impacts which could destroy life in its early, formative stages.
D) The gravitational pull of a moon can help a planet establish a rhythmic day/night cycle which is important for the evolution of life.

Question 7

One aspect of astrobiology is the attempt to replicate the steps in the process that led to the creation and evolution of life. An important step occurred in 2010 when

A) living organisms were discovered on a carbonaceous chondrite meteorite.
B) a living virus was created in a laboratory.
C) a simple artificial cell was fabricated.
D) organic structures were discovered in the Martian meteorite ALH84001.

Question 8

Why is the strategy of searches for extraterrestrial life usually based on carbon chemistry?

A) Carbon dioxide is the main ingredient of planetary atmospheres, both terrestrial and Jovian.
B) No other atom can combine easily with the abundant hydrogen and helium to form long molecules in interstellar gas.
C) Most meteorites that reach Earth are composed of carbon.
D) Carbon is abundant and is versatile in forming complex, long-chain molecules.

Question 9

Several lines of evidence now suggest that large and complex organic molecules can exist or could evolve in outer space, from which the building blocks of life could be formed. Which of these is NOT one of these observational findings?

A) radio astronomical observations of large organic molecules in giant molecular clouds
B) discovery of organic molecules inside some meteorites
C) discovery by the Viking landers of large organic molecules in the Martian regolith
D) laboratory experiments in which electrical sparks passing through a combination of simple gases such as H₂O, H₂, N₂, and CO₂ produced large organic molecules

Question 10

The earliest searches for radio signals from extraterrestrial civilizations were made about

A) 1973.
B) 1960.
C) 1995.
D) 1948.

Question 11

There have been many reports of aliens from other planets visiting Earth. Many of these reports include contacts with humans. How many of these reports have yielded scientific evidence that was analyzed to confirm the encounter?

A) none
B) one
C) four
D) dozens

Question 12

Which wavelength range in the electromagnetic spectrum has been the MOST fruitful in the search for complex organic molecules in space?

A) gamma radiation
B) visible radiation
C) ultraviolet radiation
D) microwaves and short-wavelength radio waves

Question 13

Which of these characteristics of carbon is NOT considered essential to the chemistry of life?

A) It can bond with three or more atoms.
B) The bonds it forms are covalent rather than ionic.
C) Its bonds are both strong and flexible.
D) Its bonds create gels and liquids.

Question 14

Why is it highly likely that life, should it exist elsewhere in the universe than just on Earth, would be based on carbon chemistry?

A) Carbon can form a resilient bond with many more atomic species in a wider variety of complex forms than other equivalent elements, such as silicon.
B) Carbon combines more readily than other atoms with nitrogen, the major component of atmospheres such as that of Earth, to produce complex molecules.
C) Carbon is expected to be far more abundant than silicon or other like elements that can combine to produce complex molecules.
D) Carbon releases more energy than do most other atoms when it combines with oxygen, providing the energy for life processes in living organisms.

Question 15

In the search for intelligent life, why do scientists tend to assume that its biochemistry is more likely to be based on the element carbon than on any other element?

A) Carbon is the most versatile element, combining with the largest number of other elements in many different ways to produce long-chain molecules.
B) Carbon is the only element that can combine into ring-shaped molecules, which is the shape of life-form molecular structure.
C) Carbon releases far more energy than do other similar atoms when it combines with other elements, a process that is essential for the support of life.
D) Scientists expect that life will mimic that on the surface of Earth, which is carbon-based.

Question 16

Which of these characteristics in extrasolar planets is one that astronomers look for as a likely characteristic of a life-bearing planet?

A) large size (Jupiter-sized)
B) distance from a Sunlike star of about 1 au
C) orbits a star much more massive than the Sun
D) high-eccentricity planetary orbit

Question 17

Which of these is NOT a reason carbon is thought to be the element on which complex extraterrestrial life is based?

