Life in the Universe Exam Two

What is true about the Martian seasons?

-Seasons on Mars are affected by the orbit as well as by the axis tilt. -Seasons on Mars last almost twice as long as seasons on Earth. -The carbon dioxide at the martian polar caps sublimates to gas in summer, leaving a residual polar cap of water ice. Not true: -All of Mars has summer at the same time, and half an orbit later all of Mars has winter. --The primary cause of the seasons is axis tilt, which means the two hemispheres must have opposite seasons, just as on Earth.

What evidence supports the hypothesis for a vast, deep ocean which once occupied what is now the northern plains of Mars?

-geographic features that look like ancient shorelines -many of the largest flood channels appear to have drained into the northern plains -that the rock along the proposed shoreline is sedimentary rather than volcanic

Jupiter is about five times as far from the Sun as Earth. Therefore, the strength of sunlight at Jupiter is about ________ as strong as it is at Earth.

1/25

Evidence indicates that Mars's era of being significantly warmer and wetter ended at least about ________.

3 billion years ago

Try the following sample numbers in the Drake equation (Number of Civilizations = NHP x flife x fciv x fnow). Suppose there are 1000 habitable planets in our galaxy, that 1 in 10 habitable planets has life, that 1 in 4 planets with life has at some point had an intelligent civilization, and that 1 in 5 civilizations that have ever existed is in existence now. How many civilizations would exist at present?

5

What do we mean by a "hot Jupiter"?

A massive planet that orbits very close to its star -The planet is hot because it is so close to the star.

The martian surface is usually divided into regions of three different age ranges (early, middle, and recent). How do we decide in which age range a region belongs?

By counting the number of craters in the region

Suppose you are using the Doppler technique to look for planets around another star. What must you do?

Compare many spectra of the star taken over a period of many months or years.

Europa is located outside the Sun's habitable zone and yet may be habitable. How can this be?

Europa is tidally heated, allowing liquid water to exist beneath its icy surface

Life arose relatively early in Earth's history, but intelligence evolved only recently. If we assume Earth is "typical," what would we conclude?

Intelligence is likely only around stars at least about as old as the Sun. -If it takes the same 4½ billion years to get intelligent life on other planets as it did on Earth, then the star would have to be at least this old.

Tidal heating is stronger for Io than for Europa because ________.

Io is closer to Jupiter

What do we mean when we say that a moon is in synchronous rotation?

It always keeps the same face toward its planet. -For this to occur, the Moon's orbital period and rotation period must be the same.

What is the significance of the detection of methane in Mars's atmosphere?

It suggests either some type of volcanic activity or life.

Which of the following is a reasonable hypothesis for how Valles Marineris formed on Mars?

It was created by tectonic cracking. -This may have occurred as a mantle plume pushed up the nearby Tharsis bulge.

Why do the moons of Saturn have large amounts of methane and ammonia ice, but the moons of Jupiter do not?

It was too warm for these ices to condense at Jupiter's distance in the solar nebula. -At Saturn's distance, it was much colder.

What role has Jupiter played in Earth's habitability?

Jupiter's gravitational effects helped clear the inner solar system of objects that could cause impacts. -We therefore expect that the impact rate would be higher without a Jupiter-like planet, though the implications of this fact to life are still debated.

How do the possibilities for life on Ganymede and Callisto compare to those on Europa?

Life seems less likely because these moons have less energy available for life.

Which of the following factors in the simplified Drake equation is best known?

Nhp, the number of habitable planets in our galaxy

What is the distinguishing characteristic that radio SETI experiments are looking for when searching for signs of extraterrestrial intelligence?

Radio emission that extends over only a narrow band of frequencies

What one change would make it possible for liquid water to exist stably on Mars today?

Substantially raising the atmospheric pressure

In regard to Percival Lowell's claims of a vast canal system on Mars, Alfred Russel Wallace wrote "[a network of canals,] as Mr. Lowell describes, would be the work of a body of madmen rather than of intelligent beings." Why?

