Deck 15: Astrobiology

Question 1

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 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

Answer 1

discovery by the Viking landers of large organic molecules in the Martian regolith

Question 2

There are now over 1700 known extrasolar planets.When we 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 2

hydrogen-rich planets like Jupiter.

Question 3

What do the letters 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

Answer 3

search for extraterrestrial intelligence

Question 4

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 is a fluid and therefore provides a physical medium in which the building blocks of life can move around and get together.
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.

Question 5

The meteorite ALH 84001 was discovered in Antarctica in 1984.Some researchers claimed that it came from Mars and that it showed fossilized evidence of life.At the present time,the scientific community is in general agreement that this meteorite:

A) came from Mars.
B) contains fossilized life forms.
C) does not contain fossilized life forms.
D) came from Mars and contains fossilized life forms.

Question 6

Which statement is NOT considered to be a reason carbon is thought to be the element on which complex extraterrestrial life is likely to be 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 7

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
B) stony iron
C) carboneous chondrite
D) stony

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

Frank Drake began his SETI investigations by listening for signals from two particular stars: Ʈ Ceti and ɛ Eridani.Why these two?Ʈ

A) These are among the half dozen closest stars to Earth.
B) These stars are similar to the Sun.
C) It was thought that previous signals had been detected from these sources.
D) These stars are both very old and thus would have had time to evolve an advanced civilization.

Question 10

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 11

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 12

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 13

In which environment have long-chain carbon-based molecules NOT been found?

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

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 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

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

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

Question 16

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

A) infrared radiation
B) visible radiation
C) UV radiation
D) microwaves and short-wavelength radio waves

Question 17

In which type of meteorite has evidence been found for organic molecules,some of which,in contrast to most life molecules on Earth,have both right- and left-hand spiral structure?

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

Question 18

Carbon is considered the most likely element upon which life chemistry could be based because it satisfies many requirements,three of which are listed below.Which requirement is NOT considered useful in life chemistry?

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 19

The Miller-Urey "experiment" 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 us, 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 20

One aspect of astrobiology is the attempt to replicate 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 21

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 22

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

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

Question 23

The primary constituents for the organic molecules needed for life do NOT include which compound?

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

Question 24

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) Earth

Question 25

What is the current status of our search for inhabitable,Earthlike planets circling other stars?

A) Several stars have been found with Earth-mass planets orbiting at a distance suitable for liquid water and life, but we cannot yet see if they have oxygen-rich atmospheres.
B) Many extrasolar planets have been discovered, but most are in orbits with eccentricities too high to provide a stable environment for life.
C) No extrasolar planets of any kind have yet been confirmed.
D) We have not yet discovered Earthlike planets orbiting Sunlike stars.

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

Our speculation about the possibility that life might exist in the harsh environment of Europa's subsurface oceans or in the ice-based permafrost of Mars has recently been given a boost with the discovery of life in the similarly harsh environment:

A) on the far side of the Moon.
B) in a lake deep beneath the Antarctic ice pack.
C) on meteoroids.
D) in the cold, rarified upper atmosphere above Earth's poles.

Question 28

Why was the discovery of pulsars initially misinterpreted as evidence of intelligent life elsewhere in the universe?

A) It was not thought possible for a "natural" radio source to produce the rapid and extremely regular radio pulses detected from space.
B) Radio telescopes occasionally detected the same sequence of five musical notes, which were then whistled or hummed regularly by all the people associated with these telescopes (D, E, C, lower C, and G on a piano).
C) Pulses arriving from several nearby star systems showed Doppler shifts of frequency apparently caused by orbital motion of their source around the central stars, as if coming from planets.
D) The rate of pulses detected from space appeared to contain primitive coding similar to a crude Morse code.

Question 29

Which phenomenon 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 30

Many of the extrasolar planets discovered thus far contain large planets orbiting close to their stars.It is considered unlikely to find habitable Earthlike planets in such systems.What is the reason?

A) Large planets close to their stars tend to block sunlight from reaching planets farther out in the "habitable zone."
B) The gravitational effects of these large planets would cause Earthlike planets to move into highly elliptical orbits, and that would result in large temperature variations.
C) Large planets close to their stars would tend to accumulate all of the heavy rocks and metals during the solar nebula phase. These would thus not be available for creating Earthlike planets farther out.
D) Large planets would tend to attract much space debris during the early formative phases of that solar system. This would result in other nearby planets being blasted and heavily cratered for long periods, making it difficult for a civilization to develop.

Question 31

Is a planet with a moon thought 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 that 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 32

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

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

Question 33

In which very harsh environment 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 even the harshest environments on Earth.

Question 34

On which object in our planetary system is it NOT 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 35

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 36

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

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

Question 37

The habitable zone around the Sun includes:

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

Question 38

Which idea 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 our own 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 39

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 40

The basic chemical molecules thought to have been present in abundance in the early planetary system,which were used in the classical Urey-Miller 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 41

In searching for transmissions from intelligent civilizations,SETI is concentrating its efforts on a survey of:

A) about a dozen or so of the closest stars.
B) just stars around which we believe we have detected planets.
C) thousands of stars 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 technically advanced civilizations in the Galaxy as a product of seven factors: R* fp nₑ fl fᵢ fc L.In the sample calculation in the text,these values are taken as 1 × 1 × 0.1 × 1 × 1 × 1 × 100 = 10.If we were to redo the calculation,increasing each increasable factor by a multiple of ten,what would the result be?

A) 10
B) 10⁴
C) 10⁶
D) 10⁸

Question 43

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 44

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 45

The estimates in the Drake equation are not constant but evolve over time based on increased observational evidence.Because of the discovery of over a thousand extrasolar planets,the text chose the value fp = 1 for the fraction of Sunlike stars that have planets.What would you suppose Drake chose for this parameter in 1960?