A) Carbon forms chemical bonds that are both strong and flexible.
B) Every life-form on Earth is carbon-based, over an immense range of conditions.
C) Carbon releases a significant amount of energy when it combines with hydrogen.
D) Carbon provides a basis for forming long, complex chains of molecules.

Question 18

One of the first people to look for radio signals from extraterrestrial civilizations was

A) Arno Penzias.
B) Frank Drake.
C) Jocelyn Bell.
D) Martin Schwarzschild.

Question 19

What does the acronym SETI stand for?

A) search for evidence of terrestrial-planet inhabitants
B) search for extraterrestrial intelligence
C) search for extraterrestrial invaders
D) sourcebook of extrasensory transient incidents

Question 20

What is the status of the search for life elsewhere in the universe?

A) Life has been discovered elsewhere in the solar system.
B) Signs of life have been discovered on Earthlike planets circling other stars elsewhere in the Milky Way Galaxy.
C) Earthlike planets, with an abundance of liquid water, have been discovered around other stars, but signs of life have not yet been found on them.
D) Life has not yet been discovered elsewhere in the universe.

Question 21

The primary constituents for the organic molecules needed for life do NOT include which of these compounds?

A) oxygen
B) sulfur
C) carbon
D) silicon

Question 22

Does a planet's location within the Milky Way Galaxy affect the likelihood of evolving life on the planet?

A) No. As long as a star is nearby the chances for the evolution of life would not seem to depend on the rest of the Galaxy.
B) Yes. The closer to the center of the Galaxy a planet is, the greater will be the density of stars. Being bathed in large amounts of light should increase the possibilities of the evolution of life.
C) Yes. A planet on the outer edge of the Galaxy would be susceptible to radiation from outside the Galaxy because it would not be protected by the galactic magnetosphere. Chances for life would not be good.
D) Yes. Stellar systems too far from the galactic center are deficient in metals. Such elements are necessary to build Earthlike planets and life as known.

Question 23

Modern laboratory experiments that repeated those of Urey and Miller in exploring the possibility of producing organic molecules (the building blocks of life) from mixtures of gases expected to exist in the early planetary system passed electrical discharges through which mixture of gases?

A) nitrogen, hydrogen, water vapor, and carbon dioxide
B) ammonia, methane, water vapor, and hydrogen
C) hydrogen and helium
D) carbon dioxide, water vapor, and dust

Question 24

Life has been found on Earth in a lake deep under the Antarctic ice pack. This resembles what other environment in the solar system that has been considered a possible location for life?

A) the surface of ancient Mars
B) Venus
C) Europa
D) Miranda

Question 25

What source of energy was used to trigger the manufacture of complex organic compounds in laboratory simulations of conditions in primordial planetary atmospheres?

A) thermal heating, to simulate volcanic heating
B) electric discharges, to simulate lightning
C) heat from chemical reactions in early reactive planetary atmospheres
D) UV and visible radiation, to simulate the intensity of sunlight at earlier times in planetary life

Question 26

The classical laboratory experiments performed by Urey and Miller to explore the necessary conditions for the production of organic molecules (the building blocks of living things) in the solar system involved the passing of electrical discharges through what mixture of gases?

A) ammonia, methane, water vapor, and hydrogen
B) carbon dioxide, water vapor, and dust
C) hydrogen and helium
D) nitrogen, oxygen, water vapor, and carbon dioxide

Question 27

Which of these observations regarding the likelihood of life existing elsewhere in the universe has NOT yet been made?

A) discovery of assemblies of organic molecules into cell-like, self-replicating structures in the soils of Mars and the atmosphere of Venus
B) discovery of long-chain carbon-based molecules in interstellar clouds by radio astronomers
C) manufacture of organic compounds in laboratory simulations of primordial planetary atmospheres
D) discovery of long-chain amino acid protein molecules in meteorites

Question 28

An important advance in the search for life elsewhere in the solar system was

A) the discovery of primitive life-forms on Mars.
B) the replication in laboratories of silicon-based substitutes for the most important carbon-based life molecules.
C) the discovery of liquid water on Europa, Ganymede, and various other places in the solar system.
D) the discovery in meteorites of the remains of microbes.