The canals claimed by Lowell ran in straight lines for great distances

According to the leading hypothesis, what role did a magnetic field play in Mars's global climate change?

The magnetic field shielded the atmosphere from the solar wind while it existed, and the atmosphere was lost after the magnetic field weakened.

Imagine another star system with a planet of the same mass as Jupiter orbited by a moon with the same size and orbit as Io. If this moon is not geologically active like Io, then which of the following is probably true?

The planet does not have other large moons sharing an orbital resonance with this moon.

The New Horizons mission will fly past Pluto in 2015. Why would it have been much more expensive to make the mission a Pluto orbiter rather than a flyby?

The spacecraft would have needed to carry far more fuel with it.

Why would it be surprising to find large fish-like organisms with rapid metabolism on Europa?

There does not seem to be enough energy available to support this type of metabolism.

What do the astrometric, Doppler, and transit methods share in common?

They all search for planets by measuring properties of a star rather than of the planets themselves -This is why we say they are indirect methods, as opposed to direct methods that seek to acquire images or spectra of planets themselves

Based on what we know about the terrestrial worlds, why is it surprising to find geological activity on jovian moons?

They are too small. -Small size usually means less geological activity, so the fact that some of these moons are active means they must have a heating source (tidal heating) that the terrestrial worlds do not have. Their icy compositions also make geological activity possible at lower temperatures.

What is the leading hypothesis for the close-in orbits of "hot Jupiters"?

They formed much farther from their stars, then migrated inward.

The largest Jovian moon that appears to have been captured is

Triton, the moon of Neptune

Venus's atmosphere has much more carbon dioxide than Earth's because ________.

Venus lacks oceans -Without oceans and rainfall, the carbon dioxide cannot dissolve and react to become locked up in carbonate rock.

Which of the following explains why Venus is so much hotter than Earth?

Venus's atmosphere contains far more carbon dioxide than Earth's -This large amount of carbon dioxide gives Venus an extreme greenhouse effect

Which of the following is not an advantage of water over methane, ethane, and ammonia as a potential liquid medium for life?

Water is the only one that melts from solid to liquid form as the temperature increases -All of these substances can melt from solid into liquid as long as there is sufficient atmospheric pressure. ~Advantages: -Water is the only one for which the solid form floats in the liquid form. -Water is the one that is a liquid at the highest temperatures. -Water is the only one with charge separation in its molecules.

Does Venus have any place where we may find liquid water today?

Yes, in high-altitude clouds -There are tiny droplets of acidic water in Venus' high-altitude clouds. Though they seem like an unlikely home for life, we cannot completely rule life out.

Which planet is most likely to be detected by the Doppler technique?

a massive planet orbiting close to its star

Which of the following is most likely to render our planet no longer habitable?

a runaway greenhouse effect, between about 1 to 3 billion years from now

A carbon dioxide concentration of 400 parts per million (ppm) means that carbon dioxide represents ________ of Earth's atmosphere.

about 4%

In the simplified Drake equation, a value of flife = 1 would imply that

all habitable planets in the galaxy have life on them now

Which type of electromagnetic radiation is able to carry the most information?

all types have equal ability

Suppose we started adding gases such as CFCs to Mars in an effort to terraform the planet. In the best case as now envisioned, this would _________.

allow us to walk around without pressurized spacesuits, after a few hundred thousand years

A UFO is

an unidentified object seen in the sky

The necessary chemical elements of life should

be widespread throughout the universe

Why were scientists surprised to find active geology on Enceladus?

because of its small size

The inner boundary of the Sun's habitable zone today is ________.

between the orbit of Venus and the orbit of Earth -We don't know exactly where this boundary lies, but it must be somewhere in this region

Seasonal variations on Mars are due

both to its axis tilt and its changing distance from the Sun

The result of a calculation with the Drake equation is intended to be an estimate of the number of worlds in the galaxy on which ________.

civilizations capable of radio communication currently exist -The Drake equation is a tool designed to estimate the chances of success in SETI efforts, and hence is focused on civilizations from which we could potentially get a signal.