A) zero
B) 0.01
C) something between 0.2 and 0.5
D) 1

Question 46

If we are going to "listen" for electromagnetic radiation at 21 cm from extraterrestrial sources,then we had better not generate too many waves at this wavelength from terrestrial sources.The standard FM broadcast band (as you can see by looking at your 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 47

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 (see Figure 15-8 of Comins,Discovering the Essential Universe,6th ed.)?

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 48

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) We have received on several occasions repeated signals that appear to be from some intelligent source, but we 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) We have occasionally detected particularly strong or unusual signals from space, but they have not been repeated, so we do not believe they are from an intelligent source.

Question 49

In the Drake equation for estimating the possible number of technically 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 50

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 us.
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 since water is essential for life as we know it.
D) water vapor absorption in Earth's atmosphere reaches a sharp minimum at this wavelength.

Question 51

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) microwave

Question 52

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 53

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

A) Earth's atmosphere 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 IR 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 54

What is the current state of the search for extraterrestrial radio communications?

A) Several extraterrestrial civilizations have been found, but they are not intelligent enough for us to bother with and the search is continuing.
B) Occasional single-frequency searches have been made for extraterrestrial signals, but funds are still being sought for the first major continuous monitoring effort.
C) A number of frequencies in the "water hole" are being monitored, but there has been no major effort as yet to send out continuous signals from Earth at these frequencies.
D) Continuous transmissions are being sent out from Earth at several frequencies in the "water hole," and tens of millions of other frequencies are being monitored.

Question 55

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 56

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 we are 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 57

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) fp, the fraction of stars that have planets.
C) nₑ, the number of planets per solar system that are Earthlike (suitable for life).
D) L, the lifetime of a technologically advanced civilization.

Question 58

Why would intelligent alien beings wanting to communicate with us probably choose the 21-cm atomic hydrogen radio wavelength?

A) This wavelength shows a very strong Doppler effect when its source is moving, and intelligent alien beings would know that we would be able to detect the orbital motion of their home planet around their star by this method.
B) Intelligent alien beings would expect that many of our telescopes would already be tuned to this precise wavelength for scientific work.
C) This radiation at this particular wavelength is very weak from natural sources in space, and messages would be easily distinguished from other sources.
D) Intelligent alien beings would have detected this particular wavelength from our transmitters on Earth since it is used extensively for satellite communications, and they would know that we could detect them easily.

Question 59

Part of determining the Drake factor R* is determining what is a "Sun 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 fewer of these shorter wavelengths and thus could not support efficient photosynthesis.

Question 60

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 61

In a few decades,a new generation of powerful telescopes especially designed to find extrasolar planets may be operational and sending us data.What might these results mean for our use of 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) We will have much better values for the factors fp (the fraction of stars that have planets) and nₑ (the number of planets per solar system that are Earthlike).
D) We will have much better values for the factors fl (the fraction of Earthlike planets on which life actually arises), fᵢ (the fraction of life-forms that evolve into intelligent species), and fc (the fraction of intelligent species that develop adequate technology and then choose to send messages out into space).

Question 62

Which event of the past century do you think will have announced our presence on Earth MOST effectively to extraterrestrial watchers?

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

Question 63

Earth has been sending out strong radio messages for about 115 years,so detection equipment on a hypothetical planet 115 light-years away might just now begin receiving them.What is the parallax angle subtended by a system at this distance? Can we detect such a parallax angle with our present technology?

A) 0.0027 arcseconds; no
B) 0.0087 arcseconds; yes
C) 0.028 arcseconds; yes
D) 115 arcseconds; yes

Question 64

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 (see Figure 15-10,Comins,Discovering the Essential Universe,6th ed.).Which statement is a good 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 65

One of the important numbers in determining how many extraterrestrial civilizations there may be at the present time in the Milky Way Galaxy is the following: Out of the stars that have planets,what fraction,fs,has planets suitable for life? (This number is similar to the number nₑ in the Drake equation.)Based on the extrasolar planets already found by astronomers (see Chapter 5 of Comins,Discovering the Essential Universe,6th ed.),what is a good guess for fs? (Note: If all stars with planets have at least one planet suitable for life,then fs = 1; if no such star anywhere in the Milky Way has a planet suitable for life,then fs = 0.)

A) fs = 0 since no star has yet been found to have an inhabitable planet
B) close to fs = 1 since most stars so far found to have planets have high-mass planets (similar to Jupiter or larger) orbiting far from the star, indicating that the solar system is probably typical of planetary systems in general
C) close to fs = 1/2 since about half the stars so far found to have planets have planets similar in mass to Earth orbiting the star at about Earth's distance from the Sun
D) fs less than about 1/10 since most stars so far found to have planets have high-mass planets (similar to Jupiter or larger) orbiting close to the star, which would disrupt the orbit of an inhabitable planet

Question 66

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 a 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 67

Around which types of stars are we MOST likely to find planets supporting our kind of life?

A) high-mass main-sequence stars
B) red giant stars
C) very-low-mass stars
D) low-mass main-sequence stars

Question 68

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) We cannot yet answer this question.
D) Less than one such star forms per thousand years.

Question 69

If we do eventually make contact with other civilizations across space,which condition will inevitably hold?

A) We 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

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 a 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 UV, visible, and IR light intensities would be suitable for the evolution of life.

Question 71

For which factor in the Drake equation do we actually have observational knowledge rather than just a speculative estimate?

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

Question 72

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 our planet, 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 73

Why do we 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 our kind of intelligent life?

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.