Question 29

Scientists are now targeting Europa, one of Jupiter's moons, as a likely site for searching for elementary life-forms because

A) radio signals that follow a recognizable pattern have been detected from this moon.
B) there appears to be large amounts of dark organic material spread on its surface.
C) changes seen in the dark lines crossing the icy surface have a spectral signature of vegetation.
D) there is strong evidence for liquid water beneath the thick ice layer on its surface.

Question 30

Which of these phenomena was probably NOT a source of large organic molecules, the building blocks of life, on the early Earth?

A) comets
B) meteorites
C) lightning flashes in the early terrestrial atmosphere
D) volcanic eruptions

Question 31

MOST searches of space for evidence of intelligent life concentrate on radio wavelengths because

A) the atmosphere of Earth is most transparent at these wavelengths, and radio signals will be more easily detected from Earth.
B) radio energy is least affected by dust and gas in the interstellar medium.
C) it is likely that extraterrestrial beings will have developed radio transmitters before developing more complex lasers or infrared light transmitters.
D) radio signals can carry the greatest amount of information per unit of time, so information transfer will be most efficient at these wavelengths.

Question 32

In which of these environments have long-chain carbon-based molecules NOT been found?

A) meteorites
B) massive interstellar clouds of gas and dust
C) surface of Earth
D) surfaces of planets and moons such as Venus and Jupiter's moon Callisto

Question 33

At the present time, the search for extraterrestrial life in the solar system has been concentrated on a few bodies. These do NOT include

A) Venus.
B) Mars.
C) Europa.
D) Callisto.

Question 34

Today, the habitable zone around the Sun includes

A) only Earth.
B) Earth and Mars.
C) Earth and Venus.
D) Earth, Mars, and Venus.

Question 35

According to the present understanding, on which of these objects in this planetary system is it LEAST likely that life exists or existed at an earlier time?

A) Mars
B) Callisto, a moon of Jupiter
C) Europa, a moon of Jupiter
D) Io, a moon of Jupiter

Question 36

In which of these very harsh environments has life NOT been found on Earth?

A) deep inside Earth's crust
B) in a lake locked far under the Antarctic ice pack
C) in the hot water within geothermal vents on the ocean floor
D) Life has been found in all of these environments.

Question 37

Which of these accurately explains the likelihood of technologically advanced civilizations forming within 1 kpc of the galactic center?

A) There are likely to be MORE such civilizations near the galactic center, because the density of stars is so high there.
B) There are likely to be FEWER such civilizations near the galactic center, because the density of stars is so high there.
C) There are likely to be MORE such civilizations near the galactic center, because the stars are older there.
D) There are likely to be FEWER such civilizations near the galactic center, because they would have fallen into the Galaxy's central black hole..

Question 38

The basic chemical molecules thought to have been present in abundance in the early planetary system, which were used in the classical Miller-Urey laboratory experiments in which complex compounds essential to life were formed by electric discharges, were

A) CO₂ (carbon dioxide), H₂O (water), and H₂ (hydrogen).
B) H₂ (hydrogen), O₂ (oxygen), and CO₂ (carbon dioxide).
C) CH₄ (methane), NH₃ (ammonia), H₂O (water), and H₂ (hydrogen).
D) H₂ (hydrogen), He (helium), Ar (argon), and Ne (neon).

Question 39

Other than Earth, which object in the solar system seems to be the only one capable of fostering an advanced civilization?

A) Titan, a moon of Saturn
B) Europa, a moon of Jupiter
C) Callisto, a moon of Jupiter
D) No solar system body, other than Earth, seems likely to foster an advanced civilization.