Consider a star that is less massive than the Sun. For a planet to receive the same intensity of light from this star as Earth receives from the Sun, the planet would have to orbit ________.

closer to the star than Earth is to the Sun -Less massive stars are less luminous, so a planet would have to be closer to the star to get the same intensity of light.

The geological history of Mars is divided into different

eras

Suppose that we discover life on Mars with an origin independent of life on Earth. Which term in the Drake equation would be most affected?

flife

The evidence that Mars may sometimes still have small-scale water flows comes from ________.

gullies on crater walls

Intelligence may be subject to convergent evolution because it

has survival value

Based on all current evidence, if Venus had been born at Earth's distance from the Sun, then Venus today would probably ________.

have oceans and an atmosphere much like Earth

The orbits of many extrasolar planets detected to date are

highly elliptical

Recall that stars are classified with types from the spectra sequence OBAFGKM. In general, an ordinary (hydrogen-fusing, or main-sequence) star of spectral type A is ________ than a star of spectral type K.

hotter, more luminous, and more massive

Earth's frozen lakes and seas often have liquid water beneath their ice surfaces primarily because ________.

ice floats and provides insulation to the water below

Chemical disequilibrium is likely to be present in all the following places except ________.

icy boulders in the rings of Saturn

When the Earth first formed it had large quantities of water vapor in its atmosphere while today the levels of water vapor are much lower. Where did most of the water vapor go?

it condensed into the oceans

Which one of the following properties is unique to water?

it expands on freezing

What is the most likely origin of the Valles Marineris on Mars?

it is a tectonic fracture associated with the formation of the adjacent Tharsis bulge

Which of the following fundamental properties of Mars could explain why it once had a global magnetic field but then lost it?

its size

The Curiosity rover is an example of which kind of robotic spacecraft?

lander

Which kind of robotic space mission enables us to determine the chemical composition of a planet's surface and atmosphere remotely?

lander/probe

The Jovian moons Io, Europa, Callisto and Triton are

larger than Pluto but smaller than Mercury

Climate models predict that due to the melting of the polar ice caps, sea levels by the end of this century

may rise by several meters

Scientists are currently planning a mission that should tell us definitively whether there is an ocean on Europa. This mission will do that in the cheapest way possible, which is to ________.

measure how much Europa's surface bulges up and down as it rotates

Key evidence that Mars may once have had much more water than it does today, perhaps enough to form an ocean, comes from ________.

measurements of the atmospheric ratio of deuterium to ordinary hydrogen -The relative abundance of deuterium indicates that Mars has lost a lot of hydrogen to space, presumably from water molecules broken apart in the atmosphere.

In essence, the Kepler mission searched for extrasolar planets by ____________.

monitoring stars for slight dimming that might occur as unseen planets pass in front of them -This transit method can reveal planets as small as Earth (or smaller), but only if they happen to orbit their star in the plane of our line-of-sight.

The Kepler mission is monitoring approximately 100,000 stars for transits. Suppose that, ultimately, it detects planets around 1000 of these stars. Which of the following would be a reasonable conclusion?

most stars have planets

Compared to the average surface temperature on the surface of the Earth, the average surface temperature on the surface of Mars is

much lower

Is Europa in the Sun's habitable zone?

no

The transit method allows us in principle to find planets around __________.

only a small fraction of stars that have planets -We can see transits only if the planetary orbits are nearly precisely edge-on as viewed from Earth, which means that most planetary systems cannot be detected through transits. The Kepler mission overcame this limitation by studying a large number of stars (about 150,000).

What is believed to have been the main source of Titan's atmosphere?

outgassing from the interior

Scientifically speaking, which of the following ideas relevant to global warming is subject to the greatest uncertainty?

predictions of future consequences of global warming

Which is not a critical factor that determines the habitability of a rocky planet?

presence of a magnetic field

In the Drake equation, a value of flife that is close to 1 and a value of fciv that is close to 0 would imply ________.

primitive life is common but intelligent life is rare -The first two terms (NHP flife) tell us the number of habitable planets with life of some kind. -The term fciv then tells us the fraction of these planets on which the life eventually leads to an intelligent civilization. So if intelligence is rare, then civilizations would also be rare, making fciv small.

Which of the following methods uses astrometry to detect extrasolar planets around other star systems?

regular changes in the positions of the parent stars with respect to more distant stars as they move across the sky

Any reply to a detected SETI signal should

represent a consensus of the Earth's population

Europa is most likely made of

rock and water ice

Suppose that Greenland's ice sheet were to melt. What effect would that have on sea level?

sea level would rise many meters

Based on current evidence, if Mars had been born at Earth's distance from the Sun, then Mars today would probably ________.

still have a dry surface -Mars is thought to have frozen because it lost its atmosphere to solar wind stripping. If this is correct, it is a consequence of Mars's relatively small size and would still have occurred even if Mars were closer to the Sun.

Life is probably not possible in Jupiter's atmosphere because of ________.

strong, vertical winds -These winds would carry life up and down rapidly between depths with vastly different temperatures

One of the most likely places an advanced civilization might leave an artifact for us to find would be

the L4 and L5 points in the Earth—Moon system

Suppose you had the misfortune of finding yourself outside on Titan without a spacesuit. Which would probably kill you first?

the cold temperature

Which of the following is the most convincing observation that suggests that Ganymede, like Europa, may also have a subsurface ocean?

the detection of salts on the surface that may have been brought up from below the crust

One of the fundamental principles of stellar evolution is that the more massive a star is,

the faster it evolves

If we are searching for life that is at least somewhat Earth-like, the most important criterion in identifying a potentially habitable world is ________.

the presence of surface or subsurface liquid water -Water is crucial for all life on Earth, and it is likely that some liquid medium is required for any kind of life.

The habitable zone refers to ________.

the range of distances from a star within which a planet could potentially have surface oceans of liquid water -Note that the habitable zone refers specifically to the possibility of surface oceans of liquid water; subsurface oceans (such as that thought to exist on Europa) could exist outside the habitable zone

Io experiences strong internal tidal heating because of

the strong tidal force from the massive Jupiter combined with its elliptical orbit which causes the strength and direction of the force to constantly change

The martian meteorite ALH84001 has structures that look like fossilized bacteria. Why do most scientists doubt that they are actually fossil life?

the structures are too small

What is the common property that distinguishes stars on the main sequence of the H-R diagram from other stars on the diagram?

they are fusing hydrogen in their central cores

Stars of spectral type O and B are unlikely to have planets with life because ________.

they don't live long enough for planets to form

The presence of elements heavier than helium in stars is very important because

they provide the raw materials for the formation of planets and life

The elements carbon, nitrogen, and oxygen are crucial to life on Earth, at least. These elements are

three of the six most abundant elements in the universe -Hydrogen and helium are the two most abundant elements, but they are followed by oxygen and carbon (third- and fourth-most abundant, respectively), and nitrogen is the sixth-most abundant.

What source of energy might keep an ocean beneath the surface of Ganymede liquid?

tidal heating and radioactive decay

In terms of the gases outgassed by volcanoes, Venus's atmosphere today seems to have ________.

too little water vapor -A great deal of water vapor should have been outgassed on Venus, but it is virtually absent from the atmosphere.

Mars's seasonal winds are driven primarily by ________.

vaporization of carbon dioxide ice at the summer pole -Most of the carbon dioxide at the summer pole vaporizes directly from solid to gas, creating a significant pressure difference between the summer and winter poles.

Titan shares all of the following geological features with Earth except ________.

volcanoes erupting with molten rock

Compared to today, in the future, the Sun's habitable zone will be

wider and farther from the Sun

The most important geological process occurring on Mars today is

wind erosion