Question 40

The Miller-Urey experiments consisted of

A) sending a coded message via radio toward nearby stars that are similar to the Sun and may have planets.
B) attaching a metal plaque to the Voyager spacecraft to tell extraterrestrial beings about Earth, should the spacecraft ever be recovered.
C) monitoring tens of millions of radio frequencies at once in an effort to detect extraterrestrial radio communications.
D) passing an electrical arc through a mixture of hydrogen, ammonia, methane, and water and looking for resulting organic compounds.

Question 41

Existing telescopes are capable of detecting radio signals similar to those generated by humans from

A) about a dozen or so of the closest stars.
B) any star around which planets have been detected.
C) any star within a 100 pc or so of the solar system.
D) stars in giant elliptical galaxies since these stars, being oldest, are most likely to have advanced civilizations.

Question 42

The Drake equation calculates the number of technologically advanced civilizations in the Galaxy as a product of seven factors: R* f_p n_e f_l f_i f_c L. In the sample calculation in the text, these values are taken as 1 *1 * 0.2 * 1 * 1 * 1 * 500 = 100. Suppose this estimate is too conservative, in that all the factors that can in principle become larger are increased by a factor of ten. What would be the resulting number of technologically advanced civilizations in the Galaxy?

A) 100
B) 10⁵
C) 10⁷
D) 10⁹

Question 43

Part of determining the Drake factor R* is determining what is a "Sunlike star," a star around which a habitable planet could orbit. What is the thinking concerning low-mass stars, that is, stars with masses less than about half a solar mass? (These are stars cooler than M0 type main-sequence stars.)

A) Low-mass stars are highly desirable here because they tend to live longer and allow more time for life to develop and form a civilization.
B) Planets would have to orbit relatively close to low-mass stars in order to be warm enough to be in the habitable zone. But they are still acceptable as Sunlike stars.
C) Planets would have to orbit relatively close to low-mass stars in order to be warm enough to be in the habitable zone. But this means they will be tidally locked into synchronous rotation, with one very hot side and one very cold side- not an acceptable situation.
D) Photosynthesis, the main energy-production mechanism in green plants on Earth, works best with shorter wavelengths of light. These low-mass red stars tend to produce less of these shorter wavelengths and thus could not support efficient photosynthesis.

Question 44

What strategies and electromagnetic frequencies are thought to be the MOST logical for long-range communication across the universe with other intelligent beings?

A) explosion of nuclear devices at specific intervals and in specific patterns across Earth when closest to a nearby star
B) night-by-night photography of nearby stars at hydrogen Balmer wavelengths
C) continuous radio and microwave listening and transmitting at frequencies at which the natural radio sky noise background is low
D) X-ray surveys of space at appropriate times (e.g., when Earth is closest to nearby stars in its orbit), in view of the penetrability of space at these wavelengths

Question 45

Around which types of stars are astronomers MOST likely to find planets supporting life similar to that of Earth?

A) high-mass main-sequence stars
B) red giant stars
C) very low-mass stars
D) None of these answers are correct.

Question 46

What conditions restrict the suitable wavelength range for communication with extraterrestrial intelligence to the "water hole" in the high-frequency radio range of the electromagnetic spectrum?

A) cosmic background radio noise at low frequencies and radio noise from the Sun and Jupiter at high frequencies
B) local radio noise from television, radio, and aircraft across the band, except a narrow range in which transmission is prohibited by international agreement to permit such extraterrestrial communication
C) atmospheric absorption by the ionosphere at low frequencies and by CO₂ at high frequencies in the long infrared range
D) high galactic radio background noise at low frequencies and high atmospheric absorption by H₂O and O₂ at high frequencies, with a suitable region in between

Question 47

For which of these factors in the Drake equation do astronomers actually have observational knowledge rather than just a speculative estimate?

A) R^*, the rate at which solar-type stars form in the Galaxy
B) f_l, the fraction of Earthlike planets on which life actually arises
C) f_i, the fraction of life-forms that evolve into intelligent species
D) f_c, the fraction of intelligent species that develop adequate technology and then choose to send messages out into space

Question 48

The first successful detection of signals from extraterrestrial civilizations was accomplished in which year?

A) 1985
B) Never-no such signals have been detected yet.
C) 1999
D) 1960

Question 49

What is the status of the search for extraterrestrial intelligence?

A) The search must rely upon only small, inexpensive TV satellite antennas, and thus most astronomers believe it cannot succeed.
B) Astronomers have received on several occasions repeated signals that appear to be from some intelligent source, but they are waiting to receive one from the vicinity of an Earthlike planet before declaring that SETI has made contact with an extraterrestrial race.
C) Because of funding limitations the entire program has been terminated and is no longer active.
D) Astronomers have occasionally detected particularly strong or unusual signals from space, but they have not been repeated so astronomers do not believe they are from an intelligent source.

Question 50

One of the "quiet" bands in the electromagnetic spectrum used for SETI is the so-called "water hole" between about 10³ and 10⁴ MHz. What is the principal source of the natural signals in this frequency band?

A) emissions from the water molecule
B) emissions from oxygen molecules
C) cosmic microwave background radiation
D) radio emission from terrestrial sources

Question 51

If astronomers are going to "listen" for electromagnetic radiation at 21 cm from extraterrestrial sources, then Earth had better not generate too many waves at this wavelength from terrestrial sources. The standard FM broadcast band (as observed on a radio dial) spans frequencies from 88 MHz (million cycles per second) to 108 MHz. How does the frequency of the 21-cm signal compare with the FM band? The frequency of the 21-cm line is

A) below the low frequency end of the FM band by a factor of about 9.
B) right in the middle of the FM band.
C) right at the upper end of the FM band.
D) higher than the top end of the FM band by a factor of about 13.

Question 52

The numerical value given by the Drake equation

A) is exactly 10.
B) is generally agreed to be around 10, certainly between 8 and 12.
C) could be almost any value from zero up to 1 billion.
D) has a lower limit of 1 but could be much larger than 10.

Question 53

Probably the MOST difficult factor to estimate in the Drake equation is

A) R^*, the rate at which solar-type stars form in the Galaxy.
B) f_p, the fraction of stars that have planets.
C) n_e, the number of planets per solar system that are Earthlike (suitable for life).
D) L, the lifetime of a technologically advanced civilization.

Question 54

The Drake equation attempts to predict the

A) number of inhabitable planets around stars in the Milky Way Galaxy.
B) number of intelligent civilizations that exist in the whole universe.
C) probability of primitive life existing elsewhere in the Milky Way Galaxy.
D) number of technically advanced civilizations in the Milky Way Galaxy.

Question 55

It is unlikely that planets near stars much more massive than the Sun would develop life because

A) planets would have to be too close to these cool stars in order to be sufficiently warm for life to evolve and they would become tidally linked, resulting in no night and day.
B) these stars would have evolved to red giant and even supernova stages before life could evolve sufficiently to produce a civilization.
C) no moon would form around a planet near such a star, and the Moon is considered to have been essential for the evolution of life because of tidal variations on Earth.
D) there would be no region around the star where ultraviolet, visible, and infrared light intensities would be suitable for the evolution of life.

Question 56

The galactic habitable zone is sometimes defined as a torus around the galactic center with an outer radius of 10 kpc and an inner radius of 4 kpc. The volume of such a torus is roughly 5600 (kly)³. Adopting the text's value of N = 100 technologically advanced civilizations in the Galaxy, then, on the average, each volume of 56 (kly)³ within the galactic habitable zone is occupied by one such civilization. Also adopting the value L = 500 years as the technological lifetime of such a civilization (the time over which they have been sending out radio signals at the speed of light), then through what volume of space would these signals have spread? What are the chances of two civilizations being within the same signal volume?

A) The volume of signals is 0.01 (kly)³, so the chances of two civilizations being within the same signal volume are very small.
B) The volume of signals is 0.5 (kly)³, so the chances of two civilizations being within the same signal volume are very small.
C) The volume of signals is 50 (kly)³, so the chances of two civilizations being within the same signal volume are reasonably good.
D) The volume of signals is 500 (kly)³, so the chances of two civilizations being within the same signal volume are very great.

Question 57

The so-called water hole is a range in the electromagnetic spectrum in which searches for transmissions of extraterrestrial origin are being conducted. In what region of the electromagnetic spectrum does the water hole occur?

A) ultraviolet
B) visible
C) infrared
D) radio

Question 58

The so-called water hole, a region of the radio spectrum chosen for searches for signals from intelligent life because galactic and Earth-based noise and atmospheric absorption are at a minimum, is so named because

A) water vapor (H₂O) has an intense laserlike emission line at this wavelength that extraterrestrials might use to communicate with Earth.
B) two astronomically important wavelengths, the 21-cm line of H and a line from the hydroxyl radical OH, are in this region, the letters H and OH signifying water.
C) water vapor emissions from planets at this wavelength will be a good indicator of life on other planets because water is essential for life as known.
D) water vapor absorption in Earth's atmosphere reaches a sharp minimum at this wavelength.

Question 59

In what way does the Drake equation combine the various factors (e.g., fraction of stars with planets, fraction of planets that can support life) in an attempt to determine the number of technically advanced civilizations existing elsewhere in the Milky Way Galaxy?

A) The product of all the probabilities is calculated.
B) The sum of each of the factors is determined.
C) The sum of three factors is divided by the sum of the other four factors.
D) The sum of the last six factors is subtracted from the initial factor, the rate of solar-type star formation.

Question 60

In the Drake equation for estimating the possible number of technologically advanced civilizations in the Milky Way Galaxy, why does the factor for the rate at which solar-type stars form in a galaxy exclude massive stars with masses greater than about 1.5 times that of the Sun?

A) Such stars have much shorter lifetimes than it took for intelligent life to develop on Earth and hence should probably not be considered.
B) Such stars never develop a nuclear furnace in their interiors and hence can never heat any planet sufficiently to sustain life.
C) Such stars would never develop nuclear processes that could produce heavy elements (e.g., iron) needed for planetary formation.
D) Such stars are prone to repeated and violent supernova explosions throughout their lives, which would destroy any developing life-forms.

Question 61

It is unlikely that intelligent life would develop on a planet circling a star of significantly less mass than the Sun because

A) no moon would form around a planet near such a star, and the Moon is considered to have been essential for the evolution of life because of tidal variations on Earth.
B) the lifetime of such a star on the main sequence is too short; life-forms on such a planet would not have time to evolve intelligence.
C) the planet would probably become tidally locked to the star, making one side of the planet too hot and the other side too cold.
D) there would be no region around the star where UV, visible, and IR light intensities would be suitable for the evolution of life.

Question 62

Why do astronomers NOT consider stars with masses more than about 1.5 solar masses in the Drake equation when estimating the number of possible stars in the Milky Way Galaxy around which planets could form that would support intelligent life similar to humans?

A) More massive stars would produce massive planets on which life would not be possible.
B) More massive stars would never reach temperatures sufficient to maintain life-supporting conditions on the surfaces of its planets.
C) A more massive star would produce so much damaging UV radiation that it would sterilize its planets.
D) More massive stars would have evolved so rapidly that an advanced civilization would not have had time to evolve and develop.

Question 63

Pioneer 10 and 11 carried plaques intended to show any alien civilization that found them the location of the solar system in the Galaxy. The location was marked relative to various pulsars (as seen in Figure 20-10b in the text). Which one of these is the BEST reason to choose pulsars for this purpose?

A) Pulsars can be detected a long way across the Galaxy and thus presumably would be known to the aliens.
B) Pulsars can be identified uniquely by the frequencies of the radiation they emit.
C) Pulsar pulse rates are constant, never changing.
D) Pulsars form a more-or-less uniform ring around the galactic center (like the globular cluster halo) and thus provide a good coordinate system.

Question 64

In a few decades, a new generation of powerful telescopes especially designed to find extrasolar planets may be operational and producing data. What might these results mean for the Drake equation?

A) With these results in hand, the Drake equation will become irrelevant.
B) The structure of the Drake equation itself will undoubtedly have to be drastically revised.
C) Astronomers will have much better values for the factors f_p (the fraction of stars that have planets) and n_e (the number of planets per solar system that are Earthlike).
D) Astronomers will have much better values for the factors f_l (the fraction of Earthlike planets on which life actually arises), f_i (the fraction of life-forms that evolve into intelligent species), and f_c (the fraction of intelligent species that develop adequate technology and then choose to send messages out into space).

Question 65

Earth has been sending out radio messages for about 120 years, so detection equipment on a hypothetical planet 120 light-years away might just now begin receiving them. What is the parallax angle subtended by a system at this distance? Can astronomers detect such a parallax angle with existing technology?

A) 0.0026 arcseconds; no
B) 0.0084 arcseconds; yes
C) 0.027 arcseconds; yes
D) 120 arcseconds; yes

Question 66

Which of these ideas has been borne out by actual astronomical observations over the past few centuries?

A) The probability of life existing elsewhere in the universe, even elsewhere in the solar system, is extremely great.
B) Earth appears to occupy a unique position in the universe, unrepeated anywhere, since the Sun is unique in properties and position in a remarkable galaxy.
C) All the observational evidence so far suggests that conditions for the evolution of life exist only on Earth in its position near the Sun.
D) The Sun is an unremarkable star in a commonplace galaxy, and many similar stars exist in the universe around which life might evolve on planets.

Question 67

One of the great lessons being learned from modern astronomy is that

A) Earth occupies a unique position in the universe, and nowhere else are conditions equivalent to those in the solar system likely to be found.
B) Earth's position and circumstances in the universe are quite ordinary and certainly not unique.
C) the chemistry, geology, and physics on Earth are unique to it, and the behavior of matter anywhere else appears to be significantly different from that on Earth.
D) Earth is at the center of a very massive black hole, and all the observed cosmological effects such as redshift and cosmic background radiation and even the evolution of life are a consequence of the unique position Earth occupies.

Question 68

In 1974 a radio signal was sent from the Arecibo radio telescope toward the globular cluster M13, which is about 6.8 kpc distant. How long will it take this signal to reach M13?

A) 6800 years
B) 13,600 years
C) 22,200 years
D) 44,400 years

Question 69

If humans do eventually make contact with other civilizations in the Milky Way, which of these conditions will inevitably hold?

A) Humans will not be able to understand the messages.
B) The civilization is likely to be very much more technologically primitive than ours.
C) Conversations will take a very long time.
D) The chemistry and biology of the life-forms are likely to be very different from ours-for example, silicon-based rather than carbon-based.

Question 70

Which of these events of the past 150 years announced human presence on Earth MOST effectively to extraterrestrial watchers?

A) appearance of artificial satellites orbiting Earth after 1957
B) nuclear weapon explosions producing extremely intense but brief flashes of light and electromagnetic radiation
C) slow changes in vegetation patterns and the appearance of humanmade structures such as road systems and cities on Earth
D) slow buildup of radio transmissions after the invention of radio, with modulated signals carrying sound and visual television images

Question 71

How often do Sunlike stars (of a type considered likely to be circled by an inhabitable planet) form in the Milky Way Galaxy, on average?

A) Hundreds of such stars form per year.
B) About one such star forms per year.
C) Astronomers cannot yet answer this question.
D) Less than one such star forms per thousand years.